1 /*
   2  * Copyright (c) 2001, 2015, 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.
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  24 
  25 #ifndef SHARE_VM_GC_INTERFACE_COLLECTEDHEAP_HPP
  26 #define SHARE_VM_GC_INTERFACE_COLLECTEDHEAP_HPP
  27 
  28 #include "gc_interface/gcCause.hpp"
  29 #include "gc_implementation/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/events.hpp"
  35 
  36 // A "CollectedHeap" is an implementation of a java heap for HotSpot.  This
  37 // is an abstract class: there may be many different kinds of heaps.  This
  38 // class defines the functions that a heap must implement, and contains
  39 // infrastructure common to all heaps.
  40 
  41 class AdaptiveSizePolicy;
  42 class BarrierSet;
  43 class CollectorPolicy;
  44 class GCHeapSummary;
  45 class GCTimer;
  46 class GCTracer;
  47 class MetaspaceSummary;
  48 class Thread;
  49 class ThreadClosure;
  50 class VirtualSpaceSummary;
  51 class nmethod;
  52 
  53 class GCMessage : public FormatBuffer<1024> {
  54  public:
  55   bool is_before;
  56 
  57  public:
  58   GCMessage() {}
  59 };
  60 
  61 class GCHeapLog : public EventLogBase<GCMessage> {
  62  private:
  63   void log_heap(bool before);
  64 
  65  public:
  66   GCHeapLog() : EventLogBase<GCMessage>("GC Heap History") {}
  67 
  68   void log_heap_before() {
  69     log_heap(true);
  70   }
  71   void log_heap_after() {
  72     log_heap(false);
  73   }
  74 };
  75 
  76 //
  77 // CollectedHeap
  78 //   SharedHeap
  79 //     GenCollectedHeap
  80 //     G1CollectedHeap
  81 //   ParallelScavengeHeap
  82 //
  83 class CollectedHeap : public CHeapObj<mtInternal> {
  84   friend class VMStructs;
  85   friend class IsGCActiveMark; // Block structured external access to _is_gc_active
  86 
  87  private:
  88 #ifdef ASSERT
  89   static int       _fire_out_of_memory_count;
  90 #endif
  91 
  92   // Used for filler objects (static, but initialized in ctor).
  93   static size_t _filler_array_max_size;
  94 
  95   GCHeapLog* _gc_heap_log;
  96 
  97   // Used in support of ReduceInitialCardMarks; only consulted if COMPILER2 is being used
  98   bool _defer_initial_card_mark;
  99 
 100   MemRegion _reserved;
 101 
 102  protected:
 103   BarrierSet* _barrier_set;
 104   bool _is_gc_active;
 105   uint _n_par_threads;
 106 
 107   unsigned int _total_collections;          // ... started
 108   unsigned int _total_full_collections;     // ... started
 109   NOT_PRODUCT(volatile size_t _promotion_failure_alot_count;)
 110   NOT_PRODUCT(volatile size_t _promotion_failure_alot_gc_number;)
 111 
 112   // Reason for current garbage collection.  Should be set to
 113   // a value reflecting no collection between collections.
 114   GCCause::Cause _gc_cause;
 115   GCCause::Cause _gc_lastcause;
 116   PerfStringVariable* _perf_gc_cause;
 117   PerfStringVariable* _perf_gc_lastcause;
 118 
 119   // Constructor
 120   CollectedHeap();
 121 
 122   // Do common initializations that must follow instance construction,
 123   // for example, those needing virtual calls.
 124   // This code could perhaps be moved into initialize() but would
 125   // be slightly more awkward because we want the latter to be a
 126   // pure virtual.
 127   void pre_initialize();
 128 
 129   // Create a new tlab. All TLAB allocations must go through this.
 130   virtual HeapWord* allocate_new_tlab(size_t size);
 131 
 132   // Accumulate statistics on all tlabs.
 133   virtual void accumulate_statistics_all_tlabs();
 134 
 135   // Reinitialize tlabs before resuming mutators.
 136   virtual void resize_all_tlabs();
 137 
 138   // Allocate from the current thread's TLAB, with broken-out slow path.
 139   inline static HeapWord* allocate_from_tlab(KlassHandle klass, Thread* thread, size_t size);
 140   static HeapWord* allocate_from_tlab_slow(KlassHandle klass, Thread* thread, size_t size);
 141 
 142   // Allocate an uninitialized block of the given size, or returns NULL if
 143   // this is impossible.
 144   inline static HeapWord* common_mem_allocate_noinit(KlassHandle klass, size_t size, TRAPS);
 145 
 146   // Like allocate_init, but the block returned by a successful allocation
 147   // is guaranteed initialized to zeros.
 148   inline static HeapWord* common_mem_allocate_init(KlassHandle klass, size_t size, TRAPS);
 149 
 150   // Helper functions for (VM) allocation.
 151   inline static void post_allocation_setup_common(KlassHandle klass, HeapWord* obj);
 152   inline static void post_allocation_setup_no_klass_install(KlassHandle klass,
 153                                                             HeapWord* objPtr);
 154 
 155   inline static void post_allocation_setup_obj(KlassHandle klass, HeapWord* obj, int size);
 156 
 157   inline static void post_allocation_setup_array(KlassHandle klass,
 158                                                  HeapWord* obj, int length);
 159 
 160   // Clears an allocated object.
 161   inline static void init_obj(HeapWord* obj, size_t size);
 162 
 163   // Filler object utilities.
 164   static inline size_t filler_array_hdr_size();
 165   static inline size_t filler_array_min_size();
 166 
 167   DEBUG_ONLY(static void fill_args_check(HeapWord* start, size_t words);)
 168   DEBUG_ONLY(static void zap_filler_array(HeapWord* start, size_t words, bool zap = true);)
 169 
 170   // Fill with a single array; caller must ensure filler_array_min_size() <=
 171   // words <= filler_array_max_size().
 172   static inline void fill_with_array(HeapWord* start, size_t words, bool zap = true);
 173 
 174   // Fill with a single object (either an int array or a java.lang.Object).
 175   static inline void fill_with_object_impl(HeapWord* start, size_t words, bool zap = true);
 176 
 177   virtual void trace_heap(GCWhen::Type when, const GCTracer* tracer);
 178 
 179   // Verification functions
 180   virtual void check_for_bad_heap_word_value(HeapWord* addr, size_t size)
 181     PRODUCT_RETURN;
 182   virtual void check_for_non_bad_heap_word_value(HeapWord* addr, size_t size)
 183     PRODUCT_RETURN;
 184   debug_only(static void check_for_valid_allocation_state();)
 185 
 186  public:
 187   enum Name {
 188     GenCollectedHeap,
 189     ParallelScavengeHeap,
 190     G1CollectedHeap
 191   };
 192 
 193   static inline size_t filler_array_max_size() {
 194     return _filler_array_max_size;
 195   }
 196 
 197   virtual Name kind() const = 0;
 198 
 199   /**
 200    * Returns JNI error code JNI_ENOMEM if memory could not be allocated,
 201    * and JNI_OK on success.
 202    */
 203   virtual jint initialize() = 0;
 204 
 205   // In many heaps, there will be a need to perform some initialization activities
 206   // after the Universe is fully formed, but before general heap allocation is allowed.
 207   // This is the correct place to place such initialization methods.
 208   virtual void post_initialize() = 0;
 209 
 210   // Stop any onging concurrent work and prepare for exit.
 211   virtual void stop() {}
 212 
 213   void initialize_reserved_region(HeapWord *start, HeapWord *end);
 214   MemRegion reserved_region() const { return _reserved; }
 215   address base() const { return (address)reserved_region().start(); }
 216 
 217   virtual size_t capacity() const = 0;
 218   virtual size_t used() const = 0;
 219 
 220   // Return "true" if the part of the heap that allocates Java
 221   // objects has reached the maximal committed limit that it can
 222   // reach, without a garbage collection.
 223   virtual bool is_maximal_no_gc() const = 0;
 224 
 225   // Support for java.lang.Runtime.maxMemory():  return the maximum amount of
 226   // memory that the vm could make available for storing 'normal' java objects.
 227   // This is based on the reserved address space, but should not include space
 228   // that the vm uses internally for bookkeeping or temporary storage
 229   // (e.g., in the case of the young gen, one of the survivor
 230   // spaces).
 231   virtual size_t max_capacity() const = 0;
 232 
 233   // Returns "TRUE" if "p" points into the reserved area of the heap.
 234   bool is_in_reserved(const void* p) const {
 235     return _reserved.contains(p);
 236   }
 237 
 238   bool is_in_reserved_or_null(const void* p) const {
 239     return p == NULL || is_in_reserved(p);
 240   }
 241 
 242   // Returns "TRUE" iff "p" points into the committed areas of the heap.
 243   // Since this method can be expensive in general, we restrict its
 244   // use to assertion checking only.
 245   virtual bool is_in(const void* p) const = 0;
 246 
 247   bool is_in_or_null(const void* p) const {
 248     return p == NULL || is_in(p);
 249   }
 250 
 251   bool is_in_place(Metadata** p) {
 252     return !Universe::heap()->is_in(p);
 253   }
 254   bool is_in_place(oop* p) { return Universe::heap()->is_in(p); }
 255   bool is_in_place(narrowOop* p) {
 256     oop o = oopDesc::load_decode_heap_oop_not_null(p);
 257     return Universe::heap()->is_in((const void*)o);
 258   }
 259 
 260   // Let's define some terms: a "closed" subset of a heap is one that
 261   //
 262   // 1) contains all currently-allocated objects, and
 263   //
 264   // 2) is closed under reference: no object in the closed subset
 265   //    references one outside the closed subset.
 266   //
 267   // Membership in a heap's closed subset is useful for assertions.
 268   // Clearly, the entire heap is a closed subset, so the default
 269   // implementation is to use "is_in_reserved".  But this may not be too
 270   // liberal to perform useful checking.  Also, the "is_in" predicate
 271   // defines a closed subset, but may be too expensive, since "is_in"
 272   // verifies that its argument points to an object head.  The
 273   // "closed_subset" method allows a heap to define an intermediate
 274   // predicate, allowing more precise checking than "is_in_reserved" at
 275   // lower cost than "is_in."
 276 
 277   // One important case is a heap composed of disjoint contiguous spaces,
 278   // such as the Garbage-First collector.  Such heaps have a convenient
 279   // closed subset consisting of the allocated portions of those
 280   // contiguous spaces.
 281 
 282   // Return "TRUE" iff the given pointer points into the heap's defined
 283   // closed subset (which defaults to the entire heap).
 284   virtual bool is_in_closed_subset(const void* p) const {
 285     return is_in_reserved(p);
 286   }
 287 
 288   bool is_in_closed_subset_or_null(const void* p) const {
 289     return p == NULL || is_in_closed_subset(p);
 290   }
 291 
 292   // An object is scavengable if its location may move during a scavenge.
 293   // (A scavenge is a GC which is not a full GC.)
 294   virtual bool is_scavengable(const void *p) = 0;
 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   // Number of threads currently working on GC tasks.
 307   uint n_par_threads() { return _n_par_threads; }
 308 
 309   // May be overridden to set additional parallelism.
 310   virtual void set_par_threads(uint t) { _n_par_threads = t; };
 311 
 312   // General obj/array allocation facilities.
 313   inline static oop obj_allocate(KlassHandle klass, int size, TRAPS);
 314   inline static oop array_allocate(KlassHandle klass, int size, int length, TRAPS);
 315   inline static oop array_allocate_nozero(KlassHandle klass, int size, int length, TRAPS);
 316 
 317   inline static void post_allocation_install_obj_klass(KlassHandle klass,
 318                                                        oop obj);
 319 
 320   // Raw memory allocation facilities
 321   // The obj and array allocate methods are covers for these methods.
 322   // mem_allocate() should never be
 323   // called to allocate TLABs, only individual objects.
 324   virtual HeapWord* mem_allocate(size_t size,
 325                                  bool* gc_overhead_limit_was_exceeded) = 0;
 326 
 327   // Utilities for turning raw memory into filler objects.
 328   //
 329   // min_fill_size() is the smallest region that can be filled.
 330   // fill_with_objects() can fill arbitrary-sized regions of the heap using
 331   // multiple objects.  fill_with_object() is for regions known to be smaller
 332   // than the largest array of integers; it uses a single object to fill the
 333   // region and has slightly less overhead.
 334   static size_t min_fill_size() {
 335     return size_t(align_object_size(oopDesc::header_size()));
 336   }
 337 
 338   static void fill_with_objects(HeapWord* start, size_t words, bool zap = true);
 339 
 340   static void fill_with_object(HeapWord* start, size_t words, bool zap = true);
 341   static void fill_with_object(MemRegion region, bool zap = true) {
 342     fill_with_object(region.start(), region.word_size(), zap);
 343   }
 344   static void fill_with_object(HeapWord* start, HeapWord* end, bool zap = true) {
 345     fill_with_object(start, pointer_delta(end, start), zap);
 346   }
 347 
 348   // Return the address "addr" aligned by "alignment_in_bytes" if such
 349   // an address is below "end".  Return NULL otherwise.
 350   inline static HeapWord* align_allocation_or_fail(HeapWord* addr,
 351                                                    HeapWord* end,
 352                                                    unsigned short alignment_in_bytes);
 353 
 354   // Some heaps may offer a contiguous region for shared non-blocking
 355   // allocation, via inlined code (by exporting the address of the top and
 356   // end fields defining the extent of the contiguous allocation region.)
 357 
 358   // This function returns "true" iff the heap supports this kind of
 359   // allocation.  (Default is "no".)
 360   virtual bool supports_inline_contig_alloc() const {
 361     return false;
 362   }
 363   // These functions return the addresses of the fields that define the
 364   // boundaries of the contiguous allocation area.  (These fields should be
 365   // physically near to one another.)
 366   virtual HeapWord** top_addr() const {
 367     guarantee(false, "inline contiguous allocation not supported");
 368     return NULL;
 369   }
 370   virtual HeapWord** end_addr() const {
 371     guarantee(false, "inline contiguous allocation not supported");
 372     return NULL;
 373   }
 374 
 375   // Some heaps may be in an unparseable state at certain times between
 376   // collections. This may be necessary for efficient implementation of
 377   // certain allocation-related activities. Calling this function before
 378   // attempting to parse a heap ensures that the heap is in a parsable
 379   // state (provided other concurrent activity does not introduce
 380   // unparsability). It is normally expected, therefore, that this
 381   // method is invoked with the world stopped.
 382   // NOTE: if you override this method, make sure you call
 383   // super::ensure_parsability so that the non-generational
 384   // part of the work gets done. See implementation of
 385   // CollectedHeap::ensure_parsability and, for instance,
 386   // that of GenCollectedHeap::ensure_parsability().
 387   // The argument "retire_tlabs" controls whether existing TLABs
 388   // are merely filled or also retired, thus preventing further
 389   // allocation from them and necessitating allocation of new TLABs.
 390   virtual void ensure_parsability(bool retire_tlabs);
 391 
 392   // Section on thread-local allocation buffers (TLABs)
 393   // If the heap supports thread-local allocation buffers, it should override
 394   // the following methods:
 395   // Returns "true" iff the heap supports thread-local allocation buffers.
 396   // The default is "no".
 397   virtual bool supports_tlab_allocation() const = 0;
 398 
 399   // The amount of space available for thread-local allocation buffers.
 400   virtual size_t tlab_capacity(Thread *thr) const = 0;
 401 
 402   // The amount of used space for thread-local allocation buffers for the given thread.
 403   virtual size_t tlab_used(Thread *thr) const = 0;
 404 
 405   virtual size_t max_tlab_size() const;
 406 
 407   // An estimate of the maximum allocation that could be performed
 408   // for thread-local allocation buffers without triggering any
 409   // collection or expansion activity.
 410   virtual size_t unsafe_max_tlab_alloc(Thread *thr) const {
 411     guarantee(false, "thread-local allocation buffers not supported");
 412     return 0;
 413   }
 414 
 415   // Can a compiler initialize a new object without store barriers?
 416   // This permission only extends from the creation of a new object
 417   // via a TLAB up to the first subsequent safepoint. If such permission
 418   // is granted for this heap type, the compiler promises to call
 419   // defer_store_barrier() below on any slow path allocation of
 420   // a new object for which such initializing store barriers will
 421   // have been elided.
 422   virtual bool can_elide_tlab_store_barriers() const = 0;
 423 
 424   // If a compiler is eliding store barriers for TLAB-allocated objects,
 425   // there is probably a corresponding slow path which can produce
 426   // an object allocated anywhere.  The compiler's runtime support
 427   // promises to call this function on such a slow-path-allocated
 428   // object before performing initializations that have elided
 429   // store barriers. Returns new_obj, or maybe a safer copy thereof.
 430   virtual oop new_store_pre_barrier(JavaThread* thread, oop new_obj);
 431 
 432   // Answers whether an initializing store to a new object currently
 433   // allocated at the given address doesn't need a store
 434   // barrier. Returns "true" if it doesn't need an initializing
 435   // store barrier; answers "false" if it does.
 436   virtual bool can_elide_initializing_store_barrier(oop new_obj) = 0;
 437 
 438   // If a compiler is eliding store barriers for TLAB-allocated objects,
 439   // we will be informed of a slow-path allocation by a call
 440   // to new_store_pre_barrier() above. Such a call precedes the
 441   // initialization of the object itself, and no post-store-barriers will
 442   // be issued. Some heap types require that the barrier strictly follows
 443   // the initializing stores. (This is currently implemented by deferring the
 444   // barrier until the next slow-path allocation or gc-related safepoint.)
 445   // This interface answers whether a particular heap type needs the card
 446   // mark to be thus strictly sequenced after the stores.
 447   virtual bool card_mark_must_follow_store() const = 0;
 448 
 449   // If the CollectedHeap was asked to defer a store barrier above,
 450   // this informs it to flush such a deferred store barrier to the
 451   // remembered set.
 452   virtual void flush_deferred_store_barrier(JavaThread* thread);
 453 
 454   // Does this heap support heap inspection (+PrintClassHistogram?)
 455   virtual bool supports_heap_inspection() const = 0;
 456 
 457   // Perform a collection of the heap; intended for use in implementing
 458   // "System.gc".  This probably implies as full a collection as the
 459   // "CollectedHeap" supports.
 460   virtual void collect(GCCause::Cause cause) = 0;
 461 
 462   // Perform a full collection
 463   virtual void do_full_collection(bool clear_all_soft_refs) = 0;
 464 
 465   // This interface assumes that it's being called by the
 466   // vm thread. It collects the heap assuming that the
 467   // heap lock is already held and that we are executing in
 468   // the context of the vm thread.
 469   virtual void collect_as_vm_thread(GCCause::Cause cause);
 470 
 471   // Returns the barrier set for this heap
 472   BarrierSet* barrier_set() { return _barrier_set; }
 473   void set_barrier_set(BarrierSet* barrier_set);
 474 
 475   // Returns "true" iff there is a stop-world GC in progress.  (I assume
 476   // that it should answer "false" for the concurrent part of a concurrent
 477   // collector -- dld).
 478   bool is_gc_active() const { return _is_gc_active; }
 479 
 480   // Total number of GC collections (started)
 481   unsigned int total_collections() const { return _total_collections; }
 482   unsigned int total_full_collections() const { return _total_full_collections;}
 483 
 484   // Increment total number of GC collections (started)
 485   // Should be protected but used by PSMarkSweep - cleanup for 1.4.2
 486   void increment_total_collections(bool full = false) {
 487     _total_collections++;
 488     if (full) {
 489       increment_total_full_collections();
 490     }
 491   }
 492 
 493   void increment_total_full_collections() { _total_full_collections++; }
 494 
 495   // Return the AdaptiveSizePolicy for the heap.
 496   virtual AdaptiveSizePolicy* size_policy() = 0;
 497 
 498   // Return the CollectorPolicy for the heap
 499   virtual CollectorPolicy* collector_policy() const = 0;
 500 
 501   void oop_iterate_no_header(OopClosure* cl);
 502 
 503   // Iterate over all the ref-containing fields of all objects, calling
 504   // "cl.do_oop" on each.
 505   virtual void oop_iterate(ExtendedOopClosure* cl) = 0;
 506 
 507   // Iterate over all objects, calling "cl.do_object" on each.
 508   virtual void object_iterate(ObjectClosure* cl) = 0;
 509 
 510   // Similar to object_iterate() except iterates only
 511   // over live objects.
 512   virtual void safe_object_iterate(ObjectClosure* cl) = 0;
 513 
 514   // NOTE! There is no requirement that a collector implement these
 515   // functions.
 516   //
 517   // A CollectedHeap is divided into a dense sequence of "blocks"; that is,
 518   // each address in the (reserved) heap is a member of exactly
 519   // one block.  The defining characteristic of a block is that it is
 520   // possible to find its size, and thus to progress forward to the next
 521   // block.  (Blocks may be of different sizes.)  Thus, blocks may
 522   // represent Java objects, or they might be free blocks in a
 523   // free-list-based heap (or subheap), as long as the two kinds are
 524   // distinguishable and the size of each is determinable.
 525 
 526   // Returns the address of the start of the "block" that contains the
 527   // address "addr".  We say "blocks" instead of "object" since some heaps
 528   // may not pack objects densely; a chunk may either be an object or a
 529   // non-object.
 530   virtual HeapWord* block_start(const void* addr) const = 0;
 531 
 532   // Requires "addr" to be the start of a chunk, and returns its size.
 533   // "addr + size" is required to be the start of a new chunk, or the end
 534   // of the active area of the heap.
 535   virtual size_t block_size(const HeapWord* addr) const = 0;
 536 
 537   // Requires "addr" to be the start of a block, and returns "TRUE" iff
 538   // the block is an object.
 539   virtual bool block_is_obj(const HeapWord* addr) const = 0;
 540 
 541   // Returns the longest time (in ms) that has elapsed since the last
 542   // time that any part of the heap was examined by a garbage collection.
 543   virtual jlong millis_since_last_gc() = 0;
 544 
 545   // Perform any cleanup actions necessary before allowing a verification.
 546   virtual void prepare_for_verify() = 0;
 547 
 548   // Generate any dumps preceding or following a full gc
 549   void pre_full_gc_dump(GCTimer* timer);
 550   void post_full_gc_dump(GCTimer* timer);
 551 
 552   VirtualSpaceSummary create_heap_space_summary();
 553   GCHeapSummary create_heap_summary();
 554 
 555   MetaspaceSummary create_metaspace_summary();
 556 
 557   // Print heap information on the given outputStream.
 558   virtual void print_on(outputStream* st) const = 0;
 559   // The default behavior is to call print_on() on tty.
 560   virtual void print() const {
 561     print_on(tty);
 562   }
 563   // Print more detailed heap information on the given
 564   // outputStream. The default behavior is to call print_on(). It is
 565   // up to each subclass to override it and add any additional output
 566   // it needs.
 567   virtual void print_extended_on(outputStream* st) const {
 568     print_on(st);
 569   }
 570 
 571   virtual void print_on_error(outputStream* st) const;
 572 
 573   // Print all GC threads (other than the VM thread)
 574   // used by this heap.
 575   virtual void print_gc_threads_on(outputStream* st) const = 0;
 576   // The default behavior is to call print_gc_threads_on() on tty.
 577   void print_gc_threads() {
 578     print_gc_threads_on(tty);
 579   }
 580   // Iterator for all GC threads (other than VM thread)
 581   virtual void gc_threads_do(ThreadClosure* tc) const = 0;
 582 
 583   // Print any relevant tracing info that flags imply.
 584   // Default implementation does nothing.
 585   virtual void print_tracing_info() const = 0;
 586 
 587   void print_heap_before_gc();
 588   void print_heap_after_gc();
 589 
 590   // Registering and unregistering an nmethod (compiled code) with the heap.
 591   // Override with specific mechanism for each specialized heap type.
 592   virtual void register_nmethod(nmethod* nm);
 593   virtual void unregister_nmethod(nmethod* nm);
 594 
 595   void trace_heap_before_gc(const GCTracer* gc_tracer);
 596   void trace_heap_after_gc(const GCTracer* gc_tracer);
 597 
 598   // Heap verification
 599   virtual void verify(bool silent, VerifyOption option) = 0;
 600 
 601   // Non product verification and debugging.
 602 #ifndef PRODUCT
 603   // Support for PromotionFailureALot.  Return true if it's time to cause a
 604   // promotion failure.  The no-argument version uses
 605   // this->_promotion_failure_alot_count as the counter.
 606   inline bool promotion_should_fail(volatile size_t* count);
 607   inline bool promotion_should_fail();
 608 
 609   // Reset the PromotionFailureALot counters.  Should be called at the end of a
 610   // GC in which promotion failure occurred.
 611   inline void reset_promotion_should_fail(volatile size_t* count);
 612   inline void reset_promotion_should_fail();
 613 #endif  // #ifndef PRODUCT
 614 
 615 #ifdef ASSERT
 616   static int fired_fake_oom() {
 617     return (CIFireOOMAt > 1 && _fire_out_of_memory_count >= CIFireOOMAt);
 618   }
 619 #endif
 620 
 621  public:
 622   // This is a convenience method that is used in cases where
 623   // the actual number of GC worker threads is not pertinent but
 624   // only whether there more than 0.  Use of this method helps
 625   // reduce the occurrence of ParallelGCThreads to uses where the
 626   // actual number may be germane.
 627   static bool use_parallel_gc_threads() { return ParallelGCThreads > 0; }
 628 
 629   // Copy the current allocation context statistics for the specified contexts.
 630   // For each context in contexts, set the corresponding entries in the totals
 631   // and accuracy arrays to the current values held by the statistics.  Each
 632   // array should be of length len.
 633   // Returns true if there are more stats available.
 634   virtual bool copy_allocation_context_stats(const jint* contexts,
 635                                              jlong* totals,
 636                                              jbyte* accuracy,
 637                                              jint len) {
 638     return false;
 639   }
 640 
 641   /////////////// Unit tests ///////////////
 642 
 643   NOT_PRODUCT(static void test_is_in();)
 644 };
 645 
 646 // Class to set and reset the GC cause for a CollectedHeap.
 647 
 648 class GCCauseSetter : StackObj {
 649   CollectedHeap* _heap;
 650   GCCause::Cause _previous_cause;
 651  public:
 652   GCCauseSetter(CollectedHeap* heap, GCCause::Cause cause) {
 653     assert(SafepointSynchronize::is_at_safepoint(),
 654            "This method manipulates heap state without locking");
 655     _heap = heap;
 656     _previous_cause = _heap->gc_cause();
 657     _heap->set_gc_cause(cause);
 658   }
 659 
 660   ~GCCauseSetter() {
 661     assert(SafepointSynchronize::is_at_safepoint(),
 662           "This method manipulates heap state without locking");
 663     _heap->set_gc_cause(_previous_cause);
 664   }
 665 };
 666 
 667 #endif // SHARE_VM_GC_INTERFACE_COLLECTEDHEAP_HPP