src/hotspot/share/gc/shared/genCollectedHeap.hpp - platform/libcore - Git at Google

 /*
  * Copyright (c) 2000, 2020, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  * or visit www.oracle.com if you need additional information or have any
  * questions.
  *
  */

 #ifndef SHARE_GC_SHARED_GENCOLLECTEDHEAP_HPP
 #define SHARE_GC_SHARED_GENCOLLECTEDHEAP_HPP

 #include "gc/shared/collectedHeap.hpp"
 #include "gc/shared/generation.hpp"
 #include "gc/shared/oopStorageParState.hpp"
 #include "gc/shared/preGCValues.hpp"
 #include "gc/shared/softRefGenPolicy.hpp"

 class AdaptiveSizePolicy;
 class CardTableRS;
 class GCPolicyCounters;
 class GenerationSpec;
 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 Generation;
   friend class DefNewGeneration;
   friend class TenuredGeneration;
   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;
 public:
   friend class VM_PopulateDumpSharedSpace;

   enum GenerationType {
     YoungGen,
     OldGen
   };

 protected:
   Generation* _young_gen;
   Generation* _old_gen;

 private:
   GenerationSpec* _young_gen_spec;
   GenerationSpec* _old_gen_spec;

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

   SoftRefGenPolicy _soft_ref_gen_policy;

   // The sizing of the heap is controlled by a sizing policy.
   AdaptiveSizePolicy* _size_policy;

   GCPolicyCounters* _gc_policy_counters;

   // 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.
   ReservedHeapSpace allocate(size_t alignment);

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

   PreGenGCValues get_pre_gc_values() const;

 protected:

   // The set of potentially parallel tasks in root scanning.
   enum GCH_strong_roots_tasks {
     GCH_PS_ObjectSynchronizer_oops_do,
     GCH_PS_OopStorageSet_oops_do,
     GCH_PS_ClassLoaderDataGraph_oops_do,
     GCH_PS_CodeCache_oops_do,
     AOT_ONLY(GCH_PS_aot_oops_do COMMA)
     GCH_PS_younger_gens,
     // Leave this one last.
     GCH_PS_NumElements
   };

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

   GCMemoryManager* _young_manager;
   GCMemoryManager* _old_manager;

   // 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(Generation::Name young,
                    Generation::Name old,
                    const char* policy_counters_name);

 public:

   // Returns JNI_OK on success
   virtual jint initialize();
   virtual CardTableRS* create_rem_set(const MemRegion& reserved_region);

   void initialize_size_policy(size_t init_eden_size,
                               size_t init_promo_size,
                               size_t init_survivor_size);

   // 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; }

   MemRegion reserved_region() const { return _reserved; }
   bool is_in_reserved(const void* addr) const { return _reserved.contains(addr); }

   GenerationSpec* young_gen_spec() const;
   GenerationSpec* old_gen_spec() const;

   virtual SoftRefPolicy* soft_ref_policy() { return &_soft_ref_gen_policy; }

   // Adaptive size policy
   virtual AdaptiveSizePolicy* size_policy() {
     return _size_policy;
   }

   // Performance Counter support
   GCPolicyCounters* counters()     { return _gc_policy_counters; }

   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() 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);
 #endif

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

   void prune_scavengable_nmethods();

   // Iteration functions.
   void oop_iterate(OopIterateClosure* cl);
   void 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.
   HeapWord* block_start(const void* 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.
   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 min_size,
                                       size_t requested_size,
                                       size_t* actual_size);

   // 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);

   // 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 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 gc_threads_do(ThreadClosure* tc) const;
   virtual void print_tracing_info() const;

   // Used to print information about locations in the hs_err file.
   virtual bool print_location(outputStream* st, void* addr) const;

   void print_heap_change(const PreGenGCValues& pre_gc_values) 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 {
    public:
     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
   };

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

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

  public:
   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();

   // 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);


 private:
   // Return true if an allocation should be attempted in the older generation
   // if it fails in the younger generation.  Return false, otherwise.
   bool should_try_older_generation_allocation(size_t word_size) const;

   // Try to allocate space by expanding the heap.
   HeapWord* expand_heap_and_allocate(size_t size, bool is_tlab);

   HeapWord* mem_allocate_work(size_t size,
                               bool is_tlab,
                               bool* gc_overhead_limit_was_exceeded);

 #if INCLUDE_SERIALGC
   // 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();
 #endif

   // 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;

   // Return true if we need to perform full collection.
   bool should_do_full_collection(size_t size, bool full,
                                  bool is_tlab, GenerationType max_gen) const;
 };

 #endif // SHARE_GC_SHARED_GENCOLLECTEDHEAP_HPP
	/*
	* Copyright (c) 2000, 2020, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*
	*/

	#ifndef SHARE_GC_SHARED_GENCOLLECTEDHEAP_HPP
	#define SHARE_GC_SHARED_GENCOLLECTEDHEAP_HPP

	#include "gc/shared/collectedHeap.hpp"
	#include "gc/shared/generation.hpp"
	#include "gc/shared/oopStorageParState.hpp"
	#include "gc/shared/preGCValues.hpp"
	#include "gc/shared/softRefGenPolicy.hpp"

	class AdaptiveSizePolicy;
	class CardTableRS;
	class GCPolicyCounters;
	class GenerationSpec;
	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 Generation;
	friend class DefNewGeneration;
	friend class TenuredGeneration;
	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;
	public:
	friend class VM_PopulateDumpSharedSpace;

	enum GenerationType {
	YoungGen,
	OldGen
	};

	protected:
	Generation* _young_gen;
	Generation* _old_gen;

	private:
	GenerationSpec* _young_gen_spec;
	GenerationSpec* _old_gen_spec;

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

	SoftRefGenPolicy _soft_ref_gen_policy;

	// The sizing of the heap is controlled by a sizing policy.
	AdaptiveSizePolicy* _size_policy;

	GCPolicyCounters* _gc_policy_counters;

	// 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.
	ReservedHeapSpace allocate(size_t alignment);

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

	PreGenGCValues get_pre_gc_values() const;

	protected:

	// The set of potentially parallel tasks in root scanning.
	enum GCH_strong_roots_tasks {
	GCH_PS_ObjectSynchronizer_oops_do,
	GCH_PS_OopStorageSet_oops_do,
	GCH_PS_ClassLoaderDataGraph_oops_do,
	GCH_PS_CodeCache_oops_do,
	AOT_ONLY(GCH_PS_aot_oops_do COMMA)
	GCH_PS_younger_gens,
	// Leave this one last.
	GCH_PS_NumElements
	};

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

	GCMemoryManager* _young_manager;
	GCMemoryManager* _old_manager;

	// 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(Generation::Name young,
	Generation::Name old,
	const char* policy_counters_name);

	public:

	// Returns JNI_OK on success
	virtual jint initialize();
	virtual CardTableRS* create_rem_set(const MemRegion& reserved_region);

	void initialize_size_policy(size_t init_eden_size,
	size_t init_promo_size,
	size_t init_survivor_size);

	// 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; }

	MemRegion reserved_region() const { return _reserved; }
	bool is_in_reserved(const void* addr) const { return _reserved.contains(addr); }

	GenerationSpec* young_gen_spec() const;
	GenerationSpec* old_gen_spec() const;

	virtual SoftRefPolicy* soft_ref_policy() { return &_soft_ref_gen_policy; }

	// Adaptive size policy
	virtual AdaptiveSizePolicy* size_policy() {
	return _size_policy;
	}

	// Performance Counter support
	GCPolicyCounters* counters() { return _gc_policy_counters; }

	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() 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);
	#endif

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

	void prune_scavengable_nmethods();

	// Iteration functions.
	void oop_iterate(OopIterateClosure* cl);
	void 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.
	HeapWord* block_start(const void* 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.
	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 min_size,
	size_t requested_size,
	size_t* actual_size);

	// 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);

	// 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 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 gc_threads_do(ThreadClosure* tc) const;
	virtual void print_tracing_info() const;

	// Used to print information about locations in the hs_err file.
	virtual bool print_location(outputStream* st, void* addr) const;

	void print_heap_change(const PreGenGCValues& pre_gc_values) 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 {
	public:
	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
	};

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

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

	public:
	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();

	// 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);


	private:
	// Return true if an allocation should be attempted in the older generation
	// if it fails in the younger generation. Return false, otherwise.
	bool should_try_older_generation_allocation(size_t word_size) const;

	// Try to allocate space by expanding the heap.
	HeapWord* expand_heap_and_allocate(size_t size, bool is_tlab);

	HeapWord* mem_allocate_work(size_t size,
	bool is_tlab,
	bool* gc_overhead_limit_was_exceeded);

	#if INCLUDE_SERIALGC
	// 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();
	#endif

	// 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;

	// Return true if we need to perform full collection.
	bool should_do_full_collection(size_t size, bool full,
	bool is_tlab, GenerationType max_gen) const;
	};

	#endif // SHARE_GC_SHARED_GENCOLLECTEDHEAP_HPP