1 /*
   2  * Copyright (c) 2001, 2012, 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_INTERFACE_COLLECTEDHEAP_HPP
  26 #define SHARE_VM_GC_INTERFACE_COLLECTEDHEAP_HPP
  27 
  28 #include "gc_interface/gcCause.hpp"
  29 #include "memory/allocation.hpp"
  30 #include "memory/barrierSet.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 BarrierSet;
  42 class ThreadClosure;
  43 class AdaptiveSizePolicy;
  44 class Thread;
  45 class CollectorPolicy;
  46 
  47 class GCMessage : public FormatBuffer<1024> {
  48  public:
  49   bool is_before;
  50 
  51  public:
  52   GCMessage() {}
  53 };
  54 
  55 class GCHeapLog : public EventLogBase<GCMessage> {
  56  private:
  57   void log_heap(bool before);
  58 
  59  public:
  60   GCHeapLog() : EventLogBase<GCMessage>("GC Heap History") {}
  61 
  62   void log_heap_before() {
  63     log_heap(true);
  64   }
  65   void log_heap_after() {
  66     log_heap(false);
  67   }
  68 };
  69 
  70 //
  71 // CollectedHeap
  72 //   SharedHeap
  73 //     GenCollectedHeap
  74 //     G1CollectedHeap
  75 //   ParallelScavengeHeap
  76 //
  77 class CollectedHeap : public CHeapObj {
  78   friend class VMStructs;
  79   friend class IsGCActiveMark; // Block structured external access to _is_gc_active
  80   friend class constantPoolCacheKlass; // allocate() method inserts is_conc_safe
  81 
  82 #ifdef ASSERT
  83   static int       _fire_out_of_memory_count;
  84 #endif
  85 
  86   // Used for filler objects (static, but initialized in ctor).
  87   static size_t _filler_array_max_size;
  88 
  89   GCHeapLog* _gc_heap_log;
  90 
  91   // Used in support of ReduceInitialCardMarks; only consulted if COMPILER2 is being used
  92   bool _defer_initial_card_mark;
  93 
  94  protected:
  95   MemRegion _reserved;
  96   BarrierSet* _barrier_set;
  97   bool _is_gc_active;
  98   uint _n_par_threads;
  99 
 100   unsigned int _total_collections;          // ... started
 101   unsigned int _total_full_collections;     // ... started
 102   NOT_PRODUCT(volatile size_t _promotion_failure_alot_count;)
 103   NOT_PRODUCT(volatile size_t _promotion_failure_alot_gc_number;)
 104 
 105   // Reason for current garbage collection.  Should be set to
 106   // a value reflecting no collection between collections.
 107   GCCause::Cause _gc_cause;
 108   GCCause::Cause _gc_lastcause;
 109   PerfStringVariable* _perf_gc_cause;
 110   PerfStringVariable* _perf_gc_lastcause;
 111 
 112   // Constructor
 113   CollectedHeap();
 114 
 115   // Do common initializations that must follow instance construction,
 116   // for example, those needing virtual calls.
 117   // This code could perhaps be moved into initialize() but would
 118   // be slightly more awkward because we want the latter to be a
 119   // pure virtual.
 120   void pre_initialize();
 121 
 122   // Create a new tlab. All TLAB allocations must go through this.
 123   virtual HeapWord* allocate_new_tlab(size_t size);
 124 
 125   // Accumulate statistics on all tlabs.
 126   virtual void accumulate_statistics_all_tlabs();
 127 
 128   // Reinitialize tlabs before resuming mutators.
 129   virtual void resize_all_tlabs();
 130 
 131   // Allocate from the current thread's TLAB, with broken-out slow path.
 132   inline static HeapWord* allocate_from_tlab(Thread* thread, size_t size);
 133   static HeapWord* allocate_from_tlab_slow(Thread* thread, size_t size);
 134 
 135   // Allocate an uninitialized block of the given size, or returns NULL if
 136   // this is impossible.
 137   inline static HeapWord* common_mem_allocate_noinit(size_t size, TRAPS);
 138 
 139   // Like allocate_init, but the block returned by a successful allocation
 140   // is guaranteed initialized to zeros.
 141   inline static HeapWord* common_mem_allocate_init(size_t size, TRAPS);
 142 
 143   // Same as common_mem version, except memory is allocated in the permanent area
 144   // If there is no permanent area, revert to common_mem_allocate_noinit
 145   inline static HeapWord* common_permanent_mem_allocate_noinit(size_t size, TRAPS);
 146 
 147   // Same as common_mem version, except memory is allocated in the permanent area
 148   // If there is no permanent area, revert to common_mem_allocate_init
 149   inline static HeapWord* common_permanent_mem_allocate_init(size_t size, TRAPS);
 150 
 151   // Helper functions for (VM) allocation.
 152   inline static void post_allocation_setup_common(KlassHandle klass,
 153                                                   HeapWord* obj, size_t size);
 154   inline static void post_allocation_setup_no_klass_install(KlassHandle klass,
 155                                                             HeapWord* objPtr,
 156                                                             size_t size);
 157 
 158   inline static void post_allocation_setup_obj(KlassHandle klass,
 159                                                HeapWord* obj, size_t size);
 160 
 161   inline static void post_allocation_setup_array(KlassHandle klass,
 162                                                  HeapWord* obj, size_t size,
 163                                                  int length);
 164 
 165   // Clears an allocated object.
 166   inline static void init_obj(HeapWord* obj, size_t size);
 167 
 168   // Filler object utilities.
 169   static inline size_t filler_array_hdr_size();
 170   static inline size_t filler_array_min_size();
 171 
 172   DEBUG_ONLY(static void fill_args_check(HeapWord* start, size_t words);)
 173   DEBUG_ONLY(static void zap_filler_array(HeapWord* start, size_t words, bool zap = true);)
 174 
 175   // Fill with a single array; caller must ensure filler_array_min_size() <=
 176   // words <= filler_array_max_size().
 177   static inline void fill_with_array(HeapWord* start, size_t words, bool zap = true);
 178 
 179   // Fill with a single object (either an int array or a java.lang.Object).
 180   static inline void fill_with_object_impl(HeapWord* start, size_t words, bool zap = true);
 181 
 182   // Verification functions
 183   virtual void check_for_bad_heap_word_value(HeapWord* addr, size_t size)
 184     PRODUCT_RETURN;
 185   virtual void check_for_non_bad_heap_word_value(HeapWord* addr, size_t size)
 186     PRODUCT_RETURN;
 187   debug_only(static void check_for_valid_allocation_state();)
 188 
 189  public:
 190   enum Name {
 191     Abstract,
 192     SharedHeap,
 193     GenCollectedHeap,
 194     ParallelScavengeHeap,
 195     G1CollectedHeap
 196   };
 197 
 198   static inline size_t filler_array_max_size() {
 199     return _filler_array_max_size;
 200   }
 201 
 202   virtual CollectedHeap::Name kind() const { return CollectedHeap::Abstract; }
 203 
 204   /**
 205    * Returns JNI error code JNI_ENOMEM if memory could not be allocated,
 206    * and JNI_OK on success.
 207    */
 208   virtual jint initialize() = 0;
 209 
 210   // In many heaps, there will be a need to perform some initialization activities
 211   // after the Universe is fully formed, but before general heap allocation is allowed.
 212   // This is the correct place to place such initialization methods.
 213   virtual void post_initialize() = 0;
 214 
 215   MemRegion reserved_region() const { return _reserved; }
 216   address base() const { return (address)reserved_region().start(); }
 217 
 218   // Future cleanup here. The following functions should specify bytes or
 219   // heapwords as part of their signature.
 220   virtual size_t capacity() const = 0;
 221   virtual size_t used() const = 0;
 222 
 223   // Return "true" if the part of the heap that allocates Java
 224   // objects has reached the maximal committed limit that it can
 225   // reach, without a garbage collection.
 226   virtual bool is_maximal_no_gc() const = 0;
 227 
 228   virtual size_t permanent_capacity() const = 0;
 229   virtual size_t permanent_used() const = 0;
 230 
 231   // Support for java.lang.Runtime.maxMemory():  return the maximum amount of
 232   // memory that the vm could make available for storing 'normal' java objects.
 233   // This is based on the reserved address space, but should not include space
 234   // that the vm uses internally for bookkeeping or temporary storage (e.g.,
 235   // perm gen space or, in the case of the young gen, one of the survivor
 236   // spaces).
 237   virtual size_t max_capacity() const = 0;
 238 
 239   // Returns "TRUE" if "p" points into the reserved area of the heap.
 240   bool is_in_reserved(const void* p) const {
 241     return _reserved.contains(p);
 242   }
 243 
 244   bool is_in_reserved_or_null(const void* p) const {
 245     return p == NULL || is_in_reserved(p);
 246   }
 247 
 248   // Returns "TRUE" iff "p" points into the committed areas of the heap.
 249   // Since this method can be expensive in general, we restrict its
 250   // use to assertion checking only.
 251   virtual bool is_in(const void* p) const = 0;
 252 
 253   bool is_in_or_null(const void* p) const {
 254     return p == NULL || is_in(p);
 255   }
 256 
 257   // Let's define some terms: a "closed" subset of a heap is one that
 258   //
 259   // 1) contains all currently-allocated objects, and
 260   //
 261   // 2) is closed under reference: no object in the closed subset
 262   //    references one outside the closed subset.
 263   //
 264   // Membership in a heap's closed subset is useful for assertions.
 265   // Clearly, the entire heap is a closed subset, so the default
 266   // implementation is to use "is_in_reserved".  But this may not be too
 267   // liberal to perform useful checking.  Also, the "is_in" predicate
 268   // defines a closed subset, but may be too expensive, since "is_in"
 269   // verifies that its argument points to an object head.  The
 270   // "closed_subset" method allows a heap to define an intermediate
 271   // predicate, allowing more precise checking than "is_in_reserved" at
 272   // lower cost than "is_in."
 273 
 274   // One important case is a heap composed of disjoint contiguous spaces,
 275   // such as the Garbage-First collector.  Such heaps have a convenient
 276   // closed subset consisting of the allocated portions of those
 277   // contiguous spaces.
 278 
 279   // Return "TRUE" iff the given pointer points into the heap's defined
 280   // closed subset (which defaults to the entire heap).
 281   virtual bool is_in_closed_subset(const void* p) const {
 282     return is_in_reserved(p);
 283   }
 284 
 285   bool is_in_closed_subset_or_null(const void* p) const {
 286     return p == NULL || is_in_closed_subset(p);
 287   }
 288 
 289   // XXX is_permanent() and is_in_permanent() should be better named
 290   // to distinguish one from the other.
 291 
 292   // Returns "TRUE" if "p" is allocated as "permanent" data.
 293   // If the heap does not use "permanent" data, returns the same
 294   // value is_in_reserved() would return.
 295   // NOTE: this actually returns true if "p" is in reserved space
 296   // for the space not that it is actually allocated (i.e. in committed
 297   // space). If you need the more conservative answer use is_permanent().
 298   virtual bool is_in_permanent(const void *p) const = 0;
 299 
 300 
 301 #ifdef ASSERT
 302   // Returns true if "p" is in the part of the
 303   // heap being collected.
 304   virtual bool is_in_partial_collection(const void *p) = 0;
 305 #endif
 306 
 307   bool is_in_permanent_or_null(const void *p) const {
 308     return p == NULL || is_in_permanent(p);
 309   }
 310 
 311   // Returns "TRUE" if "p" is in the committed area of  "permanent" data.
 312   // If the heap does not use "permanent" data, returns the same
 313   // value is_in() would return.
 314   virtual bool is_permanent(const void *p) const = 0;
 315 
 316   bool is_permanent_or_null(const void *p) const {
 317     return p == NULL || is_permanent(p);
 318   }
 319 
 320   // An object is scavengable if its location may move during a scavenge.
 321   // (A scavenge is a GC which is not a full GC.)
 322   virtual bool is_scavengable(const void *p) = 0;
 323 
 324   // Returns "TRUE" if "p" is a method oop in the
 325   // current heap, with high probability. This predicate
 326   // is not stable, in general.
 327   bool is_valid_method(oop p) const;
 328 
 329   void set_gc_cause(GCCause::Cause v) {
 330      if (UsePerfData) {
 331        _gc_lastcause = _gc_cause;
 332        _perf_gc_lastcause->set_value(GCCause::to_string(_gc_lastcause));
 333        _perf_gc_cause->set_value(GCCause::to_string(v));
 334      }
 335     _gc_cause = v;
 336   }
 337   GCCause::Cause gc_cause() { return _gc_cause; }
 338 
 339   // Number of threads currently working on GC tasks.
 340   uint n_par_threads() { return _n_par_threads; }
 341 
 342   // May be overridden to set additional parallelism.
 343   virtual void set_par_threads(uint t) { _n_par_threads = t; };
 344 
 345   // Preload classes into the shared portion of the heap, and then dump
 346   // that data to a file so that it can be loaded directly by another
 347   // VM (then terminate).
 348   virtual void preload_and_dump(TRAPS) { ShouldNotReachHere(); }
 349 
 350   // Allocate and initialize instances of Class
 351   static oop Class_obj_allocate(KlassHandle klass, int size, KlassHandle real_klass, TRAPS);
 352 
 353   // General obj/array allocation facilities.
 354   inline static oop obj_allocate(KlassHandle klass, int size, TRAPS);
 355   inline static oop array_allocate(KlassHandle klass, int size, int length, TRAPS);
 356   inline static oop array_allocate_nozero(KlassHandle klass, int size, int length, TRAPS);
 357 
 358   // Special obj/array allocation facilities.
 359   // Some heaps may want to manage "permanent" data uniquely. These default
 360   // to the general routines if the heap does not support such handling.
 361   inline static oop permanent_obj_allocate(KlassHandle klass, int size, TRAPS);
 362   // permanent_obj_allocate_no_klass_install() does not do the installation of
 363   // the klass pointer in the newly created object (as permanent_obj_allocate()
 364   // above does).  This allows for a delay in the installation of the klass
 365   // pointer that is needed during the create of klassKlass's.  The
 366   // method post_allocation_install_obj_klass() is used to install the
 367   // klass pointer.
 368   inline static oop permanent_obj_allocate_no_klass_install(KlassHandle klass,
 369                                                             int size,
 370                                                             TRAPS);
 371   inline static void post_allocation_install_obj_klass(KlassHandle klass,
 372                                                        oop obj,
 373                                                        int size);
 374   inline static oop permanent_array_allocate(KlassHandle klass, int size, int length, TRAPS);
 375 
 376   // Raw memory allocation facilities
 377   // The obj and array allocate methods are covers for these methods.
 378   // The permanent allocation method should default to mem_allocate if
 379   // permanent memory isn't supported. mem_allocate() should never be
 380   // called to allocate TLABs, only individual objects.
 381   virtual HeapWord* mem_allocate(size_t size,
 382                                  bool* gc_overhead_limit_was_exceeded) = 0;
 383   virtual HeapWord* permanent_mem_allocate(size_t size) = 0;
 384 
 385   // Utilities for turning raw memory into filler objects.
 386   //
 387   // min_fill_size() is the smallest region that can be filled.
 388   // fill_with_objects() can fill arbitrary-sized regions of the heap using
 389   // multiple objects.  fill_with_object() is for regions known to be smaller
 390   // than the largest array of integers; it uses a single object to fill the
 391   // region and has slightly less overhead.
 392   static size_t min_fill_size() {
 393     return size_t(align_object_size(oopDesc::header_size()));
 394   }
 395 
 396   static void fill_with_objects(HeapWord* start, size_t words, bool zap = true);
 397 
 398   static void fill_with_object(HeapWord* start, size_t words, bool zap = true);
 399   static void fill_with_object(MemRegion region, bool zap = true) {
 400     fill_with_object(region.start(), region.word_size(), zap);
 401   }
 402   static void fill_with_object(HeapWord* start, HeapWord* end, bool zap = true) {
 403     fill_with_object(start, pointer_delta(end, start), zap);
 404   }
 405 
 406   // Some heaps may offer a contiguous region for shared non-blocking
 407   // allocation, via inlined code (by exporting the address of the top and
 408   // end fields defining the extent of the contiguous allocation region.)
 409 
 410   // This function returns "true" iff the heap supports this kind of
 411   // allocation.  (Default is "no".)
 412   virtual bool supports_inline_contig_alloc() const {
 413     return false;
 414   }
 415   // These functions return the addresses of the fields that define the
 416   // boundaries of the contiguous allocation area.  (These fields should be
 417   // physically near to one another.)
 418   virtual HeapWord** top_addr() const {
 419     guarantee(false, "inline contiguous allocation not supported");
 420     return NULL;
 421   }
 422   virtual HeapWord** end_addr() const {
 423     guarantee(false, "inline contiguous allocation not supported");
 424     return NULL;
 425   }
 426 
 427   // Some heaps may be in an unparseable state at certain times between
 428   // collections. This may be necessary for efficient implementation of
 429   // certain allocation-related activities. Calling this function before
 430   // attempting to parse a heap ensures that the heap is in a parsable
 431   // state (provided other concurrent activity does not introduce
 432   // unparsability). It is normally expected, therefore, that this
 433   // method is invoked with the world stopped.
 434   // NOTE: if you override this method, make sure you call
 435   // super::ensure_parsability so that the non-generational
 436   // part of the work gets done. See implementation of
 437   // CollectedHeap::ensure_parsability and, for instance,
 438   // that of GenCollectedHeap::ensure_parsability().
 439   // The argument "retire_tlabs" controls whether existing TLABs
 440   // are merely filled or also retired, thus preventing further
 441   // allocation from them and necessitating allocation of new TLABs.
 442   virtual void ensure_parsability(bool retire_tlabs);
 443 
 444   // Return an estimate of the maximum allocation that could be performed
 445   // without triggering any collection or expansion activity.  In a
 446   // generational collector, for example, this is probably the largest
 447   // allocation that could be supported (without expansion) in the youngest
 448   // generation.  It is "unsafe" because no locks are taken; the result
 449   // should be treated as an approximation, not a guarantee, for use in
 450   // heuristic resizing decisions.
 451   virtual size_t unsafe_max_alloc() = 0;
 452 
 453   // Section on thread-local allocation buffers (TLABs)
 454   // If the heap supports thread-local allocation buffers, it should override
 455   // the following methods:
 456   // Returns "true" iff the heap supports thread-local allocation buffers.
 457   // The default is "no".
 458   virtual bool supports_tlab_allocation() const {
 459     return false;
 460   }
 461   // The amount of space available for thread-local allocation buffers.
 462   virtual size_t tlab_capacity(Thread *thr) const {
 463     guarantee(false, "thread-local allocation buffers not supported");
 464     return 0;
 465   }
 466   // An estimate of the maximum allocation that could be performed
 467   // for thread-local allocation buffers without triggering any
 468   // collection or expansion activity.
 469   virtual size_t unsafe_max_tlab_alloc(Thread *thr) const {
 470     guarantee(false, "thread-local allocation buffers not supported");
 471     return 0;
 472   }
 473 
 474   // Can a compiler initialize a new object without store barriers?
 475   // This permission only extends from the creation of a new object
 476   // via a TLAB up to the first subsequent safepoint. If such permission
 477   // is granted for this heap type, the compiler promises to call
 478   // defer_store_barrier() below on any slow path allocation of
 479   // a new object for which such initializing store barriers will
 480   // have been elided.
 481   virtual bool can_elide_tlab_store_barriers() const = 0;
 482 
 483   // If a compiler is eliding store barriers for TLAB-allocated objects,
 484   // there is probably a corresponding slow path which can produce
 485   // an object allocated anywhere.  The compiler's runtime support
 486   // promises to call this function on such a slow-path-allocated
 487   // object before performing initializations that have elided
 488   // store barriers. Returns new_obj, or maybe a safer copy thereof.
 489   virtual oop new_store_pre_barrier(JavaThread* thread, oop new_obj);
 490 
 491   // Answers whether an initializing store to a new object currently
 492   // allocated at the given address doesn't need a store
 493   // barrier. Returns "true" if it doesn't need an initializing
 494   // store barrier; answers "false" if it does.
 495   virtual bool can_elide_initializing_store_barrier(oop new_obj) = 0;
 496 
 497   // If a compiler is eliding store barriers for TLAB-allocated objects,
 498   // we will be informed of a slow-path allocation by a call
 499   // to new_store_pre_barrier() above. Such a call precedes the
 500   // initialization of the object itself, and no post-store-barriers will
 501   // be issued. Some heap types require that the barrier strictly follows
 502   // the initializing stores. (This is currently implemented by deferring the
 503   // barrier until the next slow-path allocation or gc-related safepoint.)
 504   // This interface answers whether a particular heap type needs the card
 505   // mark to be thus strictly sequenced after the stores.
 506   virtual bool card_mark_must_follow_store() const = 0;
 507 
 508   // If the CollectedHeap was asked to defer a store barrier above,
 509   // this informs it to flush such a deferred store barrier to the
 510   // remembered set.
 511   virtual void flush_deferred_store_barrier(JavaThread* thread);
 512 
 513   // Can a compiler elide a store barrier when it writes
 514   // a permanent oop into the heap?  Applies when the compiler
 515   // is storing x to the heap, where x->is_perm() is true.
 516   virtual bool can_elide_permanent_oop_store_barriers() const = 0;
 517 
 518   // Does this heap support heap inspection (+PrintClassHistogram?)
 519   virtual bool supports_heap_inspection() const = 0;
 520 
 521   // Perform a collection of the heap; intended for use in implementing
 522   // "System.gc".  This probably implies as full a collection as the
 523   // "CollectedHeap" supports.
 524   virtual void collect(GCCause::Cause cause) = 0;
 525 
 526   // This interface assumes that it's being called by the
 527   // vm thread. It collects the heap assuming that the
 528   // heap lock is already held and that we are executing in
 529   // the context of the vm thread.
 530   virtual void collect_as_vm_thread(GCCause::Cause cause) = 0;
 531 
 532   // Returns the barrier set for this heap
 533   BarrierSet* barrier_set() { return _barrier_set; }
 534 
 535   // Returns "true" iff there is a stop-world GC in progress.  (I assume
 536   // that it should answer "false" for the concurrent part of a concurrent
 537   // collector -- dld).
 538   bool is_gc_active() const { return _is_gc_active; }
 539 
 540   // Total number of GC collections (started)
 541   unsigned int total_collections() const { return _total_collections; }
 542   unsigned int total_full_collections() const { return _total_full_collections;}
 543 
 544   // Increment total number of GC collections (started)
 545   // Should be protected but used by PSMarkSweep - cleanup for 1.4.2
 546   void increment_total_collections(bool full = false) {
 547     _total_collections++;
 548     if (full) {
 549       increment_total_full_collections();
 550     }
 551   }
 552 
 553   void increment_total_full_collections() { _total_full_collections++; }
 554 
 555   // Return the AdaptiveSizePolicy for the heap.
 556   virtual AdaptiveSizePolicy* size_policy() = 0;
 557 
 558   // Return the CollectorPolicy for the heap
 559   virtual CollectorPolicy* collector_policy() const = 0;
 560 
 561   // Iterate over all the ref-containing fields of all objects, calling
 562   // "cl.do_oop" on each. This includes objects in permanent memory.
 563   virtual void oop_iterate(OopClosure* cl) = 0;
 564 
 565   // Iterate over all objects, calling "cl.do_object" on each.
 566   // This includes objects in permanent memory.
 567   virtual void object_iterate(ObjectClosure* cl) = 0;
 568 
 569   // Similar to object_iterate() except iterates only
 570   // over live objects.
 571   virtual void safe_object_iterate(ObjectClosure* cl) = 0;
 572 
 573   // Behaves the same as oop_iterate, except only traverses
 574   // interior pointers contained in permanent memory. If there
 575   // is no permanent memory, does nothing.
 576   virtual void permanent_oop_iterate(OopClosure* cl) = 0;
 577 
 578   // Behaves the same as object_iterate, except only traverses
 579   // object contained in permanent memory. If there is no
 580   // permanent memory, does nothing.
 581   virtual void permanent_object_iterate(ObjectClosure* cl) = 0;
 582 
 583   // NOTE! There is no requirement that a collector implement these
 584   // functions.
 585   //
 586   // A CollectedHeap is divided into a dense sequence of "blocks"; that is,
 587   // each address in the (reserved) heap is a member of exactly
 588   // one block.  The defining characteristic of a block is that it is
 589   // possible to find its size, and thus to progress forward to the next
 590   // block.  (Blocks may be of different sizes.)  Thus, blocks may
 591   // represent Java objects, or they might be free blocks in a
 592   // free-list-based heap (or subheap), as long as the two kinds are
 593   // distinguishable and the size of each is determinable.
 594 
 595   // Returns the address of the start of the "block" that contains the
 596   // address "addr".  We say "blocks" instead of "object" since some heaps
 597   // may not pack objects densely; a chunk may either be an object or a
 598   // non-object.
 599   virtual HeapWord* block_start(const void* addr) const = 0;
 600 
 601   // Requires "addr" to be the start of a chunk, and returns its size.
 602   // "addr + size" is required to be the start of a new chunk, or the end
 603   // of the active area of the heap.
 604   virtual size_t block_size(const HeapWord* addr) const = 0;
 605 
 606   // Requires "addr" to be the start of a block, and returns "TRUE" iff
 607   // the block is an object.
 608   virtual bool block_is_obj(const HeapWord* addr) const = 0;
 609 
 610   // Returns the longest time (in ms) that has elapsed since the last
 611   // time that any part of the heap was examined by a garbage collection.
 612   virtual jlong millis_since_last_gc() = 0;
 613 
 614   // Perform any cleanup actions necessary before allowing a verification.
 615   virtual void prepare_for_verify() = 0;
 616 
 617   // Generate any dumps preceding or following a full gc
 618   void pre_full_gc_dump();
 619   void post_full_gc_dump();
 620 
 621   // Print heap information on the given outputStream.
 622   virtual void print_on(outputStream* st) const = 0;
 623   // The default behavior is to call print_on() on tty.
 624   virtual void print() const {
 625     print_on(tty);
 626   }
 627   // Print more detailed heap information on the given
 628   // outputStream. The default behaviour is to call print_on(). It is
 629   // up to each subclass to override it and add any additional output
 630   // it needs.
 631   virtual void print_extended_on(outputStream* st) const {
 632     print_on(st);
 633   }
 634 
 635   // Print all GC threads (other than the VM thread)
 636   // used by this heap.
 637   virtual void print_gc_threads_on(outputStream* st) const = 0;
 638   // The default behavior is to call print_gc_threads_on() on tty.
 639   void print_gc_threads() {
 640     print_gc_threads_on(tty);
 641   }
 642   // Iterator for all GC threads (other than VM thread)
 643   virtual void gc_threads_do(ThreadClosure* tc) const = 0;
 644 
 645   // Print any relevant tracing info that flags imply.
 646   // Default implementation does nothing.
 647   virtual void print_tracing_info() const = 0;
 648 
 649   // If PrintHeapAtGC is set call the appropriate routi
 650   void print_heap_before_gc() {
 651     if (PrintHeapAtGC) {
 652       Universe::print_heap_before_gc();
 653     }
 654     if (_gc_heap_log != NULL) {
 655       _gc_heap_log->log_heap_before();
 656     }
 657   }
 658   void print_heap_after_gc() {
 659     if (PrintHeapAtGC) {
 660       Universe::print_heap_after_gc();
 661     }
 662     if (_gc_heap_log != NULL) {
 663       _gc_heap_log->log_heap_after();
 664     }
 665   }
 666 
 667   // Allocate GCHeapLog during VM startup
 668   static void initialize_heap_log();
 669 
 670   // Heap verification
 671   virtual void verify(bool allow_dirty, bool silent, VerifyOption option) = 0;
 672 
 673   // Non product verification and debugging.
 674 #ifndef PRODUCT
 675   // Support for PromotionFailureALot.  Return true if it's time to cause a
 676   // promotion failure.  The no-argument version uses
 677   // this->_promotion_failure_alot_count as the counter.
 678   inline bool promotion_should_fail(volatile size_t* count);
 679   inline bool promotion_should_fail();
 680 
 681   // Reset the PromotionFailureALot counters.  Should be called at the end of a
 682   // GC in which promotion failure ocurred.
 683   inline void reset_promotion_should_fail(volatile size_t* count);
 684   inline void reset_promotion_should_fail();
 685 #endif  // #ifndef PRODUCT
 686 
 687 #ifdef ASSERT
 688   static int fired_fake_oom() {
 689     return (CIFireOOMAt > 1 && _fire_out_of_memory_count >= CIFireOOMAt);
 690   }
 691 #endif
 692 
 693  public:
 694   // This is a convenience method that is used in cases where
 695   // the actual number of GC worker threads is not pertinent but
 696   // only whether there more than 0.  Use of this method helps
 697   // reduce the occurrence of ParallelGCThreads to uses where the
 698   // actual number may be germane.
 699   static bool use_parallel_gc_threads() { return ParallelGCThreads > 0; }
 700 
 701   /////////////// Unit tests ///////////////
 702 
 703   NOT_PRODUCT(static void test_is_in();)
 704 };
 705 
 706 // Class to set and reset the GC cause for a CollectedHeap.
 707 
 708 class GCCauseSetter : StackObj {
 709   CollectedHeap* _heap;
 710   GCCause::Cause _previous_cause;
 711  public:
 712   GCCauseSetter(CollectedHeap* heap, GCCause::Cause cause) {
 713     assert(SafepointSynchronize::is_at_safepoint(),
 714            "This method manipulates heap state without locking");
 715     _heap = heap;
 716     _previous_cause = _heap->gc_cause();
 717     _heap->set_gc_cause(cause);
 718   }
 719 
 720   ~GCCauseSetter() {
 721     assert(SafepointSynchronize::is_at_safepoint(),
 722           "This method manipulates heap state without locking");
 723     _heap->set_gc_cause(_previous_cause);
 724   }
 725 };
 726 
 727 #endif // SHARE_VM_GC_INTERFACE_COLLECTEDHEAP_HPP