changeset 10054:2188a4078a0a

8056248: Improve ForkJoin thread throttling Reviewed-by: psandoz, martin, chegar
author dl
date Fri, 05 Sep 2014 10:54:28 +0200
parents 6a76442406bd
children fc1ba7934a40
files src/share/classes/java/util/concurrent/ForkJoinPool.java src/share/classes/java/util/concurrent/ForkJoinTask.java src/share/classes/java/util/concurrent/ForkJoinWorkerThread.java
diffstat 3 files changed, 1565 insertions(+), 1483 deletions(-) [+]
line wrap: on
line diff
--- a/src/share/classes/java/util/concurrent/ForkJoinPool.java	Fri Sep 26 15:25:33 2014 +0400
+++ b/src/share/classes/java/util/concurrent/ForkJoinPool.java	Fri Sep 05 10:54:28 2014 +0200
@@ -49,6 +49,7 @@
 import java.util.concurrent.RunnableFuture;
 import java.util.concurrent.ThreadLocalRandom;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicLong;
 import java.security.AccessControlContext;
 import java.security.ProtectionDomain;
 import java.security.Permissions;
@@ -80,9 +81,9 @@
  *
  * <p>For applications that require separate or custom pools, a {@code
  * ForkJoinPool} may be constructed with a given target parallelism
- * level; by default, equal to the number of available processors. The
- * pool attempts to maintain enough active (or available) threads by
- * dynamically adding, suspending, or resuming internal worker
+ * level; by default, equal to the number of available processors.
+ * The pool attempts to maintain enough active (or available) threads
+ * by dynamically adding, suspending, or resuming internal worker
  * threads, even if some tasks are stalled waiting to join others.
  * However, no such adjustments are guaranteed in the face of blocked
  * I/O or other unmanaged synchronization. The nested {@link
@@ -178,7 +179,14 @@
      * that may be stolen by other workers.  Preference rules give
      * first priority to processing tasks from their own queues (LIFO
      * or FIFO, depending on mode), then to randomized FIFO steals of
-     * tasks in other queues.
+     * tasks in other queues.  This framework began as vehicle for
+     * supporting tree-structured parallelism using work-stealing.
+     * Over time, its scalability advantages led to extensions and
+     * changes to better support more diverse usage contexts.  Because
+     * most internal methods and nested classes are interrelated,
+     * their main rationale and descriptions are presented here;
+     * individual methods and nested classes contain only brief
+     * comments about details.
      *
      * WorkQueues
      * ==========
@@ -198,201 +206,318 @@
      * (http://research.sun.com/scalable/pubs/index.html) and
      * "Idempotent work stealing" by Michael, Saraswat, and Vechev,
      * PPoPP 2009 (http://portal.acm.org/citation.cfm?id=1504186).
-     * See also "Correct and Efficient Work-Stealing for Weak Memory
-     * Models" by Le, Pop, Cohen, and Nardelli, PPoPP 2013
-     * (http://www.di.ens.fr/~zappa/readings/ppopp13.pdf) for an
-     * analysis of memory ordering (atomic, volatile etc) issues.  The
-     * main differences ultimately stem from GC requirements that we
-     * null out taken slots as soon as we can, to maintain as small a
-     * footprint as possible even in programs generating huge numbers
-     * of tasks. To accomplish this, we shift the CAS arbitrating pop
-     * vs poll (steal) from being on the indices ("base" and "top") to
-     * the slots themselves.  So, both a successful pop and poll
-     * mainly entail a CAS of a slot from non-null to null.  Because
-     * we rely on CASes of references, we do not need tag bits on base
-     * or top.  They are simple ints as used in any circular
+     * The main differences ultimately stem from GC requirements that
+     * we null out taken slots as soon as we can, to maintain as small
+     * a footprint as possible even in programs generating huge
+     * numbers of tasks. To accomplish this, we shift the CAS
+     * arbitrating pop vs poll (steal) from being on the indices
+     * ("base" and "top") to the slots themselves.
+     *
+     * Adding tasks then takes the form of a classic array push(task):
+     *    q.array[q.top] = task; ++q.top;
+     *
+     * (The actual code needs to null-check and size-check the array,
+     * properly fence the accesses, and possibly signal waiting
+     * workers to start scanning -- see below.)  Both a successful pop
+     * and poll mainly entail a CAS of a slot from non-null to null.
+     *
+     * The pop operation (always performed by owner) is:
+     *   if ((base != top) and
+     *        (the task at top slot is not null) and
+     *        (CAS slot to null))
+     *           decrement top and return task;
+     *
+     * And the poll operation (usually by a stealer) is
+     *    if ((base != top) and
+     *        (the task at base slot is not null) and
+     *        (base has not changed) and
+     *        (CAS slot to null))
+     *           increment base and return task;
+     *
+     * Because we rely on CASes of references, we do not need tag bits
+     * on base or top.  They are simple ints as used in any circular
      * array-based queue (see for example ArrayDeque).  Updates to the
-     * indices must still be ordered in a way that guarantees that top
-     * == base means the queue is empty, but otherwise may err on the
-     * side of possibly making the queue appear nonempty when a push,
-     * pop, or poll have not fully committed. Note that this means
-     * that the poll operation, considered individually, is not
-     * wait-free. One thief cannot successfully continue until another
-     * in-progress one (or, if previously empty, a push) completes.
-     * However, in the aggregate, we ensure at least probabilistic
+     * indices guarantee that top == base means the queue is empty,
+     * but otherwise may err on the side of possibly making the queue
+     * appear nonempty when a push, pop, or poll have not fully
+     * committed. (Method isEmpty() checks the case of a partially
+     * completed removal of the last element.)  Because of this, the
+     * poll operation, considered individually, is not wait-free. One
+     * thief cannot successfully continue until another in-progress
+     * one (or, if previously empty, a push) completes.  However, in
+     * the aggregate, we ensure at least probabilistic
      * non-blockingness.  If an attempted steal fails, a thief always
      * chooses a different random victim target to try next. So, in
      * order for one thief to progress, it suffices for any
      * in-progress poll or new push on any empty queue to
      * complete. (This is why we normally use method pollAt and its
      * variants that try once at the apparent base index, else
-     * consider alternative actions, rather than method poll.)
+     * consider alternative actions, rather than method poll, which
+     * retries.)
      *
-     * This approach also enables support of a user mode in which local
-     * task processing is in FIFO, not LIFO order, simply by using
-     * poll rather than pop.  This can be useful in message-passing
-     * frameworks in which tasks are never joined.  However neither
-     * mode considers affinities, loads, cache localities, etc, so
-     * rarely provide the best possible performance on a given
-     * machine, but portably provide good throughput by averaging over
-     * these factors.  (Further, even if we did try to use such
-     * information, we do not usually have a basis for exploiting it.
-     * For example, some sets of tasks profit from cache affinities,
-     * but others are harmed by cache pollution effects.)
+     * This approach also enables support of a user mode in which
+     * local task processing is in FIFO, not LIFO order, simply by
+     * using poll rather than pop.  This can be useful in
+     * message-passing frameworks in which tasks are never joined.
+     * However neither mode considers affinities, loads, cache
+     * localities, etc, so rarely provide the best possible
+     * performance on a given machine, but portably provide good
+     * throughput by averaging over these factors.  Further, even if
+     * we did try to use such information, we do not usually have a
+     * basis for exploiting it.  For example, some sets of tasks
+     * profit from cache affinities, but others are harmed by cache
+     * pollution effects. Additionally, even though it requires
+     * scanning, long-term throughput is often best using random
+     * selection rather than directed selection policies, so cheap
+     * randomization of sufficient quality is used whenever
+     * applicable.  Various Marsaglia XorShifts (some with different
+     * shift constants) are inlined at use points.
      *
      * WorkQueues are also used in a similar way for tasks submitted
      * to the pool. We cannot mix these tasks in the same queues used
-     * for work-stealing (this would contaminate lifo/fifo
-     * processing). Instead, we randomly associate submission queues
+     * by workers. Instead, we randomly associate submission queues
      * with submitting threads, using a form of hashing.  The
      * ThreadLocalRandom probe value serves as a hash code for
      * choosing existing queues, and may be randomly repositioned upon
      * contention with other submitters.  In essence, submitters act
      * like workers except that they are restricted to executing local
      * tasks that they submitted (or in the case of CountedCompleters,
-     * others with the same root task).  However, because most
-     * shared/external queue operations are more expensive than
-     * internal, and because, at steady state, external submitters
-     * will compete for CPU with workers, ForkJoinTask.join and
-     * related methods disable them from repeatedly helping to process
-     * tasks if all workers are active.  Insertion of tasks in shared
+     * others with the same root task).  Insertion of tasks in shared
      * mode requires a lock (mainly to protect in the case of
-     * resizing) but we use only a simple spinlock (using bits in
-     * field qlock), because submitters encountering a busy queue move
-     * on to try or create other queues -- they block only when
-     * creating and registering new queues.
+     * resizing) but we use only a simple spinlock (using field
+     * qlock), because submitters encountering a busy queue move on to
+     * try or create other queues -- they block only when creating and
+     * registering new queues. Additionally, "qlock" saturates to an
+     * unlockable value (-1) at shutdown. Unlocking still can be and
+     * is performed by cheaper ordered writes of "qlock" in successful
+     * cases, but uses CAS in unsuccessful cases.
      *
      * Management
      * ==========
      *
      * The main throughput advantages of work-stealing stem from
      * decentralized control -- workers mostly take tasks from
-     * themselves or each other. We cannot negate this in the
-     * implementation of other management responsibilities. The main
-     * tactic for avoiding bottlenecks is packing nearly all
-     * essentially atomic control state into two volatile variables
-     * that are by far most often read (not written) as status and
-     * consistency checks.
+     * themselves or each other, at rates that can exceed a billion
+     * per second.  The pool itself creates, activates (enables
+     * scanning for and running tasks), deactivates, blocks, and
+     * terminates threads, all with minimal central information.
+     * There are only a few properties that we can globally track or
+     * maintain, so we pack them into a small number of variables,
+     * often maintaining atomicity without blocking or locking.
+     * Nearly all essentially atomic control state is held in two
+     * volatile variables that are by far most often read (not
+     * written) as status and consistency checks. (Also, field
+     * "config" holds unchanging configuration state.)
      *
-     * Field "ctl" contains 64 bits holding all the information needed
-     * to atomically decide to add, inactivate, enqueue (on an event
+     * Field "ctl" contains 64 bits holding information needed to
+     * atomically decide to add, inactivate, enqueue (on an event
      * queue), dequeue, and/or re-activate workers.  To enable this
      * packing, we restrict maximum parallelism to (1<<15)-1 (which is
      * far in excess of normal operating range) to allow ids, counts,
      * and their negations (used for thresholding) to fit into 16bit
-     * fields.
+     * subfields.
      *
-     * Field "plock" is a form of sequence lock with a saturating
-     * shutdown bit (similarly for per-queue "qlocks"), mainly
-     * protecting updates to the workQueues array, as well as to
-     * enable shutdown.  When used as a lock, it is normally only very
-     * briefly held, so is nearly always available after at most a
-     * brief spin, but we use a monitor-based backup strategy to
-     * block when needed.
+     * Field "runState" holds lockable state bits (STARTED, STOP, etc)
+     * also protecting updates to the workQueues array.  When used as
+     * a lock, it is normally held only for a few instructions (the
+     * only exceptions are one-time array initialization and uncommon
+     * resizing), so is nearly always available after at most a brief
+     * spin. But to be extra-cautious, after spinning, method
+     * awaitRunStateLock (called only if an initial CAS fails), uses a
+     * wait/notify mechanics on a builtin monitor to block when
+     * (rarely) needed. This would be a terrible idea for a highly
+     * contended lock, but most pools run without the lock ever
+     * contending after the spin limit, so this works fine as a more
+     * conservative alternative. Because we don't otherwise have an
+     * internal Object to use as a monitor, the "stealCounter" (an
+     * AtomicLong) is used when available (it too must be lazily
+     * initialized; see externalSubmit).
+     *
+     * Usages of "runState" vs "ctl" interact in only one case:
+     * deciding to add a worker thread (see tryAddWorker), in which
+     * case the ctl CAS is performed while the lock is held.
      *
      * Recording WorkQueues.  WorkQueues are recorded in the
-     * "workQueues" array that is created upon first use and expanded
-     * if necessary.  Updates to the array while recording new workers
-     * and unrecording terminated ones are protected from each other
-     * by a lock but the array is otherwise concurrently readable, and
-     * accessed directly.  To simplify index-based operations, the
-     * array size is always a power of two, and all readers must
-     * tolerate null slots. Worker queues are at odd indices. Shared
-     * (submission) queues are at even indices, up to a maximum of 64
-     * slots, to limit growth even if array needs to expand to add
-     * more workers. Grouping them together in this way simplifies and
-     * speeds up task scanning.
+     * "workQueues" array. The array is created upon first use (see
+     * externalSubmit) and expanded if necessary.  Updates to the
+     * array while recording new workers and unrecording terminated
+     * ones are protected from each other by the runState lock, but
+     * the array is otherwise concurrently readable, and accessed
+     * directly. We also ensure that reads of the array reference
+     * itself never become too stale. To simplify index-based
+     * operations, the array size is always a power of two, and all
+     * readers must tolerate null slots. Worker queues are at odd
+     * indices. Shared (submission) queues are at even indices, up to
+     * a maximum of 64 slots, to limit growth even if array needs to
+     * expand to add more workers. Grouping them together in this way
+     * simplifies and speeds up task scanning.
      *
      * All worker thread creation is on-demand, triggered by task
      * submissions, replacement of terminated workers, and/or
      * compensation for blocked workers. However, all other support
      * code is set up to work with other policies.  To ensure that we
-     * do not hold on to worker references that would prevent GC, ALL
+     * do not hold on to worker references that would prevent GC, All
      * accesses to workQueues are via indices into the workQueues
      * array (which is one source of some of the messy code
      * constructions here). In essence, the workQueues array serves as
-     * a weak reference mechanism. Thus for example the wait queue
-     * field of ctl stores indices, not references.  Access to the
-     * workQueues in associated methods (for example signalWork) must
-     * both index-check and null-check the IDs. All such accesses
-     * ignore bad IDs by returning out early from what they are doing,
-     * since this can only be associated with termination, in which
-     * case it is OK to give up.  All uses of the workQueues array
-     * also check that it is non-null (even if previously
-     * non-null). This allows nulling during termination, which is
-     * currently not necessary, but remains an option for
-     * resource-revocation-based shutdown schemes. It also helps
-     * reduce JIT issuance of uncommon-trap code, which tends to
-     * unnecessarily complicate control flow in some methods.
+     * a weak reference mechanism. Thus for example the stack top
+     * subfield of ctl stores indices, not references.
      *
-     * Event Queuing. Unlike HPC work-stealing frameworks, we cannot
-     * let workers spin indefinitely scanning for tasks when none can
-     * be found immediately, and we cannot start/resume workers unless
-     * there appear to be tasks available.  On the other hand, we must
-     * quickly prod them into action when new tasks are submitted or
-     * generated. In many usages, ramp-up time to activate workers is
-     * the main limiting factor in overall performance (this is
-     * compounded at program start-up by JIT compilation and
-     * allocation). So we try to streamline this as much as possible.
-     * We park/unpark workers after placing in an event wait queue
-     * when they cannot find work. This "queue" is actually a simple
-     * Treiber stack, headed by the "id" field of ctl, plus a 15bit
-     * counter value (that reflects the number of times a worker has
-     * been inactivated) to avoid ABA effects (we need only as many
-     * version numbers as worker threads). Successors are held in
-     * field WorkQueue.nextWait.  Queuing deals with several intrinsic
-     * races, mainly that a task-producing thread can miss seeing (and
-     * signalling) another thread that gave up looking for work but
-     * has not yet entered the wait queue. We solve this by requiring
-     * a full sweep of all workers (via repeated calls to method
-     * scan()) both before and after a newly waiting worker is added
-     * to the wait queue.  Because enqueued workers may actually be
-     * rescanning rather than waiting, we set and clear the "parker"
+     * Queuing Idle Workers. Unlike HPC work-stealing frameworks, we
+     * cannot let workers spin indefinitely scanning for tasks when
+     * none can be found immediately, and we cannot start/resume
+     * workers unless there appear to be tasks available.  On the
+     * other hand, we must quickly prod them into action when new
+     * tasks are submitted or generated. In many usages, ramp-up time
+     * to activate workers is the main limiting factor in overall
+     * performance, which is compounded at program start-up by JIT
+     * compilation and allocation. So we streamline this as much as
+     * possible.
+     *
+     * The "ctl" field atomically maintains active and total worker
+     * counts as well as a queue to place waiting threads so they can
+     * be located for signalling. Active counts also play the role of
+     * quiescence indicators, so are decremented when workers believe
+     * that there are no more tasks to execute. The "queue" is
+     * actually a form of Treiber stack.  A stack is ideal for
+     * activating threads in most-recently used order. This improves
+     * performance and locality, outweighing the disadvantages of
+     * being prone to contention and inability to release a worker
+     * unless it is topmost on stack.  We park/unpark workers after
+     * pushing on the idle worker stack (represented by the lower
+     * 32bit subfield of ctl) when they cannot find work.  The top
+     * stack state holds the value of the "scanState" field of the
+     * worker: its index and status, plus a version counter that, in
+     * addition to the count subfields (also serving as version
+     * stamps) provide protection against Treiber stack ABA effects.
+     *
+     * Field scanState is used by both workers and the pool to manage
+     * and track whether a worker is INACTIVE (possibly blocked
+     * waiting for a signal), or SCANNING for tasks (when neither hold
+     * it is busy running tasks).  When a worker is inactivated, its
+     * scanState field is set, and is prevented from executing tasks,
+     * even though it must scan once for them to avoid queuing
+     * races. Note that scanState updates lag queue CAS releases so
+     * usage requires care. When queued, the lower 16 bits of
+     * scanState must hold its pool index. So we place the index there
+     * upon initialization (see registerWorker) and otherwise keep it
+     * there or restore it when necessary.
+     *
+     * Memory ordering.  See "Correct and Efficient Work-Stealing for
+     * Weak Memory Models" by Le, Pop, Cohen, and Nardelli, PPoPP 2013
+     * (http://www.di.ens.fr/~zappa/readings/ppopp13.pdf) for an
+     * analysis of memory ordering requirements in work-stealing
+     * algorithms similar to the one used here.  We usually need
+     * stronger than minimal ordering because we must sometimes signal
+     * workers, requiring Dekker-like full-fences to avoid lost
+     * signals.  Arranging for enough ordering without expensive
+     * over-fencing requires tradeoffs among the supported means of
+     * expressing access constraints. The most central operations,
+     * taking from queues and updating ctl state, require full-fence
+     * CAS.  Array slots are read using the emulation of volatiles
+     * provided by Unsafe.  Access from other threads to WorkQueue
+     * base, top, and array requires a volatile load of the first of
+     * any of these read.  We use the convention of declaring the
+     * "base" index volatile, and always read it before other fields.
+     * The owner thread must ensure ordered updates, so writes use
+     * ordered intrinsics unless they can piggyback on those for other
+     * writes.  Similar conventions and rationales hold for other
+     * WorkQueue fields (such as "currentSteal") that are only written
+     * by owners but observed by others.
+     *
+     * Creating workers. To create a worker, we pre-increment total
+     * count (serving as a reservation), and attempt to construct a
+     * ForkJoinWorkerThread via its factory. Upon construction, the
+     * new thread invokes registerWorker, where it constructs a
+     * WorkQueue and is assigned an index in the workQueues array
+     * (expanding the array if necessary). The thread is then
+     * started. Upon any exception across these steps, or null return
+     * from factory, deregisterWorker adjusts counts and records
+     * accordingly.  If a null return, the pool continues running with
+     * fewer than the target number workers. If exceptional, the
+     * exception is propagated, generally to some external caller.
+     * Worker index assignment avoids the bias in scanning that would
+     * occur if entries were sequentially packed starting at the front
+     * of the workQueues array. We treat the array as a simple
+     * power-of-two hash table, expanding as needed. The seedIndex
+     * increment ensures no collisions until a resize is needed or a
+     * worker is deregistered and replaced, and thereafter keeps
+     * probability of collision low. We cannot use
+     * ThreadLocalRandom.getProbe() for similar purposes here because
+     * the thread has not started yet, but do so for creating
+     * submission queues for existing external threads.
+     *
+     * Deactivation and waiting. Queuing encounters several intrinsic
+     * races; most notably that a task-producing thread can miss
+     * seeing (and signalling) another thread that gave up looking for
+     * work but has not yet entered the wait queue.  When a worker
+     * cannot find a task to steal, it deactivates and enqueues. Very
+     * often, the lack of tasks is transient due to GC or OS
+     * scheduling. To reduce false-alarm deactivation, scanners
+     * compute checksums of queue states during sweeps.  (The
+     * stability checks used here and elsewhere are probabilistic
+     * variants of snapshot techniques -- see Herlihy & Shavit.)
+     * Workers give up and try to deactivate only after the sum is
+     * stable across scans. Further, to avoid missed signals, they
+     * repeat this scanning process after successful enqueuing until
+     * again stable.  In this state, the worker cannot take/run a task
+     * it sees until it is released from the queue, so the worker
+     * itself eventually tries to release itself or any successor (see
+     * tryRelease).  Otherwise, upon an empty scan, a deactivated
+     * worker uses an adaptive local spin construction (see awaitWork)
+     * before blocking (via park). Note the unusual conventions about
+     * Thread.interrupts surrounding parking and other blocking:
+     * Because interrupts are used solely to alert threads to check
+     * termination, which is checked anyway upon blocking, we clear
+     * status (using Thread.interrupted) before any call to park, so
+     * that park does not immediately return due to status being set
+     * via some other unrelated call to interrupt in user code.
+     *
+     * Signalling and activation.  Workers are created or activated
+     * only when there appears to be at least one task they might be
+     * able to find and execute.  Upon push (either by a worker or an
+     * external submission) to a previously (possibly) empty queue,
+     * workers are signalled if idle, or created if fewer exist than
+     * the given parallelism level.  These primary signals are
+     * buttressed by others whenever other threads remove a task from
+     * a queue and notice that there are other tasks there as well.
+     * On most platforms, signalling (unpark) overhead time is
+     * noticeably long, and the time between signalling a thread and
+     * it actually making progress can be very noticeably long, so it
+     * is worth offloading these delays from critical paths as much as
+     * possible. Also, because inactive workers are often rescanning
+     * or spinning rather than blocking, we set and clear the "parker"
      * field of WorkQueues to reduce unnecessary calls to unpark.
      * (This requires a secondary recheck to avoid missed signals.)
-     * Note the unusual conventions about Thread.interrupts
-     * surrounding parking and other blocking: Because interrupts are
-     * used solely to alert threads to check termination, which is
-     * checked anyway upon blocking, we clear status (using
-     * Thread.interrupted) before any call to park, so that park does
-     * not immediately return due to status being set via some other
-     * unrelated call to interrupt in user code.
-     *
-     * Signalling.  We create or wake up workers only when there
-     * appears to be at least one task they might be able to find and
-     * execute.  When a submission is added or another worker adds a
-     * task to a queue that has fewer than two tasks, they signal
-     * waiting workers (or trigger creation of new ones if fewer than
-     * the given parallelism level -- signalWork).  These primary
-     * signals are buttressed by others whenever other threads remove
-     * a task from a queue and notice that there are other tasks there
-     * as well.  So in general, pools will be over-signalled. On most
-     * platforms, signalling (unpark) overhead time is noticeably
-     * long, and the time between signalling a thread and it actually
-     * making progress can be very noticeably long, so it is worth
-     * offloading these delays from critical paths as much as
-     * possible. Additionally, workers spin-down gradually, by staying
-     * alive so long as they see the ctl state changing.  Similar
-     * stability-sensing techniques are also used before blocking in
-     * awaitJoin and helpComplete.
      *
      * Trimming workers. To release resources after periods of lack of
      * use, a worker starting to wait when the pool is quiescent will
-     * time out and terminate if the pool has remained quiescent for a
-     * given period -- a short period if there are more threads than
-     * parallelism, longer as the number of threads decreases. This
-     * will slowly propagate, eventually terminating all workers after
-     * periods of non-use.
+     * time out and terminate (see awaitWork) if the pool has remained
+     * quiescent for period IDLE_TIMEOUT, increasing the period as the
+     * number of threads decreases, eventually removing all workers.
+     * Also, when more than two spare threads exist, excess threads
+     * are immediately terminated at the next quiescent point.
+     * (Padding by two avoids hysteresis.)
      *
-     * Shutdown and Termination. A call to shutdownNow atomically sets
-     * a plock bit and then (non-atomically) sets each worker's
-     * qlock status, cancels all unprocessed tasks, and wakes up
-     * all waiting workers.  Detecting whether termination should
-     * commence after a non-abrupt shutdown() call requires more work
-     * and bookkeeping. We need consensus about quiescence (i.e., that
-     * there is no more work). The active count provides a primary
-     * indication but non-abrupt shutdown still requires a rechecking
-     * scan for any workers that are inactive but not queued.
+     * Shutdown and Termination. A call to shutdownNow invokes
+     * tryTerminate to atomically set a runState bit. The calling
+     * thread, as well as every other worker thereafter terminating,
+     * helps terminate others by setting their (qlock) status,
+     * cancelling their unprocessed tasks, and waking them up, doing
+     * so repeatedly until stable (but with a loop bounded by the
+     * number of workers).  Calls to non-abrupt shutdown() preface
+     * this by checking whether termination should commence. This
+     * relies primarily on the active count bits of "ctl" maintaining
+     * consensus -- tryTerminate is called from awaitWork whenever
+     * quiescent. However, external submitters do not take part in
+     * this consensus.  So, tryTerminate sweeps through queues (until
+     * stable) to ensure lack of in-flight submissions and workers
+     * about to process them before triggering the "STOP" phase of
+     * termination. (Note: there is an intrinsic conflict if
+     * helpQuiescePool is called when shutdown is enabled. Both wait
+     * for quiescence, but tryTerminate is biased to not trigger until
+     * helpQuiescePool completes.)
+     *
      *
      * Joining Tasks
      * =============
@@ -403,9 +528,9 @@
      * just let them block (as in Thread.join).  We also cannot just
      * reassign the joiner's run-time stack with another and replace
      * it later, which would be a form of "continuation", that even if
-     * possible is not necessarily a good idea since we sometimes need
-     * both an unblocked task and its continuation to progress.
-     * Instead we combine two tactics:
+     * possible is not necessarily a good idea since we may need both
+     * an unblocked task and its continuation to progress.  Instead we
+     * combine two tactics:
      *
      *   Helping: Arranging for the joiner to execute some task that it
      *      would be running if the steal had not occurred.
@@ -425,16 +550,16 @@
      * The ManagedBlocker extension API can't use helping so relies
      * only on compensation in method awaitBlocker.
      *
-     * The algorithm in tryHelpStealer entails a form of "linear"
-     * helping: Each worker records (in field currentSteal) the most
-     * recent task it stole from some other worker. Plus, it records
-     * (in field currentJoin) the task it is currently actively
-     * joining. Method tryHelpStealer uses these markers to try to
-     * find a worker to help (i.e., steal back a task from and execute
-     * it) that could hasten completion of the actively joined task.
-     * In essence, the joiner executes a task that would be on its own
-     * local deque had the to-be-joined task not been stolen. This may
-     * be seen as a conservative variant of the approach in Wagner &
+     * The algorithm in helpStealer entails a form of "linear
+     * helping".  Each worker records (in field currentSteal) the most
+     * recent task it stole from some other worker (or a submission).
+     * It also records (in field currentJoin) the task it is currently
+     * actively joining. Method helpStealer uses these markers to try
+     * to find a worker to help (i.e., steal back a task from and
+     * execute it) that could hasten completion of the actively joined
+     * task.  Thus, the joiner executes a task that would be on its
+     * own local deque had the to-be-joined task not been stolen. This
+     * is a conservative variant of the approach described in Wagner &
      * Calder "Leapfrogging: a portable technique for implementing
      * efficient futures" SIGPLAN Notices, 1993
      * (http://portal.acm.org/citation.cfm?id=155354). It differs in
@@ -452,37 +577,40 @@
      * which means that we miss links in the chain during long-lived
      * tasks, GC stalls etc (which is OK since blocking in such cases
      * is usually a good idea).  (4) We bound the number of attempts
-     * to find work (see MAX_HELP) and fall back to suspending the
+     * to find work using checksums and fall back to suspending the
      * worker and if necessary replacing it with another.
      *
-     * Helping actions for CountedCompleters are much simpler: Method
-     * helpComplete can take and execute any task with the same root
-     * as the task being waited on. However, this still entails some
-     * traversal of completer chains, so is less efficient than using
-     * CountedCompleters without explicit joins.
+     * Helping actions for CountedCompleters do not require tracking
+     * currentJoins: Method helpComplete takes and executes any task
+     * with the same root as the task being waited on (preferring
+     * local pops to non-local polls). However, this still entails
+     * some traversal of completer chains, so is less efficient than
+     * using CountedCompleters without explicit joins.
      *
-     * It is impossible to keep exactly the target parallelism number
-     * of threads running at any given time.  Determining the
-     * existence of conservatively safe helping targets, the
-     * availability of already-created spares, and the apparent need
-     * to create new spares are all racy, so we rely on multiple
-     * retries of each.  Compensation in the apparent absence of
-     * helping opportunities is challenging to control on JVMs, where
-     * GC and other activities can stall progress of tasks that in
-     * turn stall out many other dependent tasks, without us being
-     * able to determine whether they will ever require compensation.
-     * Even though work-stealing otherwise encounters little
-     * degradation in the presence of more threads than cores,
-     * aggressively adding new threads in such cases entails risk of
-     * unwanted positive feedback control loops in which more threads
-     * cause more dependent stalls (as well as delayed progress of
-     * unblocked threads to the point that we know they are available)
-     * leading to more situations requiring more threads, and so
-     * on. This aspect of control can be seen as an (analytically
-     * intractable) game with an opponent that may choose the worst
-     * (for us) active thread to stall at any time.  We take several
-     * precautions to bound losses (and thus bound gains), mainly in
-     * methods tryCompensate and awaitJoin.
+     * Compensation does not aim to keep exactly the target
+     * parallelism number of unblocked threads running at any given
+     * time. Some previous versions of this class employed immediate
+     * compensations for any blocked join. However, in practice, the
+     * vast majority of blockages are transient byproducts of GC and
+     * other JVM or OS activities that are made worse by replacement.
+     * Currently, compensation is attempted only after validating that
+     * all purportedly active threads are processing tasks by checking
+     * field WorkQueue.scanState, which eliminates most false
+     * positives.  Also, compensation is bypassed (tolerating fewer
+     * threads) in the most common case in which it is rarely
+     * beneficial: when a worker with an empty queue (thus no
+     * continuation tasks) blocks on a join and there still remain
+     * enough threads to ensure liveness.
+     *
+     * The compensation mechanism may be bounded.  Bounds for the
+     * commonPool (see commonMaxSpares) better enable JVMs to cope
+     * with programming errors and abuse before running out of
+     * resources to do so. In other cases, users may supply factories
+     * that limit thread construction. The effects of bounding in this
+     * pool (like all others) is imprecise.  Total worker counts are
+     * decremented when threads deregister, not when they exit and
+     * resources are reclaimed by the JVM and OS. So the number of
+     * simultaneously live threads may transiently exceed bounds.
      *
      * Common Pool
      * ===========
@@ -492,34 +620,52 @@
      * never be used, we minimize initial construction overhead and
      * footprint to the setup of about a dozen fields, with no nested
      * allocation. Most bootstrapping occurs within method
-     * fullExternalPush during the first submission to the pool.
+     * externalSubmit during the first submission to the pool.
      *
      * When external threads submit to the common pool, they can
-     * perform subtask processing (see externalHelpJoin and related
-     * methods).  This caller-helps policy makes it sensible to set
-     * common pool parallelism level to one (or more) less than the
-     * total number of available cores, or even zero for pure
-     * caller-runs.  We do not need to record whether external
-     * submissions are to the common pool -- if not, externalHelpJoin
-     * returns quickly (at the most helping to signal some common pool
-     * workers). These submitters would otherwise be blocked waiting
-     * for completion, so the extra effort (with liberally sprinkled
-     * task status checks) in inapplicable cases amounts to an odd
-     * form of limited spin-wait before blocking in ForkJoinTask.join.
+     * perform subtask processing (see externalHelpComplete and
+     * related methods) upon joins.  This caller-helps policy makes it
+     * sensible to set common pool parallelism level to one (or more)
+     * less than the total number of available cores, or even zero for
+     * pure caller-runs.  We do not need to record whether external
+     * submissions are to the common pool -- if not, external help
+     * methods return quickly. These submitters would otherwise be
+     * blocked waiting for completion, so the extra effort (with
+     * liberally sprinkled task status checks) in inapplicable cases
+     * amounts to an odd form of limited spin-wait before blocking in
+     * ForkJoinTask.join.
      *
      * As a more appropriate default in managed environments, unless
      * overridden by system properties, we use workers of subclass
      * InnocuousForkJoinWorkerThread when there is a SecurityManager
      * present. These workers have no permissions set, do not belong
      * to any user-defined ThreadGroup, and erase all ThreadLocals
-     * after executing any top-level task (see WorkQueue.runTask). The
-     * associated mechanics (mainly in ForkJoinWorkerThread) may be
-     * JVM-dependent and must access particular Thread class fields to
-     * achieve this effect.
+     * after executing any top-level task (see WorkQueue.runTask).
+     * The associated mechanics (mainly in ForkJoinWorkerThread) may
+     * be JVM-dependent and must access particular Thread class fields
+     * to achieve this effect.
      *
      * Style notes
      * ===========
      *
+     * Memory ordering relies mainly on Unsafe intrinsics that carry
+     * the further responsibility of explicitly performing null- and
+     * bounds- checks otherwise carried out implicitly by JVMs.  This
+     * can be awkward and ugly, but also reflects the need to control
+     * outcomes across the unusual cases that arise in very racy code
+     * with very few invariants. So these explicit checks would exist
+     * in some form anyway.  All fields are read into locals before
+     * use, and null-checked if they are references.  This is usually
+     * done in a "C"-like style of listing declarations at the heads
+     * of methods or blocks, and using inline assignments on first
+     * encounter.  Array bounds-checks are usually performed by
+     * masking with array.length-1, which relies on the invariant that
+     * these arrays are created with positive lengths, which is itself
+     * paranoically checked. Nearly all explicit checks lead to
+     * bypass/return, not exception throws, because they may
+     * legitimately arise due to cancellation/revocation during
+     * shutdown.
+     *
      * There is a lot of representation-level coupling among classes
      * ForkJoinPool, ForkJoinWorkerThread, and ForkJoinTask.  The
      * fields of WorkQueue maintain data structures managed by
@@ -527,22 +673,13 @@
      * trying to reduce this, since any associated future changes in
      * representations will need to be accompanied by algorithmic
      * changes anyway. Several methods intrinsically sprawl because
-     * they must accumulate sets of consistent reads of volatiles held
-     * in local variables.  Methods signalWork() and scan() are the
-     * main bottlenecks, so are especially heavily
-     * micro-optimized/mangled.  There are lots of inline assignments
-     * (of form "while ((local = field) != 0)") which are usually the
-     * simplest way to ensure the required read orderings (which are
-     * sometimes critical). This leads to a "C"-like style of listing
-     * declarations of these locals at the heads of methods or blocks.
-     * There are several occurrences of the unusual "do {} while
-     * (!cas...)"  which is the simplest way to force an update of a
-     * CAS'ed variable. There are also other coding oddities (including
-     * several unnecessary-looking hoisted null checks) that help
-     * some methods perform reasonably even when interpreted (not
-     * compiled).
+     * they must accumulate sets of consistent reads of fields held in
+     * local variables.  There are also other coding oddities
+     * (including several unnecessary-looking hoisted null checks)
+     * that help some methods perform reasonably even when interpreted
+     * (not compiled).
      *
-     * The order of declarations in this file is:
+     * The order of declarations in this file is (with a few exceptions):
      * (1) Static utility functions
      * (2) Nested (static) classes
      * (3) Static fields
@@ -609,56 +746,37 @@
         public final boolean exec() { return true; }
     }
 
+    // Constants shared across ForkJoinPool and WorkQueue
+
+    // Bounds
+    static final int SMASK        = 0xffff;        // short bits == max index
+    static final int MAX_CAP      = 0x7fff;        // max #workers - 1
+    static final int EVENMASK     = 0xfffe;        // even short bits
+    static final int SQMASK       = 0x007e;        // max 64 (even) slots
+
+    // Masks and units for WorkQueue.scanState and ctl sp subfield
+    static final int SCANNING     = 1;             // false when running tasks
+    static final int INACTIVE     = 1 << 31;       // must be negative
+    static final int SS_SEQ       = 1 << 16;       // version count
+
+    // Mode bits for ForkJoinPool.config and WorkQueue.config
+    static final int MODE_MASK    = 0xffff << 16;  // top half of int
+    static final int LIFO_QUEUE   = 0;
+    static final int FIFO_QUEUE   = 1 << 16;
+    static final int SHARED_QUEUE = 1 << 31;       // must be negative
+
     /**
      * Queues supporting work-stealing as well as external task
-     * submission. See above for main rationale and algorithms.
-     * Implementation relies heavily on "Unsafe" intrinsics
-     * and selective use of "volatile":
-     *
-     * Field "base" is the index (mod array.length) of the least valid
-     * queue slot, which is always the next position to steal (poll)
-     * from if nonempty. Reads and writes require volatile orderings
-     * but not CAS, because updates are only performed after slot
-     * CASes.
-     *
-     * Field "top" is the index (mod array.length) of the next queue
-     * slot to push to or pop from. It is written only by owner thread
-     * for push, or under lock for external/shared push, and accessed
-     * by other threads only after reading (volatile) base.  Both top
-     * and base are allowed to wrap around on overflow, but (top -
-     * base) (or more commonly -(base - top) to force volatile read of
-     * base before top) still estimates size. The lock ("qlock") is
-     * forced to -1 on termination, causing all further lock attempts
-     * to fail. (Note: we don't need CAS for termination state because
-     * upon pool shutdown, all shared-queues will stop being used
-     * anyway.)  Nearly all lock bodies are set up so that exceptions
-     * within lock bodies are "impossible" (modulo JVM errors that
-     * would cause failure anyway.)
-     *
-     * The array slots are read and written using the emulation of
-     * volatiles/atomics provided by Unsafe. Insertions must in
-     * general use putOrderedObject as a form of releasing store to
-     * ensure that all writes to the task object are ordered before
-     * its publication in the queue.  All removals entail a CAS to
-     * null.  The array is always a power of two. To ensure safety of
-     * Unsafe array operations, all accesses perform explicit null
-     * checks and implicit bounds checks via power-of-two masking.
-     *
-     * In addition to basic queuing support, this class contains
-     * fields described elsewhere to control execution. It turns out
-     * to work better memory-layout-wise to include them in this class
-     * rather than a separate class.
-     *
+     * submission. See above for descriptions and algorithms.
      * Performance on most platforms is very sensitive to placement of
      * instances of both WorkQueues and their arrays -- we absolutely
      * do not want multiple WorkQueue instances or multiple queue
-     * arrays sharing cache lines. (It would be best for queue objects
-     * and their arrays to share, but there is nothing available to
-     * help arrange that). The @Contended annotation alerts JVMs to
-     * try to keep instances apart.
+     * arrays sharing cache lines. The @Contended annotation alerts
+     * JVMs to try to keep instances apart.
      */
     @sun.misc.Contended
     static final class WorkQueue {
+
         /**
          * Capacity of work-stealing queue array upon initialization.
          * Must be a power of two; at least 4, but should be larger to
@@ -679,13 +797,13 @@
          */
         static final int MAXIMUM_QUEUE_CAPACITY = 1 << 26; // 64M
 
-        volatile int eventCount;   // encoded inactivation count; < 0 if inactive
-        int nextWait;              // encoded record of next event waiter
+        // Instance fields
+        volatile int scanState;    // versioned, <0: inactive; odd:scanning
+        int stackPred;             // pool stack (ctl) predecessor
         int nsteals;               // number of steals
-        int hint;                  // steal index hint
-        short poolIndex;           // index of this queue in pool
-        final short mode;          // 0: lifo, > 0: fifo, < 0: shared
-        volatile int qlock;        // 1: locked, -1: terminate; else 0
+        int hint;                  // randomization and stealer index hint
+        int config;                // pool index and mode
+        volatile int qlock;        // 1: locked, < 0: terminate; else 0
         volatile int base;         // index of next slot for poll
         int top;                   // index of next slot for push
         ForkJoinTask<?>[] array;   // the elements (initially unallocated)
@@ -693,19 +811,23 @@
         final ForkJoinWorkerThread owner; // owning thread or null if shared
         volatile Thread parker;    // == owner during call to park; else null
         volatile ForkJoinTask<?> currentJoin;  // task being joined in awaitJoin
-        ForkJoinTask<?> currentSteal; // current non-local task being executed
+        volatile ForkJoinTask<?> currentSteal; // mainly used by helpStealer
 
-        WorkQueue(ForkJoinPool pool, ForkJoinWorkerThread owner, int mode,
-                  int seed) {
+        WorkQueue(ForkJoinPool pool, ForkJoinWorkerThread owner) {
             this.pool = pool;
             this.owner = owner;
-            this.mode = (short)mode;
-            this.hint = seed; // store initial seed for runWorker
             // Place indices in the center of array (that is not yet allocated)
             base = top = INITIAL_QUEUE_CAPACITY >>> 1;
         }
 
         /**
+         * Returns an exportable index (used by ForkJoinWorkerThread).
+         */
+        final int getPoolIndex() {
+            return (config & 0xffff) >>> 1; // ignore odd/even tag bit
+        }
+
+        /**
          * Returns the approximate number of tasks in the queue.
          */
         final int queueSize() {
@@ -719,12 +841,10 @@
          * near-empty queue has at least one unclaimed task.
          */
         final boolean isEmpty() {
-            ForkJoinTask<?>[] a; int m, s;
-            int n = base - (s = top);
-            return (n >= 0 ||
-                    (n == -1 &&
-                     ((a = array) == null ||
-                      (m = a.length - 1) < 0 ||
+            ForkJoinTask<?>[] a; int n, m, s;
+            return ((n = base - (s = top)) >= 0 ||
+                    (n == -1 &&           // possibly one task
+                     ((a = array) == null || (m = a.length - 1) < 0 ||
                       U.getObject
                       (a, (long)((m & (s - 1)) << ASHIFT) + ABASE) == null)));
         }
@@ -738,12 +858,15 @@
          */
         final void push(ForkJoinTask<?> task) {
             ForkJoinTask<?>[] a; ForkJoinPool p;
-            int s = top, n;
+            int b = base, s = top, n;
             if ((a = array) != null) {    // ignore if queue removed
-                int m = a.length - 1;
+                int m = a.length - 1;     // fenced write for task visibility
                 U.putOrderedObject(a, ((m & s) << ASHIFT) + ABASE, task);
-                if ((n = (top = s + 1) - base) <= 2)
-                    (p = pool).signalWork(p.workQueues, this);
+                U.putOrderedInt(this, QTOP, s + 1);
+                if ((n = s - b) <= 1) {
+                    if ((p = pool) != null)
+                        p.signalWork(p.workQueues, this);
+                }
                 else if (n >= m)
                     growArray();
             }
@@ -764,7 +887,7 @@
             if (oldA != null && (oldMask = oldA.length - 1) >= 0 &&
                 (t = top) - (b = base) > 0) {
                 int mask = size - 1;
-                do {
+                do { // emulate poll from old array, push to new array
                     ForkJoinTask<?> x;
                     int oldj = ((b & oldMask) << ASHIFT) + ABASE;
                     int j    = ((b &    mask) << ASHIFT) + ABASE;
@@ -789,7 +912,7 @@
                     if ((t = (ForkJoinTask<?>)U.getObject(a, j)) == null)
                         break;
                     if (U.compareAndSwapObject(a, j, t, null)) {
-                        top = s;
+                        U.putOrderedInt(this, QTOP, s);
                         return t;
                     }
                 }
@@ -800,7 +923,7 @@
         /**
          * Takes a task in FIFO order if b is base of queue and a task
          * can be claimed without contention. Specialized versions
-         * appear in ForkJoinPool methods scan and tryHelpStealer.
+         * appear in ForkJoinPool methods scan and helpStealer.
          */
         final ForkJoinTask<?> pollAt(int b) {
             ForkJoinTask<?> t; ForkJoinTask<?>[] a;
@@ -808,7 +931,7 @@
                 int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
                 if ((t = (ForkJoinTask<?>)U.getObjectVolatile(a, j)) != null &&
                     base == b && U.compareAndSwapObject(a, j, t, null)) {
-                    U.putOrderedInt(this, QBASE, b + 1);
+                    base = b + 1;
                     return t;
                 }
             }
@@ -823,16 +946,15 @@
             while ((b = base) - top < 0 && (a = array) != null) {
                 int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
                 t = (ForkJoinTask<?>)U.getObjectVolatile(a, j);
-                if (t != null) {
-                    if (U.compareAndSwapObject(a, j, t, null)) {
-                        U.putOrderedInt(this, QBASE, b + 1);
-                        return t;
+                if (base == b) {
+                    if (t != null) {
+                        if (U.compareAndSwapObject(a, j, t, null)) {
+                            base = b + 1;
+                            return t;
+                        }
                     }
-                }
-                else if (base == b) {
-                    if (b + 1 == top)
+                    else if (b + 1 == top) // now empty
                         break;
-                    Thread.yield(); // wait for lagging update (very rare)
                 }
             }
             return null;
@@ -842,7 +964,7 @@
          * Takes next task, if one exists, in order specified by mode.
          */
         final ForkJoinTask<?> nextLocalTask() {
-            return mode == 0 ? pop() : poll();
+            return (config & FIFO_QUEUE) == 0 ? pop() : poll();
         }
 
         /**
@@ -852,7 +974,7 @@
             ForkJoinTask<?>[] a = array; int m;
             if (a == null || (m = a.length - 1) < 0)
                 return null;
-            int i = mode == 0 ? top - 1 : base;
+            int i = (config & FIFO_QUEUE) == 0 ? top - 1 : base;
             int j = ((i & m) << ASHIFT) + ABASE;
             return (ForkJoinTask<?>)U.getObjectVolatile(a, j);
         }
@@ -860,13 +982,13 @@
         /**
          * Pops the given task only if it is at the current top.
          * (A shared version is available only via FJP.tryExternalUnpush)
-         */
+        */
         final boolean tryUnpush(ForkJoinTask<?> t) {
             ForkJoinTask<?>[] a; int s;
             if ((a = array) != null && (s = top) != base &&
                 U.compareAndSwapObject
                 (a, (((a.length - 1) & --s) << ASHIFT) + ABASE, t, null)) {
-                top = s;
+                U.putOrderedInt(this, QTOP, s);
                 return true;
             }
             return false;
@@ -876,9 +998,16 @@
          * Removes and cancels all known tasks, ignoring any exceptions.
          */
         final void cancelAll() {
-            ForkJoinTask.cancelIgnoringExceptions(currentJoin);
-            ForkJoinTask.cancelIgnoringExceptions(currentSteal);
-            for (ForkJoinTask<?> t; (t = poll()) != null; )
+            ForkJoinTask<?> t;
+            if ((t = currentJoin) != null) {
+                currentJoin = null;
+                ForkJoinTask.cancelIgnoringExceptions(t);
+            }
+            if ((t = currentSteal) != null) {
+                currentSteal = null;
+                ForkJoinTask.cancelIgnoringExceptions(t);
+            }
+            while ((t = poll()) != null)
                 ForkJoinTask.cancelIgnoringExceptions(t);
         }
 
@@ -893,167 +1022,186 @@
         }
 
         /**
-         * Executes a top-level task and any local tasks remaining
-         * after execution.
+         * Removes and executes all local tasks. If LIFO, invokes
+         * pollAndExecAll. Otherwise implements a specialized pop loop
+         * to exec until empty.
+         */
+        final void execLocalTasks() {
+            int b = base, m, s;
+            ForkJoinTask<?>[] a = array;
+            if (b - (s = top - 1) <= 0 && a != null &&
+                (m = a.length - 1) >= 0) {
+                if ((config & FIFO_QUEUE) == 0) {
+                    for (ForkJoinTask<?> t;;) {
+                        if ((t = (ForkJoinTask<?>)U.getAndSetObject
+                             (a, ((m & s) << ASHIFT) + ABASE, null)) == null)
+                            break;
+                        U.putOrderedInt(this, QTOP, s);
+                        t.doExec();
+                        if (base - (s = top - 1) > 0)
+                            break;
+                    }
+                }
+                else
+                    pollAndExecAll();
+            }
+        }
+
+        /**
+         * Executes the given task and any remaining local tasks.
          */
         final void runTask(ForkJoinTask<?> task) {
-            if ((currentSteal = task) != null) {
-                ForkJoinWorkerThread thread;
-                task.doExec();
-                ForkJoinTask<?>[] a = array;
-                int md = mode;
-                ++nsteals;
-                currentSteal = null;
-                if (md != 0)
-                    pollAndExecAll();
-                else if (a != null) {
-                    int s, m = a.length - 1;
-                    ForkJoinTask<?> t;
-                    while ((s = top - 1) - base >= 0 &&
-                           (t = (ForkJoinTask<?>)U.getAndSetObject
-                            (a, ((m & s) << ASHIFT) + ABASE, null)) != null) {
-                        top = s;
-                        t.doExec();
-                    }
-                }
-                if ((thread = owner) != null) // no need to do in finally clause
+            if (task != null) {
+                scanState &= ~SCANNING; // mark as busy
+                (currentSteal = task).doExec();
+                U.putOrderedObject(this, QCURRENTSTEAL, null); // release for GC
+                execLocalTasks();
+                ForkJoinWorkerThread thread = owner;
+                if (++nsteals < 0)      // collect on overflow
+                    transferStealCount(pool);
+                scanState |= SCANNING;
+                if (thread != null)
                     thread.afterTopLevelExec();
             }
         }
 
         /**
-         * If present, removes from queue and executes the given task,
-         * or any other cancelled task. Returns (true) on any CAS
-         * or consistency check failure so caller can retry.
-         *
-         * @return false if no progress can be made, else true
+         * Adds steal count to pool stealCounter if it exists, and resets.
          */
-        final boolean tryRemoveAndExec(ForkJoinTask<?> task) {
-            boolean stat;
-            ForkJoinTask<?>[] a; int m, s, b, n;
-            if (task != null && (a = array) != null && (m = a.length - 1) >= 0 &&
-                (n = (s = top) - (b = base)) > 0) {
-                boolean removed = false, empty = true;
-                stat = true;
-                for (ForkJoinTask<?> t;;) {           // traverse from s to b
-                    long j = ((--s & m) << ASHIFT) + ABASE;
-                    t = (ForkJoinTask<?>)U.getObject(a, j);
-                    if (t == null)                    // inconsistent length
-                        break;
-                    else if (t == task) {
-                        if (s + 1 == top) {           // pop
-                            if (!U.compareAndSwapObject(a, j, task, null))
-                                break;
-                            top = s;
-                            removed = true;
-                        }
-                        else if (base == b)           // replace with proxy
-                            removed = U.compareAndSwapObject(a, j, task,
-                                                             new EmptyTask());
-                        break;
-                    }
-                    else if (t.status >= 0)
-                        empty = false;
-                    else if (s + 1 == top) {          // pop and throw away
-                        if (U.compareAndSwapObject(a, j, t, null))
-                            top = s;
-                        break;
-                    }
-                    if (--n == 0) {
-                        if (!empty && base == b)
-                            stat = false;
-                        break;
-                    }
-                }
-                if (removed)
-                    task.doExec();
+        final void transferStealCount(ForkJoinPool p) {
+            AtomicLong sc;
+            if (p != null && (sc = p.stealCounter) != null) {
+                int s = nsteals;
+                nsteals = 0;            // if negative, correct for overflow
+                sc.getAndAdd((long)(s < 0 ? Integer.MAX_VALUE : s));
             }
-            else
-                stat = false;
-            return stat;
         }
 
         /**
-         * Tries to poll for and execute the given task or any other
-         * task in its CountedCompleter computation.
+         * If present, removes from queue and executes the given task,
+         * or any other cancelled task. Used only by awaitJoin.
+         *
+         * @return true if queue empty and task not known to be done
          */
-        final boolean pollAndExecCC(CountedCompleter<?> root) {
-            ForkJoinTask<?>[] a; int b; Object o; CountedCompleter<?> t, r;
-            if ((b = base) - top < 0 && (a = array) != null) {
-                long j = (((a.length - 1) & b) << ASHIFT) + ABASE;
-                if ((o = U.getObjectVolatile(a, j)) == null)
-                    return true; // retry
-                if (o instanceof CountedCompleter) {
-                    for (t = (CountedCompleter<?>)o, r = t;;) {
-                        if (r == root) {
-                            if (base == b &&
-                                U.compareAndSwapObject(a, j, t, null)) {
-                                U.putOrderedInt(this, QBASE, b + 1);
-                                t.doExec();
+        final boolean tryRemoveAndExec(ForkJoinTask<?> task) {
+            ForkJoinTask<?>[] a; int m, s, b, n;
+            if ((a = array) != null && (m = a.length - 1) >= 0 &&
+                task != null) {
+                while ((n = (s = top) - (b = base)) > 0) {
+                    for (ForkJoinTask<?> t;;) {      // traverse from s to b
+                        long j = ((--s & m) << ASHIFT) + ABASE;
+                        if ((t = (ForkJoinTask<?>)U.getObject(a, j)) == null)
+                            return s + 1 == top;     // shorter than expected
+                        else if (t == task) {
+                            boolean removed = false;
+                            if (s + 1 == top) {      // pop
+                                if (U.compareAndSwapObject(a, j, task, null)) {
+                                    U.putOrderedInt(this, QTOP, s);
+                                    removed = true;
+                                }
                             }
-                            return true;
+                            else if (base == b)      // replace with proxy
+                                removed = U.compareAndSwapObject(
+                                    a, j, task, new EmptyTask());
+                            if (removed)
+                                task.doExec();
+                            break;
                         }
-                        else if ((r = r.completer) == null)
-                            break; // not part of root computation
+                        else if (t.status < 0 && s + 1 == top) {
+                            if (U.compareAndSwapObject(a, j, t, null))
+                                U.putOrderedInt(this, QTOP, s);
+                            break;                  // was cancelled
+                        }
+                        if (--n == 0)
+                            return false;
                     }
+                    if (task.status < 0)
+                        return false;
                 }
             }
-            return false;
+            return true;
         }
 
         /**
-         * Tries to pop and execute the given task or any other task
-         * in its CountedCompleter computation.
+         * Pops task if in the same CC computation as the given task,
+         * in either shared or owned mode. Used only by helpComplete.
          */
-        final boolean externalPopAndExecCC(CountedCompleter<?> root) {
-            ForkJoinTask<?>[] a; int s; Object o; CountedCompleter<?> t, r;
+        final CountedCompleter<?> popCC(CountedCompleter<?> task, int mode) {
+            int s; ForkJoinTask<?>[] a; Object o;
             if (base - (s = top) < 0 && (a = array) != null) {
                 long j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE;
-                if ((o = U.getObject(a, j)) instanceof CountedCompleter) {
-                    for (t = (CountedCompleter<?>)o, r = t;;) {
-                        if (r == root) {
-                            if (U.compareAndSwapInt(this, QLOCK, 0, 1)) {
-                                if (top == s && array == a &&
-                                    U.compareAndSwapObject(a, j, t, null)) {
-                                    top = s - 1;
-                                    qlock = 0;
-                                    t.doExec();
+                if ((o = U.getObjectVolatile(a, j)) != null &&
+                    (o instanceof CountedCompleter)) {
+                    CountedCompleter<?> t = (CountedCompleter<?>)o;
+                    for (CountedCompleter<?> r = t;;) {
+                        if (r == task) {
+                            if (mode < 0) { // must lock
+                                if (U.compareAndSwapInt(this, QLOCK, 0, 1)) {
+                                    if (top == s && array == a &&
+                                        U.compareAndSwapObject(a, j, t, null)) {
+                                        U.putOrderedInt(this, QTOP, s - 1);
+                                        U.putOrderedInt(this, QLOCK, 0);
+                                        return t;
+                                    }
+                                    U.compareAndSwapInt(this, QLOCK, 1, 0);
                                 }
-                                else
-                                    qlock = 0;
                             }
-                            return true;
+                            else if (U.compareAndSwapObject(a, j, t, null)) {
+                                U.putOrderedInt(this, QTOP, s - 1);
+                                return t;
+                            }
+                            break;
                         }
-                        else if ((r = r.completer) == null)
+                        else if ((r = r.completer) == null) // try parent
                             break;
                     }
                 }
             }
-            return false;
+            return null;
         }
 
         /**
-         * Internal version
+         * Steals and runs a task in the same CC computation as the
+         * given task if one exists and can be taken without
+         * contention. Otherwise returns a checksum/control value for
+         * use by method helpComplete.
+         *
+         * @return 1 if successful, 2 if retryable (lost to another
+         * stealer), -1 if non-empty but no matching task found, else
+         * the base index, forced negative.
          */
-        final boolean internalPopAndExecCC(CountedCompleter<?> root) {
-            ForkJoinTask<?>[] a; int s; Object o; CountedCompleter<?> t, r;
-            if (base - (s = top) < 0 && (a = array) != null) {
-                long j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE;
-                if ((o = U.getObject(a, j)) instanceof CountedCompleter) {
-                    for (t = (CountedCompleter<?>)o, r = t;;) {
-                        if (r == root) {
-                            if (U.compareAndSwapObject(a, j, t, null)) {
-                                top = s - 1;
+        final int pollAndExecCC(CountedCompleter<?> task) {
+            int b, h; ForkJoinTask<?>[] a; Object o;
+            if ((b = base) - top >= 0 || (a = array) == null)
+                h = b | Integer.MIN_VALUE;  // to sense movement on re-poll
+            else {
+                long j = (((a.length - 1) & b) << ASHIFT) + ABASE;
+                if ((o = U.getObjectVolatile(a, j)) == null)
+                    h = 2;                  // retryable
+                else if (!(o instanceof CountedCompleter))
+                    h = -1;                 // unmatchable
+                else {
+                    CountedCompleter<?> t = (CountedCompleter<?>)o;
+                    for (CountedCompleter<?> r = t;;) {
+                        if (r == task) {
+                            if (base == b &&
+                                U.compareAndSwapObject(a, j, t, null)) {
+                                base = b + 1;
                                 t.doExec();
+                                h = 1;      // success
                             }
-                            return true;
+                            else
+                                h = 2;      // lost CAS
+                            break;
                         }
-                        else if ((r = r.completer) == null)
+                        else if ((r = r.completer) == null) {
+                            h = -1;         // unmatched
                             break;
+                        }
                     }
                 }
             }
-            return false;
+            return h;
         }
 
         /**
@@ -1061,28 +1209,31 @@
          */
         final boolean isApparentlyUnblocked() {
             Thread wt; Thread.State s;
-            return (eventCount >= 0 &&
+            return (scanState >= 0 &&
                     (wt = owner) != null &&
                     (s = wt.getState()) != Thread.State.BLOCKED &&
                     s != Thread.State.WAITING &&
                     s != Thread.State.TIMED_WAITING);
         }
 
-        // Unsafe mechanics
+        // Unsafe mechanics. Note that some are (and must be) the same as in FJP
         private static final sun.misc.Unsafe U;
-        private static final long QBASE;
+        private static final int  ABASE;
+        private static final int  ASHIFT;
+        private static final long QTOP;
         private static final long QLOCK;
-        private static final int ABASE;
-        private static final int ASHIFT;
+        private static final long QCURRENTSTEAL;
         static {
             try {
                 U = sun.misc.Unsafe.getUnsafe();
-                Class<?> k = WorkQueue.class;
+                Class<?> wk = WorkQueue.class;
                 Class<?> ak = ForkJoinTask[].class;
-                QBASE = U.objectFieldOffset
-                    (k.getDeclaredField("base"));
+                QTOP = U.objectFieldOffset
+                    (wk.getDeclaredField("top"));
                 QLOCK = U.objectFieldOffset
-                    (k.getDeclaredField("qlock"));
+                    (wk.getDeclaredField("qlock"));
+                QCURRENTSTEAL = U.objectFieldOffset
+                    (wk.getDeclaredField("currentSteal"));
                 ABASE = U.arrayBaseOffset(ak);
                 int scale = U.arrayIndexScale(ak);
                 if ((scale & (scale - 1)) != 0)
@@ -1126,6 +1277,11 @@
     static final int commonParallelism;
 
     /**
+     * Limit on spare thread construction in tryCompensate.
+     */
+    private static int commonMaxSpares;
+
+    /**
      * Sequence number for creating workerNamePrefix.
      */
     private static int poolNumberSequence;
@@ -1138,7 +1294,7 @@
         return ++poolNumberSequence;
     }
 
-    // static constants
+    // static configuration constants
 
     /**
      * Initial timeout value (in nanoseconds) for the thread
@@ -1148,27 +1304,32 @@
      * aggressive shrinkage during most transient stalls (long GCs
      * etc).
      */
-    private static final long IDLE_TIMEOUT      = 2000L * 1000L * 1000L; // 2sec
-
-    /**
-     * Timeout value when there are more threads than parallelism level
-     */
-    private static final long FAST_IDLE_TIMEOUT =  200L * 1000L * 1000L;
+    private static final long IDLE_TIMEOUT = 2000L * 1000L * 1000L; // 2sec
 
     /**
      * Tolerance for idle timeouts, to cope with timer undershoots
      */
-    private static final long TIMEOUT_SLOP = 2000000L;
+    private static final long TIMEOUT_SLOP = 20L * 1000L * 1000L;  // 20ms
 
     /**
-     * The maximum stolen->joining link depth allowed in method
-     * tryHelpStealer.  Must be a power of two.  Depths for legitimate
-     * chains are unbounded, but we use a fixed constant to avoid
-     * (otherwise unchecked) cycles and to bound staleness of
-     * traversal parameters at the expense of sometimes blocking when
-     * we could be helping.
+     * The initial value for commonMaxSpares during static
+     * initialization. The value is far in excess of normal
+     * requirements, but also far short of MAX_CAP and typical
+     * OS thread limits, so allows JVMs to catch misuse/abuse
+     * before running out of resources needed to do so.
      */
-    private static final int MAX_HELP = 64;
+    private static final int DEFAULT_COMMON_MAX_SPARES = 256;
+
+    /**
+     * Number of times to spin-wait before blocking. The spins (in
+     * awaitRunStateLock and awaitWork) currently use randomized
+     * spins. If/when MWAIT-like intrinsics becomes available, they
+     * may allow quieter spinning. The value of SPINS must be a power
+     * of two, at least 4. The current value causes spinning for a
+     * small fraction of typical context-switch times, well worthwhile
+     * given the typical likelihoods that blocking is not necessary.
+     */
+    private static final int SPINS  = 1 << 11;
 
     /**
      * Increment for seed generators. See class ThreadLocal for
@@ -1177,209 +1338,212 @@
     private static final int SEED_INCREMENT = 0x9e3779b9;
 
     /*
-     * Bits and masks for control variables
+     * Bits and masks for field ctl, packed with 4 16 bit subfields:
+     * AC: Number of active running workers minus target parallelism
+     * TC: Number of total workers minus target parallelism
+     * SS: version count and status of top waiting thread
+     * ID: poolIndex of top of Treiber stack of waiters
      *
-     * Field ctl is a long packed with:
-     * AC: Number of active running workers minus target parallelism (16 bits)
-     * TC: Number of total workers minus target parallelism (16 bits)
-     * ST: true if pool is terminating (1 bit)
-     * EC: the wait count of top waiting thread (15 bits)
-     * ID: poolIndex of top of Treiber stack of waiters (16 bits)
+     * When convenient, we can extract the lower 32 stack top bits
+     * (including version bits) as sp=(int)ctl.  The offsets of counts
+     * by the target parallelism and the positionings of fields makes
+     * it possible to perform the most common checks via sign tests of
+     * fields: When ac is negative, there are not enough active
+     * workers, when tc is negative, there are not enough total
+     * workers.  When sp is non-zero, there are waiting workers.  To
+     * deal with possibly negative fields, we use casts in and out of
+     * "short" and/or signed shifts to maintain signedness.
      *
-     * When convenient, we can extract the upper 32 bits of counts and
-     * the lower 32 bits of queue state, u = (int)(ctl >>> 32) and e =
-     * (int)ctl.  The ec field is never accessed alone, but always
-     * together with id and st. The offsets of counts by the target
-     * parallelism and the positionings of fields makes it possible to
-     * perform the most common checks via sign tests of fields: When
-     * ac is negative, there are not enough active workers, when tc is
-     * negative, there are not enough total workers, and when e is
-     * negative, the pool is terminating.  To deal with these possibly
-     * negative fields, we use casts in and out of "short" and/or
-     * signed shifts to maintain signedness.
-     *
-     * When a thread is queued (inactivated), its eventCount field is
-     * set negative, which is the only way to tell if a worker is
-     * prevented from executing tasks, even though it must continue to
-     * scan for them to avoid queuing races. Note however that
-     * eventCount updates lag releases so usage requires care.
-     *
-     * Field plock is an int packed with:
-     * SHUTDOWN: true if shutdown is enabled (1 bit)
-     * SEQ:  a sequence lock, with PL_LOCK bit set if locked (30 bits)
-     * SIGNAL: set when threads may be waiting on the lock (1 bit)
-     *
-     * The sequence number enables simple consistency checks:
-     * Staleness of read-only operations on the workQueues array can
-     * be checked by comparing plock before vs after the reads.
+     * Because it occupies uppermost bits, we can add one active count
+     * using getAndAddLong of AC_UNIT, rather than CAS, when returning
+     * from a blocked join.  Other updates entail multiple subfields
+     * and masking, requiring CAS.
      */
 
-    // bit positions/shifts for fields
+    // Lower and upper word masks
+    private static final long SP_MASK    = 0xffffffffL;
+    private static final long UC_MASK    = ~SP_MASK;
+
+    // Active counts
     private static final int  AC_SHIFT   = 48;
+    private static final long AC_UNIT    = 0x0001L << AC_SHIFT;
+    private static final long AC_MASK    = 0xffffL << AC_SHIFT;
+
+    // Total counts
     private static final int  TC_SHIFT   = 32;
-    private static final int  ST_SHIFT   = 31;
-    private static final int  EC_SHIFT   = 16;
+    private static final long TC_UNIT    = 0x0001L << TC_SHIFT;
+    private static final long TC_MASK    = 0xffffL << TC_SHIFT;
+    private static final long ADD_WORKER = 0x0001L << (TC_SHIFT + 15); // sign
 
-    // bounds
-    private static final int  SMASK      = 0xffff;  // short bits
-    private static final int  MAX_CAP    = 0x7fff;  // max #workers - 1
-    private static final int  EVENMASK   = 0xfffe;  // even short bits
-    private static final int  SQMASK     = 0x007e;  // max 64 (even) slots
-    private static final int  SHORT_SIGN = 1 << 15;
-    private static final int  INT_SIGN   = 1 << 31;
-
-    // masks
-    private static final long STOP_BIT   = 0x0001L << ST_SHIFT;
-    private static final long AC_MASK    = ((long)SMASK) << AC_SHIFT;
-    private static final long TC_MASK    = ((long)SMASK) << TC_SHIFT;
-
-    // units for incrementing and decrementing
-    private static final long TC_UNIT    = 1L << TC_SHIFT;
-    private static final long AC_UNIT    = 1L << AC_SHIFT;
-
-    // masks and units for dealing with u = (int)(ctl >>> 32)
-    private static final int  UAC_SHIFT  = AC_SHIFT - 32;
-    private static final int  UTC_SHIFT  = TC_SHIFT - 32;
-    private static final int  UAC_MASK   = SMASK << UAC_SHIFT;
-    private static final int  UTC_MASK   = SMASK << UTC_SHIFT;
-    private static final int  UAC_UNIT   = 1 << UAC_SHIFT;
-    private static final int  UTC_UNIT   = 1 << UTC_SHIFT;
-
-    // masks and units for dealing with e = (int)ctl
-    private static final int E_MASK      = 0x7fffffff; // no STOP_BIT
-    private static final int E_SEQ       = 1 << EC_SHIFT;
-
-    // plock bits
-    private static final int SHUTDOWN    = 1 << 31;
-    private static final int PL_LOCK     = 2;
-    private static final int PL_SIGNAL   = 1;
-    private static final int PL_SPINS    = 1 << 8;
-
-    // access mode for WorkQueue
-    static final int LIFO_QUEUE          =  0;
-    static final int FIFO_QUEUE          =  1;
-    static final int SHARED_QUEUE        = -1;
+    // runState bits: SHUTDOWN must be negative, others arbitrary powers of two
+    private static final int  RSLOCK     = 1;
+    private static final int  RSIGNAL    = 1 << 1;
+    private static final int  STARTED    = 1 << 2;
+    private static final int  STOP       = 1 << 29;
+    private static final int  TERMINATED = 1 << 30;
+    private static final int  SHUTDOWN   = 1 << 31;
 
     // Instance fields
-    volatile long stealCount;                  // collects worker counts
-    volatile long ctl;                         // main pool control
-    volatile int plock;                        // shutdown status and seqLock
-    volatile int indexSeed;                    // worker/submitter index seed
-    final short parallelism;                   // parallelism level
-    final short mode;                          // LIFO/FIFO
-    WorkQueue[] workQueues;                    // main registry
+    volatile long ctl;                   // main pool control
+    volatile int runState;               // lockable status
+    final int config;                    // parallelism, mode
+    int indexSeed;                       // to generate worker index
+    volatile WorkQueue[] workQueues;     // main registry
     final ForkJoinWorkerThreadFactory factory;
-    final UncaughtExceptionHandler ueh;        // per-worker UEH
-    final String workerNamePrefix;             // to create worker name string
+    final UncaughtExceptionHandler ueh;  // per-worker UEH
+    final String workerNamePrefix;       // to create worker name string
+    volatile AtomicLong stealCounter;    // also used as sync monitor
 
     /**
-     * Acquires the plock lock to protect worker array and related
-     * updates. This method is called only if an initial CAS on plock
-     * fails. This acts as a spinlock for normal cases, but falls back
-     * to builtin monitor to block when (rarely) needed. This would be
-     * a terrible idea for a highly contended lock, but works fine as
-     * a more conservative alternative to a pure spinlock.
+     * Acquires the runState lock; returns current (locked) runState.
      */
-    private int acquirePlock() {
-        int spins = PL_SPINS, ps, nps;
-        for (;;) {
-            if (((ps = plock) & PL_LOCK) == 0 &&
-                U.compareAndSwapInt(this, PLOCK, ps, nps = ps + PL_LOCK))
-                return nps;
-            else if (spins >= 0) {
-                if (ThreadLocalRandom.nextSecondarySeed() >= 0)
+    private int lockRunState() {
+        int rs;
+        return ((((rs = runState) & RSLOCK) != 0 ||
+                 !U.compareAndSwapInt(this, RUNSTATE, rs, rs |= RSLOCK)) ?
+                awaitRunStateLock() : rs);
+    }
+
+    /**
+     * Spins and/or blocks until runstate lock is available.  See
+     * above for explanation.
+     */
+    private int awaitRunStateLock() {
+        Object lock;
+        boolean wasInterrupted = false;
+        for (int spins = SPINS, r = 0, rs, ns;;) {
+            if (((rs = runState) & RSLOCK) == 0) {
+                if (U.compareAndSwapInt(this, RUNSTATE, rs, ns = rs | RSLOCK)) {
+                    if (wasInterrupted) {
+                        try {
+                            Thread.currentThread().interrupt();
+                        } catch (SecurityException ignore) {
+                        }
+                    }
+                    return ns;
+                }
+            }
+            else if (r == 0)
+                r = ThreadLocalRandom.nextSecondarySeed();
+            else if (spins > 0) {
+                r ^= r << 6; r ^= r >>> 21; r ^= r << 7; // xorshift
+                if (r >= 0)
                     --spins;
             }
-            else if (U.compareAndSwapInt(this, PLOCK, ps, ps | PL_SIGNAL)) {
-                synchronized (this) {
-                    if ((plock & PL_SIGNAL) != 0) {
+            else if ((rs & STARTED) == 0 || (lock = stealCounter) == null)
+                Thread.yield();   // initialization race
+            else if (U.compareAndSwapInt(this, RUNSTATE, rs, rs | RSIGNAL)) {
+                synchronized (lock) {
+                    if ((runState & RSIGNAL) != 0) {
                         try {
-                            wait();
+                            lock.wait();
                         } catch (InterruptedException ie) {
-                            try {
-                                Thread.currentThread().interrupt();
-                            } catch (SecurityException ignore) {
-                            }
+                            if (!(Thread.currentThread() instanceof
+                                  ForkJoinWorkerThread))
+                                wasInterrupted = true;
                         }
                     }
                     else
-                        notifyAll();
+                        lock.notifyAll();
                 }
             }
         }
     }
 
     /**
-     * Unlocks and signals any thread waiting for plock. Called only
-     * when CAS of seq value for unlock fails.
+     * Unlocks and sets runState to newRunState.
+     *
+     * @param oldRunState a value returned from lockRunState
+     * @param newRunState the next value (must have lock bit clear).
      */
-    private void releasePlock(int ps) {
-        plock = ps;
-        synchronized (this) { notifyAll(); }
+    private void unlockRunState(int oldRunState, int newRunState) {
+        if (!U.compareAndSwapInt(this, RUNSTATE, oldRunState, newRunState)) {
+            Object lock = stealCounter;
+            runState = newRunState;              // clears RSIGNAL bit
+            if (lock != null)
+                synchronized (lock) { lock.notifyAll(); }
+        }
+    }
+
+    // Creating, registering and deregistering workers
+
+    /**
+     * Tries to construct and start one worker. Assumes that total
+     * count has already been incremented as a reservation.  Invokes
+     * deregisterWorker on any failure.
+     *
+     * @return true if successful
+     */
+    private boolean createWorker() {
+        ForkJoinWorkerThreadFactory fac = factory;
+        Throwable ex = null;
+        ForkJoinWorkerThread wt = null;
+        try {
+            if (fac != null && (wt = fac.newThread(this)) != null) {
+                wt.start();
+                return true;
+            }
+        } catch (Throwable rex) {
+            ex = rex;
+        }
+        deregisterWorker(wt, ex);
+        return false;
     }
 
     /**
-     * Tries to create and start one worker if fewer than target
-     * parallelism level exist. Adjusts counts etc on failure.
+     * Tries to add one worker, incrementing ctl counts before doing
+     * so, relying on createWorker to back out on failure.
+     *
+     * @param c incoming ctl value, with total count negative and no
+     * idle workers.  On CAS failure, c is refreshed and retried if
+     * this holds (otherwise, a new worker is not needed).
      */
-    private void tryAddWorker() {
-        long c; int u, e;
-        while ((u = (int)((c = ctl) >>> 32)) < 0 &&
-               (u & SHORT_SIGN) != 0 && (e = (int)c) >= 0) {
-            long nc = ((long)(((u + UTC_UNIT) & UTC_MASK) |
-                              ((u + UAC_UNIT) & UAC_MASK)) << 32) | (long)e;
-            if (U.compareAndSwapLong(this, CTL, c, nc)) {
-                ForkJoinWorkerThreadFactory fac;
-                Throwable ex = null;
-                ForkJoinWorkerThread wt = null;
-                try {
-                    if ((fac = factory) != null &&
-                        (wt = fac.newThread(this)) != null) {
-                        wt.start();
-                        break;
-                    }
-                } catch (Throwable rex) {
-                    ex = rex;
+    private void tryAddWorker(long c) {
+        boolean add = false;
+        do {
+            long nc = ((AC_MASK & (c + AC_UNIT)) |
+                       (TC_MASK & (c + TC_UNIT)));
+            if (ctl == c) {
+                int rs, stop;                 // check if terminating
+                if ((stop = (rs = lockRunState()) & STOP) == 0)
+                    add = U.compareAndSwapLong(this, CTL, c, nc);
+                unlockRunState(rs, rs & ~RSLOCK);
+                if (stop != 0)
+                    break;
+                if (add) {
+                    createWorker();
+                    break;
                 }
-                deregisterWorker(wt, ex);
-                break;
             }
-        }
+        } while (((c = ctl) & ADD_WORKER) != 0L && (int)c == 0);
     }
 
-    //  Registering and deregistering workers
-
     /**
-     * Callback from ForkJoinWorkerThread to establish and record its
-     * WorkQueue. To avoid scanning bias due to packing entries in
-     * front of the workQueues array, we treat the array as a simple
-     * power-of-two hash table using per-thread seed as hash,
-     * expanding as needed.
+     * Callback from ForkJoinWorkerThread constructor to establish and
+     * record its WorkQueue.
      *
      * @param wt the worker thread
      * @return the worker's queue
      */
     final WorkQueue registerWorker(ForkJoinWorkerThread wt) {
-        UncaughtExceptionHandler handler; WorkQueue[] ws; int s, ps;
-        wt.setDaemon(true);
+        UncaughtExceptionHandler handler;
+        wt.setDaemon(true);                           // configure thread
         if ((handler = ueh) != null)
             wt.setUncaughtExceptionHandler(handler);
-        do {} while (!U.compareAndSwapInt(this, INDEXSEED, s = indexSeed,
-                                          s += SEED_INCREMENT) ||
-                     s == 0); // skip 0
-        WorkQueue w = new WorkQueue(this, wt, mode, s);
-        if (((ps = plock) & PL_LOCK) != 0 ||
-            !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
-            ps = acquirePlock();
-        int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
+        WorkQueue w = new WorkQueue(this, wt);
+        int i = 0;                                    // assign a pool index
+        int mode = config & MODE_MASK;
+        int rs = lockRunState();
         try {
-            if ((ws = workQueues) != null) {    // skip if shutting down
-                int n = ws.length, m = n - 1;
-                int r = (s << 1) | 1;           // use odd-numbered indices
-                if (ws[r &= m] != null) {       // collision
-                    int probes = 0;             // step by approx half size
+            WorkQueue[] ws; int n;                    // skip if no array
+            if ((ws = workQueues) != null && (n = ws.length) > 0) {
+                int s = indexSeed += SEED_INCREMENT;  // unlikely to collide
+                int m = n - 1;
+                i = ((s << 1) | 1) & m;               // odd-numbered indices
+                if (ws[i] != null) {                  // collision
+                    int probes = 0;                   // step by approx half n
                     int step = (n <= 4) ? 2 : ((n >>> 1) & EVENMASK) + 2;
-                    while (ws[r = (r + step) & m] != null) {
+                    while (ws[i = (i + step) & m] != null) {
                         if (++probes >= n) {
                             workQueues = ws = Arrays.copyOf(ws, n <<= 1);
                             m = n - 1;
@@ -1387,15 +1551,15 @@
                         }
                     }
                 }
-                w.poolIndex = (short)r;
-                w.eventCount = r; // volatile write orders
-                ws[r] = w;
+                w.hint = s;                           // use as random seed
+                w.config = i | mode;
+                w.scanState = i;                      // publication fence
+                ws[i] = w;
             }
         } finally {
-            if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
-                releasePlock(nps);
+            unlockRunState(rs, rs & ~RSLOCK);
         }
-        wt.setName(workerNamePrefix.concat(Integer.toString(w.poolIndex >>> 1)));
+        wt.setName(workerNamePrefix.concat(Integer.toString(i >>> 1)));
         return w;
     }
 
@@ -1411,384 +1575,322 @@
     final void deregisterWorker(ForkJoinWorkerThread wt, Throwable ex) {
         WorkQueue w = null;
         if (wt != null && (w = wt.workQueue) != null) {
-            int ps;
-            w.qlock = -1;                // ensure set
-            U.getAndAddLong(this, STEALCOUNT, w.nsteals); // collect steals
-            if (((ps = plock) & PL_LOCK) != 0 ||
-                !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
-                ps = acquirePlock();
-            int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
-            try {
-                int idx = w.poolIndex;
-                WorkQueue[] ws = workQueues;
-                if (ws != null && idx >= 0 && idx < ws.length && ws[idx] == w)
-                    ws[idx] = null;
-            } finally {
-                if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
-                    releasePlock(nps);
+            WorkQueue[] ws;                           // remove index from array
+            int idx = w.config & SMASK;
+            int rs = lockRunState();
+            if ((ws = workQueues) != null && ws.length > idx && ws[idx] == w)
+                ws[idx] = null;
+            unlockRunState(rs, rs & ~RSLOCK);
+        }
+        long c;                                       // decrement counts
+        do {} while (!U.compareAndSwapLong
+                     (this, CTL, c = ctl, ((AC_MASK & (c - AC_UNIT)) |
+                                           (TC_MASK & (c - TC_UNIT)) |
+                                           (SP_MASK & c))));
+        if (w != null) {
+            w.qlock = -1;                             // ensure set
+            w.transferStealCount(this);
+            w.cancelAll();                            // cancel remaining tasks
+        }
+        for (;;) {                                    // possibly replace
+            WorkQueue[] ws; int m, sp;
+            if (tryTerminate(false, false) || w == null || w.array == null ||
+                (runState & STOP) != 0 || (ws = workQueues) == null ||
+                (m = ws.length - 1) < 0)              // already terminating
+                break;
+            if ((sp = (int)(c = ctl)) != 0) {         // wake up replacement
+                if (tryRelease(c, ws[sp & m], AC_UNIT))
+                    break;
             }
+            else if (ex != null && (c & ADD_WORKER) != 0L) {
+                tryAddWorker(c);                      // create replacement
+                break;
+            }
+            else                                      // don't need replacement
+                break;
         }
-
-        long c;                          // adjust ctl counts
-        do {} while (!U.compareAndSwapLong
-                     (this, CTL, c = ctl, (((c - AC_UNIT) & AC_MASK) |
-                                           ((c - TC_UNIT) & TC_MASK) |
-                                           (c & ~(AC_MASK|TC_MASK)))));
-
-        if (!tryTerminate(false, false) && w != null && w.array != null) {
-            w.cancelAll();               // cancel remaining tasks
-            WorkQueue[] ws; WorkQueue v; Thread p; int u, i, e;
-            while ((u = (int)((c = ctl) >>> 32)) < 0 && (e = (int)c) >= 0) {
-                if (e > 0) {             // activate or create replacement
-                    if ((ws = workQueues) == null ||
-                        (i = e & SMASK) >= ws.length ||
-                        (v = ws[i]) == null)
-                        break;
-                    long nc = (((long)(v.nextWait & E_MASK)) |
-                               ((long)(u + UAC_UNIT) << 32));
-                    if (v.eventCount != (e | INT_SIGN))
-                        break;
-                    if (U.compareAndSwapLong(this, CTL, c, nc)) {
-                        v.eventCount = (e + E_SEQ) & E_MASK;
-                        if ((p = v.parker) != null)
-                            U.unpark(p);
-                        break;
-                    }
-                }
-                else {
-                    if ((short)u < 0)
-                        tryAddWorker();
-                    break;
-                }
-            }
-        }
-        if (ex == null)                     // help clean refs on way out
+        if (ex == null)                               // help clean on way out
             ForkJoinTask.helpExpungeStaleExceptions();
-        else                                // rethrow
+        else                                          // rethrow
             ForkJoinTask.rethrow(ex);
     }
 
-    // Submissions
-
-    /**
-     * Unless shutting down, adds the given task to a submission queue
-     * at submitter's current queue index (modulo submission
-     * range). Only the most common path is directly handled in this
-     * method. All others are relayed to fullExternalPush.
-     *
-     * @param task the task. Caller must ensure non-null.
-     */
-    final void externalPush(ForkJoinTask<?> task) {
-        WorkQueue q; int m, s, n, am; ForkJoinTask<?>[] a;
-        int r = ThreadLocalRandom.getProbe();
-        int ps = plock;
-        WorkQueue[] ws = workQueues;
-        if (ps > 0 && ws != null && (m = (ws.length - 1)) >= 0 &&
-            (q = ws[m & r & SQMASK]) != null && r != 0 &&
-            U.compareAndSwapInt(q, QLOCK, 0, 1)) { // lock
-            if ((a = q.array) != null &&
-                (am = a.length - 1) > (n = (s = q.top) - q.base)) {
-                int j = ((am & s) << ASHIFT) + ABASE;
-                U.putOrderedObject(a, j, task);
-                q.top = s + 1;                     // push on to deque
-                q.qlock = 0;
-                if (n <= 1)
-                    signalWork(ws, q);
-                return;
-            }
-            q.qlock = 0;
-        }
-        fullExternalPush(task);
-    }
-
-    /**
-     * Full version of externalPush. This method is called, among
-     * other times, upon the first submission of the first task to the
-     * pool, so must perform secondary initialization.  It also
-     * detects first submission by an external thread by looking up
-     * its ThreadLocal, and creates a new shared queue if the one at
-     * index if empty or contended. The plock lock body must be
-     * exception-free (so no try/finally) so we optimistically
-     * allocate new queues outside the lock and throw them away if
-     * (very rarely) not needed.
-     *
-     * Secondary initialization occurs when plock is zero, to create
-     * workQueue array and set plock to a valid value.  This lock body
-     * must also be exception-free. Because the plock seq value can
-     * eventually wrap around zero, this method harmlessly fails to
-     * reinitialize if workQueues exists, while still advancing plock.
-     */
-    private void fullExternalPush(ForkJoinTask<?> task) {
-        int r;
-        if ((r = ThreadLocalRandom.getProbe()) == 0) {
-            ThreadLocalRandom.localInit();
-            r = ThreadLocalRandom.getProbe();
-        }
-        for (;;) {
-            WorkQueue[] ws; WorkQueue q; int ps, m, k;
-            boolean move = false;
-            if ((ps = plock) < 0)
-                throw new RejectedExecutionException();
-            else if (ps == 0 || (ws = workQueues) == null ||
-                     (m = ws.length - 1) < 0) { // initialize workQueues
-                int p = parallelism;            // find power of two table size
-                int n = (p > 1) ? p - 1 : 1;    // ensure at least 2 slots
-                n |= n >>> 1; n |= n >>> 2;  n |= n >>> 4;
-                n |= n >>> 8; n |= n >>> 16; n = (n + 1) << 1;
-                WorkQueue[] nws = ((ws = workQueues) == null || ws.length == 0 ?
-                                   new WorkQueue[n] : null);
-                if (((ps = plock) & PL_LOCK) != 0 ||
-                    !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
-                    ps = acquirePlock();
-                if (((ws = workQueues) == null || ws.length == 0) && nws != null)
-                    workQueues = nws;
-                int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
-                if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
-                    releasePlock(nps);
-            }
-            else if ((q = ws[k = r & m & SQMASK]) != null) {
-                if (q.qlock == 0 && U.compareAndSwapInt(q, QLOCK, 0, 1)) {
-                    ForkJoinTask<?>[] a = q.array;
-                    int s = q.top;
-                    boolean submitted = false;
-                    try {                      // locked version of push
-                        if ((a != null && a.length > s + 1 - q.base) ||
-                            (a = q.growArray()) != null) {   // must presize
-                            int j = (((a.length - 1) & s) << ASHIFT) + ABASE;
-                            U.putOrderedObject(a, j, task);
-                            q.top = s + 1;
-                            submitted = true;
-                        }
-                    } finally {
-                        q.qlock = 0;  // unlock
-                    }
-                    if (submitted) {
-                        signalWork(ws, q);
-                        return;
-                    }
-                }
-                move = true; // move on failure
-            }
-            else if (((ps = plock) & PL_LOCK) == 0) { // create new queue
-                q = new WorkQueue(this, null, SHARED_QUEUE, r);
-                q.poolIndex = (short)k;
-                if (((ps = plock) & PL_LOCK) != 0 ||
-                    !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
-                    ps = acquirePlock();
-                if ((ws = workQueues) != null && k < ws.length && ws[k] == null)
-                    ws[k] = q;
-                int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
-                if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
-                    releasePlock(nps);
-            }
-            else
-                move = true; // move if busy
-            if (move)
-                r = ThreadLocalRandom.advanceProbe(r);
-        }
-    }
-
-    // Maintaining ctl counts
-
-    /**
-     * Increments active count; mainly called upon return from blocking.
-     */
-    final void incrementActiveCount() {
-        long c;
-        do {} while (!U.compareAndSwapLong
-                     (this, CTL, c = ctl, ((c & ~AC_MASK) |
-                                           ((c & AC_MASK) + AC_UNIT))));
-    }
+    // Signalling
 
     /**
      * Tries to create or activate a worker if too few are active.
      *
      * @param ws the worker array to use to find signallees
-     * @param q if non-null, the queue holding tasks to be processed
+     * @param q a WorkQueue --if non-null, don't retry if now empty
      */
     final void signalWork(WorkQueue[] ws, WorkQueue q) {
-        for (;;) {
-            long c; int e, u, i; WorkQueue w; Thread p;
-            if ((u = (int)((c = ctl) >>> 32)) >= 0)
-                break;
-            if ((e = (int)c) <= 0) {
-                if ((short)u < 0)
-                    tryAddWorker();
+        long c; int sp, i; WorkQueue v; Thread p;
+        while ((c = ctl) < 0L) {                       // too few active
+            if ((sp = (int)c) == 0) {                  // no idle workers
+                if ((c & ADD_WORKER) != 0L)            // too few workers
+                    tryAddWorker(c);
                 break;
             }
-            if (ws == null || ws.length <= (i = e & SMASK) ||
-                (w = ws[i]) == null)
+            if (ws == null)                            // unstarted/terminated
                 break;
-            long nc = (((long)(w.nextWait & E_MASK)) |
-                       ((long)(u + UAC_UNIT)) << 32);
-            int ne = (e + E_SEQ) & E_MASK;
-            if (w.eventCount == (e | INT_SIGN) &&
-                U.compareAndSwapLong(this, CTL, c, nc)) {
-                w.eventCount = ne;
-                if ((p = w.parker) != null)
+            if (ws.length <= (i = sp & SMASK))         // terminated
+                break;
+            if ((v = ws[i]) == null)                   // terminating
+                break;
+            int vs = (sp + SS_SEQ) & ~INACTIVE;        // next scanState
+            int d = sp - v.scanState;                  // screen CAS
+            long nc = (UC_MASK & (c + AC_UNIT)) | (SP_MASK & v.stackPred);
+            if (d == 0 && U.compareAndSwapLong(this, CTL, c, nc)) {
+                v.scanState = vs;                      // activate v
+                if ((p = v.parker) != null)
                     U.unpark(p);
                 break;
             }
-            if (q != null && q.base >= q.top)
+            if (q != null && q.base == q.top)          // no more work
                 break;
         }
     }
 
+    /**
+     * Signals and releases worker v if it is top of idle worker
+     * stack.  This performs a one-shot version of signalWork only if
+     * there is (apparently) at least one idle worker.
+     *
+     * @param c incoming ctl value
+     * @param v if non-null, a worker
+     * @param inc the increment to active count (zero when compensating)
+     * @return true if successful
+     */
+    private boolean tryRelease(long c, WorkQueue v, long inc) {
+        int sp = (int)c, vs = (sp + SS_SEQ) & ~INACTIVE; Thread p;
+        if (v != null && v.scanState == sp) {          // v is at top of stack
+            long nc = (UC_MASK & (c + inc)) | (SP_MASK & v.stackPred);
+            if (U.compareAndSwapLong(this, CTL, c, nc)) {
+                v.scanState = vs;
+                if ((p = v.parker) != null)
+                    U.unpark(p);
+                return true;
+            }
+        }
+        return false;
+    }
+
     // Scanning for tasks
 
     /**
      * Top-level runloop for workers, called by ForkJoinWorkerThread.run.
      */
     final void runWorker(WorkQueue w) {
-        w.growArray(); // allocate queue
-        for (int r = w.hint; scan(w, r) == 0; ) {
+        w.growArray();                   // allocate queue
+        int seed = w.hint;               // initially holds randomization hint
+        int r = (seed == 0) ? 1 : seed;  // avoid 0 for xorShift
+        for (ForkJoinTask<?> t;;) {
+            if ((t = scan(w, r)) != null)
+                w.runTask(t);
+            else if (!awaitWork(w, r))
+                break;
             r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // xorshift
         }
     }
 
     /**
-     * Scans for and, if found, runs one task, else possibly
-     * inactivates the worker. This method operates on single reads of
-     * volatile state and is designed to be re-invoked continuously,
-     * in part because it returns upon detecting inconsistencies,
-     * contention, or state changes that indicate possible success on
-     * re-invocation.
-     *
-     * The scan searches for tasks across queues starting at a random
-     * index, checking each at least twice.  The scan terminates upon
-     * either finding a non-empty queue, or completing the sweep. If
-     * the worker is not inactivated, it takes and runs a task from
-     * this queue. Otherwise, if not activated, it tries to activate
-     * itself or some other worker by signalling. On failure to find a
-     * task, returns (for retry) if pool state may have changed during
-     * an empty scan, or tries to inactivate if active, else possibly
-     * blocks or terminates via method awaitWork.
+     * Scans for and tries to steal a top-level task. Scans start at a
+     * random location, randomly moving on apparent contention,
+     * otherwise continuing linearly until reaching two consecutive
+     * empty passes over all queues with the same checksum (summing
+     * each base index of each queue, that moves on each steal), at
+     * which point the worker tries to inactivate and then re-scans,
+     * attempting to re-activate (itself or some other worker) if
+     * finding a task; otherwise returning null to await work.  Scans
+     * otherwise touch as little memory as possible, to reduce
+     * disruption on other scanning threads.
      *
      * @param w the worker (via its WorkQueue)
      * @param r a random seed
-     * @return worker qlock status if would have waited, else 0
+     * @return a task, or null if none found
      */
-    private final int scan(WorkQueue w, int r) {
+    private ForkJoinTask<?> scan(WorkQueue w, int r) {
         WorkQueue[] ws; int m;
-        long c = ctl;                            // for consistency check
-        if ((ws = workQueues) != null && (m = ws.length - 1) >= 0 && w != null) {
-            for (int j = m + m + 1, ec = w.eventCount;;) {
-                WorkQueue q; int b, e; ForkJoinTask<?>[] a; ForkJoinTask<?> t;
-                if ((q = ws[(r - j) & m]) != null &&
-                    (b = q.base) - q.top < 0 && (a = q.array) != null) {
-                    long i = (((a.length - 1) & b) << ASHIFT) + ABASE;
-                    if ((t = ((ForkJoinTask<?>)
-                              U.getObjectVolatile(a, i))) != null) {
-                        if (ec < 0)
-                            helpRelease(c, ws, w, q, b);
-                        else if (q.base == b &&
-                                 U.compareAndSwapObject(a, i, t, null)) {
-                            U.putOrderedInt(q, QBASE, b + 1);
-                            if ((b + 1) - q.top < 0)
-                                signalWork(ws, q);
-                            w.runTask(t);
+        if ((ws = workQueues) != null && (m = ws.length - 1) > 0 && w != null) {
+            int ss = w.scanState;                     // initially non-negative
+            for (int origin = r & m, k = origin, oldSum = 0, checkSum = 0;;) {
+                WorkQueue q; ForkJoinTask<?>[] a; ForkJoinTask<?> t;
+                int b, n; long c;
+                if ((q = ws[k]) != null) {
+                    if ((n = (b = q.base) - q.top) < 0 &&
+                        (a = q.array) != null) {      // non-empty
+                        long i = (((a.length - 1) & b) << ASHIFT) + ABASE;
+                        if ((t = ((ForkJoinTask<?>)
+                                  U.getObjectVolatile(a, i))) != null &&
+                            q.base == b) {
+                            if (ss >= 0) {
+                                if (U.compareAndSwapObject(a, i, t, null)) {
+                                    q.base = b + 1;
+                                    if (n < -1)       // signal others
+                                        signalWork(ws, q);
+                                    return t;
+                                }
+                            }
+                            else if (oldSum == 0 &&   // try to activate
+                                     w.scanState < 0)
+                                tryRelease(c = ctl, ws[m & (int)c], AC_UNIT);
                         }
+                        if (ss < 0)                   // refresh
+                            ss = w.scanState;
+                        r ^= r << 1; r ^= r >>> 3; r ^= r << 10;
+                        origin = k = r & m;           // move and rescan
+                        oldSum = checkSum = 0;
+                        continue;
                     }
-                    break;
+                    checkSum += b;
                 }
-                else if (--j < 0) {
-                    if ((ec | (e = (int)c)) < 0) // inactive or terminating
-                        return awaitWork(w, c, ec);
-                    else if (ctl == c) {         // try to inactivate and enqueue
-                        long nc = (long)ec | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
-                        w.nextWait = e;
-                        w.eventCount = ec | INT_SIGN;
-                        if (!U.compareAndSwapLong(this, CTL, c, nc))
-                            w.eventCount = ec;   // back out
+                if ((k = (k + 1) & m) == origin) {    // continue until stable
+                    if ((ss >= 0 || (ss == (ss = w.scanState))) &&
+                        oldSum == (oldSum = checkSum)) {
+                        if (ss < 0 || w.qlock < 0)    // already inactive
+                            break;
+                        int ns = ss | INACTIVE;       // try to inactivate
+                        long nc = ((SP_MASK & ns) |
+                                   (UC_MASK & ((c = ctl) - AC_UNIT)));
+                        w.stackPred = (int)c;         // hold prev stack top
+                        U.putInt(w, QSCANSTATE, ns);
+                        if (U.compareAndSwapLong(this, CTL, c, nc))
+                            ss = ns;
+                        else
+                            w.scanState = ss;         // back out
                     }
-                    break;
+                    checkSum = 0;
                 }
             }
         }
-        return 0;
+        return null;
     }
 
     /**
-     * A continuation of scan(), possibly blocking or terminating
-     * worker w. Returns without blocking if pool state has apparently
-     * changed since last invocation.  Also, if inactivating w has
-     * caused the pool to become quiescent, checks for pool
+     * Possibly blocks worker w waiting for a task to steal, or
+     * returns false if the worker should terminate.  If inactivating
+     * w has caused the pool to become quiescent, checks for pool
      * termination, and, so long as this is not the only worker, waits
-     * for event for up to a given duration.  On timeout, if ctl has
-     * not changed, terminates the worker, which will in turn wake up
+     * for up to a given duration.  On timeout, if ctl has not
+     * changed, terminates the worker, which will in turn wake up
      * another worker to possibly repeat this process.
      *
      * @param w the calling worker
-     * @param c the ctl value on entry to scan
-     * @param ec the worker's eventCount on entry to scan
+     * @param r a random seed (for spins)
+     * @return false if the worker should terminate
      */
-    private final int awaitWork(WorkQueue w, long c, int ec) {
-        int stat, ns; long parkTime, deadline;
-        if ((stat = w.qlock) >= 0 && w.eventCount == ec && ctl == c &&
-            !Thread.interrupted()) {
-            int e = (int)c;
-            int u = (int)(c >>> 32);
-            int d = (u >> UAC_SHIFT) + parallelism; // active count
-
-            if (e < 0 || (d <= 0 && tryTerminate(false, false)))
-                stat = w.qlock = -1;          // pool is terminating
-            else if ((ns = w.nsteals) != 0) { // collect steals and retry
-                w.nsteals = 0;
-                U.getAndAddLong(this, STEALCOUNT, (long)ns);
+    private boolean awaitWork(WorkQueue w, int r) {
+        if (w == null || w.qlock < 0)                 // w is terminating
+            return false;
+        for (int pred = w.stackPred, spins = SPINS, ss;;) {
+            if ((ss = w.scanState) >= 0)
+                break;
+            else if (spins > 0) {
+                r ^= r << 6; r ^= r >>> 21; r ^= r << 7;
+                if (r >= 0 && --spins == 0) {         // randomize spins
+                    WorkQueue v; WorkQueue[] ws; int s, j; AtomicLong sc;
+                    if (pred != 0 && (ws = workQueues) != null &&
+                        (j = pred & SMASK) < ws.length &&
+                        (v = ws[j]) != null &&        // see if pred parking
+                        (v.parker == null || v.scanState >= 0))
+                        spins = SPINS;                // continue spinning
+                }
             }
-            else {
-                long pc = ((d > 0 || ec != (e | INT_SIGN)) ? 0L :
-                           ((long)(w.nextWait & E_MASK)) | // ctl to restore
-                           ((long)(u + UAC_UNIT)) << 32);
-                if (pc != 0L) {               // timed wait if last waiter
-                    int dc = -(short)(c >>> TC_SHIFT);
-                    parkTime = (dc < 0 ? FAST_IDLE_TIMEOUT:
-                                (dc + 1) * IDLE_TIMEOUT);
+            else if (w.qlock < 0)                     // recheck after spins
+                return false;
+            else if (!Thread.interrupted()) {
+                long c, prevctl, parkTime, deadline;
+                int ac = (int)((c = ctl) >> AC_SHIFT) + (config & SMASK);
+                if ((ac <= 0 && tryTerminate(false, false)) ||
+                    (runState & STOP) != 0)           // pool terminating
+                    return false;
+                if (ac <= 0 && ss == (int)c) {        // is last waiter
+                    prevctl = (UC_MASK & (c + AC_UNIT)) | (SP_MASK & pred);
+                    int t = (short)(c >>> TC_SHIFT);  // shrink excess spares
+                    if (t > 2 && U.compareAndSwapLong(this, CTL, c, prevctl))
+                        return false;                 // else use timed wait
+                    parkTime = IDLE_TIMEOUT * ((t >= 0) ? 1 : 1 - t);
                     deadline = System.nanoTime() + parkTime - TIMEOUT_SLOP;
                 }
                 else
-                    parkTime = deadline = 0L;
-                if (w.eventCount == ec && ctl == c) {
-                    Thread wt = Thread.currentThread();
-                    U.putObject(wt, PARKBLOCKER, this);
-                    w.parker = wt;            // emulate LockSupport.park
-                    if (w.eventCount == ec && ctl == c)
-                        U.park(false, parkTime);  // must recheck before park
-                    w.parker = null;
-                    U.putObject(wt, PARKBLOCKER, null);
-                    if (parkTime != 0L && ctl == c &&
-                        deadline - System.nanoTime() <= 0L &&
-                        U.compareAndSwapLong(this, CTL, c, pc))
-                        stat = w.qlock = -1;  // shrink pool
+                    prevctl = parkTime = deadline = 0L;
+                Thread wt = Thread.currentThread();
+                U.putObject(wt, PARKBLOCKER, this);   // emulate LockSupport
+                w.parker = wt;
+                if (w.scanState < 0 && ctl == c)      // recheck before park
+                    U.park(false, parkTime);
+                U.putOrderedObject(w, QPARKER, null);
+                U.putObject(wt, PARKBLOCKER, null);
+                if (w.scanState >= 0)
+                    break;
+                if (parkTime != 0L && ctl == c &&
+                    deadline - System.nanoTime() <= 0L &&
+                    U.compareAndSwapLong(this, CTL, c, prevctl))
+                    return false;                     // shrink pool
+            }
+        }
+        return true;
+    }
+
+    // Joining tasks
+
+    /**
+     * Tries to steal and run tasks within the target's computation.
+     * Uses a variant of the top-level algorithm, restricted to tasks
+     * with the given task as ancestor: It prefers taking and running
+     * eligible tasks popped from the worker's own queue (via
+     * popCC). Otherwise it scans others, randomly moving on
+     * contention or execution, deciding to give up based on a
+     * checksum (via return codes frob pollAndExecCC). The maxTasks
+     * argument supports external usages; internal calls use zero,
+     * allowing unbounded steps (external calls trap non-positive
+     * values).
+     *
+     * @param w caller
+     * @param maxTasks if non-zero, the maximum number of other tasks to run
+     * @return task status on exit
+     */
+    final int helpComplete(WorkQueue w, CountedCompleter<?> task,
+                           int maxTasks) {
+        WorkQueue[] ws; int s = 0, m;
+        if ((ws = workQueues) != null && (m = ws.length - 1) >= 0 &&
+            task != null && w != null) {
+            int mode = w.config;                 // for popCC
+            int r = w.hint ^ w.top;              // arbitrary seed for origin
+            int origin = r & m;                  // first queue to scan
+            int h = 1;                           // 1:ran, >1:contended, <0:hash
+            for (int k = origin, oldSum = 0, checkSum = 0;;) {
+                CountedCompleter<?> p; WorkQueue q;
+                if ((s = task.status) < 0)
+                    break;
+                if (h == 1 && (p = w.popCC(task, mode)) != null) {
+                    p.doExec();                  // run local task
+                    if (maxTasks != 0 && --maxTasks == 0)
+                        break;
+                    origin = k;                  // reset
+                    oldSum = checkSum = 0;
+                }
+                else {                           // poll other queues
+                    if ((q = ws[k]) == null)
+                        h = 0;
+                    else if ((h = q.pollAndExecCC(task)) < 0)
+                        checkSum += h;
+                    if (h > 0) {
+                        if (h == 1 && maxTasks != 0 && --maxTasks == 0)
+                            break;
+                        r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // xorshift
+                        origin = k = r & m;      // move and restart
+                        oldSum = checkSum = 0;
+                    }
+                    else if ((k = (k + 1) & m) == origin) {
+                        if (oldSum == (oldSum = checkSum))
+                            break;
+                        checkSum = 0;
+                    }
                 }
             }
         }
-        return stat;
-    }
-
-    /**
-     * Possibly releases (signals) a worker. Called only from scan()
-     * when a worker with apparently inactive status finds a non-empty
-     * queue. This requires revalidating all of the associated state
-     * from caller.
-     */
-    private final void helpRelease(long c, WorkQueue[] ws, WorkQueue w,
-                                   WorkQueue q, int b) {
-        WorkQueue v; int e, i; Thread p;
-        if (w != null && w.eventCount < 0 && (e = (int)c) > 0 &&
-            ws != null && ws.length > (i = e & SMASK) &&
-            (v = ws[i]) != null && ctl == c) {
-            long nc = (((long)(v.nextWait & E_MASK)) |
-                       ((long)((int)(c >>> 32) + UAC_UNIT)) << 32);
-            int ne = (e + E_SEQ) & E_MASK;
-            if (q != null && q.base == b && w.eventCount < 0 &&
-                v.eventCount == (e | INT_SIGN) &&
-                U.compareAndSwapLong(this, CTL, c, nc)) {
-                v.eventCount = ne;
-                if ((p = v.parker) != null)
-                    U.unpark(p);
-            }
-        }
+        return s;
     }
 
     /**
@@ -1799,268 +1901,167 @@
      * execute tasks from. The first call to this method upon a
      * waiting join will often entail scanning/search, (which is OK
      * because the joiner has nothing better to do), but this method
-     * leaves hints in workers to speed up subsequent calls. The
-     * implementation is very branchy to cope with potential
-     * inconsistencies or loops encountering chains that are stale,
-     * unknown, or so long that they are likely cyclic.
+     * leaves hints in workers to speed up subsequent calls.
      *
-     * @param joiner the joining worker
+     * @param w caller
      * @param task the task to join
-     * @return 0 if no progress can be made, negative if task
-     * known complete, else positive
      */
-    private int tryHelpStealer(WorkQueue joiner, ForkJoinTask<?> task) {
-        int stat = 0, steps = 0;                    // bound to avoid cycles
-        if (task != null && joiner != null &&
-            joiner.base - joiner.top >= 0) {        // hoist checks
-            restart: for (;;) {
-                ForkJoinTask<?> subtask = task;     // current target
-                for (WorkQueue j = joiner, v;;) {   // v is stealer of subtask
-                    WorkQueue[] ws; int m, s, h;
-                    if ((s = task.status) < 0) {
-                        stat = s;
-                        break restart;
-                    }
-                    if ((ws = workQueues) == null || (m = ws.length - 1) <= 0)
-                        break restart;              // shutting down
-                    if ((v = ws[h = (j.hint | 1) & m]) == null ||
-                        v.currentSteal != subtask) {
-                        for (int origin = h;;) {    // find stealer
-                            if (((h = (h + 2) & m) & 15) == 1 &&
-                                (subtask.status < 0 || j.currentJoin != subtask))
-                                continue restart;   // occasional staleness check
-                            if ((v = ws[h]) != null &&
-                                v.currentSteal == subtask) {
-                                j.hint = h;        // save hint
+    private void helpStealer(WorkQueue w, ForkJoinTask<?> task) {
+        WorkQueue[] ws = workQueues;
+        int oldSum = 0, checkSum, m;
+        if (ws != null && (m = ws.length - 1) >= 0 && w != null &&
+            task != null) {
+            do {                                       // restart point
+                checkSum = 0;                          // for stability check
+                ForkJoinTask<?> subtask;
+                WorkQueue j = w, v;                    // v is subtask stealer
+                descent: for (subtask = task; subtask.status >= 0; ) {
+                    for (int h = j.hint | 1, k = 0, i; ; k += 2) {
+                        if (k > m)                     // can't find stealer
+                            break descent;
+                        if ((v = ws[i = (h + k) & m]) != null) {
+                            if (v.currentSteal == subtask) {
+                                j.hint = i;
                                 break;
                             }
-                            if (h == origin)
-                                break restart;      // cannot find stealer
+                            checkSum += v.base;
                         }
                     }
-                    for (;;) { // help stealer or descend to its stealer
+                    for (;;) {                         // help v or descend
                         ForkJoinTask<?>[] a; int b;
-                        if (subtask.status < 0)     // surround probes with
-                            continue restart;       //   consistency checks
-                        if ((b = v.base) - v.top < 0 && (a = v.array) != null) {
-                            int i = (((a.length - 1) & b) << ASHIFT) + ABASE;
-                            ForkJoinTask<?> t =
-                                (ForkJoinTask<?>)U.getObjectVolatile(a, i);
-                            if (subtask.status < 0 || j.currentJoin != subtask ||
-                                v.currentSteal != subtask)
-                                continue restart;   // stale
-                            stat = 1;               // apparent progress
-                            if (v.base == b) {
-                                if (t == null)
-                                    break restart;
-                                if (U.compareAndSwapObject(a, i, t, null)) {
-                                    U.putOrderedInt(v, QBASE, b + 1);
-                                    ForkJoinTask<?> ps = joiner.currentSteal;
-                                    int jt = joiner.top;
-                                    do {
-                                        joiner.currentSteal = t;
-                                        t.doExec(); // clear local tasks too
-                                    } while (task.status >= 0 &&
-                                             joiner.top != jt &&
-                                             (t = joiner.pop()) != null);
-                                    joiner.currentSteal = ps;
-                                    break restart;
-                                }
-                            }
+                        checkSum += (b = v.base);
+                        ForkJoinTask<?> next = v.currentJoin;
+                        if (subtask.status < 0 || j.currentJoin != subtask ||
+                            v.currentSteal != subtask) // stale
+                            break descent;
+                        if (b - v.top >= 0 || (a = v.array) == null) {
+                            if ((subtask = next) == null)
+                                break descent;
+                            j = v;
+                            break;
                         }
-                        else {                      // empty -- try to descend
-                            ForkJoinTask<?> next = v.currentJoin;
-                            if (subtask.status < 0 || j.currentJoin != subtask ||
-                                v.currentSteal != subtask)
-                                continue restart;   // stale
-                            else if (next == null || ++steps == MAX_HELP)
-                                break restart;      // dead-end or maybe cyclic
-                            else {
-                                subtask = next;
-                                j = v;
-                                break;
+                        int i = (((a.length - 1) & b) << ASHIFT) + ABASE;
+                        ForkJoinTask<?> t = ((ForkJoinTask<?>)
+                                             U.getObjectVolatile(a, i));
+                        if (v.base == b) {
+                            if (t == null)             // stale
+                                break descent;
+                            if (U.compareAndSwapObject(a, i, t, null)) {
+                                v.base = b + 1;
+                                ForkJoinTask<?> ps = w.currentSteal;
+                                int top = w.top;
+                                do {
+                                    U.putOrderedObject(w, QCURRENTSTEAL, t);
+                                    t.doExec();        // clear local tasks too
+                                } while (task.status >= 0 &&
+                                         w.top != top &&
+                                         (t = w.pop()) != null);
+                                U.putOrderedObject(w, QCURRENTSTEAL, ps);
+                                if (w.base != w.top)
+                                    return;            // can't further help
                             }
                         }
                     }
                 }
-            }
+            } while (task.status >= 0 && oldSum != (oldSum = checkSum));
         }
-        return stat;
-    }
-
-    /**
-     * Analog of tryHelpStealer for CountedCompleters. Tries to steal
-     * and run tasks within the target's computation.
-     *
-     * @param task the task to join
-     * @param maxTasks the maximum number of other tasks to run
-     */
-    final int helpComplete(WorkQueue joiner, CountedCompleter<?> task,
-                           int maxTasks) {
-        WorkQueue[] ws; int m;
-        int s = 0;
-        if ((ws = workQueues) != null && (m = ws.length - 1) >= 0 &&
-            joiner != null && task != null) {
-            int j = joiner.poolIndex;
-            int scans = m + m + 1;
-            long c = 0L;              // for stability check
-            for (int k = scans; ; j += 2) {
-                WorkQueue q;
-                if ((s = task.status) < 0)
-                    break;
-                else if (joiner.internalPopAndExecCC(task)) {
-                    if (--maxTasks <= 0) {
-                        s = task.status;
-                        break;
-                    }
-                    k = scans;
-                }
-                else if ((s = task.status) < 0)
-                    break;
-                else if ((q = ws[j & m]) != null && q.pollAndExecCC(task)) {
-                    if (--maxTasks <= 0) {
-                        s = task.status;
-                        break;
-                    }
-                    k = scans;
-                }
-                else if (--k < 0) {
-                    if (c == (c = ctl))
-                        break;
-                    k = scans;
-                }
-            }
-        }
-        return s;
     }
 
     /**
      * Tries to decrement active count (sometimes implicitly) and
      * possibly release or create a compensating worker in preparation
-     * for blocking. Fails on contention or termination. Otherwise,
-     * adds a new thread if no idle workers are available and pool
-     * may become starved.
+     * for blocking. Returns false (retryable by caller), on
+     * contention, detected staleness, instability, or termination.
      *
-     * @param c the assumed ctl value
+     * @param w caller
      */
-    final boolean tryCompensate(long c) {
-        WorkQueue[] ws = workQueues;
-        int pc = parallelism, e = (int)c, m, tc;
-        if (ws != null && (m = ws.length - 1) >= 0 && e >= 0 && ctl == c) {
-            WorkQueue w = ws[e & m];
-            if (e != 0 && w != null) {
-                Thread p;
-                long nc = ((long)(w.nextWait & E_MASK) |
-                           (c & (AC_MASK|TC_MASK)));
-                int ne = (e + E_SEQ) & E_MASK;
-                if (w.eventCount == (e | INT_SIGN) &&
-                    U.compareAndSwapLong(this, CTL, c, nc)) {
-                    w.eventCount = ne;
-                    if ((p = w.parker) != null)
-                        U.unpark(p);
-                    return true;   // replace with idle worker
+    private boolean tryCompensate(WorkQueue w) {
+        boolean canBlock;
+        WorkQueue[] ws; long c; int m, pc, sp;
+        if (w == null || w.qlock < 0 ||           // caller terminating
+            (ws = workQueues) == null || (m = ws.length - 1) <= 0 ||
+            (pc = config & SMASK) == 0)           // parallelism disabled
+            canBlock = false;
+        else if ((sp = (int)(c = ctl)) != 0)      // release idle worker
+            canBlock = tryRelease(c, ws[sp & m], 0L);
+        else {
+            int ac = (int)(c >> AC_SHIFT) + pc;
+            int tc = (short)(c >> TC_SHIFT) + pc;
+            int nbusy = 0;                        // validate saturation
+            for (int i = 0; i <= m; ++i) {        // two passes of odd indices
+                WorkQueue v;
+                if ((v = ws[((i << 1) | 1) & m]) != null) {
+                    if ((v.scanState & SCANNING) != 0)
+                        break;
+                    ++nbusy;
                 }
             }
-            else if ((tc = (short)(c >>> TC_SHIFT)) >= 0 &&
-                     (int)(c >> AC_SHIFT) + pc > 1) {
-                long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
-                if (U.compareAndSwapLong(this, CTL, c, nc))
-                    return true;   // no compensation
+            if (nbusy != (tc << 1) || ctl != c)
+                canBlock = false;                 // unstable or stale
+            else if (tc >= pc && ac > 1 && w.isEmpty()) {
+                long nc = ((AC_MASK & (c - AC_UNIT)) |
+                           (~AC_MASK & c));       // uncompensated
+                canBlock = U.compareAndSwapLong(this, CTL, c, nc);
             }
-            else if (tc + pc < MAX_CAP) {
-                long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
-                if (U.compareAndSwapLong(this, CTL, c, nc)) {
-                    ForkJoinWorkerThreadFactory fac;
-                    Throwable ex = null;
-                    ForkJoinWorkerThread wt = null;
-                    try {
-                        if ((fac = factory) != null &&
-                            (wt = fac.newThread(this)) != null) {
-                            wt.start();
-                            return true;
-                        }
-                    } catch (Throwable rex) {
-                        ex = rex;
-                    }
-                    deregisterWorker(wt, ex); // clean up and return false
-                }
+            else if (tc >= MAX_CAP ||
+                     (this == common && tc >= pc + commonMaxSpares))
+                throw new RejectedExecutionException(
+                    "Thread limit exceeded replacing blocked worker");
+            else {                                // similar to tryAddWorker
+                boolean add = false; int rs;      // CAS within lock
+                long nc = ((AC_MASK & c) |
+                           (TC_MASK & (c + TC_UNIT)));
+                if (((rs = lockRunState()) & STOP) == 0)
+                    add = U.compareAndSwapLong(this, CTL, c, nc);
+                unlockRunState(rs, rs & ~RSLOCK);
+                canBlock = add && createWorker(); // throws on exception
             }
         }
-        return false;
+        return canBlock;
     }
 
     /**
-     * Helps and/or blocks until the given task is done.
+     * Helps and/or blocks until the given task is done or timeout.
      *
-     * @param joiner the joining worker
+     * @param w caller
      * @param task the task
+     * @param deadline for timed waits, if nonzero
      * @return task status on exit
      */
-    final int awaitJoin(WorkQueue joiner, ForkJoinTask<?> task) {
+    final int awaitJoin(WorkQueue w, ForkJoinTask<?> task, long deadline) {
         int s = 0;
-        if (task != null && (s = task.status) >= 0 && joiner != null) {
-            ForkJoinTask<?> prevJoin = joiner.currentJoin;
-            joiner.currentJoin = task;
-            do {} while (joiner.tryRemoveAndExec(task) && // process local tasks
-                         (s = task.status) >= 0);
-            if (s >= 0 && (task instanceof CountedCompleter))
-                s = helpComplete(joiner, (CountedCompleter<?>)task, Integer.MAX_VALUE);
-            long cc = 0;        // for stability checks
-            while (s >= 0 && (s = task.status) >= 0) {
-                if ((s = tryHelpStealer(joiner, task)) == 0 &&
-                    (s = task.status) >= 0) {
-                    if (!tryCompensate(cc))
-                        cc = ctl;
-                    else {
-                        if (task.trySetSignal() && (s = task.status) >= 0) {
-                            synchronized (task) {
-                                if (task.status >= 0) {
-                                    try {                // see ForkJoinTask
-                                        task.wait();     //  for explanation
-                                    } catch (InterruptedException ie) {
-                                    }
-                                }
-                                else
-                                    task.notifyAll();
-                            }
-                        }
-                        long c; // reactivate
-                        do {} while (!U.compareAndSwapLong
-                                     (this, CTL, c = ctl,
-                                      ((c & ~AC_MASK) |
-                                       ((c & AC_MASK) + AC_UNIT))));
-                    }
+        if (task != null && w != null) {
+            ForkJoinTask<?> prevJoin = w.currentJoin;
+            U.putOrderedObject(w, QCURRENTJOIN, task);
+            CountedCompleter<?> cc = (task instanceof CountedCompleter) ?
+                (CountedCompleter<?>)task : null;
+            for (;;) {
+                if ((s = task.status) < 0)
+                    break;
+                if (cc != null)
+                    helpComplete(w, cc, 0);
+                else if (w.base == w.top || w.tryRemoveAndExec(task))
+                    helpStealer(w, task);
+                if ((s = task.status) < 0)
+                    break;
+                long ms, ns;
+                if (deadline == 0L)
+                    ms = 0L;
+                else if ((ns = deadline - System.nanoTime()) <= 0L)
+                    break;
+                else if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) <= 0L)
+                    ms = 1L;
+                if (tryCompensate(w)) {
+                    task.internalWait(ms);
+                    U.getAndAddLong(this, CTL, AC_UNIT);
                 }
             }
-            joiner.currentJoin = prevJoin;
+            U.putOrderedObject(w, QCURRENTJOIN, prevJoin);
         }
         return s;
     }
 
-    /**
-     * Stripped-down variant of awaitJoin used by timed joins. Tries
-     * to help join only while there is continuous progress. (Caller
-     * will then enter a timed wait.)
-     *
-     * @param joiner the joining worker
-     * @param task the task
-     */
-    final void helpJoinOnce(WorkQueue joiner, ForkJoinTask<?> task) {
-        int s;
-        if (joiner != null && task != null && (s = task.status) >= 0) {
-            ForkJoinTask<?> prevJoin = joiner.currentJoin;
-            joiner.currentJoin = task;
-            do {} while (joiner.tryRemoveAndExec(task) && // process local tasks
-                         (s = task.status) >= 0);
-            if (s >= 0) {
-                if (task instanceof CountedCompleter)
-                    helpComplete(joiner, (CountedCompleter<?>)task, Integer.MAX_VALUE);
-                do {} while (task.status >= 0 &&
-                             tryHelpStealer(joiner, task) > 0);
-            }
-            joiner.currentJoin = prevJoin;
-        }
-    }
+    // Specialized scanning
 
     /**
      * Returns a (probably) non-empty steal queue, if one is found
@@ -2068,19 +2069,24 @@
      * caller if, by the time it tries to use the queue, it is empty.
      */
     private WorkQueue findNonEmptyStealQueue() {
+        WorkQueue[] ws; int m;  // one-shot version of scan loop
         int r = ThreadLocalRandom.nextSecondarySeed();
-        for (;;) {
-            int ps = plock, m; WorkQueue[] ws; WorkQueue q;
-            if ((ws = workQueues) != null && (m = ws.length - 1) >= 0) {
-                for (int j = (m + 1) << 2; j >= 0; --j) {
-                    if ((q = ws[(((r - j) << 1) | 1) & m]) != null &&
-                        q.base - q.top < 0)
+        if ((ws = workQueues) != null && (m = ws.length - 1) >= 0) {
+            for (int origin = r & m, k = origin, oldSum = 0, checkSum = 0;;) {
+                WorkQueue q; int b;
+                if ((q = ws[k]) != null) {
+                    if ((b = q.base) - q.top < 0)
                         return q;
+                    checkSum += b;
+                }
+                if ((k = (k + 1) & m) == origin) {
+                    if (oldSum == (oldSum = checkSum))
+                        break;
+                    checkSum = 0;
                 }
             }
-            if (plock == ps)
-                return null;
         }
+        return null;
     }
 
     /**
@@ -2090,35 +2096,34 @@
      * find tasks either.
      */
     final void helpQuiescePool(WorkQueue w) {
-        ForkJoinTask<?> ps = w.currentSteal;
+        ForkJoinTask<?> ps = w.currentSteal; // save context
         for (boolean active = true;;) {
             long c; WorkQueue q; ForkJoinTask<?> t; int b;
-            while ((t = w.nextLocalTask()) != null)
-                t.doExec();
+            w.execLocalTasks();     // run locals before each scan
             if ((q = findNonEmptyStealQueue()) != null) {
                 if (!active) {      // re-establish active count
                     active = true;
-                    do {} while (!U.compareAndSwapLong
-                                 (this, CTL, c = ctl,
-                                  ((c & ~AC_MASK) |
-                                   ((c & AC_MASK) + AC_UNIT))));
+                    U.getAndAddLong(this, CTL, AC_UNIT);
                 }
-                if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null)
-                    w.runTask(t);
+                if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null) {
+                    U.putOrderedObject(w, QCURRENTSTEAL, t);
+                    t.doExec();
+                    if (++w.nsteals < 0)
+                        w.transferStealCount(this);
+                }
             }
             else if (active) {      // decrement active count without queuing
-                long nc = ((c = ctl) & ~AC_MASK) | ((c & AC_MASK) - AC_UNIT);
-                if ((int)(nc >> AC_SHIFT) + parallelism == 0)
+                long nc = (AC_MASK & ((c = ctl) - AC_UNIT)) | (~AC_MASK & c);
+                if ((int)(nc >> AC_SHIFT) + (config & SMASK) <= 0)
                     break;          // bypass decrement-then-increment
                 if (U.compareAndSwapLong(this, CTL, c, nc))
                     active = false;
             }
-            else if ((int)((c = ctl) >> AC_SHIFT) + parallelism <= 0 &&
-                     U.compareAndSwapLong
-                     (this, CTL, c, ((c & ~AC_MASK) |
-                                     ((c & AC_MASK) + AC_UNIT))))
+            else if ((int)((c = ctl) >> AC_SHIFT) + (config & SMASK) <= 0 &&
+                     U.compareAndSwapLong(this, CTL, c, c + AC_UNIT))
                 break;
         }
+        U.putOrderedObject(w, QCURRENTSTEAL, ps);
     }
 
     /**
@@ -2141,7 +2146,7 @@
     /**
      * Returns a cheap heuristic guide for task partitioning when
      * programmers, frameworks, tools, or languages have little or no
-     * idea about task granularity.  In essence by offering this
+     * idea about task granularity.  In essence, by offering this
      * method, we ask users only about tradeoffs in overhead vs
      * expected throughput and its variance, rather than how finely to
      * partition tasks.
@@ -2179,15 +2184,12 @@
      * many of these by further considering the number of "idle"
      * threads, that are known to have zero queued tasks, so
      * compensate by a factor of (#idle/#active) threads.
-     *
-     * Note: The approximation of #busy workers as #active workers is
-     * not very good under current signalling scheme, and should be
-     * improved.
      */
     static int getSurplusQueuedTaskCount() {
         Thread t; ForkJoinWorkerThread wt; ForkJoinPool pool; WorkQueue q;
         if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)) {
-            int p = (pool = (wt = (ForkJoinWorkerThread)t).pool).parallelism;
+            int p = (pool = (wt = (ForkJoinWorkerThread)t).pool).
+                config & SMASK;
             int n = (q = wt.workQueue).top - q.base;
             int a = (int)(pool.ctl >> AC_SHIFT) + p;
             return n - (a > (p >>>= 1) ? 0 :
@@ -2202,13 +2204,7 @@
     //  Termination
 
     /**
-     * Possibly initiates and/or completes termination.  The caller
-     * triggering termination runs three passes through workQueues:
-     * (0) Setting termination status, followed by wakeups of queued
-     * workers; (1) cancelling all tasks; (2) interrupting lagging
-     * threads (likely in external tasks, but possibly also blocked in
-     * joins).  Each pass repeats previous steps because of potential
-     * lagging thread creation.
+     * Possibly initiates and/or completes termination.
      *
      * @param now if true, unconditionally terminate, else only
      * if no work and no active workers
@@ -2216,166 +2212,256 @@
      * @return true if now terminating or terminated
      */
     private boolean tryTerminate(boolean now, boolean enable) {
-        int ps;
-        if (this == common)                        // cannot shut down
+        int rs;
+        if (this == common)                       // cannot shut down
             return false;
-        if ((ps = plock) >= 0) {                   // enable by setting plock
+        if ((rs = runState) >= 0) {
             if (!enable)
                 return false;
-            if ((ps & PL_LOCK) != 0 ||
-                !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
-                ps = acquirePlock();
-            int nps = ((ps + PL_LOCK) & ~SHUTDOWN) | SHUTDOWN;
-            if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
-                releasePlock(nps);
+            rs = lockRunState();                  // enter SHUTDOWN phase
+            unlockRunState(rs, (rs & ~RSLOCK) | SHUTDOWN);
         }
-        for (long c;;) {
-            if (((c = ctl) & STOP_BIT) != 0) {     // already terminating
-                if ((short)(c >>> TC_SHIFT) + parallelism <= 0) {
-                    synchronized (this) {
-                        notifyAll();               // signal when 0 workers
+
+        if ((rs & STOP) == 0) {
+            if (!now) {                           // check quiescence
+                for (long oldSum = 0L;;) {        // repeat until stable
+                    WorkQueue[] ws; WorkQueue w; int m, b; long c;
+                    long checkSum = ctl;
+                    if ((int)(checkSum >> AC_SHIFT) + (config & SMASK) > 0)
+                        return false;             // still active workers
+                    if ((ws = workQueues) == null || (m = ws.length - 1) <= 0)
+                        break;                    // check queues
+                    for (int i = 0; i <= m; ++i) {
+                        if ((w = ws[i]) != null) {
+                            if ((b = w.base) != w.top || w.scanState >= 0 ||
+                                w.currentSteal != null) {
+                                tryRelease(c = ctl, ws[m & (int)c], AC_UNIT);
+                                return false;     // arrange for recheck
+                            }
+                            checkSum += b;
+                            if ((i & 1) == 0)
+                                w.qlock = -1;     // try to disable external
+                        }
                     }
+                    if (oldSum == (oldSum = checkSum))
+                        break;
                 }
-                return true;
             }
-            if (!now) {                            // check if idle & no tasks
-                WorkQueue[] ws; WorkQueue w;
-                if ((int)(c >> AC_SHIFT) + parallelism > 0)
-                    return false;
-                if ((ws = workQueues) != null) {
-                    for (int i = 0; i < ws.length; ++i) {
-                        if ((w = ws[i]) != null &&
-                            (!w.isEmpty() ||
-                             ((i & 1) != 0 && w.eventCount >= 0))) {
-                            signalWork(ws, w);
-                            return false;
+            if ((runState & STOP) == 0) {
+                rs = lockRunState();              // enter STOP phase
+                unlockRunState(rs, (rs & ~RSLOCK) | STOP);
+            }
+        }
+
+        int pass = 0;                             // 3 passes to help terminate
+        for (long oldSum = 0L;;) {                // or until done or stable
+            WorkQueue[] ws; WorkQueue w; ForkJoinWorkerThread wt; int m;
+            long checkSum = ctl;
+            if ((short)(checkSum >>> TC_SHIFT) + (config & SMASK) <= 0 ||
+                (ws = workQueues) == null || (m = ws.length - 1) <= 0) {
+                if ((runState & TERMINATED) == 0) {
+                    rs = lockRunState();          // done
+                    unlockRunState(rs, (rs & ~RSLOCK) | TERMINATED);
+                    synchronized (this) { notifyAll(); } // for awaitTermination
+                }
+                break;
+            }
+            for (int i = 0; i <= m; ++i) {
+                if ((w = ws[i]) != null) {
+                    checkSum += w.base;
+                    w.qlock = -1;                 // try to disable
+                    if (pass > 0) {
+                        w.cancelAll();            // clear queue
+                        if (pass > 1 && (wt = w.owner) != null) {
+                            if (!wt.isInterrupted()) {
+                                try {             // unblock join
+                                    wt.interrupt();
+                                } catch (Throwable ignore) {
+                                }
+                            }
+                            if (w.scanState < 0)
+                                U.unpark(wt);     // wake up
                         }
                     }
                 }
             }
-            if (U.compareAndSwapLong(this, CTL, c, c | STOP_BIT)) {
-                for (int pass = 0; pass < 3; ++pass) {
-                    WorkQueue[] ws; WorkQueue w; Thread wt;
-                    if ((ws = workQueues) != null) {
-                        int n = ws.length;
-                        for (int i = 0; i < n; ++i) {
-                            if ((w = ws[i]) != null) {
-                                w.qlock = -1;
-                                if (pass > 0) {
-                                    w.cancelAll();
-                                    if (pass > 1 && (wt = w.owner) != null) {
-                                        if (!wt.isInterrupted()) {
-                                            try {
-                                                wt.interrupt();
-                                            } catch (Throwable ignore) {
-                                            }
-                                        }
-                                        U.unpark(wt);
-                                    }
-                                }
-                            }
+            if (checkSum != oldSum) {             // unstable
+                oldSum = checkSum;
+                pass = 0;
+            }
+            else if (pass > 3 && pass > m)        // can't further help
+                break;
+            else if (++pass > 1) {                // try to dequeue
+                long c; int j = 0, sp;            // bound attempts
+                while (j++ <= m && (sp = (int)(c = ctl)) != 0)
+                    tryRelease(c, ws[sp & m], AC_UNIT);
+            }
+        }
+        return true;
+    }
+
+    // External operations
+
+    /**
+     * Full version of externalPush, handling uncommon cases, as well
+     * as performing secondary initialization upon the first
+     * submission of the first task to the pool.  It also detects
+     * first submission by an external thread and creates a new shared
+     * queue if the one at index if empty or contended.
+     *
+     * @param task the task. Caller must ensure non-null.
+     */
+    private void externalSubmit(ForkJoinTask<?> task) {
+        int r;                                    // initialize caller's probe
+        if ((r = ThreadLocalRandom.getProbe()) == 0) {
+            ThreadLocalRandom.localInit();
+            r = ThreadLocalRandom.getProbe();
+        }
+        for (;;) {
+            WorkQueue[] ws; WorkQueue q; int rs, m, k;
+            boolean move = false;
+            if ((rs = runState) < 0) {
+                tryTerminate(false, false);     // help terminate
+                throw new RejectedExecutionException();
+            }
+            else if ((rs & STARTED) == 0 ||     // initialize
+                     ((ws = workQueues) == null || (m = ws.length - 1) < 0)) {
+                int ns = 0;
+                rs = lockRunState();
+                try {
+                    if ((rs & STARTED) == 0) {
+                        U.compareAndSwapObject(this, STEALCOUNTER, null,
+                                               new AtomicLong());
+                        // create workQueues array with size a power of two
+                        int p = config & SMASK; // ensure at least 2 slots
+                        int n = (p > 1) ? p - 1 : 1;
+                        n |= n >>> 1; n |= n >>> 2;  n |= n >>> 4;
+                        n |= n >>> 8; n |= n >>> 16; n = (n + 1) << 1;
+                        workQueues = new WorkQueue[n];
+                        ns = STARTED;
+                    }
+                } finally {
+                    unlockRunState(rs, (rs & ~RSLOCK) | ns);
+                }
+            }
+            else if ((q = ws[k = r & m & SQMASK]) != null) {
+                if (q.qlock == 0 && U.compareAndSwapInt(q, QLOCK, 0, 1)) {
+                    ForkJoinTask<?>[] a = q.array;
+                    int s = q.top;
+                    boolean submitted = false; // initial submission or resizing
+                    try {                      // locked version of push
+                        if ((a != null && a.length > s + 1 - q.base) ||
+                            (a = q.growArray()) != null) {
+                            int j = (((a.length - 1) & s) << ASHIFT) + ABASE;
+                            U.putOrderedObject(a, j, task);
+                            U.putOrderedInt(q, QTOP, s + 1);
+                            submitted = true;
                         }
-                        // Wake up workers parked on event queue
-                        int i, e; long cc; Thread p;
-                        while ((e = (int)(cc = ctl) & E_MASK) != 0 &&
-                               (i = e & SMASK) < n && i >= 0 &&
-                               (w = ws[i]) != null) {
-                            long nc = ((long)(w.nextWait & E_MASK) |
-                                       ((cc + AC_UNIT) & AC_MASK) |
-                                       (cc & (TC_MASK|STOP_BIT)));
-                            if (w.eventCount == (e | INT_SIGN) &&
-                                U.compareAndSwapLong(this, CTL, cc, nc)) {
-                                w.eventCount = (e + E_SEQ) & E_MASK;
-                                w.qlock = -1;
-                                if ((p = w.parker) != null)
-                                    U.unpark(p);
-                            }
-                        }
+                    } finally {
+                        U.compareAndSwapInt(q, QLOCK, 1, 0);
+                    }
+                    if (submitted) {
+                        signalWork(ws, q);
+                        return;
                     }
                 }
+                move = true;                   // move on failure
             }
+            else if (((rs = runState) & RSLOCK) == 0) { // create new queue
+                q = new WorkQueue(this, null);
+                q.hint = r;
+                q.config = k | SHARED_QUEUE;
+                q.scanState = INACTIVE;
+                rs = lockRunState();           // publish index
+                if (rs > 0 &&  (ws = workQueues) != null &&
+                    k < ws.length && ws[k] == null)
+                    ws[k] = q;                 // else terminated
+                unlockRunState(rs, rs & ~RSLOCK);
+            }
+            else
+                move = true;                   // move if busy
+            if (move)
+                r = ThreadLocalRandom.advanceProbe(r);
         }
     }
 
-    // external operations on common pool
-
     /**
-     * Returns common pool queue for a thread that has submitted at
-     * least one task.
+     * Tries to add the given task to a submission queue at
+     * submitter's current queue. Only the (vastly) most common path
+     * is directly handled in this method, while screening for need
+     * for externalSubmit.
+     *
+     * @param task the task. Caller must ensure non-null.
      */
-    static WorkQueue commonSubmitterQueue() {
-        ForkJoinPool p; WorkQueue[] ws; int m, z;
-        return ((z = ThreadLocalRandom.getProbe()) != 0 &&
-                (p = common) != null &&
-                (ws = p.workQueues) != null &&
-                (m = ws.length - 1) >= 0) ?
-            ws[m & z & SQMASK] : null;
+    final void externalPush(ForkJoinTask<?> task) {
+        WorkQueue[] ws; WorkQueue q; int m;
+        int r = ThreadLocalRandom.getProbe();
+        int rs = runState;
+        if ((ws = workQueues) != null && (m = (ws.length - 1)) >= 0 &&
+            (q = ws[m & r & SQMASK]) != null && r != 0 && rs > 0 &&
+            U.compareAndSwapInt(q, QLOCK, 0, 1)) {
+            ForkJoinTask<?>[] a; int am, n, s;
+            if ((a = q.array) != null &&
+                (am = a.length - 1) > (n = (s = q.top) - q.base)) {
+                int j = ((am & s) << ASHIFT) + ABASE;
+                U.putOrderedObject(a, j, task);
+                U.putOrderedInt(q, QTOP, s + 1);
+                U.putOrderedInt(q, QLOCK, 0);
+                if (n <= 1)
+                    signalWork(ws, q);
+                return;
+            }
+            U.compareAndSwapInt(q, QLOCK, 1, 0);
+        }
+        externalSubmit(task);
     }
 
     /**
-     * Tries to pop the given task from submitter's queue in common pool.
+     * Returns common pool queue for an external thread.
+     */
+    static WorkQueue commonSubmitterQueue() {
+        ForkJoinPool p = common;
+        int r = ThreadLocalRandom.getProbe();
+        WorkQueue[] ws; int m;
+        return (p != null && (ws = p.workQueues) != null &&
+                (m = ws.length - 1) >= 0) ?
+            ws[m & r & SQMASK] : null;
+    }
+
+    /**
+     * Performs tryUnpush for an external submitter: Finds queue,
+     * locks if apparently non-empty, validates upon locking, and
+     * adjusts top. Each check can fail but rarely does.
      */
     final boolean tryExternalUnpush(ForkJoinTask<?> task) {
-        WorkQueue joiner; ForkJoinTask<?>[] a; int m, s;
-        WorkQueue[] ws = workQueues;
-        int z = ThreadLocalRandom.getProbe();
-        boolean popped = false;
-        if (ws != null && (m = ws.length - 1) >= 0 &&
-            (joiner = ws[z & m & SQMASK]) != null &&
-            joiner.base != (s = joiner.top) &&
-            (a = joiner.array) != null) {
+        WorkQueue[] ws; WorkQueue w; ForkJoinTask<?>[] a; int m, s;
+        int r = ThreadLocalRandom.getProbe();
+        if ((ws = workQueues) != null && (m = ws.length - 1) >= 0 &&
+            (w = ws[m & r & SQMASK]) != null &&
+            (a = w.array) != null && (s = w.top) != w.base) {
             long j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE;
-            if (U.getObject(a, j) == task &&
-                U.compareAndSwapInt(joiner, QLOCK, 0, 1)) {
-                if (joiner.top == s && joiner.array == a &&
+            if (U.compareAndSwapInt(w, QLOCK, 0, 1)) {
+                if (w.top == s && w.array == a &&
+                    U.getObject(a, j) == task &&
                     U.compareAndSwapObject(a, j, task, null)) {
-                    joiner.top = s - 1;
-                    popped = true;
+                    U.putOrderedInt(w, QTOP, s - 1);
+                    U.putOrderedInt(w, QLOCK, 0);
+                    return true;
                 }
-                joiner.qlock = 0;
+                U.compareAndSwapInt(w, QLOCK, 1, 0);
             }
         }
-        return popped;
+        return false;
     }
 
+    /**
+     * Performs helpComplete for an external submitter.
+     */
     final int externalHelpComplete(CountedCompleter<?> task, int maxTasks) {
-        WorkQueue joiner; int m;
-        WorkQueue[] ws = workQueues;
-        int j = ThreadLocalRandom.getProbe();
-        int s = 0;
-        if (ws != null && (m = ws.length - 1) >= 0 &&
-            (joiner = ws[j & m & SQMASK]) != null && task != null) {
-            int scans = m + m + 1;
-            long c = 0L;             // for stability check
-            j |= 1;                  // poll odd queues
-            for (int k = scans; ; j += 2) {
-                WorkQueue q;
-                if ((s = task.status) < 0)
-                    break;
-                else if (joiner.externalPopAndExecCC(task)) {
-                    if (--maxTasks <= 0) {
-                        s = task.status;
-                        break;
-                    }
-                    k = scans;
-                }
-                else if ((s = task.status) < 0)
-                    break;
-                else if ((q = ws[j & m]) != null && q.pollAndExecCC(task)) {
-                    if (--maxTasks <= 0) {
-                        s = task.status;
-                        break;
-                    }
-                    k = scans;
-                }
-                else if (--k < 0) {
-                    if (c == (c = ctl))
-                        break;
-                    k = scans;
-                }
-            }
-        }
-        return s;
+        WorkQueue[] ws; int n;
+        int r = ThreadLocalRandom.getProbe();
+        return ((ws = workQueues) == null || (n = ws.length) == 0) ? 0 :
+            helpComplete(ws[(n - 1) & r & SQMASK], task, maxTasks);
     }
 
     // Exported methods
@@ -2447,7 +2533,7 @@
         this(checkParallelism(parallelism),
              checkFactory(factory),
              handler,
-             (asyncMode ? FIFO_QUEUE : LIFO_QUEUE),
+             asyncMode ? FIFO_QUEUE : LIFO_QUEUE,
              "ForkJoinPool-" + nextPoolId() + "-worker-");
         checkPermission();
     }
@@ -2478,8 +2564,7 @@
         this.workerNamePrefix = workerNamePrefix;
         this.factory = factory;
         this.ueh = handler;
-        this.mode = (short)mode;
-        this.parallelism = (short)parallelism;
+        this.config = (parallelism & SMASK) | mode;
         long np = (long)(-parallelism); // offset ctl counts
         this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
     }
@@ -2624,7 +2709,7 @@
         // In previous versions of this class, this method constructed
         // a task to run ForkJoinTask.invokeAll, but now external
         // invocation of multiple tasks is at least as efficient.
-        ArrayList<Future<T>> futures = new ArrayList<Future<T>>(tasks.size());
+        ArrayList<Future<T>> futures = new ArrayList<>(tasks.size());
 
         boolean done = false;
         try {
@@ -2670,7 +2755,7 @@
      */
     public int getParallelism() {
         int par;
-        return ((par = parallelism) > 0) ? par : 1;
+        return ((par = config & SMASK) > 0) ? par : 1;
     }
 
     /**
@@ -2692,7 +2777,7 @@
      * @return the number of worker threads
      */
     public int getPoolSize() {
-        return parallelism + (short)(ctl >>> TC_SHIFT);
+        return (config & SMASK) + (short)(ctl >>> TC_SHIFT);
     }
 
     /**
@@ -2702,7 +2787,7 @@
      * @return {@code true} if this pool uses async mode
      */
     public boolean getAsyncMode() {
-        return mode == FIFO_QUEUE;
+        return (config & FIFO_QUEUE) != 0;
     }
 
     /**
@@ -2733,7 +2818,7 @@
      * @return the number of active threads
      */
     public int getActiveThreadCount() {
-        int r = parallelism + (int)(ctl >> AC_SHIFT);
+        int r = (config & SMASK) + (int)(ctl >> AC_SHIFT);
         return (r <= 0) ? 0 : r; // suppress momentarily negative values
     }
 
@@ -2749,7 +2834,7 @@
      * @return {@code true} if all threads are currently idle
      */
     public boolean isQuiescent() {
-        return parallelism + (int)(ctl >> AC_SHIFT) <= 0;
+        return (config & SMASK) + (int)(ctl >> AC_SHIFT) <= 0;
     }
 
     /**
@@ -2764,7 +2849,8 @@
      * @return the number of steals
      */
     public long getStealCount() {
-        long count = stealCount;
+        AtomicLong sc = stealCounter;
+        long count = (sc == null) ? 0L : sc.get();
         WorkQueue[] ws; WorkQueue w;
         if ((ws = workQueues) != null) {
             for (int i = 1; i < ws.length; i += 2) {
@@ -2894,7 +2980,8 @@
     public String toString() {
         // Use a single pass through workQueues to collect counts
         long qt = 0L, qs = 0L; int rc = 0;
-        long st = stealCount;
+        AtomicLong sc = stealCounter;
+        long st = (sc == null) ? 0L : sc.get();
         long c = ctl;
         WorkQueue[] ws; WorkQueue w;
         if ((ws = workQueues) != null) {
@@ -2912,16 +2999,16 @@
                 }
             }
         }
-        int pc = parallelism;
+        int pc = (config & SMASK);
         int tc = pc + (short)(c >>> TC_SHIFT);
         int ac = pc + (int)(c >> AC_SHIFT);
         if (ac < 0) // ignore transient negative
             ac = 0;
-        String level;
-        if ((c & STOP_BIT) != 0)
-            level = (tc == 0) ? "Terminated" : "Terminating";
-        else
-            level = plock < 0 ? "Shutting down" : "Running";
+        int rs = runState;
+        String level = ((rs & TERMINATED) != 0 ? "Terminated" :
+                        (rs & STOP)       != 0 ? "Terminating" :
+                        (rs & SHUTDOWN)   != 0 ? "Shutting down" :
+                        "Running");
         return super.toString() +
             "[" + level +
             ", parallelism = " + pc +
@@ -2983,9 +3070,7 @@
      * @return {@code true} if all tasks have completed following shut down
      */
     public boolean isTerminated() {
-        long c = ctl;
-        return ((c & STOP_BIT) != 0L &&
-                (short)(c >>> TC_SHIFT) + parallelism <= 0);
+        return (runState & TERMINATED) != 0;
     }
 
     /**
@@ -3002,9 +3087,8 @@
      * @return {@code true} if terminating but not yet terminated
      */
     public boolean isTerminating() {
-        long c = ctl;
-        return ((c & STOP_BIT) != 0L &&
-                (short)(c >>> TC_SHIFT) + parallelism > 0);
+        int rs = runState;
+        return (rs & STOP) != 0 && (rs & TERMINATED) == 0;
     }
 
     /**
@@ -3013,7 +3097,7 @@
      * @return {@code true} if this pool has been shut down
      */
     public boolean isShutdown() {
-        return plock < 0;
+        return (runState & SHUTDOWN) != 0;
     }
 
     /**
@@ -3090,8 +3174,9 @@
             }
             found = false;
             for (int j = (m + 1) << 2; j >= 0; --j) {
-                ForkJoinTask<?> t; WorkQueue q; int b;
-                if ((q = ws[r++ & m]) != null && (b = q.base) - q.top < 0) {
+                ForkJoinTask<?> t; WorkQueue q; int b, k;
+                if ((k = r++ & m) <= m && k >= 0 && (q = ws[k]) != null &&
+                    (b = q.base) - q.top < 0) {
                     found = true;
                     if ((t = q.pollAt(b)) != null)
                         t.doExec();
@@ -3115,8 +3200,8 @@
      * in {@link ForkJoinPool}s.
      *
      * <p>A {@code ManagedBlocker} provides two methods.  Method
-     * {@code isReleasable} must return {@code true} if blocking is
-     * not necessary. Method {@code block} blocks the current thread
+     * {@link #isReleasable} must return {@code true} if blocking is
+     * not necessary. Method {@link #block} blocks the current thread
      * if necessary (perhaps internally invoking {@code isReleasable}
      * before actually blocking). These actions are performed by any
      * thread invoking {@link ForkJoinPool#managedBlock(ManagedBlocker)}.
@@ -3185,37 +3270,46 @@
     }
 
     /**
-     * Blocks in accord with the given blocker.  If the current thread
-     * is a {@link ForkJoinWorkerThread}, this method possibly
-     * arranges for a spare thread to be activated if necessary to
-     * ensure sufficient parallelism while the current thread is blocked.
+     * Runs the given possibly blocking task.  When {@linkplain
+     * ForkJoinTask#inForkJoinPool() running in a ForkJoinPool}, this
+     * method possibly arranges for a spare thread to be activated if
+     * necessary to ensure sufficient parallelism while the current
+     * thread is blocked in {@link ManagedBlocker#block blocker.block()}.
      *
-     * <p>If the caller is not a {@link ForkJoinTask}, this method is
+     * <p>This method repeatedly calls {@code blocker.isReleasable()} and
+     * {@code blocker.block()} until either method returns {@code true}.
+     * Every call to {@code blocker.block()} is preceded by a call to
+     * {@code blocker.isReleasable()} that returned {@code false}.
+     *
+     * <p>If not running in a ForkJoinPool, this method is
      * behaviorally equivalent to
      *  <pre> {@code
      * while (!blocker.isReleasable())
      *   if (blocker.block())
-     *     return;
-     * }</pre>
+     *     break;}</pre>
      *
-     * If the caller is a {@code ForkJoinTask}, then the pool may
-     * first be expanded to ensure parallelism, and later adjusted.
+     * If running in a ForkJoinPool, the pool may first be expanded to
+     * ensure sufficient parallelism available during the call to
+     * {@code blocker.block()}.
      *
-     * @param blocker the blocker
-     * @throws InterruptedException if blocker.block did so
+     * @param blocker the blocker task
+     * @throws InterruptedException if {@code blocker.block()} did so
      */
     public static void managedBlock(ManagedBlocker blocker)
         throws InterruptedException {
+        ForkJoinPool p;
+        ForkJoinWorkerThread wt;
         Thread t = Thread.currentThread();
-        if (t instanceof ForkJoinWorkerThread) {
-            ForkJoinPool p = ((ForkJoinWorkerThread)t).pool;
+        if ((t instanceof ForkJoinWorkerThread) &&
+            (p = (wt = (ForkJoinWorkerThread)t).pool) != null) {
+            WorkQueue w = wt.workQueue;
             while (!blocker.isReleasable()) {
-                if (p.tryCompensate(p.ctl)) {
+                if (p.tryCompensate(w)) {
                     try {
                         do {} while (!blocker.isReleasable() &&
                                      !blocker.block());
                     } finally {
-                        p.incrementActiveCount();
+                        U.getAndAddLong(p, CTL, AC_UNIT);
                     }
                     break;
                 }
@@ -3241,15 +3335,18 @@
 
     // Unsafe mechanics
     private static final sun.misc.Unsafe U;
+    private static final int  ABASE;
+    private static final int  ASHIFT;
     private static final long CTL;
+    private static final long RUNSTATE;
+    private static final long STEALCOUNTER;
     private static final long PARKBLOCKER;
-    private static final int ABASE;
-    private static final int ASHIFT;
-    private static final long STEALCOUNT;
-    private static final long PLOCK;
-    private static final long INDEXSEED;
-    private static final long QBASE;
+    private static final long QTOP;
     private static final long QLOCK;
+    private static final long QSCANSTATE;
+    private static final long QPARKER;
+    private static final long QCURRENTSTEAL;
+    private static final long QCURRENTJOIN;
 
     static {
         // initialize field offsets for CAS etc
@@ -3258,20 +3355,26 @@
             Class<?> k = ForkJoinPool.class;
             CTL = U.objectFieldOffset
                 (k.getDeclaredField("ctl"));
-            STEALCOUNT = U.objectFieldOffset
-                (k.getDeclaredField("stealCount"));
-            PLOCK = U.objectFieldOffset
-                (k.getDeclaredField("plock"));
-            INDEXSEED = U.objectFieldOffset
-                (k.getDeclaredField("indexSeed"));
+            RUNSTATE = U.objectFieldOffset
+                (k.getDeclaredField("runState"));
+            STEALCOUNTER = U.objectFieldOffset
+                (k.getDeclaredField("stealCounter"));
             Class<?> tk = Thread.class;
             PARKBLOCKER = U.objectFieldOffset
                 (tk.getDeclaredField("parkBlocker"));
             Class<?> wk = WorkQueue.class;
-            QBASE = U.objectFieldOffset
-                (wk.getDeclaredField("base"));
+            QTOP = U.objectFieldOffset
+                (wk.getDeclaredField("top"));
             QLOCK = U.objectFieldOffset
                 (wk.getDeclaredField("qlock"));
+            QSCANSTATE = U.objectFieldOffset
+                (wk.getDeclaredField("scanState"));
+            QPARKER = U.objectFieldOffset
+                (wk.getDeclaredField("parker"));
+            QCURRENTSTEAL = U.objectFieldOffset
+                (wk.getDeclaredField("currentSteal"));
+            QCURRENTJOIN = U.objectFieldOffset
+                (wk.getDeclaredField("currentJoin"));
             Class<?> ak = ForkJoinTask[].class;
             ABASE = U.arrayBaseOffset(ak);
             int scale = U.arrayIndexScale(ak);
@@ -3282,6 +3385,7 @@
             throw new Error(e);
         }
 
+        commonMaxSpares = DEFAULT_COMMON_MAX_SPARES;
         defaultForkJoinWorkerThreadFactory =
             new DefaultForkJoinWorkerThreadFactory();
         modifyThreadPermission = new RuntimePermission("modifyThread");
@@ -3289,7 +3393,7 @@
         common = java.security.AccessController.doPrivileged
             (new java.security.PrivilegedAction<ForkJoinPool>() {
                 public ForkJoinPool run() { return makeCommonPool(); }});
-        int par = common.parallelism; // report 1 even if threads disabled
+        int par = common.config & SMASK; // report 1 even if threads disabled
         commonParallelism = par > 0 ? par : 1;
     }
 
--- a/src/share/classes/java/util/concurrent/ForkJoinTask.java	Fri Sep 26 15:25:33 2014 +0400
+++ b/src/share/classes/java/util/concurrent/ForkJoinTask.java	Fri Sep 05 10:54:28 2014 +0200
@@ -297,15 +297,22 @@
     }
 
     /**
-     * Tries to set SIGNAL status unless already completed. Used by
-     * ForkJoinPool. Other variants are directly incorporated into
-     * externalAwaitDone etc.
+     * If not done, sets SIGNAL status and performs Object.wait(timeout).
+     * This task may or may not be done on exit. Ignores interrupts.
      *
-     * @return true if successful
+     * @param timeout using Object.wait conventions.
      */
-    final boolean trySetSignal() {
-        int s = status;
-        return s >= 0 && U.compareAndSwapInt(this, STATUS, s, s | SIGNAL);
+    final void internalWait(long timeout) {
+        int s;
+        if ((s = status) >= 0 && // force completer to issue notify
+            U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
+            synchronized (this) {
+                if (status >= 0)
+                    try { wait(timeout); } catch (InterruptedException ie) { }
+                else
+                    notifyAll();
+            }
+        }
     }
 
     /**
@@ -313,35 +320,29 @@
      * @return status upon completion
      */
     private int externalAwaitDone() {
-        int s;
-        ForkJoinPool cp = ForkJoinPool.common;
-        if ((s = status) >= 0) {
-            if (cp != null) {
-                if (this instanceof CountedCompleter)
-                    s = cp.externalHelpComplete((CountedCompleter<?>)this, Integer.MAX_VALUE);
-                else if (cp.tryExternalUnpush(this))
-                    s = doExec();
-            }
-            if (s >= 0 && (s = status) >= 0) {
-                boolean interrupted = false;
-                do {
-                    if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
-                        synchronized (this) {
-                            if (status >= 0) {
-                                try {
-                                    wait();
-                                } catch (InterruptedException ie) {
-                                    interrupted = true;
-                                }
+        int s = ((this instanceof CountedCompleter) ? // try helping
+                 ForkJoinPool.common.externalHelpComplete(
+                     (CountedCompleter<?>)this, 0) :
+                 ForkJoinPool.common.tryExternalUnpush(this) ? doExec() : 0);
+        if (s >= 0 && (s = status) >= 0) {
+            boolean interrupted = false;
+            do {
+                if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
+                    synchronized (this) {
+                        if (status >= 0) {
+                            try {
+                                wait(0L);
+                            } catch (InterruptedException ie) {
+                                interrupted = true;
                             }
-                            else
-                                notifyAll();
                         }
+                        else
+                            notifyAll();
                     }
-                } while ((s = status) >= 0);
-                if (interrupted)
-                    Thread.currentThread().interrupt();
-            }
+                }
+            } while ((s = status) >= 0);
+            if (interrupted)
+                Thread.currentThread().interrupt();
         }
         return s;
     }
@@ -351,22 +352,22 @@
      */
     private int externalInterruptibleAwaitDone() throws InterruptedException {
         int s;
-        ForkJoinPool cp = ForkJoinPool.common;
         if (Thread.interrupted())
             throw new InterruptedException();
-        if ((s = status) >= 0 && cp != null) {
-            if (this instanceof CountedCompleter)
-                cp.externalHelpComplete((CountedCompleter<?>)this, Integer.MAX_VALUE);
-            else if (cp.tryExternalUnpush(this))
-                doExec();
-        }
-        while ((s = status) >= 0) {
-            if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
-                synchronized (this) {
-                    if (status >= 0)
-                        wait();
-                    else
-                        notifyAll();
+        if ((s = status) >= 0 &&
+            (s = ((this instanceof CountedCompleter) ?
+                  ForkJoinPool.common.externalHelpComplete(
+                      (CountedCompleter<?>)this, 0) :
+                  ForkJoinPool.common.tryExternalUnpush(this) ? doExec() :
+                  0)) >= 0) {
+            while ((s = status) >= 0) {
+                if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
+                    synchronized (this) {
+                        if (status >= 0)
+                            wait(0L);
+                        else
+                            notifyAll();
+                    }
                 }
             }
         }
@@ -386,7 +387,7 @@
             ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
             (w = (wt = (ForkJoinWorkerThread)t).workQueue).
             tryUnpush(this) && (s = doExec()) < 0 ? s :
-            wt.pool.awaitJoin(w, this) :
+            wt.pool.awaitJoin(w, this, 0L) :
             externalAwaitDone();
     }
 
@@ -399,7 +400,8 @@
         int s; Thread t; ForkJoinWorkerThread wt;
         return (s = doExec()) < 0 ? s :
             ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
-            (wt = (ForkJoinWorkerThread)t).pool.awaitJoin(wt.workQueue, this) :
+            (wt = (ForkJoinWorkerThread)t).pool.
+            awaitJoin(wt.workQueue, this, 0L) :
             externalAwaitDone();
     }
 
@@ -577,7 +579,7 @@
         Throwable ex;
         if (e == null || (ex = e.ex) == null)
             return null;
-        if (false && e.thrower != Thread.currentThread().getId()) {
+        if (e.thrower != Thread.currentThread().getId()) {
             Class<? extends Throwable> ec = ex.getClass();
             try {
                 Constructor<?> noArgCtor = null;
@@ -587,13 +589,17 @@
                     Class<?>[] ps = c.getParameterTypes();
                     if (ps.length == 0)
                         noArgCtor = c;
-                    else if (ps.length == 1 && ps[0] == Throwable.class)
-                        return (Throwable)(c.newInstance(ex));
+                    else if (ps.length == 1 && ps[0] == Throwable.class) {
+                        Throwable wx = (Throwable)c.newInstance(ex);
+                        return (wx == null) ? ex : wx;
+                    }
                 }
                 if (noArgCtor != null) {
                     Throwable wx = (Throwable)(noArgCtor.newInstance());
-                    wx.initCause(ex);
-                    return wx;
+                    if (wx != null) {
+                        wx.initCause(ex);
+                        return wx;
+                    }
                 }
             } catch (Exception ignore) {
             }
@@ -1017,67 +1023,40 @@
      */
     public final V get(long timeout, TimeUnit unit)
         throws InterruptedException, ExecutionException, TimeoutException {
+        int s;
+        long nanos = unit.toNanos(timeout);
         if (Thread.interrupted())
             throw new InterruptedException();
-        // Messy in part because we measure in nanosecs, but wait in millisecs
-        int s; long ms;
-        long ns = unit.toNanos(timeout);
-        ForkJoinPool cp;
-        if ((s = status) >= 0 && ns > 0L) {
-            long deadline = System.nanoTime() + ns;
-            ForkJoinPool p = null;
-            ForkJoinPool.WorkQueue w = null;
+        if ((s = status) >= 0 && nanos > 0L) {
+            long d = System.nanoTime() + nanos;
+            long deadline = (d == 0L) ? 1L : d; // avoid 0
             Thread t = Thread.currentThread();
             if (t instanceof ForkJoinWorkerThread) {
                 ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
-                p = wt.pool;
-                w = wt.workQueue;
-                p.helpJoinOnce(w, this); // no retries on failure
+                s = wt.pool.awaitJoin(wt.workQueue, this, deadline);
             }
-            else if ((cp = ForkJoinPool.common) != null) {
-                if (this instanceof CountedCompleter)
-                    cp.externalHelpComplete((CountedCompleter<?>)this, Integer.MAX_VALUE);
-                else if (cp.tryExternalUnpush(this))
-                    doExec();
-            }
-            boolean canBlock = false;
-            boolean interrupted = false;
-            try {
-                while ((s = status) >= 0) {
-                    if (w != null && w.qlock < 0)
-                        cancelIgnoringExceptions(this);
-                    else if (!canBlock) {
-                        if (p == null || p.tryCompensate(p.ctl))
-                            canBlock = true;
-                    }
-                    else {
-                        if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) > 0L &&
-                            U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
-                            synchronized (this) {
-                                if (status >= 0) {
-                                    try {
-                                        wait(ms);
-                                    } catch (InterruptedException ie) {
-                                        if (p == null)
-                                            interrupted = true;
-                                    }
-                                }
-                                else
-                                    notifyAll();
-                            }
+            else if ((s = ((this instanceof CountedCompleter) ?
+                           ForkJoinPool.common.externalHelpComplete(
+                               (CountedCompleter<?>)this, 0) :
+                           ForkJoinPool.common.tryExternalUnpush(this) ?
+                           doExec() : 0)) >= 0) {
+                long ns, ms; // measure in nanosecs, but wait in millisecs
+                while ((s = status) >= 0 &&
+                       (ns = deadline - System.nanoTime()) > 0L) {
+                    if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) > 0L &&
+                        U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
+                        synchronized (this) {
+                            if (status >= 0)
+                                wait(ms); // OK to throw InterruptedException
+                            else
+                                notifyAll();
                         }
-                        if ((s = status) < 0 || interrupted ||
-                            (ns = deadline - System.nanoTime()) <= 0L)
-                            break;
                     }
                 }
-            } finally {
-                if (p != null && canBlock)
-                    p.incrementActiveCount();
             }
-            if (interrupted)
-                throw new InterruptedException();
         }
+        if (s >= 0)
+            s = status;
         if ((s &= DONE_MASK) != NORMAL) {
             Throwable ex;
             if (s == CANCELLED)
--- a/src/share/classes/java/util/concurrent/ForkJoinWorkerThread.java	Fri Sep 26 15:25:33 2014 +0400
+++ b/src/share/classes/java/util/concurrent/ForkJoinWorkerThread.java	Fri Sep 05 10:54:28 2014 +0200
@@ -66,7 +66,7 @@
      * owning thread.
      *
      * Support for (non-public) subclass InnocuousForkJoinWorkerThread
-     * requires that we break quite a lot of encapulation (via Unsafe)
+     * requires that we break quite a lot of encapsulation (via Unsafe)
      * both here and in the subclass to access and set Thread fields.
      */
 
@@ -118,7 +118,7 @@
      * @return the index number
      */
     public int getPoolIndex() {
-        return workQueue.poolIndex >>> 1; // ignore odd/even tag bit
+        return workQueue.getPoolIndex();
     }
 
     /**
@@ -171,7 +171,7 @@
     }
 
     /**
-     * Erases ThreadLocals by nulling out Thread maps
+     * Erases ThreadLocals by nulling out Thread maps.
      */
     final void eraseThreadLocals() {
         U.putObject(this, THREADLOCALS, null);
@@ -246,8 +246,8 @@
 
         /**
          * Returns a new group with the system ThreadGroup (the
-         * topmost, parentless group) as parent.  Uses Unsafe to
-         * traverse Thread group and ThreadGroup parent fields.
+         * topmost, parent-less group) as parent.  Uses Unsafe to
+         * traverse Thread.group and ThreadGroup.parent fields.
          */
         private static ThreadGroup createThreadGroup() {
             try {
@@ -274,4 +274,3 @@
     }
 
 }
-