view src/share/vm/memory/genCollectedHeap.hpp @ 5761:b86041bd7b99

8010722: assert: failed: heap size is too big for compressed oops Summary: Use conservative assumptions of required alignment for the various garbage collector components into account when determining the maximum heap size that supports compressed oops. Using this conservative value avoids several circular dependencies in the calculation. Reviewed-by: stefank, dholmes
author tschatzl
date Tue, 18 Apr 2017 06:37:32 +0100
parents fada199d881a
line wrap: on
line source
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 * published by the Free Software Foundation.
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 * 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).
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 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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 * questions.


#include "gc_implementation/shared/adaptiveSizePolicy.hpp"
#include "memory/collectorPolicy.hpp"
#include "memory/generation.hpp"
#include "memory/sharedHeap.hpp"

class SubTasksDone;

// A "GenCollectedHeap" is a SharedHeap that uses generational
// collection.  It is represented with a sequence of Generation's.
class GenCollectedHeap : public SharedHeap {
  friend class GenCollectorPolicy;
  friend class Generation;
  friend class DefNewGeneration;
  friend class TenuredGeneration;
  friend class ConcurrentMarkSweepGeneration;
  friend class CMSCollector;
  friend class GenMarkSweep;
  friend class VM_GenCollectForAllocation;
  friend class VM_GenCollectForPermanentAllocation;
  friend class VM_GenCollectFull;
  friend class VM_GenCollectFullConcurrent;
  friend class VM_GC_HeapInspection;
  friend class VM_HeapDumper;
  friend class HeapInspection;
  friend class GCCauseSetter;
  friend class VMStructs;
  enum SomeConstants {
    max_gens = 10

  friend class VM_PopulateDumpSharedSpace;

  // Fields:
  static GenCollectedHeap* _gch;

  int _n_gens;
  Generation* _gens[max_gens];
  GenerationSpec** _gen_specs;

  // The generational collector policy.
  GenCollectorPolicy* _gen_policy;

  // Indicates that the most recent previous incremental collection failed.
  // The flag is cleared when an action is taken that might clear the
  // condition that caused that incremental collection to fail.
  bool _incremental_collection_failed;

  // In support of ExplicitGCInvokesConcurrent functionality
  unsigned int _full_collections_completed;

  // Data structure for claiming the (potentially) parallel tasks in
  // (gen-specific) strong roots processing.
  SubTasksDone* _gen_process_strong_tasks;
  SubTasksDone* gen_process_strong_tasks() { return _gen_process_strong_tasks; }

  // In block contents verification, the number of header words to skip
  NOT_PRODUCT(static size_t _skip_header_HeapWords;)

  // GC is not allowed during the dump of the shared classes.  Keep track
  // of this in order to provide an reasonable error message when terminating.
  bool _preloading_shared_classes;

  // Directs each generation up to and including "collectedGen" to recompute
  // its desired size.
  void compute_new_generation_sizes(int collectedGen);

  // Helper functions for allocation
  HeapWord* attempt_allocation(size_t size,
                               bool   is_tlab,
                               bool   first_only);

  // Helper function for two callbacks below.
  // Considers collection of the first max_level+1 generations.
  void do_collection(bool   full,
                     bool   clear_all_soft_refs,
                     size_t size,
                     bool   is_tlab,
                     int    max_level);

  // Callback from VM_GenCollectForAllocation operation.
  // This function does everything necessary/possible to satisfy an
  // allocation request that failed in the youngest generation that should
  // have handled it (including collection, expansion, etc.)
  HeapWord* satisfy_failed_allocation(size_t size, bool is_tlab);

  // Callback from VM_GenCollectFull operation.
  // Perform a full collection of the first max_level+1 generations.
  void do_full_collection(bool clear_all_soft_refs, int max_level);

  // Does the "cause" of GC indicate that
  // we absolutely __must__ clear soft refs?
  bool must_clear_all_soft_refs();

  GenCollectedHeap(GenCollectorPolicy *policy);

  GCStats* gc_stats(int level) const;

  // Returns JNI_OK on success
  virtual jint initialize();
  char* allocate(size_t alignment, PermanentGenerationSpec* perm_gen_spec,
                 size_t* _total_reserved, int* _n_covered_regions,
                 ReservedSpace* heap_rs);

  // Does operations required after initialization has been done.
  void post_initialize();

  // Initialize ("weak") refs processing support
  virtual void ref_processing_init();

  virtual CollectedHeap::Name kind() const {
    return CollectedHeap::GenCollectedHeap;

  // The generational collector policy.
  GenCollectorPolicy* gen_policy() const { return _gen_policy; }

  // Adaptive size policy
  virtual AdaptiveSizePolicy* size_policy() {
    return gen_policy()->size_policy();

  // Return the (conservative) maximum heap alignment
  static size_t conservative_max_heap_alignment() {
    return Generation::GenGrain;

  size_t capacity() const;
  size_t used() const;

  // Save the "used_region" for generations level and lower,
  // and, if perm is true, for perm gen.
  void save_used_regions(int level, bool perm);

  size_t max_capacity() const;

  HeapWord* mem_allocate(size_t size,
                         bool*  gc_overhead_limit_was_exceeded);

  // We may support a shared contiguous allocation area, if the youngest
  // generation does.
  bool supports_inline_contig_alloc() const;
  HeapWord** top_addr() const;
  HeapWord** end_addr() const;

  // Return an estimate of the maximum allocation that could be performed
  // without triggering any collection activity.  In a generational
  // collector, for example, this is probably the largest allocation that
  // could be supported in the youngest generation.  It is "unsafe" because
  // no locks are taken; the result should be treated as an approximation,
  // not a guarantee.
  size_t unsafe_max_alloc();

  // Does this heap support heap inspection? (+PrintClassHistogram)
  virtual bool supports_heap_inspection() const { return true; }

  // Perform a full collection of the heap; intended for use in implementing
  // "System.gc". This implies as full a collection as the CollectedHeap
  // supports. Caller does not hold the Heap_lock on entry.
  void collect(GCCause::Cause cause);

  // This interface assumes that it's being called by the
  // vm thread. It collects the heap assuming that the
  // heap lock is already held and that we are executing in
  // the context of the vm thread.
  void collect_as_vm_thread(GCCause::Cause cause);

  // The same as above but assume that the caller holds the Heap_lock.
  void collect_locked(GCCause::Cause cause);

  // Perform a full collection of the first max_level+1 generations.
  // Mostly used for testing purposes. Caller does not hold the Heap_lock on entry.
  void collect(GCCause::Cause cause, int max_level);

  // Returns "TRUE" iff "p" points into the committed areas of the heap.
  // The methods is_in(), is_in_closed_subset() and is_in_youngest() may
  // be expensive to compute in general, so, to prevent
  // their inadvertent use in product jvm's, we restrict their use to
  // assertion checking or verification only.
  bool is_in(const void* p) const;

  // override
  bool is_in_closed_subset(const void* p) const {
    if (UseConcMarkSweepGC) {
      return is_in_reserved(p);
    } else {
      return is_in(p);

  // Returns true if the reference is to an object in the reserved space
  // for the young generation.
  // Assumes the the young gen address range is less than that of the old gen.
  bool is_in_young(oop p);

#ifdef ASSERT
  virtual bool is_in_partial_collection(const void* p);

  virtual bool is_scavengable(const void* addr) {
    return is_in_young((oop)addr);

  // Iteration functions.
  void oop_iterate(OopClosure* cl);
  void oop_iterate(MemRegion mr, OopClosure* cl);
  void object_iterate(ObjectClosure* cl);
  void safe_object_iterate(ObjectClosure* cl);
  void object_iterate_since_last_GC(ObjectClosure* cl);
  Space* space_containing(const void* addr) const;

  // A CollectedHeap is divided into a dense sequence of "blocks"; that is,
  // each address in the (reserved) heap is a member of exactly
  // one block.  The defining characteristic of a block is that it is
  // possible to find its size, and thus to progress forward to the next
  // block.  (Blocks may be of different sizes.)  Thus, blocks may
  // represent Java objects, or they might be free blocks in a
  // free-list-based heap (or subheap), as long as the two kinds are
  // distinguishable and the size of each is determinable.

  // Returns the address of the start of the "block" that contains the
  // address "addr".  We say "blocks" instead of "object" since some heaps
  // may not pack objects densely; a chunk may either be an object or a
  // non-object.
  virtual HeapWord* block_start(const void* addr) const;

  // Requires "addr" to be the start of a chunk, and returns its size.
  // "addr + size" is required to be the start of a new chunk, or the end
  // of the active area of the heap. Assumes (and verifies in non-product
  // builds) that addr is in the allocated part of the heap and is
  // the start of a chunk.
  virtual size_t block_size(const HeapWord* addr) const;

  // Requires "addr" to be the start of a block, and returns "TRUE" iff
  // the block is an object. Assumes (and verifies in non-product
  // builds) that addr is in the allocated part of the heap and is
  // the start of a chunk.
  virtual bool block_is_obj(const HeapWord* addr) const;

  // Section on TLAB's.
  virtual bool supports_tlab_allocation() const;
  virtual size_t tlab_capacity(Thread* thr) const;
  virtual size_t unsafe_max_tlab_alloc(Thread* thr) const;
  virtual HeapWord* allocate_new_tlab(size_t size);

  // Can a compiler initialize a new object without store barriers?
  // This permission only extends from the creation of a new object
  // via a TLAB up to the first subsequent safepoint.
  virtual bool can_elide_tlab_store_barriers() const {
    return true;

  virtual bool card_mark_must_follow_store() const {
    return UseConcMarkSweepGC;

  // We don't need barriers for stores to objects in the
  // young gen and, a fortiori, for initializing stores to
  // objects therein. This applies to {DefNew,ParNew}+{Tenured,CMS}
  // only and may need to be re-examined in case other
  // kinds of collectors are implemented in the future.
  virtual bool can_elide_initializing_store_barrier(oop new_obj) {
    // We wanted to assert that:-
    // assert(UseParNewGC || UseSerialGC || UseConcMarkSweepGC,
    //       "Check can_elide_initializing_store_barrier() for this collector");
    // but unfortunately the flag UseSerialGC need not necessarily always
    // be set when DefNew+Tenured are being used.
    return is_in_young(new_obj);

  // Can a compiler elide a store barrier when it writes
  // a permanent oop into the heap?  Applies when the compiler
  // is storing x to the heap, where x->is_perm() is true.
  virtual bool can_elide_permanent_oop_store_barriers() const {
    // CMS needs to see all, even intra-generational, ref updates.
    return !UseConcMarkSweepGC;

  // The "requestor" generation is performing some garbage collection
  // action for which it would be useful to have scratch space.  The
  // requestor promises to allocate no more than "max_alloc_words" in any
  // older generation (via promotion say.)   Any blocks of space that can
  // be provided are returned as a list of ScratchBlocks, sorted by
  // decreasing size.
  ScratchBlock* gather_scratch(Generation* requestor, size_t max_alloc_words);
  // Allow each generation to reset any scratch space that it has
  // contributed as it needs.
  void release_scratch();

  // Ensure parsability: override
  virtual void ensure_parsability(bool retire_tlabs);

  // Time in ms since the longest time a collector ran in
  // in any generation.
  virtual jlong millis_since_last_gc();

  // Total number of full collections completed.
  unsigned int total_full_collections_completed() {
    assert(_full_collections_completed <= _total_full_collections,
           "Can't complete more collections than were started");
    return _full_collections_completed;

  // Update above counter, as appropriate, at the end of a stop-world GC cycle
  unsigned int update_full_collections_completed();
  // Update above counter, as appropriate, at the end of a concurrent GC cycle
  unsigned int update_full_collections_completed(unsigned int count);

  // Update "time of last gc" for all constituent generations
  // to "now".
  void update_time_of_last_gc(jlong now) {
    for (int i = 0; i < _n_gens; i++) {

  // Update the gc statistics for each generation.
  // "level" is the level of the lastest collection
  void update_gc_stats(int current_level, bool full) {
    for (int i = 0; i < _n_gens; i++) {
      _gens[i]->update_gc_stats(current_level, full);
    perm_gen()->update_gc_stats(current_level, full);

  // Override.
  bool no_gc_in_progress() { return !is_gc_active(); }

  // Override.
  void prepare_for_verify();

  // Override.
  void verify(bool silent, VerifyOption option);

  // Override.
  virtual void print_on(outputStream* st) const;
  virtual void print_gc_threads_on(outputStream* st) const;
  virtual void gc_threads_do(ThreadClosure* tc) const;
  virtual void print_tracing_info() const;

  // PrintGC, PrintGCDetails support
  void print_heap_change(size_t prev_used) const;
  void print_perm_heap_change(size_t perm_prev_used) const;

  // The functions below are helper functions that a subclass of
  // "CollectedHeap" can use in the implementation of its virtual
  // functions.

  class GenClosure : public StackObj {
    virtual void do_generation(Generation* gen) = 0;

  // Apply "cl.do_generation" to all generations in the heap (not including
  // the permanent generation).  If "old_to_young" determines the order.
  void generation_iterate(GenClosure* cl, bool old_to_young);

  void space_iterate(SpaceClosure* cl);

  // Return "true" if all generations (but perm) have reached the
  // maximal committed limit that they can reach, without a garbage
  // collection.
  virtual bool is_maximal_no_gc() const;

  // Return the generation before "gen", or else NULL.
  Generation* prev_gen(Generation* gen) const {
    int l = gen->level();
    if (l == 0) return NULL;
    else return _gens[l-1];

  // Return the generation after "gen", or else NULL.
  Generation* next_gen(Generation* gen) const {
    int l = gen->level() + 1;
    if (l == _n_gens) return NULL;
    else return _gens[l];

  Generation* get_gen(int i) const {
    if (i >= 0 && i < _n_gens)
      return _gens[i];
      return NULL;

  int n_gens() const {
    assert(_n_gens == gen_policy()->number_of_generations(), "Sanity");
    return _n_gens;

  // Convenience function to be used in situations where the heap type can be
  // asserted to be this type.
  static GenCollectedHeap* heap();

  void set_par_threads(uint t);

  // Invoke the "do_oop" method of one of the closures "not_older_gens"
  // or "older_gens" on root locations for the generation at
  // "level".  (The "older_gens" closure is used for scanning references
  // from older generations; "not_older_gens" is used everywhere else.)
  // If "younger_gens_as_roots" is false, younger generations are
  // not scanned as roots; in this case, the caller must be arranging to
  // scan the younger generations itself.  (For example, a generation might
  // explicitly mark reachable objects in younger generations, to avoid
  // excess storage retention.)  If "collecting_perm_gen" is false, then
  // roots that may only contain references to permGen objects are not
  // scanned; instead, the older_gens closure is applied to all outgoing
  // references in the perm gen.  The "so" argument determines which of the roots
  // the closure is applied to:
  // "SO_None" does none;
  // "SO_AllClasses" applies the closure to all entries in the SystemDictionary;
  // "SO_SystemClasses" to all the "system" classes and loaders;
  // "SO_Strings" applies the closure to all entries in the StringTable.
  void gen_process_strong_roots(int level,
                                bool younger_gens_as_roots,
                                // The remaining arguments are in an order
                                // consistent with SharedHeap::process_strong_roots:
                                bool activate_scope,
                                bool collecting_perm_gen,
                                SharedHeap::ScanningOption so,
                                OopsInGenClosure* not_older_gens,
                                bool do_code_roots,
                                OopsInGenClosure* older_gens);

  // Apply "blk" to all the weak roots of the system.  These include
  // JNI weak roots, the code cache, system dictionary, symbol table,
  // string table, and referents of reachable weak refs.
  void gen_process_weak_roots(OopClosure* root_closure,
                              CodeBlobClosure* code_roots,
                              OopClosure* non_root_closure);

  // Set the saved marks of generations, if that makes sense.
  // In particular, if any generation might iterate over the oops
  // in other generations, it should call this method.
  void save_marks();

  // Apply "cur->do_oop" or "older->do_oop" to all the oops in objects
  // allocated since the last call to save_marks in generations at or above
  // "level" (including the permanent generation.)  The "cur" closure is
  // applied to references in the generation at "level", and the "older"
  // closure to older (and permanent) generations.
#define GCH_SINCE_SAVE_MARKS_ITERATE_DECL(OopClosureType, nv_suffix)    \
  void oop_since_save_marks_iterate(int level,                          \
                                    OopClosureType* cur,                \
                                    OopClosureType* older);



  // Returns "true" iff no allocations have occurred in any generation at
  // "level" or above (including the permanent generation) since the last
  // call to "save_marks".
  bool no_allocs_since_save_marks(int level);

  // Returns true if an incremental collection is likely to fail.
  // We optionally consult the young gen, if asked to do so;
  // otherwise we base our answer on whether the previous incremental
  // collection attempt failed with no corrective action as of yet.
  bool incremental_collection_will_fail(bool consult_young) {
    // Assumes a 2-generation system; the first disjunct remembers if an
    // incremental collection failed, even when we thought (second disjunct)
    // that it would not.
           "the following definition may not be suitable for an n(>2)-generation system");
    return incremental_collection_failed() ||
           (consult_young && !get_gen(0)->collection_attempt_is_safe());

  // If a generation bails out of an incremental collection,
  // it sets this flag.
  bool incremental_collection_failed() const {
    return _incremental_collection_failed;
  void set_incremental_collection_failed() {
    _incremental_collection_failed = true;
  void clear_incremental_collection_failed() {
    _incremental_collection_failed = false;

  // Promotion of obj into gen failed.  Try to promote obj to higher non-perm
  // gens in ascending order; return the new location of obj if successful.
  // Otherwise, try expand-and-allocate for obj in each generation starting at
  // gen; return the new location of obj if successful.  Otherwise, return NULL.
  oop handle_failed_promotion(Generation* gen,
                              oop obj,
                              size_t obj_size);

  // Accessor for memory state verification support
    static size_t skip_header_HeapWords() { return _skip_header_HeapWords; }

  // Override
  void check_for_non_bad_heap_word_value(HeapWord* addr,
    size_t size) PRODUCT_RETURN;

  // For use by mark-sweep.  As implemented, mark-sweep-compact is global
  // in an essential way: compaction is performed across generations, by
  // iterating over spaces.
  void prepare_for_compaction();

  // Perform a full collection of the first max_level+1 generations.
  // This is the low level interface used by the public versions of
  // collect() and collect_locked(). Caller holds the Heap_lock on entry.
  void collect_locked(GCCause::Cause cause, int max_level);

  // Returns success or failure.
  bool create_cms_collector();

  // In support of ExplicitGCInvokesConcurrent functionality
  bool should_do_concurrent_full_gc(GCCause::Cause cause);
  void collect_mostly_concurrent(GCCause::Cause cause);

  // Save the tops of the spaces in all generations
  void record_gen_tops_before_GC() PRODUCT_RETURN;

  virtual void gc_prologue(bool full);
  virtual void gc_epilogue(bool full);

  virtual void preload_and_dump(TRAPS);