view src/hotspot/share/gc/shared/genCollectedHeap.hpp @ 48073:5caa1d5f74c1

8186571: Implementation: JEP 307: Parallel Full GC for G1 Summary: Improve G1 worst-case latencies by making the full GC parallel. Reviewed-by: tschatzl, sangheki, ehelin
author sjohanss
date Tue, 14 Nov 2017 11:33:23 +0100
parents b055cb5170f5
children cb5d2d4453d0
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 * 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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#include "gc/shared/adaptiveSizePolicy.hpp"
#include "gc/shared/collectedHeap.hpp"
#include "gc/shared/collectorPolicy.hpp"
#include "gc/shared/generation.hpp"

class StrongRootsScope;
class SubTasksDone;
class WorkGang;

// A "GenCollectedHeap" is a CollectedHeap that uses generational
// collection.  It has two generations, young and old.
class GenCollectedHeap : public CollectedHeap {
  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_GenCollectFull;
  friend class VM_GenCollectFullConcurrent;
  friend class VM_GC_HeapInspection;
  friend class VM_HeapDumper;
  friend class HeapInspection;
  friend class GCCauseSetter;
  friend class VMStructs;
  friend class VM_PopulateDumpSharedSpace;

  enum GenerationType {

  Generation* _young_gen;
  Generation* _old_gen;

  // The singleton CardTable Remembered Set.
  CardTableRS* _rem_set;

  // 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;

  // Collects the given generation.
  void collect_generation(Generation* gen, bool full, size_t size, bool is_tlab,
                          bool run_verification, bool clear_soft_refs,
                          bool restore_marks_for_biased_locking);

  // Reserve aligned space for the heap as needed by the contained generations.
  char* allocate(size_t alignment, ReservedSpace* heap_rs);

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


  // The set of potentially parallel tasks in root scanning.
  enum GCH_strong_roots_tasks {
    // Leave this one last.

  // Data structure for claiming the (potentially) parallel tasks in
  // (gen-specific) roots processing.
  SubTasksDone* _process_strong_tasks;

  // 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,
                     GenerationType max_generation);

  // 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.
  virtual void do_full_collection(bool clear_all_soft_refs);
  void do_full_collection(bool clear_all_soft_refs, GenerationType max_generation);

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

  GenCollectedHeap(GenCollectorPolicy *policy);

  virtual void check_gen_kinds() = 0;


  // Returns JNI_OK on success
  virtual jint initialize();

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

  Generation* young_gen() const { return _young_gen; }
  Generation* old_gen()   const { return _old_gen; }

  bool is_young_gen(const Generation* gen) const { return gen == _young_gen; }
  bool is_old_gen(const Generation* gen) const { return gen == _old_gen; }

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

  virtual CollectorPolicy* collector_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 both generations.
  void save_used_regions();

  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* volatile* top_addr() const;
  HeapWord** end_addr() const;

  // 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.
  virtual void collect(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 generations up to and including max_generation.
  // Mostly used for testing purposes. Caller does not hold the Heap_lock on entry.
  void collect(GCCause::Cause cause, GenerationType max_generation);

  // 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;

  // 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
  bool is_in_partial_collection(const void* p);

  virtual bool is_scavengable(oop obj) {
    return is_in_young(obj);

  // Optimized nmethod scanning support routines
  virtual void register_nmethod(nmethod* nm);
  virtual void verify_nmethod(nmethod* nmethod);

  // Iteration functions.
  void oop_iterate_no_header(OopClosure* cl);
  void oop_iterate(ExtendedOopClosure* cl);
  void object_iterate(ObjectClosure* cl);
  void safe_object_iterate(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 tlab_used(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;

  // 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+Tenured and ParNew+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) {
    return is_in_young(new_obj);

  // 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 generations to "now".
  void update_time_of_last_gc(jlong now) {

  // Update the gc statistics for each generation.
  void update_gc_stats(Generation* current_generation, bool full) {
    _old_gen->update_gc_stats(current_generation, full);

  bool no_gc_in_progress() { return !is_gc_active(); }

  // Override.
  void prepare_for_verify();

  // Override.
  void verify(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;

  void print_heap_change(size_t young_prev_used, size_t old_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
  // If "old_to_young" determines the order.
  void generation_iterate(GenClosure* cl, bool old_to_young);

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

  // This function returns the CardTableRS object that allows us to scan
  // generations in a fully generational heap.
  CardTableRS* rem_set() { return _rem_set; }

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

  // The ScanningOption determines which of the roots
  // the closure is applied to:
  // "SO_None" does none;
  enum ScanningOption {
    SO_None                =  0x0,
    SO_AllCodeCache        =  0x8,
    SO_ScavengeCodeCache   = 0x10

  void process_roots(StrongRootsScope* scope,
                     ScanningOption so,
                     OopClosure* strong_roots,
                     OopClosure* weak_roots,
                     CLDClosure* strong_cld_closure,
                     CLDClosure* weak_cld_closure,
                     CodeBlobToOopClosure* code_roots);

  void process_string_table_roots(StrongRootsScope* scope,
                                  OopClosure* root_closure);

  // Accessor for memory state verification support
    virtual size_t skip_header_HeapWords() { return 0; }

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

  void young_process_roots(StrongRootsScope* scope,
                           OopsInGenClosure* root_closure,
                           OopsInGenClosure* old_gen_closure,
                           CLDClosure* cld_closure);

  void full_process_roots(StrongRootsScope* scope,
                          bool is_adjust_phase,
                          ScanningOption so,
                          bool only_strong_roots,
                          OopsInGenClosure* root_closure,
                          CLDClosure* cld_closure);

  // Apply "root_closure" to all the weak roots of the system.
  // These include JNI weak roots, string table,
  // and referents of reachable weak refs.
  void gen_process_weak_roots(OopClosure* 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".  The "cur" closure is
  // applied to references in the generation at "level", and the "older"
  // closure to older generations.
#define GCH_SINCE_SAVE_MARKS_ITERATE_DECL(OopClosureType, nv_suffix)    \
  void oop_since_save_marks_iterate(GenerationType start_gen,           \
                                    OopClosureType* cur,                \
                                    OopClosureType* older);



  // Returns "true" iff no allocations have occurred since the last
  // call to "save_marks".
  bool no_allocs_since_save_marks();

  // 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) {
    // The first disjunct remembers if an incremental collection failed, even
    // when we thought (second disjunct) that it would not.
    return incremental_collection_failed() ||
           (consult_young && !_young_gen->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
  // gens in ascending order; return the new location of obj if successful.
  // Otherwise, try expand-and-allocate for obj in both the young and old
  // generation; return the new location of obj if successful.  Otherwise, return NULL.
  oop handle_failed_promotion(Generation* old_gen,
                              oop obj,
                              size_t obj_size);

  // 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 generations up to and including max_generation.
  // 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, GenerationType max_generation);

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