rev 50392 : JEP 331

   1 /*
   2  * Copyright (c) 2001, 2018, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #ifndef SHARE_VM_GC_SHARED_COLLECTEDHEAP_HPP
  26 #define SHARE_VM_GC_SHARED_COLLECTEDHEAP_HPP
  27 
  28 #include "gc/shared/gcCause.hpp"
  29 #include "gc/shared/gcWhen.hpp"
  30 #include "memory/allocation.hpp"
  31 #include "runtime/handles.hpp"
  32 #include "runtime/perfData.hpp"
  33 #include "runtime/safepoint.hpp"
  34 #include "utilities/debug.hpp"
  35 #include "utilities/events.hpp"
  36 #include "utilities/formatBuffer.hpp"
  37 #include "utilities/growableArray.hpp"
  38 
  39 // A "CollectedHeap" is an implementation of a java heap for HotSpot.  This
  40 // is an abstract class: there may be many different kinds of heaps.  This
  41 // class defines the functions that a heap must implement, and contains
  42 // infrastructure common to all heaps.
  43 
  44 class AdaptiveSizePolicy;
  45 class BarrierSet;
  46 class CollectorPolicy;
  47 class GCHeapSummary;
  48 class GCTimer;
  49 class GCTracer;
  50 class GCMemoryManager;
  51 class MemoryPool;
  52 class MetaspaceSummary;
  53 class SoftRefPolicy;
  54 class Thread;
  55 class ThreadClosure;
  56 class VirtualSpaceSummary;
  57 class WorkGang;
  58 class nmethod;
  59 
  60 class GCMessage : public FormatBuffer<1024> {
  61  public:
  62   bool is_before;
  63 
  64  public:
  65   GCMessage() {}
  66 };
  67 
  68 class CollectedHeap;
  69 
  70 class GCHeapLog : public EventLogBase<GCMessage> {
  71  private:
  72   void log_heap(CollectedHeap* heap, bool before);
  73 
  74  public:
  75   GCHeapLog() : EventLogBase<GCMessage>("GC Heap History") {}
  76 
  77   void log_heap_before(CollectedHeap* heap) {
  78     log_heap(heap, true);
  79   }
  80   void log_heap_after(CollectedHeap* heap) {
  81     log_heap(heap, false);
  82   }
  83 };
  84 
  85 //
  86 // CollectedHeap
  87 //   GenCollectedHeap
  88 //     SerialHeap
  89 //     CMSHeap
  90 //   G1CollectedHeap
  91 //   ParallelScavengeHeap
  92 //
  93 class CollectedHeap : public CHeapObj<mtInternal> {
  94   friend class VMStructs;
  95   friend class JVMCIVMStructs;
  96   friend class IsGCActiveMark; // Block structured external access to _is_gc_active
  97 
  98  private:
  99 #ifdef ASSERT
 100   static int       _fire_out_of_memory_count;
 101 #endif
 102 
 103   GCHeapLog* _gc_heap_log;
 104 
 105   MemRegion _reserved;
 106 
 107  protected:
 108   bool _is_gc_active;
 109 
 110   // Used for filler objects (static, but initialized in ctor).
 111   static size_t _filler_array_max_size;
 112 
 113   unsigned int _total_collections;          // ... started
 114   unsigned int _total_full_collections;     // ... started
 115   NOT_PRODUCT(volatile size_t _promotion_failure_alot_count;)
 116   NOT_PRODUCT(volatile size_t _promotion_failure_alot_gc_number;)
 117 
 118   // Reason for current garbage collection.  Should be set to
 119   // a value reflecting no collection between collections.
 120   GCCause::Cause _gc_cause;
 121   GCCause::Cause _gc_lastcause;
 122   PerfStringVariable* _perf_gc_cause;
 123   PerfStringVariable* _perf_gc_lastcause;
 124 
 125   // Constructor
 126   CollectedHeap();
 127 
 128   // Create a new tlab. All TLAB allocations must go through this.
 129   // To allow more flexible TLAB allocations min_size specifies
 130   // the minimum size needed, while requested_size is the requested
 131   // size based on ergonomics. The actually allocated size will be
 132   // returned in actual_size.
 133   virtual HeapWord* allocate_new_tlab(size_t min_size,
 134                                       size_t requested_size,
 135                                       size_t* actual_size);
 136 
 137   // Accumulate statistics on all tlabs.
 138   virtual void accumulate_statistics_all_tlabs();
 139 
 140   // Reinitialize tlabs before resuming mutators.
 141   virtual void resize_all_tlabs();
 142 
 143   // Allocate from the current thread's TLAB, with broken-out slow path.
 144   inline static HeapWord* allocate_from_tlab(Klass* klass, Thread* thread, size_t size);
 145   static HeapWord* allocate_from_tlab_slow(Klass* klass, Thread* thread, size_t size);
 146 
 147   // Allocate an uninitialized block of the given size, or returns NULL if
 148   // this is impossible.
 149   inline static HeapWord* common_mem_allocate_noinit(Klass* klass, size_t size, TRAPS);
 150 
 151   // Like allocate_init, but the block returned by a successful allocation
 152   // is guaranteed initialized to zeros.
 153   inline static HeapWord* common_mem_allocate_init(Klass* klass, size_t size, TRAPS);
 154 
 155   // Helper functions for (VM) allocation.
 156   inline static void post_allocation_setup_common(Klass* klass, HeapWord* obj);
 157   inline static void post_allocation_setup_no_klass_install(Klass* klass,
 158                                                             HeapWord* objPtr);
 159 
 160   inline static void post_allocation_setup_obj(Klass* klass, HeapWord* obj, int size);
 161 
 162   inline static void post_allocation_setup_array(Klass* klass,
 163                                                  HeapWord* obj, int length);
 164 
 165   inline static void post_allocation_setup_class(Klass* klass, HeapWord* obj, int size);
 166 
 167   // Clears an allocated object.
 168   inline static void init_obj(HeapWord* obj, size_t size);
 169 
 170   // Filler object utilities.
 171   static inline size_t filler_array_hdr_size();
 172   static inline size_t filler_array_min_size();
 173 
 174   DEBUG_ONLY(static void fill_args_check(HeapWord* start, size_t words);)
 175   DEBUG_ONLY(static void zap_filler_array(HeapWord* start, size_t words, bool zap = true);)
 176 
 177   // Fill with a single array; caller must ensure filler_array_min_size() <=
 178   // words <= filler_array_max_size().
 179   static inline void fill_with_array(HeapWord* start, size_t words, bool zap = true);
 180 
 181   // Fill with a single object (either an int array or a java.lang.Object).
 182   static inline void fill_with_object_impl(HeapWord* start, size_t words, bool zap = true);
 183 
 184   virtual void trace_heap(GCWhen::Type when, const GCTracer* tracer);
 185 












 186   // Verification functions
 187   virtual void check_for_bad_heap_word_value(HeapWord* addr, size_t size)
 188     PRODUCT_RETURN;
 189   virtual void check_for_non_bad_heap_word_value(HeapWord* addr, size_t size)
 190     PRODUCT_RETURN;
 191   debug_only(static void check_for_valid_allocation_state();)
 192 
 193  public:
 194   enum Name {
 195     None,
 196     Serial,
 197     Parallel,
 198     CMS,
 199     G1
 200   };
 201 
 202   static inline size_t filler_array_max_size() {
 203     return _filler_array_max_size;
 204   }
 205 
 206   virtual Name kind() const = 0;
 207 
 208   virtual const char* name() const = 0;
 209 
 210   /**
 211    * Returns JNI error code JNI_ENOMEM if memory could not be allocated,
 212    * and JNI_OK on success.
 213    */
 214   virtual jint initialize() = 0;
 215 
 216   // In many heaps, there will be a need to perform some initialization activities
 217   // after the Universe is fully formed, but before general heap allocation is allowed.
 218   // This is the correct place to place such initialization methods.
 219   virtual void post_initialize();
 220 
 221   // Stop any onging concurrent work and prepare for exit.
 222   virtual void stop() {}
 223 
 224   // Stop and resume concurrent GC threads interfering with safepoint operations
 225   virtual void safepoint_synchronize_begin() {}
 226   virtual void safepoint_synchronize_end() {}
 227 
 228   void initialize_reserved_region(HeapWord *start, HeapWord *end);
 229   MemRegion reserved_region() const { return _reserved; }
 230   address base() const { return (address)reserved_region().start(); }
 231 
 232   virtual size_t capacity() const = 0;
 233   virtual size_t used() const = 0;
 234 
 235   // Return "true" if the part of the heap that allocates Java
 236   // objects has reached the maximal committed limit that it can
 237   // reach, without a garbage collection.
 238   virtual bool is_maximal_no_gc() const = 0;
 239 
 240   // Support for java.lang.Runtime.maxMemory():  return the maximum amount of
 241   // memory that the vm could make available for storing 'normal' java objects.
 242   // This is based on the reserved address space, but should not include space
 243   // that the vm uses internally for bookkeeping or temporary storage
 244   // (e.g., in the case of the young gen, one of the survivor
 245   // spaces).
 246   virtual size_t max_capacity() const = 0;
 247 
 248   // Returns "TRUE" if "p" points into the reserved area of the heap.
 249   bool is_in_reserved(const void* p) const {
 250     return _reserved.contains(p);
 251   }
 252 
 253   bool is_in_reserved_or_null(const void* p) const {
 254     return p == NULL || is_in_reserved(p);
 255   }
 256 
 257   // Returns "TRUE" iff "p" points into the committed areas of the heap.
 258   // This method can be expensive so avoid using it in performance critical
 259   // code.
 260   virtual bool is_in(const void* p) const = 0;
 261 
 262   DEBUG_ONLY(bool is_in_or_null(const void* p) const { return p == NULL || is_in(p); })
 263 
 264   // Let's define some terms: a "closed" subset of a heap is one that
 265   //
 266   // 1) contains all currently-allocated objects, and
 267   //
 268   // 2) is closed under reference: no object in the closed subset
 269   //    references one outside the closed subset.
 270   //
 271   // Membership in a heap's closed subset is useful for assertions.
 272   // Clearly, the entire heap is a closed subset, so the default
 273   // implementation is to use "is_in_reserved".  But this may not be too
 274   // liberal to perform useful checking.  Also, the "is_in" predicate
 275   // defines a closed subset, but may be too expensive, since "is_in"
 276   // verifies that its argument points to an object head.  The
 277   // "closed_subset" method allows a heap to define an intermediate
 278   // predicate, allowing more precise checking than "is_in_reserved" at
 279   // lower cost than "is_in."
 280 
 281   // One important case is a heap composed of disjoint contiguous spaces,
 282   // such as the Garbage-First collector.  Such heaps have a convenient
 283   // closed subset consisting of the allocated portions of those
 284   // contiguous spaces.
 285 
 286   // Return "TRUE" iff the given pointer points into the heap's defined
 287   // closed subset (which defaults to the entire heap).
 288   virtual bool is_in_closed_subset(const void* p) const {
 289     return is_in_reserved(p);
 290   }
 291 
 292   bool is_in_closed_subset_or_null(const void* p) const {
 293     return p == NULL || is_in_closed_subset(p);
 294   }
 295 
 296   void set_gc_cause(GCCause::Cause v) {
 297      if (UsePerfData) {
 298        _gc_lastcause = _gc_cause;
 299        _perf_gc_lastcause->set_value(GCCause::to_string(_gc_lastcause));
 300        _perf_gc_cause->set_value(GCCause::to_string(v));
 301      }
 302     _gc_cause = v;
 303   }
 304   GCCause::Cause gc_cause() { return _gc_cause; }
 305 
 306   // General obj/array allocation facilities.
 307   inline static oop obj_allocate(Klass* klass, int size, TRAPS);
 308   inline static oop array_allocate(Klass* klass, int size, int length, TRAPS);
 309   inline static oop array_allocate_nozero(Klass* klass, int size, int length, TRAPS);
 310   inline static oop class_allocate(Klass* klass, int size, TRAPS);
 311 
 312   // Raw memory allocation facilities
 313   // The obj and array allocate methods are covers for these methods.
 314   // mem_allocate() should never be
 315   // called to allocate TLABs, only individual objects.
 316   virtual HeapWord* mem_allocate(size_t size,
 317                                  bool* gc_overhead_limit_was_exceeded) = 0;
 318 
 319   // Utilities for turning raw memory into filler objects.
 320   //
 321   // min_fill_size() is the smallest region that can be filled.
 322   // fill_with_objects() can fill arbitrary-sized regions of the heap using
 323   // multiple objects.  fill_with_object() is for regions known to be smaller
 324   // than the largest array of integers; it uses a single object to fill the
 325   // region and has slightly less overhead.
 326   static size_t min_fill_size() {
 327     return size_t(align_object_size(oopDesc::header_size()));
 328   }
 329 
 330   static void fill_with_objects(HeapWord* start, size_t words, bool zap = true);
 331 
 332   static void fill_with_object(HeapWord* start, size_t words, bool zap = true);
 333   static void fill_with_object(MemRegion region, bool zap = true) {
 334     fill_with_object(region.start(), region.word_size(), zap);
 335   }
 336   static void fill_with_object(HeapWord* start, HeapWord* end, bool zap = true) {
 337     fill_with_object(start, pointer_delta(end, start), zap);
 338   }
 339 
 340   // Return the address "addr" aligned by "alignment_in_bytes" if such
 341   // an address is below "end".  Return NULL otherwise.
 342   inline static HeapWord* align_allocation_or_fail(HeapWord* addr,
 343                                                    HeapWord* end,
 344                                                    unsigned short alignment_in_bytes);
 345 
 346   // Some heaps may offer a contiguous region for shared non-blocking
 347   // allocation, via inlined code (by exporting the address of the top and
 348   // end fields defining the extent of the contiguous allocation region.)
 349 
 350   // This function returns "true" iff the heap supports this kind of
 351   // allocation.  (Default is "no".)
 352   virtual bool supports_inline_contig_alloc() const {
 353     return false;
 354   }
 355   // These functions return the addresses of the fields that define the
 356   // boundaries of the contiguous allocation area.  (These fields should be
 357   // physically near to one another.)
 358   virtual HeapWord* volatile* top_addr() const {
 359     guarantee(false, "inline contiguous allocation not supported");
 360     return NULL;
 361   }
 362   virtual HeapWord** end_addr() const {
 363     guarantee(false, "inline contiguous allocation not supported");
 364     return NULL;
 365   }
 366 
 367   // Some heaps may be in an unparseable state at certain times between
 368   // collections. This may be necessary for efficient implementation of
 369   // certain allocation-related activities. Calling this function before
 370   // attempting to parse a heap ensures that the heap is in a parsable
 371   // state (provided other concurrent activity does not introduce
 372   // unparsability). It is normally expected, therefore, that this
 373   // method is invoked with the world stopped.
 374   // NOTE: if you override this method, make sure you call
 375   // super::ensure_parsability so that the non-generational
 376   // part of the work gets done. See implementation of
 377   // CollectedHeap::ensure_parsability and, for instance,
 378   // that of GenCollectedHeap::ensure_parsability().
 379   // The argument "retire_tlabs" controls whether existing TLABs
 380   // are merely filled or also retired, thus preventing further
 381   // allocation from them and necessitating allocation of new TLABs.
 382   virtual void ensure_parsability(bool retire_tlabs);
 383 
 384   // Section on thread-local allocation buffers (TLABs)
 385   // If the heap supports thread-local allocation buffers, it should override
 386   // the following methods:
 387   // Returns "true" iff the heap supports thread-local allocation buffers.
 388   // The default is "no".
 389   virtual bool supports_tlab_allocation() const = 0;
 390 
 391   // The amount of space available for thread-local allocation buffers.
 392   virtual size_t tlab_capacity(Thread *thr) const = 0;
 393 
 394   // The amount of used space for thread-local allocation buffers for the given thread.
 395   virtual size_t tlab_used(Thread *thr) const = 0;
 396 
 397   virtual size_t max_tlab_size() const;
 398 
 399   // An estimate of the maximum allocation that could be performed
 400   // for thread-local allocation buffers without triggering any
 401   // collection or expansion activity.
 402   virtual size_t unsafe_max_tlab_alloc(Thread *thr) const {
 403     guarantee(false, "thread-local allocation buffers not supported");
 404     return 0;
 405   }
 406 
 407   // Perform a collection of the heap; intended for use in implementing
 408   // "System.gc".  This probably implies as full a collection as the
 409   // "CollectedHeap" supports.
 410   virtual void collect(GCCause::Cause cause) = 0;
 411 
 412   // Perform a full collection
 413   virtual void do_full_collection(bool clear_all_soft_refs) = 0;
 414 
 415   // This interface assumes that it's being called by the
 416   // vm thread. It collects the heap assuming that the
 417   // heap lock is already held and that we are executing in
 418   // the context of the vm thread.
 419   virtual void collect_as_vm_thread(GCCause::Cause cause);
 420 
 421   virtual MetaWord* satisfy_failed_metadata_allocation(ClassLoaderData* loader_data,
 422                                                        size_t size,
 423                                                        Metaspace::MetadataType mdtype);
 424 
 425   // Returns "true" iff there is a stop-world GC in progress.  (I assume
 426   // that it should answer "false" for the concurrent part of a concurrent
 427   // collector -- dld).
 428   bool is_gc_active() const { return _is_gc_active; }
 429 
 430   // Total number of GC collections (started)
 431   unsigned int total_collections() const { return _total_collections; }
 432   unsigned int total_full_collections() const { return _total_full_collections;}
 433 
 434   // Increment total number of GC collections (started)
 435   // Should be protected but used by PSMarkSweep - cleanup for 1.4.2
 436   void increment_total_collections(bool full = false) {
 437     _total_collections++;
 438     if (full) {
 439       increment_total_full_collections();
 440     }
 441   }
 442 
 443   void increment_total_full_collections() { _total_full_collections++; }
 444 
 445   // Return the CollectorPolicy for the heap
 446   virtual CollectorPolicy* collector_policy() const = 0;
 447 
 448   // Return the SoftRefPolicy for the heap;
 449   virtual SoftRefPolicy* soft_ref_policy() = 0;
 450 
 451   virtual GrowableArray<GCMemoryManager*> memory_managers() = 0;
 452   virtual GrowableArray<MemoryPool*> memory_pools() = 0;
 453 
 454   // Iterate over all objects, calling "cl.do_object" on each.
 455   virtual void object_iterate(ObjectClosure* cl) = 0;
 456 
 457   // Similar to object_iterate() except iterates only
 458   // over live objects.
 459   virtual void safe_object_iterate(ObjectClosure* cl) = 0;
 460 
 461   // NOTE! There is no requirement that a collector implement these
 462   // functions.
 463   //
 464   // A CollectedHeap is divided into a dense sequence of "blocks"; that is,
 465   // each address in the (reserved) heap is a member of exactly
 466   // one block.  The defining characteristic of a block is that it is
 467   // possible to find its size, and thus to progress forward to the next
 468   // block.  (Blocks may be of different sizes.)  Thus, blocks may
 469   // represent Java objects, or they might be free blocks in a
 470   // free-list-based heap (or subheap), as long as the two kinds are
 471   // distinguishable and the size of each is determinable.
 472 
 473   // Returns the address of the start of the "block" that contains the
 474   // address "addr".  We say "blocks" instead of "object" since some heaps
 475   // may not pack objects densely; a chunk may either be an object or a
 476   // non-object.
 477   virtual HeapWord* block_start(const void* addr) const = 0;
 478 
 479   // Requires "addr" to be the start of a chunk, and returns its size.
 480   // "addr + size" is required to be the start of a new chunk, or the end
 481   // of the active area of the heap.
 482   virtual size_t block_size(const HeapWord* addr) const = 0;
 483 
 484   // Requires "addr" to be the start of a block, and returns "TRUE" iff
 485   // the block is an object.
 486   virtual bool block_is_obj(const HeapWord* addr) const = 0;
 487 
 488   // Returns the longest time (in ms) that has elapsed since the last
 489   // time that any part of the heap was examined by a garbage collection.
 490   virtual jlong millis_since_last_gc() = 0;
 491 
 492   // Perform any cleanup actions necessary before allowing a verification.
 493   virtual void prepare_for_verify() = 0;
 494 
 495   // Generate any dumps preceding or following a full gc
 496  private:
 497   void full_gc_dump(GCTimer* timer, bool before);
 498 
 499   virtual void initialize_serviceability() = 0;
 500 
 501  public:
 502   void pre_full_gc_dump(GCTimer* timer);
 503   void post_full_gc_dump(GCTimer* timer);
 504 
 505   virtual VirtualSpaceSummary create_heap_space_summary();
 506   GCHeapSummary create_heap_summary();
 507 
 508   MetaspaceSummary create_metaspace_summary();
 509 
 510   // Print heap information on the given outputStream.
 511   virtual void print_on(outputStream* st) const = 0;
 512   // The default behavior is to call print_on() on tty.
 513   virtual void print() const {
 514     print_on(tty);
 515   }
 516   // Print more detailed heap information on the given
 517   // outputStream. The default behavior is to call print_on(). It is
 518   // up to each subclass to override it and add any additional output
 519   // it needs.
 520   virtual void print_extended_on(outputStream* st) const {
 521     print_on(st);
 522   }
 523 
 524   virtual void print_on_error(outputStream* st) const;
 525 
 526   // Print all GC threads (other than the VM thread)
 527   // used by this heap.
 528   virtual void print_gc_threads_on(outputStream* st) const = 0;
 529   // The default behavior is to call print_gc_threads_on() on tty.
 530   void print_gc_threads() {
 531     print_gc_threads_on(tty);
 532   }
 533   // Iterator for all GC threads (other than VM thread)
 534   virtual void gc_threads_do(ThreadClosure* tc) const = 0;
 535 
 536   // Print any relevant tracing info that flags imply.
 537   // Default implementation does nothing.
 538   virtual void print_tracing_info() const = 0;
 539 
 540   void print_heap_before_gc();
 541   void print_heap_after_gc();
 542 
 543   // An object is scavengable if its location may move during a scavenge.
 544   // (A scavenge is a GC which is not a full GC.)
 545   virtual bool is_scavengable(oop obj) = 0;
 546   // Registering and unregistering an nmethod (compiled code) with the heap.
 547   // Override with specific mechanism for each specialized heap type.
 548   virtual void register_nmethod(nmethod* nm) {}
 549   virtual void unregister_nmethod(nmethod* nm) {}
 550   virtual void verify_nmethod(nmethod* nmethod) {}
 551 
 552   void trace_heap_before_gc(const GCTracer* gc_tracer);
 553   void trace_heap_after_gc(const GCTracer* gc_tracer);
 554 
 555   // Heap verification
 556   virtual void verify(VerifyOption option) = 0;
 557 
 558   // Return true if concurrent phase control (via
 559   // request_concurrent_phase_control) is supported by this collector.
 560   // The default implementation returns false.
 561   virtual bool supports_concurrent_phase_control() const;
 562 
 563   // Return a NULL terminated array of concurrent phase names provided
 564   // by this collector.  Supports Whitebox testing.  These are the
 565   // names recognized by request_concurrent_phase(). The default
 566   // implementation returns an array of one NULL element.
 567   virtual const char* const* concurrent_phases() const;
 568 
 569   // Request the collector enter the indicated concurrent phase, and
 570   // wait until it does so.  Supports WhiteBox testing.  Only one
 571   // request may be active at a time.  Phases are designated by name;
 572   // the set of names and their meaning is GC-specific.  Once the
 573   // requested phase has been reached, the collector will attempt to
 574   // avoid transitioning to a new phase until a new request is made.
 575   // [Note: A collector might not be able to remain in a given phase.
 576   // For example, a full collection might cancel an in-progress
 577   // concurrent collection.]
 578   //
 579   // Returns true when the phase is reached.  Returns false for an
 580   // unknown phase.  The default implementation returns false.
 581   virtual bool request_concurrent_phase(const char* phase);
 582 
 583   // Provides a thread pool to SafepointSynchronize to use
 584   // for parallel safepoint cleanup.
 585   // GCs that use a GC worker thread pool may want to share
 586   // it for use during safepoint cleanup. This is only possible
 587   // if the GC can pause and resume concurrent work (e.g. G1
 588   // concurrent marking) for an intermittent non-GC safepoint.
 589   // If this method returns NULL, SafepointSynchronize will
 590   // perform cleanup tasks serially in the VMThread.
 591   virtual WorkGang* get_safepoint_workers() { return NULL; }
 592 
 593   // Support for object pinning. This is used by JNI Get*Critical()
 594   // and Release*Critical() family of functions. If supported, the GC
 595   // must guarantee that pinned objects never move.
 596   virtual bool supports_object_pinning() const;
 597   virtual oop pin_object(JavaThread* thread, oop obj);
 598   virtual void unpin_object(JavaThread* thread, oop obj);
 599 
 600   // Deduplicate the string, iff the GC supports string deduplication.
 601   virtual void deduplicate_string(oop str);
 602 
 603   virtual bool is_oop(oop object) const;
 604 
 605   // Non product verification and debugging.
 606 #ifndef PRODUCT
 607   // Support for PromotionFailureALot.  Return true if it's time to cause a
 608   // promotion failure.  The no-argument version uses
 609   // this->_promotion_failure_alot_count as the counter.
 610   bool promotion_should_fail(volatile size_t* count);
 611   bool promotion_should_fail();
 612 
 613   // Reset the PromotionFailureALot counters.  Should be called at the end of a
 614   // GC in which promotion failure occurred.
 615   void reset_promotion_should_fail(volatile size_t* count);
 616   void reset_promotion_should_fail();
 617 #endif  // #ifndef PRODUCT
 618 
 619 #ifdef ASSERT
 620   static int fired_fake_oom() {
 621     return (CIFireOOMAt > 1 && _fire_out_of_memory_count >= CIFireOOMAt);
 622   }
 623 #endif
 624 };
 625 
 626 // Class to set and reset the GC cause for a CollectedHeap.
 627 
 628 class GCCauseSetter : StackObj {
 629   CollectedHeap* _heap;
 630   GCCause::Cause _previous_cause;
 631  public:
 632   GCCauseSetter(CollectedHeap* heap, GCCause::Cause cause) {
 633     _heap = heap;
 634     _previous_cause = _heap->gc_cause();
 635     _heap->set_gc_cause(cause);
 636   }
 637 
 638   ~GCCauseSetter() {
 639     _heap->set_gc_cause(_previous_cause);
 640   }
 641 };
 642 
 643 #endif // SHARE_VM_GC_SHARED_COLLECTEDHEAP_HPP
--- EOF ---