1 /*
   2  * Copyright (c) 1997, 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.
  22  *
  23  */
  24 
  25 #ifndef SHARE_VM_MEMORY_GENERATION_HPP
  26 #define SHARE_VM_MEMORY_GENERATION_HPP
  27 
  28 #include "gc_implementation/shared/collectorCounters.hpp"
  29 #include "memory/allocation.hpp"
  30 #include "memory/memRegion.hpp"
  31 #include "memory/referenceProcessor.hpp"
  32 #include "memory/universe.hpp"
  33 #include "memory/watermark.hpp"
  34 #include "runtime/mutex.hpp"
  35 #include "runtime/perfData.hpp"
  36 #include "runtime/virtualspace.hpp"
  37 
  38 // A Generation models a heap area for similarly-aged objects.
  39 // It will contain one ore more spaces holding the actual objects.
  40 //
  41 // The Generation class hierarchy:
  42 //
  43 // Generation                      - abstract base class
  44 // - DefNewGeneration              - allocation area (copy collected)
  45 //   - ParNewGeneration            - a DefNewGeneration that is collected by
  46 //                                   several threads
  47 // - CardGeneration                 - abstract class adding offset array behavior
  48 //   - TenuredGeneration             - tenured (old object) space (markSweepCompact)
  49 //   - ConcurrentMarkSweepGeneration - Mostly Concurrent Mark Sweep Generation
  50 //                                       (Detlefs-Printezis refinement of
  51 //                                       Boehm-Demers-Schenker)
  52 //
  53 // The system configurations currently allowed are:
  54 //
  55 //   DefNewGeneration + TenuredGeneration
  56 //
  57 //   ParNewGeneration + ConcurrentMarkSweepGeneration
  58 //
  59 
  60 class DefNewGeneration;
  61 class GenerationSpec;
  62 class CompactibleSpace;
  63 class ContiguousSpace;
  64 class CompactPoint;
  65 class OopsInGenClosure;
  66 class OopClosure;
  67 class ScanClosure;
  68 class FastScanClosure;
  69 class GenCollectedHeap;
  70 class GenRemSet;
  71 class GCStats;
  72 
  73 // A "ScratchBlock" represents a block of memory in one generation usable by
  74 // another.  It represents "num_words" free words, starting at and including
  75 // the address of "this".
  76 struct ScratchBlock {
  77   ScratchBlock* next;
  78   size_t num_words;
  79   HeapWord scratch_space[1];  // Actually, of size "num_words-2" (assuming
  80                               // first two fields are word-sized.)
  81 };
  82 
  83 
  84 class Generation: public CHeapObj<mtGC> {
  85   friend class VMStructs;
  86  private:
  87   jlong _time_of_last_gc; // time when last gc on this generation happened (ms)
  88   MemRegion _prev_used_region; // for collectors that want to "remember" a value for
  89                                // used region at some specific point during collection.
  90 
  91  protected:
  92   // Minimum and maximum addresses for memory reserved (not necessarily
  93   // committed) for generation.
  94   // Used by card marking code. Must not overlap with address ranges of
  95   // other generations.
  96   MemRegion _reserved;
  97 
  98   // Memory area reserved for generation
  99   VirtualSpace _virtual_space;
 100 
 101   // Level in the generation hierarchy.
 102   int _level;
 103 
 104   // ("Weak") Reference processing support
 105   ReferenceProcessor* _ref_processor;
 106 
 107   // Performance Counters
 108   CollectorCounters* _gc_counters;
 109 
 110   // Statistics for garbage collection
 111   GCStats* _gc_stats;
 112 
 113   // Returns the next generation in the configuration, or else NULL if this
 114   // is the highest generation.
 115   Generation* next_gen() const;
 116 
 117   // Initialize the generation.
 118   Generation(ReservedSpace rs, size_t initial_byte_size, int level);
 119 
 120   // Apply "cl->do_oop" to (the address of) (exactly) all the ref fields in
 121   // "sp" that point into younger generations.
 122   // The iteration is only over objects allocated at the start of the
 123   // iterations; objects allocated as a result of applying the closure are
 124   // not included.
 125   void younger_refs_in_space_iterate(Space* sp, OopsInGenClosure* cl);
 126 
 127  public:
 128   // The set of possible generation kinds.
 129   enum Name {
 130     DefNew,
 131     ParNew,
 132     MarkSweepCompact,
 133     ConcurrentMarkSweep,
 134     Other
 135   };
 136 
 137   enum SomePublicConstants {
 138     // Generations are GenGrain-aligned and have size that are multiples of
 139     // GenGrain.
 140     // Note: on ARM we add 1 bit for card_table_base to be properly aligned
 141     // (we expect its low byte to be zero - see implementation of post_barrier)
 142     LogOfGenGrain = 16 ARM32_ONLY(+1),
 143     GenGrain = 1 << LogOfGenGrain
 144   };
 145 
 146   // allocate and initialize ("weak") refs processing support
 147   virtual void ref_processor_init();
 148   void set_ref_processor(ReferenceProcessor* rp) {
 149     assert(_ref_processor == NULL, "clobbering existing _ref_processor");
 150     _ref_processor = rp;
 151   }
 152 
 153   virtual Generation::Name kind() { return Generation::Other; }
 154   GenerationSpec* spec();
 155 
 156   // This properly belongs in the collector, but for now this
 157   // will do.
 158   virtual bool refs_discovery_is_atomic() const { return true;  }
 159   virtual bool refs_discovery_is_mt()     const { return false; }
 160 
 161   // Space enquiries (results in bytes)
 162   virtual size_t capacity() const = 0;  // The maximum number of object bytes the
 163                                         // generation can currently hold.
 164   virtual size_t used() const = 0;      // The number of used bytes in the gen.
 165   virtual size_t free() const = 0;      // The number of free bytes in the gen.
 166 
 167   // Support for java.lang.Runtime.maxMemory(); see CollectedHeap.
 168   // Returns the total number of bytes  available in a generation
 169   // for the allocation of objects.
 170   virtual size_t max_capacity() const;
 171 
 172   // If this is a young generation, the maximum number of bytes that can be
 173   // allocated in this generation before a GC is triggered.
 174   virtual size_t capacity_before_gc() const { return 0; }
 175 
 176   // The largest number of contiguous free bytes in the generation,
 177   // including expansion  (Assumes called at a safepoint.)
 178   virtual size_t contiguous_available() const = 0;
 179   // The largest number of contiguous free bytes in this or any higher generation.
 180   virtual size_t max_contiguous_available() const;
 181 
 182   // Returns true if promotions of the specified amount are
 183   // likely to succeed without a promotion failure.
 184   // Promotion of the full amount is not guaranteed but
 185   // might be attempted in the worst case.
 186   virtual bool promotion_attempt_is_safe(size_t max_promotion_in_bytes) const;
 187 
 188   // For a non-young generation, this interface can be used to inform a
 189   // generation that a promotion attempt into that generation failed.
 190   // Typically used to enable diagnostic output for post-mortem analysis,
 191   // but other uses of the interface are not ruled out.
 192   virtual void promotion_failure_occurred() { /* does nothing */ }
 193 
 194   // Return an estimate of the maximum allocation that could be performed
 195   // in the generation without triggering any collection or expansion
 196   // activity.  It is "unsafe" because no locks are taken; the result
 197   // should be treated as an approximation, not a guarantee, for use in
 198   // heuristic resizing decisions.
 199   virtual size_t unsafe_max_alloc_nogc() const = 0;
 200 
 201   // Returns true if this generation cannot be expanded further
 202   // without a GC. Override as appropriate.
 203   virtual bool is_maximal_no_gc() const {
 204     return _virtual_space.uncommitted_size() == 0;
 205   }
 206 
 207   MemRegion reserved() const { return _reserved; }
 208 
 209   // Returns a region guaranteed to contain all the objects in the
 210   // generation.
 211   virtual MemRegion used_region() const { return _reserved; }
 212 
 213   MemRegion prev_used_region() const { return _prev_used_region; }
 214   virtual void  save_used_region()   { _prev_used_region = used_region(); }
 215 
 216   // Returns "TRUE" iff "p" points into the committed areas in the generation.
 217   // For some kinds of generations, this may be an expensive operation.
 218   // To avoid performance problems stemming from its inadvertent use in
 219   // product jvm's, we restrict its use to assertion checking or
 220   // verification only.
 221   virtual bool is_in(const void* p) const;
 222 
 223   /* Returns "TRUE" iff "p" points into the reserved area of the generation. */
 224   bool is_in_reserved(const void* p) const {
 225     return _reserved.contains(p);
 226   }
 227 
 228   // If some space in the generation contains the given "addr", return a
 229   // pointer to that space, else return "NULL".
 230   virtual Space* space_containing(const void* addr) const;
 231 
 232   // Iteration - do not use for time critical operations
 233   virtual void space_iterate(SpaceClosure* blk, bool usedOnly = false) = 0;
 234 
 235   // Returns the first space, if any, in the generation that can participate
 236   // in compaction, or else "NULL".
 237   virtual CompactibleSpace* first_compaction_space() const = 0;
 238 
 239   // Returns "true" iff this generation should be used to allocate an
 240   // object of the given size.  Young generations might
 241   // wish to exclude very large objects, for example, since, if allocated
 242   // often, they would greatly increase the frequency of young-gen
 243   // collection.
 244   virtual bool should_allocate(size_t word_size, bool is_tlab) {
 245     bool result = false;
 246     size_t overflow_limit = (size_t)1 << (BitsPerSize_t - LogHeapWordSize);
 247     if (!is_tlab || supports_tlab_allocation()) {
 248       result = (word_size > 0) && (word_size < overflow_limit);
 249     }
 250     return result;
 251   }
 252 
 253   // Allocate and returns a block of the requested size, or returns "NULL".
 254   // Assumes the caller has done any necessary locking.
 255   virtual HeapWord* allocate(size_t word_size, bool is_tlab) = 0;
 256 
 257   // Like "allocate", but performs any necessary locking internally.
 258   virtual HeapWord* par_allocate(size_t word_size, bool is_tlab) = 0;
 259 
 260   // Some generation may offer a region for shared, contiguous allocation,
 261   // via inlined code (by exporting the address of the top and end fields
 262   // defining the extent of the contiguous allocation region.)
 263 
 264   // This function returns "true" iff the heap supports this kind of
 265   // allocation.  (More precisely, this means the style of allocation that
 266   // increments *top_addr()" with a CAS.) (Default is "no".)
 267   // A generation that supports this allocation style must use lock-free
 268   // allocation for *all* allocation, since there are times when lock free
 269   // allocation will be concurrent with plain "allocate" calls.
 270   virtual bool supports_inline_contig_alloc() const { return false; }
 271 
 272   // These functions return the addresses of the fields that define the
 273   // boundaries of the contiguous allocation area.  (These fields should be
 274   // physically near to one another.)
 275   virtual HeapWord** top_addr() const { return NULL; }
 276   virtual HeapWord** end_addr() const { return NULL; }
 277 
 278   // Thread-local allocation buffers
 279   virtual bool supports_tlab_allocation() const { return false; }
 280   virtual size_t tlab_capacity() const {
 281     guarantee(false, "Generation doesn't support thread local allocation buffers");
 282     return 0;
 283   }
 284   virtual size_t tlab_used() const {
 285     guarantee(false, "Generation doesn't support thread local allocation buffers");
 286     return 0;
 287   }
 288   virtual size_t unsafe_max_tlab_alloc() const {
 289     guarantee(false, "Generation doesn't support thread local allocation buffers");
 290     return 0;
 291   }
 292 
 293   // "obj" is the address of an object in a younger generation.  Allocate space
 294   // for "obj" in the current (or some higher) generation, and copy "obj" into
 295   // the newly allocated space, if possible, returning the result (or NULL if
 296   // the allocation failed).
 297   //
 298   // The "obj_size" argument is just obj->size(), passed along so the caller can
 299   // avoid repeating the virtual call to retrieve it.
 300   virtual oop promote(oop obj, size_t obj_size);
 301 
 302   // Thread "thread_num" (0 <= i < ParalleGCThreads) wants to promote
 303   // object "obj", whose original mark word was "m", and whose size is
 304   // "word_sz".  If possible, allocate space for "obj", copy obj into it
 305   // (taking care to copy "m" into the mark word when done, since the mark
 306   // word of "obj" may have been overwritten with a forwarding pointer, and
 307   // also taking care to copy the klass pointer *last*.  Returns the new
 308   // object if successful, or else NULL.
 309   virtual oop par_promote(int thread_num,
 310                           oop obj, markOop m, size_t word_sz);
 311 
 312   // Informs the current generation that all par_promote_alloc's in the
 313   // collection have been completed; any supporting data structures can be
 314   // reset.  Default is to do nothing.
 315   virtual void par_promote_alloc_done(int thread_num) {}
 316 
 317   // Informs the current generation that all oop_since_save_marks_iterates
 318   // performed by "thread_num" in the current collection, if any, have been
 319   // completed; any supporting data structures can be reset.  Default is to
 320   // do nothing.
 321   virtual void par_oop_since_save_marks_iterate_done(int thread_num) {}
 322 
 323   // This generation will collect all younger generations
 324   // during a full collection.
 325   virtual bool full_collects_younger_generations() const { return false; }
 326 
 327   // This generation does in-place marking, meaning that mark words
 328   // are mutated during the marking phase and presumably reinitialized
 329   // to a canonical value after the GC. This is currently used by the
 330   // biased locking implementation to determine whether additional
 331   // work is required during the GC prologue and epilogue.
 332   virtual bool performs_in_place_marking() const { return true; }
 333 
 334   // Returns "true" iff collect() should subsequently be called on this
 335   // this generation. See comment below.
 336   // This is a generic implementation which can be overridden.
 337   //
 338   // Note: in the current (1.4) implementation, when genCollectedHeap's
 339   // incremental_collection_will_fail flag is set, all allocations are
 340   // slow path (the only fast-path place to allocate is DefNew, which
 341   // will be full if the flag is set).
 342   // Thus, older generations which collect younger generations should
 343   // test this flag and collect if it is set.
 344   virtual bool should_collect(bool   full,
 345                               size_t word_size,
 346                               bool   is_tlab) {
 347     return (full || should_allocate(word_size, is_tlab));
 348   }
 349 
 350   // Returns true if the collection is likely to be safely
 351   // completed. Even if this method returns true, a collection
 352   // may not be guaranteed to succeed, and the system should be
 353   // able to safely unwind and recover from that failure, albeit
 354   // at some additional cost.
 355   virtual bool collection_attempt_is_safe() {
 356     guarantee(false, "Are you sure you want to call this method?");
 357     return true;
 358   }
 359 
 360   // Perform a garbage collection.
 361   // If full is true attempt a full garbage collection of this generation.
 362   // Otherwise, attempting to (at least) free enough space to support an
 363   // allocation of the given "word_size".
 364   virtual void collect(bool   full,
 365                        bool   clear_all_soft_refs,
 366                        size_t word_size,
 367                        bool   is_tlab) = 0;
 368 
 369   // Perform a heap collection, attempting to create (at least) enough
 370   // space to support an allocation of the given "word_size".  If
 371   // successful, perform the allocation and return the resulting
 372   // "oop" (initializing the allocated block). If the allocation is
 373   // still unsuccessful, return "NULL".
 374   virtual HeapWord* expand_and_allocate(size_t word_size,
 375                                         bool is_tlab,
 376                                         bool parallel = false) = 0;
 377 
 378   // Some generations may require some cleanup or preparation actions before
 379   // allowing a collection.  The default is to do nothing.
 380   virtual void gc_prologue(bool full) {};
 381 
 382   // Some generations may require some cleanup actions after a collection.
 383   // The default is to do nothing.
 384   virtual void gc_epilogue(bool full) {};
 385 
 386   // Save the high water marks for the used space in a generation.
 387   virtual void record_spaces_top() {};
 388 
 389   // Some generations may need to be "fixed-up" after some allocation
 390   // activity to make them parsable again. The default is to do nothing.
 391   virtual void ensure_parsability() {};
 392 
 393   // Time (in ms) when we were last collected or now if a collection is
 394   // in progress.
 395   virtual jlong time_of_last_gc(jlong now) {
 396     // Both _time_of_last_gc and now are set using a time source
 397     // that guarantees monotonically non-decreasing values provided
 398     // the underlying platform provides such a source. So we still
 399     // have to guard against non-monotonicity.
 400     NOT_PRODUCT(
 401       if (now < _time_of_last_gc) {
 402         warning("time warp: "INT64_FORMAT" to "INT64_FORMAT, (int64_t)_time_of_last_gc, (int64_t)now);
 403       }
 404     )
 405     return _time_of_last_gc;
 406   }
 407 
 408   virtual void update_time_of_last_gc(jlong now)  {
 409     _time_of_last_gc = now;
 410   }
 411 
 412   // Generations may keep statistics about collection.  This
 413   // method updates those statistics.  current_level is
 414   // the level of the collection that has most recently
 415   // occurred.  This allows the generation to decide what
 416   // statistics are valid to collect.  For example, the
 417   // generation can decide to gather the amount of promoted data
 418   // if the collection of the younger generations has completed.
 419   GCStats* gc_stats() const { return _gc_stats; }
 420   virtual void update_gc_stats(int current_level, bool full) {}
 421 
 422   // Mark sweep support phase2
 423   virtual void prepare_for_compaction(CompactPoint* cp);
 424   // Mark sweep support phase3
 425   virtual void adjust_pointers();
 426   // Mark sweep support phase4
 427   virtual void compact();
 428   virtual void post_compact() {ShouldNotReachHere();}
 429 
 430   // Support for CMS's rescan. In this general form we return a pointer
 431   // to an abstract object that can be used, based on specific previously
 432   // decided protocols, to exchange information between generations,
 433   // information that may be useful for speeding up certain types of
 434   // garbage collectors. A NULL value indicates to the client that
 435   // no data recording is expected by the provider. The data-recorder is
 436   // expected to be GC worker thread-local, with the worker index
 437   // indicated by "thr_num".
 438   virtual void* get_data_recorder(int thr_num) { return NULL; }
 439   virtual void sample_eden_chunk() {}
 440 
 441   // Some generations may require some cleanup actions before allowing
 442   // a verification.
 443   virtual void prepare_for_verify() {};
 444 
 445   // Accessing "marks".
 446 
 447   // This function gives a generation a chance to note a point between
 448   // collections.  For example, a contiguous generation might note the
 449   // beginning allocation point post-collection, which might allow some later
 450   // operations to be optimized.
 451   virtual void save_marks() {}
 452 
 453   // This function allows generations to initialize any "saved marks".  That
 454   // is, should only be called when the generation is empty.
 455   virtual void reset_saved_marks() {}
 456 
 457   // This function is "true" iff any no allocations have occurred in the
 458   // generation since the last call to "save_marks".
 459   virtual bool no_allocs_since_save_marks() = 0;
 460 
 461   // Apply "cl->apply" to (the addresses of) all reference fields in objects
 462   // allocated in the current generation since the last call to "save_marks".
 463   // If more objects are allocated in this generation as a result of applying
 464   // the closure, iterates over reference fields in those objects as well.
 465   // Calls "save_marks" at the end of the iteration.
 466   // General signature...
 467   virtual void oop_since_save_marks_iterate_v(OopsInGenClosure* cl) = 0;
 468   // ...and specializations for de-virtualization.  (The general
 469   // implementation of the _nv versions call the virtual version.
 470   // Note that the _nv suffix is not really semantically necessary,
 471   // but it avoids some not-so-useful warnings on Solaris.)
 472 #define Generation_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix)             \
 473   virtual void oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) {    \
 474     oop_since_save_marks_iterate_v((OopsInGenClosure*)cl);                      \
 475   }
 476   SPECIALIZED_SINCE_SAVE_MARKS_CLOSURES(Generation_SINCE_SAVE_MARKS_DECL)
 477 
 478 #undef Generation_SINCE_SAVE_MARKS_DECL
 479 
 480   // The "requestor" generation is performing some garbage collection
 481   // action for which it would be useful to have scratch space.  If
 482   // the target is not the requestor, no gc actions will be required
 483   // of the target.  The requestor promises to allocate no more than
 484   // "max_alloc_words" in the target generation (via promotion say,
 485   // if the requestor is a young generation and the target is older).
 486   // If the target generation can provide any scratch space, it adds
 487   // it to "list", leaving "list" pointing to the head of the
 488   // augmented list.  The default is to offer no space.
 489   virtual void contribute_scratch(ScratchBlock*& list, Generation* requestor,
 490                                   size_t max_alloc_words) {}
 491 
 492   // Give each generation an opportunity to do clean up for any
 493   // contributed scratch.
 494   virtual void reset_scratch() {};
 495 
 496   // When an older generation has been collected, and perhaps resized,
 497   // this method will be invoked on all younger generations (from older to
 498   // younger), allowing them to resize themselves as appropriate.
 499   virtual void compute_new_size() = 0;
 500 
 501   // Printing
 502   virtual const char* name() const = 0;
 503   virtual const char* short_name() const = 0;
 504 
 505   int level() const { return _level; }
 506 
 507   // Reference Processing accessor
 508   ReferenceProcessor* const ref_processor() { return _ref_processor; }
 509 
 510   // Iteration.
 511 
 512   // Iterate over all the ref-containing fields of all objects in the
 513   // generation, calling "cl.do_oop" on each.
 514   virtual void oop_iterate(ExtendedOopClosure* cl);
 515 
 516   // Iterate over all objects in the generation, calling "cl.do_object" on
 517   // each.
 518   virtual void object_iterate(ObjectClosure* cl);
 519 
 520   // Iterate over all safe objects in the generation, calling "cl.do_object" on
 521   // each.  An object is safe if its references point to other objects in
 522   // the heap.  This defaults to object_iterate() unless overridden.
 523   virtual void safe_object_iterate(ObjectClosure* cl);
 524 
 525   // Apply "cl->do_oop" to (the address of) all and only all the ref fields
 526   // in the current generation that contain pointers to objects in younger
 527   // generations. Objects allocated since the last "save_marks" call are
 528   // excluded.
 529   virtual void younger_refs_iterate(OopsInGenClosure* cl) = 0;
 530 
 531   // Inform a generation that it longer contains references to objects
 532   // in any younger generation.    [e.g. Because younger gens are empty,
 533   // clear the card table.]
 534   virtual void clear_remembered_set() { }
 535 
 536   // Inform a generation that some of its objects have moved.  [e.g. The
 537   // generation's spaces were compacted, invalidating the card table.]
 538   virtual void invalidate_remembered_set() { }
 539 
 540   // Block abstraction.
 541 
 542   // Returns the address of the start of the "block" that contains the
 543   // address "addr".  We say "blocks" instead of "object" since some heaps
 544   // may not pack objects densely; a chunk may either be an object or a
 545   // non-object.
 546   virtual HeapWord* block_start(const void* addr) const;
 547 
 548   // Requires "addr" to be the start of a chunk, and returns its size.
 549   // "addr + size" is required to be the start of a new chunk, or the end
 550   // of the active area of the heap.
 551   virtual size_t block_size(const HeapWord* addr) const ;
 552 
 553   // Requires "addr" to be the start of a block, and returns "TRUE" iff
 554   // the block is an object.
 555   virtual bool block_is_obj(const HeapWord* addr) const;
 556 
 557 
 558   // PrintGC, PrintGCDetails support
 559   void print_heap_change(size_t prev_used) const;
 560 
 561   // PrintHeapAtGC support
 562   virtual void print() const;
 563   virtual void print_on(outputStream* st) const;
 564 
 565   virtual void verify() = 0;
 566 
 567   struct StatRecord {
 568     int invocations;
 569     elapsedTimer accumulated_time;
 570     StatRecord() :
 571       invocations(0),
 572       accumulated_time(elapsedTimer()) {}
 573   };
 574 private:
 575   StatRecord _stat_record;
 576 public:
 577   StatRecord* stat_record() { return &_stat_record; }
 578 
 579   virtual void print_summary_info();
 580   virtual void print_summary_info_on(outputStream* st);
 581 
 582   // Performance Counter support
 583   virtual void update_counters() = 0;
 584   virtual CollectorCounters* counters() { return _gc_counters; }
 585 };
 586 
 587 #endif // SHARE_VM_MEMORY_GENERATION_HPP