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