changeset 36:9f7046dbd9ab

6602600: Fast removal of cancelled scheduled thread pool tasks Reviewed-by: alanb Contributed-by: Doug Lea <dl@cs.oswego.edu>
author martin
date Mon, 10 Mar 2008 23:23:47 -0700
parents 3654a4ce7d54
children 944d0faa0c50
files src/share/classes/java/util/concurrent/ScheduledThreadPoolExecutor.java test/java/util/concurrent/ScheduledThreadPoolExecutor/BasicCancelTest.java test/java/util/concurrent/ScheduledThreadPoolExecutor/Stress.java
diffstat 3 files changed, 688 insertions(+), 53 deletions(-) [+]
line wrap: on
line diff
--- a/src/share/classes/java/util/concurrent/ScheduledThreadPoolExecutor.java	Mon Mar 10 23:23:47 2008 -0700
+++ b/src/share/classes/java/util/concurrent/ScheduledThreadPoolExecutor.java	Mon Mar 10 23:23:47 2008 -0700
@@ -35,6 +35,7 @@
 
 package java.util.concurrent;
 import java.util.concurrent.atomic.*;
+import java.util.concurrent.locks.*;
 import java.util.*;
 
 /**
@@ -45,12 +46,21 @@
  * flexibility or capabilities of {@link ThreadPoolExecutor} (which
  * this class extends) are required.
  *
- * <p> Delayed tasks execute no sooner than they are enabled, but
+ * <p>Delayed tasks execute no sooner than they are enabled, but
  * without any real-time guarantees about when, after they are
  * enabled, they will commence. Tasks scheduled for exactly the same
  * execution time are enabled in first-in-first-out (FIFO) order of
  * submission.
  *
+ * <p>When a submitted task is cancelled before it is run, execution
+ * is suppressed. By default, such a cancelled task is not
+ * automatically removed from the work queue until its delay
+ * elapses. While this enables further inspection and monitoring, it
+ * may also cause unbounded retention of cancelled tasks. To avoid
+ * this, set {@link #setRemoveOnCancelPolicy} to {@code true}, which
+ * causes tasks to be immediately removed from the work queue at
+ * time of cancellation.
+ *
  * <p>While this class inherits from {@link ThreadPoolExecutor}, a few
  * of the inherited tuning methods are not useful for it. In
  * particular, because it acts as a fixed-sized pool using
@@ -111,21 +121,11 @@
      *    ScheduledExecutorService methods) which are treated as
      *    delayed tasks with a delay of zero.
      *
-     * 2. Using a custom queue (DelayedWorkQueue) based on an
+     * 2. Using a custom queue (DelayedWorkQueue), a variant of
      *    unbounded DelayQueue. The lack of capacity constraint and
      *    the fact that corePoolSize and maximumPoolSize are
      *    effectively identical simplifies some execution mechanics
-     *    (see delayedExecute) compared to ThreadPoolExecutor
-     *    version.
-     *
-     *    The DelayedWorkQueue class is defined below for the sake of
-     *    ensuring that all elements are instances of
-     *    RunnableScheduledFuture.  Since DelayQueue otherwise
-     *    requires type be Delayed, but not necessarily Runnable, and
-     *    the workQueue requires the opposite, we need to explicitly
-     *    define a class that requires both to ensure that users don't
-     *    add objects that aren't RunnableScheduledFutures via
-     *    getQueue().add() etc.
+     *    (see delayedExecute) compared to ThreadPoolExecutor.
      *
      * 3. Supporting optional run-after-shutdown parameters, which
      *    leads to overrides of shutdown methods to remove and cancel
@@ -150,6 +150,11 @@
     private volatile boolean executeExistingDelayedTasksAfterShutdown = true;
 
     /**
+     * True if ScheduledFutureTask.cancel should remove from queue
+     */
+    private volatile boolean removeOnCancel = false;
+
+    /**
      * Sequence number to break scheduling ties, and in turn to
      * guarantee FIFO order among tied entries.
      */
@@ -167,8 +172,10 @@
 
         /** Sequence number to break ties FIFO */
         private final long sequenceNumber;
+
         /** The time the task is enabled to execute in nanoTime units */
         private long time;
+
         /**
          * Period in nanoseconds for repeating tasks.  A positive
          * value indicates fixed-rate execution.  A negative value
@@ -181,6 +188,11 @@
         RunnableScheduledFuture<V> outerTask = this;
 
         /**
+         * Index into delay queue, to support faster cancellation.
+         */
+        int heapIndex;
+
+        /**
          * Creates a one-shot action with given nanoTime-based trigger time.
          */
         ScheduledFutureTask(Runnable r, V result, long ns) {
@@ -255,6 +267,13 @@
                 time = now() - p;
         }
 
+        public boolean cancel(boolean mayInterruptIfRunning) {
+            boolean cancelled = super.cancel(mayInterruptIfRunning);
+            if (cancelled && removeOnCancel && heapIndex >= 0)
+                remove(this);
+            return cancelled;
+        }
+
         /**
          * Overrides FutureTask version so as to reset/requeue if periodic.
          */
@@ -655,6 +674,33 @@
     }
 
     /**
+     * Sets the policy on whether cancelled tasks should be immediately
+     * removed from the work queue at time of cancellation.  This value is
+     * by default {@code false}.
+     *
+     * @param value if {@code true}, remove on cancellation, else don't
+     * @see #getRemoveOnCancelPolicy
+     * @since 1.7
+     */
+    public void setRemoveOnCancelPolicy(boolean value) {
+        removeOnCancel = value;
+    }
+
+    /**
+     * Gets the policy on whether cancelled tasks should be immediately
+     * removed from the work queue at time of cancellation.  This value is
+     * by default {@code false}.
+     *
+     * @return {@code true} if cancelled tasks are immediately removed
+     *         from the queue
+     * @see #setRemoveOnCancelPolicy
+     * @since 1.7
+     */
+    public boolean getRemoveOnCancelPolicy() {
+        return removeOnCancel;
+    }
+
+    /**
      * Initiates an orderly shutdown in which previously submitted
      * tasks are executed, but no new tasks will be accepted.  If the
      * {@code ExecuteExistingDelayedTasksAfterShutdownPolicy} has
@@ -707,56 +753,478 @@
     }
 
     /**
-     * An annoying wrapper class to convince javac to use a
-     * DelayQueue<RunnableScheduledFuture> as a BlockingQueue<Runnable>
+     * Specialized delay queue. To mesh with TPE declarations, this
+     * class must be declared as a BlockingQueue<Runnable> even though
+     * it can only hold RunnableScheduledFutures.
      */
-    private static class DelayedWorkQueue
-        extends AbstractCollection<Runnable>
+    static class DelayedWorkQueue extends AbstractQueue<Runnable>
         implements BlockingQueue<Runnable> {
 
-        private final DelayQueue<RunnableScheduledFuture> dq = new DelayQueue<RunnableScheduledFuture>();
-        public Runnable poll() { return dq.poll(); }
-        public Runnable peek() { return dq.peek(); }
-        public Runnable take() throws InterruptedException { return dq.take(); }
-        public Runnable poll(long timeout, TimeUnit unit) throws InterruptedException {
-            return dq.poll(timeout, unit);
+        /*
+         * A DelayedWorkQueue is based on a heap-based data structure
+         * like those in DelayQueue and PriorityQueue, except that
+         * every ScheduledFutureTask also records its index into the
+         * heap array. This eliminates the need to find a task upon
+         * cancellation, greatly speeding up removal (down from O(n)
+         * to O(log n)), and reducing garbage retention that would
+         * otherwise occur by waiting for the element to rise to top
+         * before clearing. But because the queue may also hold
+         * RunnableScheduledFutures that are not ScheduledFutureTasks,
+         * we are not guaranteed to have such indices available, in
+         * which case we fall back to linear search. (We expect that
+         * most tasks will not be decorated, and that the faster cases
+         * will be much more common.)
+         *
+         * All heap operations must record index changes -- mainly
+         * within siftUp and siftDown. Upon removal, a task's
+         * heapIndex is set to -1. Note that ScheduledFutureTasks can
+         * appear at most once in the queue (this need not be true for
+         * other kinds of tasks or work queues), so are uniquely
+         * identified by heapIndex.
+         */
+
+        private static final int INITIAL_CAPACITY = 16;
+        private RunnableScheduledFuture[] queue =
+            new RunnableScheduledFuture[INITIAL_CAPACITY];
+        private final ReentrantLock lock = new ReentrantLock();
+        private int size = 0;
+
+        /**
+         * Thread designated to wait for the task at the head of the
+         * queue.  This variant of the Leader-Follower pattern
+         * (http://www.cs.wustl.edu/~schmidt/POSA/POSA2/) serves to
+         * minimize unnecessary timed waiting.  When a thread becomes
+         * the leader, it waits only for the next delay to elapse, but
+         * other threads await indefinitely.  The leader thread must
+         * signal some other thread before returning from take() or
+         * poll(...), unless some other thread becomes leader in the
+         * interim.  Whenever the head of the queue is replaced with a
+         * task with an earlier expiration time, the leader field is
+         * invalidated by being reset to null, and some waiting
+         * thread, but not necessarily the current leader, is
+         * signalled.  So waiting threads must be prepared to acquire
+         * and lose leadership while waiting.
+         */
+        private Thread leader = null;
+
+        /**
+         * Condition signalled when a newer task becomes available at the
+         * head of the queue or a new thread may need to become leader.
+         */
+        private final Condition available = lock.newCondition();
+
+        /**
+         * Set f's heapIndex if it is a ScheduledFutureTask.
+         */
+        private void setIndex(RunnableScheduledFuture f, int idx) {
+            if (f instanceof ScheduledFutureTask)
+                ((ScheduledFutureTask)f).heapIndex = idx;
         }
 
-        public boolean add(Runnable x) {
-            return dq.add((RunnableScheduledFuture)x);
-        }
-        public boolean offer(Runnable x) {
-            return dq.offer((RunnableScheduledFuture)x);
-        }
-        public void put(Runnable x) {
-            dq.put((RunnableScheduledFuture)x);
-        }
-        public boolean offer(Runnable x, long timeout, TimeUnit unit) {
-            return dq.offer((RunnableScheduledFuture)x, timeout, unit);
+        /**
+         * Sift element added at bottom up to its heap-ordered spot.
+         * Call only when holding lock.
+         */
+        private void siftUp(int k, RunnableScheduledFuture key) {
+            while (k > 0) {
+                int parent = (k - 1) >>> 1;
+                RunnableScheduledFuture e = queue[parent];
+                if (key.compareTo(e) >= 0)
+                    break;
+                queue[k] = e;
+                setIndex(e, k);
+                k = parent;
+            }
+            queue[k] = key;
+            setIndex(key, k);
         }
 
-        public Runnable remove() { return dq.remove(); }
-        public Runnable element() { return dq.element(); }
-        public void clear() { dq.clear(); }
-        public int drainTo(Collection<? super Runnable> c) { return dq.drainTo(c); }
-        public int drainTo(Collection<? super Runnable> c, int maxElements) {
-            return dq.drainTo(c, maxElements);
+        /**
+         * Sift element added at top down to its heap-ordered spot.
+         * Call only when holding lock.
+         */
+        private void siftDown(int k, RunnableScheduledFuture key) {
+            int half = size >>> 1;
+            while (k < half) {
+                int child = (k << 1) + 1;
+                RunnableScheduledFuture c = queue[child];
+                int right = child + 1;
+                if (right < size && c.compareTo(queue[right]) > 0)
+                    c = queue[child = right];
+                if (key.compareTo(c) <= 0)
+                    break;
+                queue[k] = c;
+                setIndex(c, k);
+                k = child;
+            }
+            queue[k] = key;
+            setIndex(key, k);
         }
 
-        public int remainingCapacity() { return dq.remainingCapacity(); }
-        public boolean remove(Object x) { return dq.remove(x); }
-        public boolean contains(Object x) { return dq.contains(x); }
-        public int size() { return dq.size(); }
-        public boolean isEmpty() { return dq.isEmpty(); }
-        public Object[] toArray() { return dq.toArray(); }
-        public <T> T[] toArray(T[] array) { return dq.toArray(array); }
+        /**
+         * Resize the heap array.  Call only when holding lock.
+         */
+        private void grow() {
+            int oldCapacity = queue.length;
+            int newCapacity = oldCapacity + (oldCapacity >> 1); // grow 50%
+            if (newCapacity < 0) // overflow
+                newCapacity = Integer.MAX_VALUE;
+            queue = Arrays.copyOf(queue, newCapacity);
+        }
+
+        /**
+         * Find index of given object, or -1 if absent
+         */
+        private int indexOf(Object x) {
+            if (x != null) {
+                if (x instanceof ScheduledFutureTask) {
+                    int i = ((ScheduledFutureTask) x).heapIndex;
+                    // Sanity check; x could conceivably be a
+                    // ScheduledFutureTask from some other pool.
+                    if (i >= 0 && i < size && queue[i] == x)
+                        return i;
+                } else {
+                    for (int i = 0; i < size; i++)
+                        if (x.equals(queue[i]))
+                            return i;
+                }
+            }
+            return -1;
+        }
+
+        public boolean contains(Object x) {
+            final ReentrantLock lock = this.lock;
+            lock.lock();
+            try {
+                return indexOf(x) != -1;
+            } finally {
+                lock.unlock();
+            }
+        }
+
+        public boolean remove(Object x) {
+            final ReentrantLock lock = this.lock;
+            lock.lock();
+            try {
+                int i = indexOf(x);
+                if (i < 0)
+                    return false;
+
+                setIndex(queue[i], -1);
+                int s = --size;
+                RunnableScheduledFuture replacement = queue[s];
+                queue[s] = null;
+                if (s != i) {
+                    siftDown(i, replacement);
+                    if (queue[i] == replacement)
+                        siftUp(i, replacement);
+                }
+                return true;
+            } finally {
+                lock.unlock();
+            }
+        }
+
+        public int size() {
+            final ReentrantLock lock = this.lock;
+            lock.lock();
+            try {
+                return size;
+            } finally {
+                lock.unlock();
+            }
+        }
+
+        public boolean isEmpty() {
+            return size() == 0;
+        }
+
+        public int remainingCapacity() {
+            return Integer.MAX_VALUE;
+        }
+
+        public RunnableScheduledFuture peek() {
+            final ReentrantLock lock = this.lock;
+            lock.lock();
+            try {
+                return queue[0];
+            } finally {
+                lock.unlock();
+            }
+        }
+
+        public boolean offer(Runnable x) {
+            if (x == null)
+                throw new NullPointerException();
+            RunnableScheduledFuture e = (RunnableScheduledFuture)x;
+            final ReentrantLock lock = this.lock;
+            lock.lock();
+            try {
+                int i = size;
+                if (i >= queue.length)
+                    grow();
+                size = i + 1;
+                if (i == 0) {
+                    queue[0] = e;
+                    setIndex(e, 0);
+                } else {
+                    siftUp(i, e);
+                }
+                if (queue[0] == e) {
+                    leader = null;
+                    available.signal();
+                }
+            } finally {
+                lock.unlock();
+            }
+            return true;
+        }
+
+        public void put(Runnable e) {
+            offer(e);
+        }
+
+        public boolean add(Runnable e) {
+            return offer(e);
+        }
+
+        public boolean offer(Runnable e, long timeout, TimeUnit unit) {
+            return offer(e);
+        }
+
+        /**
+         * Performs common bookkeeping for poll and take: Replaces
+         * first element with last and sifts it down.  Call only when
+         * holding lock.
+         * @param f the task to remove and return
+         */
+        private RunnableScheduledFuture finishPoll(RunnableScheduledFuture f) {
+            int s = --size;
+            RunnableScheduledFuture x = queue[s];
+            queue[s] = null;
+            if (s != 0)
+                siftDown(0, x);
+            setIndex(f, -1);
+            return f;
+        }
+
+        public RunnableScheduledFuture poll() {
+            final ReentrantLock lock = this.lock;
+            lock.lock();
+            try {
+                RunnableScheduledFuture first = queue[0];
+                if (first == null || first.getDelay(TimeUnit.NANOSECONDS) > 0)
+                    return null;
+                else
+                    return finishPoll(first);
+            } finally {
+                lock.unlock();
+            }
+        }
+
+        public RunnableScheduledFuture take() throws InterruptedException {
+            final ReentrantLock lock = this.lock;
+            lock.lockInterruptibly();
+            try {
+                for (;;) {
+                    RunnableScheduledFuture first = queue[0];
+                    if (first == null)
+                        available.await();
+                    else {
+                        long delay = first.getDelay(TimeUnit.NANOSECONDS);
+                        if (delay <= 0)
+                            return finishPoll(first);
+                        else if (leader != null)
+                            available.await();
+                        else {
+                            Thread thisThread = Thread.currentThread();
+                            leader = thisThread;
+                            try {
+                                available.awaitNanos(delay);
+                            } finally {
+                                if (leader == thisThread)
+                                    leader = null;
+                            }
+                        }
+                    }
+                }
+            } finally {
+                if (leader == null && queue[0] != null)
+                    available.signal();
+                lock.unlock();
+            }
+        }
+
+        public RunnableScheduledFuture poll(long timeout, TimeUnit unit)
+            throws InterruptedException {
+            long nanos = unit.toNanos(timeout);
+            final ReentrantLock lock = this.lock;
+            lock.lockInterruptibly();
+            try {
+                for (;;) {
+                    RunnableScheduledFuture first = queue[0];
+                    if (first == null) {
+                        if (nanos <= 0)
+                            return null;
+                        else
+                            nanos = available.awaitNanos(nanos);
+                    } else {
+                        long delay = first.getDelay(TimeUnit.NANOSECONDS);
+                        if (delay <= 0)
+                            return finishPoll(first);
+                        if (nanos <= 0)
+                            return null;
+                        if (nanos < delay || leader != null)
+                            nanos = available.awaitNanos(nanos);
+                        else {
+                            Thread thisThread = Thread.currentThread();
+                            leader = thisThread;
+                            try {
+                                long timeLeft = available.awaitNanos(delay);
+                                nanos -= delay - timeLeft;
+                            } finally {
+                                if (leader == thisThread)
+                                    leader = null;
+                            }
+                        }
+                    }
+                }
+            } finally {
+                if (leader == null && queue[0] != null)
+                    available.signal();
+                lock.unlock();
+            }
+        }
+
+        public void clear() {
+            final ReentrantLock lock = this.lock;
+            lock.lock();
+            try {
+                for (int i = 0; i < size; i++) {
+                    RunnableScheduledFuture t = queue[i];
+                    if (t != null) {
+                        queue[i] = null;
+                        setIndex(t, -1);
+                    }
+                }
+                size = 0;
+            } finally {
+                lock.unlock();
+            }
+        }
+
+        /**
+         * Return and remove first element only if it is expired.
+         * Used only by drainTo.  Call only when holding lock.
+         */
+        private RunnableScheduledFuture pollExpired() {
+            RunnableScheduledFuture first = queue[0];
+            if (first == null || first.getDelay(TimeUnit.NANOSECONDS) > 0)
+                return null;
+            return finishPoll(first);
+        }
+
+        public int drainTo(Collection<? super Runnable> c) {
+            if (c == null)
+                throw new NullPointerException();
+            if (c == this)
+                throw new IllegalArgumentException();
+            final ReentrantLock lock = this.lock;
+            lock.lock();
+            try {
+                RunnableScheduledFuture first;
+                int n = 0;
+                while ((first = pollExpired()) != null) {
+                    c.add(first);
+                    ++n;
+                }
+                return n;
+            } finally {
+                lock.unlock();
+            }
+        }
+
+        public int drainTo(Collection<? super Runnable> c, int maxElements) {
+            if (c == null)
+                throw new NullPointerException();
+            if (c == this)
+                throw new IllegalArgumentException();
+            if (maxElements <= 0)
+                return 0;
+            final ReentrantLock lock = this.lock;
+            lock.lock();
+            try {
+                RunnableScheduledFuture first;
+                int n = 0;
+                while (n < maxElements && (first = pollExpired()) != null) {
+                    c.add(first);
+                    ++n;
+                }
+                return n;
+            } finally {
+                lock.unlock();
+            }
+        }
+
+        public Object[] toArray() {
+            final ReentrantLock lock = this.lock;
+            lock.lock();
+            try {
+                return Arrays.copyOf(queue, size, Object[].class);
+            } finally {
+                lock.unlock();
+            }
+        }
+
+        @SuppressWarnings("unchecked")
+        public <T> T[] toArray(T[] a) {
+            final ReentrantLock lock = this.lock;
+            lock.lock();
+            try {
+                if (a.length < size)
+                    return (T[]) Arrays.copyOf(queue, size, a.getClass());
+                System.arraycopy(queue, 0, a, 0, size);
+                if (a.length > size)
+                    a[size] = null;
+                return a;
+            } finally {
+                lock.unlock();
+            }
+        }
+
         public Iterator<Runnable> iterator() {
-            return new Iterator<Runnable>() {
-                private Iterator<RunnableScheduledFuture> it = dq.iterator();
-                public boolean hasNext() { return it.hasNext(); }
-                public Runnable next() { return it.next(); }
-                public void remove() { it.remove(); }
-            };
+            return new Itr(Arrays.copyOf(queue, size));
+        }
+
+        /**
+         * Snapshot iterator that works off copy of underlying q array.
+         */
+        private class Itr implements Iterator<Runnable> {
+            final RunnableScheduledFuture[] array;
+            int cursor = 0;     // index of next element to return
+            int lastRet = -1;   // index of last element, or -1 if no such
+
+            Itr(RunnableScheduledFuture[] array) {
+                this.array = array;
+            }
+
+            public boolean hasNext() {
+                return cursor < array.length;
+            }
+
+            public Runnable next() {
+                if (cursor >= array.length)
+                    throw new NoSuchElementException();
+                lastRet = cursor;
+                return array[cursor++];
+            }
+
+            public void remove() {
+                if (lastRet < 0)
+                    throw new IllegalStateException();
+                DelayedWorkQueue.this.remove(array[lastRet]);
+                lastRet = -1;
+            }
         }
     }
 }
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/java/util/concurrent/ScheduledThreadPoolExecutor/BasicCancelTest.java	Mon Mar 10 23:23:47 2008 -0700
@@ -0,0 +1,113 @@
+/*
+ * Copyright 2008 Sun Microsystems, Inc.  All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * @test
+ * @bug 6602600
+ * @run main/othervm -Xmx8m BasicCancelTest
+ * @summary Check effectiveness of RemoveOnCancelPolicy
+ */
+
+import java.util.concurrent.*;
+import java.util.Random;
+
+/**
+ * Simple timer cancellation test. Submits tasks to a scheduled executor
+ * service and immediately cancels them.
+ */
+public class BasicCancelTest {
+
+    void checkShutdown(final ExecutorService es) {
+        final Runnable nop = new Runnable() {public void run() {}};
+        try {
+            if (new Random().nextBoolean()) {
+                check(es.isShutdown());
+                if (es instanceof ThreadPoolExecutor)
+                    check(((ThreadPoolExecutor) es).isTerminating()
+                          || es.isTerminated());
+                THROWS(RejectedExecutionException.class,
+                       new F(){void f(){es.execute(nop);}});
+            }
+        } catch (Throwable t) { unexpected(t); }
+    }
+
+    void checkTerminated(final ThreadPoolExecutor tpe) {
+        try {
+            checkShutdown(tpe);
+            check(tpe.getQueue().isEmpty());
+            check(tpe.isTerminated());
+            check(! tpe.isTerminating());
+            equal(tpe.getActiveCount(), 0);
+            equal(tpe.getPoolSize(), 0);
+            equal(tpe.getTaskCount(), tpe.getCompletedTaskCount());
+            check(tpe.awaitTermination(0, TimeUnit.SECONDS));
+        } catch (Throwable t) { unexpected(t); }
+    }
+
+    void test(String[] args) throws Throwable {
+
+        final ScheduledThreadPoolExecutor pool =
+            new ScheduledThreadPoolExecutor(1);
+
+        // Needed to avoid OOME
+        pool.setRemoveOnCancelPolicy(true);
+
+        final long moreThanYouCanChew = Runtime.getRuntime().freeMemory() / 4;
+        System.out.printf("moreThanYouCanChew=%d%n", moreThanYouCanChew);
+
+        Runnable noopTask = new Runnable() { public void run() {}};
+
+        for (long i = 0; i < moreThanYouCanChew; i++)
+            pool.schedule(noopTask, 10, TimeUnit.MINUTES).cancel(true);
+
+        pool.shutdown();
+        check(pool.awaitTermination(1L, TimeUnit.DAYS));
+        checkTerminated(pool);
+        equal(pool.getTaskCount(), 0L);
+        equal(pool.getCompletedTaskCount(), 0L);
+    }
+
+    //--------------------- Infrastructure ---------------------------
+    volatile int passed = 0, failed = 0;
+    void pass() {passed++;}
+    void fail() {failed++; Thread.dumpStack();}
+    void fail(String msg) {System.err.println(msg); fail();}
+    void unexpected(Throwable t) {failed++; t.printStackTrace();}
+    void check(boolean cond) {if (cond) pass(); else fail();}
+    void equal(Object x, Object y) {
+        if (x == null ? y == null : x.equals(y)) pass();
+        else fail(x + " not equal to " + y);}
+    public static void main(String[] args) throws Throwable {
+        new BasicCancelTest().instanceMain(args);}
+    void instanceMain(String[] args) throws Throwable {
+        try {test(args);} catch (Throwable t) {unexpected(t);}
+        System.out.printf("%nPassed = %d, failed = %d%n%n", passed, failed);
+        if (failed > 0) throw new AssertionError("Some tests failed");}
+    abstract class F {abstract void f() throws Throwable;}
+    void THROWS(Class<? extends Throwable> k, F... fs) {
+        for (F f : fs)
+            try {f.f(); fail("Expected " + k.getName() + " not thrown");}
+            catch (Throwable t) {
+                if (k.isAssignableFrom(t.getClass())) pass();
+                else unexpected(t);}}
+}
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/java/util/concurrent/ScheduledThreadPoolExecutor/Stress.java	Mon Mar 10 23:23:47 2008 -0700
@@ -0,0 +1,54 @@
+/*
+ * Copyright 2008 Sun Microsystems, Inc.  All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+import java.util.concurrent.*;
+
+/**
+ * This is not a regression test, but a stress benchmark test for
+ * 6602600: Fast removal of cancelled scheduled thread pool tasks
+ *
+ * This runs in the same wall clock time, but much reduced cpu time,
+ * with the changes for 6602600.
+ */
+public class Stress {
+
+    public static void main(String[] args) throws Throwable {
+
+        final CountDownLatch count = new CountDownLatch(1000);
+
+        final ScheduledThreadPoolExecutor pool =
+            new ScheduledThreadPoolExecutor(100);
+        pool.prestartAllCoreThreads();
+
+        final Runnable incTask = new Runnable() { public void run() {
+            count.countDown();
+        }};
+
+        pool.scheduleAtFixedRate(incTask, 0, 10, TimeUnit.MILLISECONDS);
+
+        count.await();
+
+        pool.shutdown();
+        pool.awaitTermination(1L, TimeUnit.DAYS);
+    }
+}