1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   6  * under the terms of the GNU General Public License version 2 only, as
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  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).
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  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 //   - OneContigSpaceCardGeneration - abstract class holding a single
  49 //                                    contiguous space with card marking
  50 //     - TenuredGeneration         - tenured (old object) space (markSweepCompact)
  51 //   - ConcurrentMarkSweepGeneration - Mostly Concurrent Mark Sweep Generation
  52 //                                       (Detlefs-Printezis refinement of
  53 //                                       Boehm-Demers-Schenker)
  54 //
  55 // The system configurations currently allowed are:
  56 //
  57 //   DefNewGeneration + TenuredGeneration
  58 //   DefNewGeneration + ConcurrentMarkSweepGeneration
  59 //
  60 //   ParNewGeneration + TenuredGeneration
  61 //   ParNewGeneration + ConcurrentMarkSweepGeneration
  62 //
  63 
  64 class DefNewGeneration;
  65 class GenerationSpec;
  66 class CompactibleSpace;
  67 class ContiguousSpace;
  68 class CompactPoint;
  69 class OopsInGenClosure;
  70 class OopClosure;
  71 class ScanClosure;
  72 class FastScanClosure;
  73 class GenCollectedHeap;
  74 class GenRemSet;
  75 class GCStats;
  76 
  77 // A "ScratchBlock" represents a block of memory in one generation usable by
  78 // another.  It represents "num_words" free words, starting at and including
  79 // the address of "this".
  80 struct ScratchBlock {
  81   ScratchBlock* next;
  82   size_t num_words;
  83   HeapWord scratch_space[1];  // Actually, of size "num_words-2" (assuming
  84                               // first two fields are word-sized.)
  85 };
  86 
  87 
  88 class Generation: public CHeapObj<mtGC> {
  89   friend class VMStructs;
  90  private:
  91   jlong _time_of_last_gc; // time when last gc on this generation happened (ms)
  92   MemRegion _prev_used_region; // for collectors that want to "remember" a value for
  93                                // used region at some specific point during collection.
  94 
  95  protected:
  96   // Minimum and maximum addresses for memory reserved (not necessarily
  97   // committed) for generation.
  98   // Used by card marking code. Must not overlap with address ranges of
  99   // other generations.
 100   MemRegion _reserved;
 101 
 102   // Memory area reserved for generation
 103   VirtualSpace _virtual_space;
 104 
 105   // Level in the generation hierarchy.
 106   int _level;
 107 
 108   // ("Weak") Reference processing support
 109   ReferenceProcessor* _ref_processor;
 110 
 111   // Performance Counters
 112   CollectorCounters* _gc_counters;
 113 
 114   // Statistics for garbage collection
 115   GCStats* _gc_stats;
 116 
 117   // Returns the next generation in the configuration, or else NULL if this
 118   // is the highest generation.
 119   Generation* next_gen() const;
 120 
 121   // Initialize the generation.
 122   Generation(ReservedSpace rs, size_t initial_byte_size, int level);
 123 
 124   // Apply "cl->do_oop" to (the address of) (exactly) all the ref fields in
 125   // "sp" that point into younger generations.
 126   // The iteration is only over objects allocated at the start of the
 127   // iterations; objects allocated as a result of applying the closure are
 128   // not included.
 129   void younger_refs_in_space_iterate(Space* sp, OopsInGenClosure* cl);
 130 
 131  public:
 132   // The set of possible generation kinds.
 133   enum Name {
 134     ASParNew,
 135     ASConcurrentMarkSweep,
 136     DefNew,
 137     ParNew,
 138     MarkSweepCompact,
 139     ConcurrentMarkSweep,
 140     Other
 141   };
 142 
 143   enum SomePublicConstants {
 144     // Generations are GenGrain-aligned and have size that are multiples of
 145     // GenGrain.
 146     // Note: on ARM we add 1 bit for card_table_base to be properly aligned
 147     // (we expect its low byte to be zero - see implementation of post_barrier)
 148     LogOfGenGrain = 16 ARM_ONLY(+1),
 149     GenGrain = 1 << LogOfGenGrain
 150   };
 151 
 152   // allocate and initialize ("weak") refs processing support
 153   virtual void ref_processor_init();
 154   void set_ref_processor(ReferenceProcessor* rp) {
 155     assert(_ref_processor == NULL, "clobbering existing _ref_processor");
 156     _ref_processor = rp;
 157   }
 158 
 159   virtual Generation::Name kind() { return Generation::Other; }
 160   GenerationSpec* spec();
 161 
 162   // This properly belongs in the collector, but for now this
 163   // will do.
 164   virtual bool refs_discovery_is_atomic() const { return true;  }
 165   virtual bool refs_discovery_is_mt()     const { return false; }
 166 
 167   // Space enquiries (results in bytes)
 168   virtual size_t capacity() const = 0;  // The maximum number of object bytes the
 169                                         // generation can currently hold.
 170   virtual size_t used() const = 0;      // The number of used bytes in the gen.
 171   virtual size_t free() const = 0;      // The number of free bytes in the gen.
 172 
 173   // Support for java.lang.Runtime.maxMemory(); see CollectedHeap.
 174   // Returns the total number of bytes  available in a generation
 175   // for the allocation of objects.
 176   virtual size_t max_capacity() const;
 177 
 178   // If this is a young generation, the maximum number of bytes that can be
 179   // allocated in this generation before a GC is triggered.
 180   virtual size_t capacity_before_gc() const { return 0; }
 181 
 182   // The largest number of contiguous free bytes in the generation,
 183   // including expansion  (Assumes called at a safepoint.)
 184   virtual size_t contiguous_available() const = 0;
 185   // The largest number of contiguous free bytes in this or any higher generation.
 186   virtual size_t max_contiguous_available() const;
 187 
 188   // Returns true if promotions of the specified amount are
 189   // likely to succeed without a promotion failure.
 190   // Promotion of the full amount is not guaranteed but
 191   // might be attempted in the worst case.
 192   virtual bool promotion_attempt_is_safe(size_t max_promotion_in_bytes) const;
 193 
 194   // For a non-young generation, this interface can be used to inform a
 195   // generation that a promotion attempt into that generation failed.
 196   // Typically used to enable diagnostic output for post-mortem analysis,
 197   // but other uses of the interface are not ruled out.
 198   virtual void promotion_failure_occurred() { /* does nothing */ }
 199 
 200   // Return an estimate of the maximum allocation that could be performed
 201   // in the generation without triggering any collection or expansion
 202   // activity.  It is "unsafe" because no locks are taken; the result
 203   // should be treated as an approximation, not a guarantee, for use in
 204   // heuristic resizing decisions.
 205   virtual size_t unsafe_max_alloc_nogc() const = 0;
 206 
 207   // Returns true if this generation cannot be expanded further
 208   // without a GC. Override as appropriate.
 209   virtual bool is_maximal_no_gc() const {
 210     return _virtual_space.uncommitted_size() == 0;
 211   }
 212 
 213   MemRegion reserved() const { return _reserved; }
 214 
 215   // Returns a region guaranteed to contain all the objects in the
 216   // generation.
 217   virtual MemRegion used_region() const { return _reserved; }
 218 
 219   MemRegion prev_used_region() const { return _prev_used_region; }
 220   virtual void  save_used_region()   { _prev_used_region = used_region(); }
 221 
 222   // Returns "TRUE" iff "p" points into the committed areas in the generation.
 223   // For some kinds of generations, this may be an expensive operation.
 224   // To avoid performance problems stemming from its inadvertent use in
 225   // product jvm's, we restrict its use to assertion checking or
 226   // verification only.
 227   virtual bool is_in(const void* p) const;
 228 
 229   /* Returns "TRUE" iff "p" points into the reserved area of the generation. */
 230   bool is_in_reserved(const void* p) const {
 231     return _reserved.contains(p);
 232   }
 233 
 234   // Check that the generation kind is DefNewGeneration or a sub
 235   // class of DefNewGeneration and return a DefNewGeneration*
 236   DefNewGeneration*  as_DefNewGeneration();
 237 
 238   // If some space in the generation contains the given "addr", return a
 239   // pointer to that space, else return "NULL".
 240   virtual Space* space_containing(const void* addr) const;
 241 
 242   // Iteration - do not use for time critical operations
 243   virtual void space_iterate(SpaceClosure* blk, bool usedOnly = false) = 0;
 244 
 245   // Returns the first space, if any, in the generation that can participate
 246   // in compaction, or else "NULL".
 247   virtual CompactibleSpace* first_compaction_space() const = 0;
 248 
 249   // Returns "true" iff this generation should be used to allocate an
 250   // object of the given size.  Young generations might
 251   // wish to exclude very large objects, for example, since, if allocated
 252   // often, they would greatly increase the frequency of young-gen
 253   // collection.
 254   virtual bool should_allocate(size_t word_size, bool is_tlab) {
 255     bool result = false;
 256     size_t overflow_limit = (size_t)1 << (BitsPerSize_t - LogHeapWordSize);
 257     if (!is_tlab || supports_tlab_allocation()) {
 258       result = (word_size > 0) && (word_size < overflow_limit);
 259     }
 260     return result;
 261   }
 262 
 263   // Allocate and returns a block of the requested size, or returns "NULL".
 264   // Assumes the caller has done any necessary locking.
 265   virtual HeapWord* allocate(size_t word_size, bool is_tlab) = 0;
 266 
 267   // Like "allocate", but performs any necessary locking internally.
 268   virtual HeapWord* par_allocate(size_t word_size, bool is_tlab) = 0;
 269 
 270   // A 'younger' gen has reached an allocation limit, and uses this to notify
 271   // the next older gen.  The return value is a new limit, or NULL if none.  The
 272   // caller must do the necessary locking.
 273   virtual HeapWord* allocation_limit_reached(Space* space, HeapWord* top,
 274                                              size_t word_size) {
 275     return NULL;
 276   }
 277 
 278   // Some generation may offer a region for shared, contiguous allocation,
 279   // via inlined code (by exporting the address of the top and end fields
 280   // defining the extent of the contiguous allocation region.)
 281 
 282   // This function returns "true" iff the heap supports this kind of
 283   // allocation.  (More precisely, this means the style of allocation that
 284   // increments *top_addr()" with a CAS.) (Default is "no".)
 285   // A generation that supports this allocation style must use lock-free
 286   // allocation for *all* allocation, since there are times when lock free
 287   // allocation will be concurrent with plain "allocate" calls.
 288   virtual bool supports_inline_contig_alloc() const { return false; }
 289 
 290   // These functions return the addresses of the fields that define the
 291   // boundaries of the contiguous allocation area.  (These fields should be
 292   // physicall near to one another.)
 293   virtual HeapWord** top_addr() const { return NULL; }
 294   virtual HeapWord** end_addr() const { return NULL; }
 295 
 296   // Thread-local allocation buffers
 297   virtual bool supports_tlab_allocation() const { return false; }
 298   virtual size_t tlab_capacity() const {
 299     guarantee(false, "Generation doesn't support thread local allocation buffers");
 300     return 0;
 301   }
 302   virtual size_t tlab_used() const {
 303     guarantee(false, "Generation doesn't support thread local allocation buffers");
 304     return 0;
 305   }
 306   virtual size_t unsafe_max_tlab_alloc() const {
 307     guarantee(false, "Generation doesn't support thread local allocation buffers");
 308     return 0;
 309   }
 310 
 311   // "obj" is the address of an object in a younger generation.  Allocate space
 312   // for "obj" in the current (or some higher) generation, and copy "obj" into
 313   // the newly allocated space, if possible, returning the result (or NULL if
 314   // the allocation failed).
 315   //
 316   // The "obj_size" argument is just obj->size(), passed along so the caller can
 317   // avoid repeating the virtual call to retrieve it.
 318   virtual oop promote(oop obj, size_t obj_size);
 319 
 320   // Thread "thread_num" (0 <= i < ParalleGCThreads) wants to promote
 321   // object "obj", whose original mark word was "m", and whose size is
 322   // "word_sz".  If possible, allocate space for "obj", copy obj into it
 323   // (taking care to copy "m" into the mark word when done, since the mark
 324   // word of "obj" may have been overwritten with a forwarding pointer, and
 325   // also taking care to copy the klass pointer *last*.  Returns the new
 326   // object if successful, or else NULL.
 327   virtual oop par_promote(int thread_num,
 328                           oop obj, markOop m, size_t word_sz);
 329 
 330   // Undo, if possible, the most recent par_promote_alloc allocation by
 331   // "thread_num" ("obj", of "word_sz").
 332   virtual void par_promote_alloc_undo(int thread_num,
 333                                       HeapWord* obj, size_t word_sz);
 334 
 335   // Informs the current generation that all par_promote_alloc's in the
 336   // collection have been completed; any supporting data structures can be
 337   // reset.  Default is to do nothing.
 338   virtual void par_promote_alloc_done(int thread_num) {}
 339 
 340   // Informs the current generation that all oop_since_save_marks_iterates
 341   // performed by "thread_num" in the current collection, if any, have been
 342   // completed; any supporting data structures can be reset.  Default is to
 343   // do nothing.
 344   virtual void par_oop_since_save_marks_iterate_done(int thread_num) {}
 345 
 346   // This generation will collect all younger generations
 347   // during a full collection.
 348   virtual bool full_collects_younger_generations() const { return false; }
 349 
 350   // This generation does in-place marking, meaning that mark words
 351   // are mutated during the marking phase and presumably reinitialized
 352   // to a canonical value after the GC. This is currently used by the
 353   // biased locking implementation to determine whether additional
 354   // work is required during the GC prologue and epilogue.
 355   virtual bool performs_in_place_marking() const { return true; }
 356 
 357   // Returns "true" iff collect() should subsequently be called on this
 358   // this generation. See comment below.
 359   // This is a generic implementation which can be overridden.
 360   //
 361   // Note: in the current (1.4) implementation, when genCollectedHeap's
 362   // incremental_collection_will_fail flag is set, all allocations are
 363   // slow path (the only fast-path place to allocate is DefNew, which
 364   // will be full if the flag is set).
 365   // Thus, older generations which collect younger generations should
 366   // test this flag and collect if it is set.
 367   virtual bool should_collect(bool   full,
 368                               size_t word_size,
 369                               bool   is_tlab) {
 370     return (full || should_allocate(word_size, is_tlab));
 371   }
 372 
 373   // Returns true if the collection is likely to be safely
 374   // completed. Even if this method returns true, a collection
 375   // may not be guaranteed to succeed, and the system should be
 376   // able to safely unwind and recover from that failure, albeit
 377   // at some additional cost.
 378   virtual bool collection_attempt_is_safe() {
 379     guarantee(false, "Are you sure you want to call this method?");
 380     return true;
 381   }
 382 
 383   // Perform a garbage collection.
 384   // If full is true attempt a full garbage collection of this generation.
 385   // Otherwise, attempting to (at least) free enough space to support an
 386   // allocation of the given "word_size".
 387   virtual void collect(bool   full,
 388                        bool   clear_all_soft_refs,
 389                        size_t word_size,
 390                        bool   is_tlab) = 0;
 391 
 392   // Perform a heap collection, attempting to create (at least) enough
 393   // space to support an allocation of the given "word_size".  If
 394   // successful, perform the allocation and return the resulting
 395   // "oop" (initializing the allocated block). If the allocation is
 396   // still unsuccessful, return "NULL".
 397   virtual HeapWord* expand_and_allocate(size_t word_size,
 398                                         bool is_tlab,
 399                                         bool parallel = false) = 0;
 400 
 401   // Some generations may require some cleanup or preparation actions before
 402   // allowing a collection.  The default is to do nothing.
 403   virtual void gc_prologue(bool full) {};
 404 
 405   // Some generations may require some cleanup actions after a collection.
 406   // The default is to do nothing.
 407   virtual void gc_epilogue(bool full) {};
 408 
 409   // Save the high water marks for the used space in a generation.
 410   virtual void record_spaces_top() {};
 411 
 412   // Some generations may need to be "fixed-up" after some allocation
 413   // activity to make them parsable again. The default is to do nothing.
 414   virtual void ensure_parsability() {};
 415 
 416   // Time (in ms) when we were last collected or now if a collection is
 417   // in progress.
 418   virtual jlong time_of_last_gc(jlong now) {
 419     // Both _time_of_last_gc and now are set using a time source
 420     // that guarantees monotonically non-decreasing values provided
 421     // the underlying platform provides such a source. So we still
 422     // have to guard against non-monotonicity.
 423     NOT_PRODUCT(
 424       if (now < _time_of_last_gc) {
 425         warning("time warp: "INT64_FORMAT" to "INT64_FORMAT, (int64_t)_time_of_last_gc, (int64_t)now);
 426       }
 427     )
 428     return _time_of_last_gc;
 429   }
 430 
 431   virtual void update_time_of_last_gc(jlong now)  {
 432     _time_of_last_gc = now;
 433   }
 434 
 435   // Generations may keep statistics about collection.  This
 436   // method updates those statistics.  current_level is
 437   // the level of the collection that has most recently
 438   // occurred.  This allows the generation to decide what
 439   // statistics are valid to collect.  For example, the
 440   // generation can decide to gather the amount of promoted data
 441   // if the collection of the younger generations has completed.
 442   GCStats* gc_stats() const { return _gc_stats; }
 443   virtual void update_gc_stats(int current_level, bool full) {}
 444 
 445   // Mark sweep support phase2
 446   virtual void prepare_for_compaction(CompactPoint* cp);
 447   // Mark sweep support phase3
 448   virtual void adjust_pointers();
 449   // Mark sweep support phase4
 450   virtual void compact();
 451   virtual void post_compact() {ShouldNotReachHere();}
 452 
 453   // Support for CMS's rescan. In this general form we return a pointer
 454   // to an abstract object that can be used, based on specific previously
 455   // decided protocols, to exchange information between generations,
 456   // information that may be useful for speeding up certain types of
 457   // garbage collectors. A NULL value indicates to the client that
 458   // no data recording is expected by the provider. The data-recorder is
 459   // expected to be GC worker thread-local, with the worker index
 460   // indicated by "thr_num".
 461   virtual void* get_data_recorder(int thr_num) { return NULL; }
 462   virtual void sample_eden_chunk() {}
 463 
 464   // Some generations may require some cleanup actions before allowing
 465   // a verification.
 466   virtual void prepare_for_verify() {};
 467 
 468   // Accessing "marks".
 469 
 470   // This function gives a generation a chance to note a point between
 471   // collections.  For example, a contiguous generation might note the
 472   // beginning allocation point post-collection, which might allow some later
 473   // operations to be optimized.
 474   virtual void save_marks() {}
 475 
 476   // This function allows generations to initialize any "saved marks".  That
 477   // is, should only be called when the generation is empty.
 478   virtual void reset_saved_marks() {}
 479 
 480   // This function is "true" iff any no allocations have occurred in the
 481   // generation since the last call to "save_marks".
 482   virtual bool no_allocs_since_save_marks() = 0;
 483 
 484   // Apply "cl->apply" to (the addresses of) all reference fields in objects
 485   // allocated in the current generation since the last call to "save_marks".
 486   // If more objects are allocated in this generation as a result of applying
 487   // the closure, iterates over reference fields in those objects as well.
 488   // Calls "save_marks" at the end of the iteration.
 489   // General signature...
 490   virtual void oop_since_save_marks_iterate_v(OopsInGenClosure* cl) = 0;
 491   // ...and specializations for de-virtualization.  (The general
 492   // implemention of the _nv versions call the virtual version.
 493   // Note that the _nv suffix is not really semantically necessary,
 494   // but it avoids some not-so-useful warnings on Solaris.)
 495 #define Generation_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix)             \
 496   virtual void oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) {    \
 497     oop_since_save_marks_iterate_v((OopsInGenClosure*)cl);                      \
 498   }
 499   SPECIALIZED_SINCE_SAVE_MARKS_CLOSURES(Generation_SINCE_SAVE_MARKS_DECL)
 500 
 501 #undef Generation_SINCE_SAVE_MARKS_DECL
 502 
 503   // The "requestor" generation is performing some garbage collection
 504   // action for which it would be useful to have scratch space.  If
 505   // the target is not the requestor, no gc actions will be required
 506   // of the target.  The requestor promises to allocate no more than
 507   // "max_alloc_words" in the target generation (via promotion say,
 508   // if the requestor is a young generation and the target is older).
 509   // If the target generation can provide any scratch space, it adds
 510   // it to "list", leaving "list" pointing to the head of the
 511   // augmented list.  The default is to offer no space.
 512   virtual void contribute_scratch(ScratchBlock*& list, Generation* requestor,
 513                                   size_t max_alloc_words) {}
 514 
 515   // Give each generation an opportunity to do clean up for any
 516   // contributed scratch.
 517   virtual void reset_scratch() {};
 518 
 519   // When an older generation has been collected, and perhaps resized,
 520   // this method will be invoked on all younger generations (from older to
 521   // younger), allowing them to resize themselves as appropriate.
 522   virtual void compute_new_size() = 0;
 523 
 524   // Printing
 525   virtual const char* name() const = 0;
 526   virtual const char* short_name() const = 0;
 527 
 528   int level() const { return _level; }
 529 
 530   // Attributes
 531 
 532   // True iff the given generation may only be the youngest generation.
 533   virtual bool must_be_youngest() const = 0;
 534   // True iff the given generation may only be the oldest generation.
 535   virtual bool must_be_oldest() const = 0;
 536 
 537   // Reference Processing accessor
 538   ReferenceProcessor* const ref_processor() { return _ref_processor; }
 539 
 540   // Iteration.
 541 
 542   // Iterate over all the ref-containing fields of all objects in the
 543   // generation, calling "cl.do_oop" on each.
 544   virtual void oop_iterate(ExtendedOopClosure* cl);
 545 
 546   // Iterate over all objects in the generation, calling "cl.do_object" on
 547   // each.
 548   virtual void object_iterate(ObjectClosure* cl);
 549 
 550   // Iterate over all safe objects in the generation, calling "cl.do_object" on
 551   // each.  An object is safe if its references point to other objects in
 552   // the heap.  This defaults to object_iterate() unless overridden.
 553   virtual void safe_object_iterate(ObjectClosure* cl);
 554 
 555   // Apply "cl->do_oop" to (the address of) all and only all the ref fields
 556   // in the current generation that contain pointers to objects in younger
 557   // generations. Objects allocated since the last "save_marks" call are
 558   // excluded.
 559   virtual void younger_refs_iterate(OopsInGenClosure* cl) = 0;
 560 
 561   // Inform a generation that it longer contains references to objects
 562   // in any younger generation.    [e.g. Because younger gens are empty,
 563   // clear the card table.]
 564   virtual void clear_remembered_set() { }
 565 
 566   // Inform a generation that some of its objects have moved.  [e.g. The
 567   // generation's spaces were compacted, invalidating the card table.]
 568   virtual void invalidate_remembered_set() { }
 569 
 570   // Block abstraction.
 571 
 572   // Returns the address of the start of the "block" that contains the
 573   // address "addr".  We say "blocks" instead of "object" since some heaps
 574   // may not pack objects densely; a chunk may either be an object or a
 575   // non-object.
 576   virtual HeapWord* block_start(const void* addr) const;
 577 
 578   // Requires "addr" to be the start of a chunk, and returns its size.
 579   // "addr + size" is required to be the start of a new chunk, or the end
 580   // of the active area of the heap.
 581   virtual size_t block_size(const HeapWord* addr) const ;
 582 
 583   // Requires "addr" to be the start of a block, and returns "TRUE" iff
 584   // the block is an object.
 585   virtual bool block_is_obj(const HeapWord* addr) const;
 586 
 587 
 588   // PrintGC, PrintGCDetails support
 589   void print_heap_change(size_t prev_used) const;
 590 
 591   // PrintHeapAtGC support
 592   virtual void print() const;
 593   virtual void print_on(outputStream* st) const;
 594 
 595   virtual void verify() = 0;
 596 
 597   struct StatRecord {
 598     int invocations;
 599     elapsedTimer accumulated_time;
 600     StatRecord() :
 601       invocations(0),
 602       accumulated_time(elapsedTimer()) {}
 603   };
 604 private:
 605   StatRecord _stat_record;
 606 public:
 607   StatRecord* stat_record() { return &_stat_record; }
 608 
 609   virtual void print_summary_info();
 610   virtual void print_summary_info_on(outputStream* st);
 611 
 612   // Performance Counter support
 613   virtual void update_counters() = 0;
 614   virtual CollectorCounters* counters() { return _gc_counters; }
 615 };
 616 
 617 // Class CardGeneration is a generation that is covered by a card table,
 618 // and uses a card-size block-offset array to implement block_start.
 619 
 620 // class BlockOffsetArray;
 621 // class BlockOffsetArrayContigSpace;
 622 class BlockOffsetSharedArray;
 623 
 624 class CardGeneration: public Generation {
 625   friend class VMStructs;
 626  protected:
 627   // This is shared with other generations.
 628   GenRemSet* _rs;
 629   // This is local to this generation.
 630   BlockOffsetSharedArray* _bts;
 631 
 632   // current shrinking effect: this damps shrinking when the heap gets empty.
 633   size_t _shrink_factor;
 634 
 635   size_t _min_heap_delta_bytes;   // Minimum amount to expand.
 636 
 637   // Some statistics from before gc started.
 638   // These are gathered in the gc_prologue (and should_collect)
 639   // to control growing/shrinking policy in spite of promotions.
 640   size_t _capacity_at_prologue;
 641   size_t _used_at_prologue;
 642 
 643   CardGeneration(ReservedSpace rs, size_t initial_byte_size, int level,
 644                  GenRemSet* remset);
 645 
 646  public:
 647 
 648   // Attempt to expand the generation by "bytes".  Expand by at a
 649   // minimum "expand_bytes".  Return true if some amount (not
 650   // necessarily the full "bytes") was done.
 651   virtual bool expand(size_t bytes, size_t expand_bytes);
 652 
 653   // Shrink generation with specified size (returns false if unable to shrink)
 654   virtual void shrink(size_t bytes) = 0;
 655 
 656   virtual void compute_new_size();
 657 
 658   virtual void clear_remembered_set();
 659 
 660   virtual void invalidate_remembered_set();
 661 
 662   virtual void prepare_for_verify();
 663 
 664   // Grow generation with specified size (returns false if unable to grow)
 665   virtual bool grow_by(size_t bytes) = 0;
 666   // Grow generation to reserved size.
 667   virtual bool grow_to_reserved() = 0;
 668 };
 669 
 670 // OneContigSpaceCardGeneration models a heap of old objects contained in a single
 671 // contiguous space.
 672 //
 673 // Garbage collection is performed using mark-compact.
 674 
 675 class OneContigSpaceCardGeneration: public CardGeneration {
 676   friend class VMStructs;
 677   // Abstractly, this is a subtype that gets access to protected fields.
 678   friend class VM_PopulateDumpSharedSpace;
 679 
 680  protected:
 681   ContiguousSpace*  _the_space;       // actual space holding objects
 682   WaterMark  _last_gc;                // watermark between objects allocated before
 683                                       // and after last GC.
 684 
 685   // Grow generation with specified size (returns false if unable to grow)
 686   virtual bool grow_by(size_t bytes);
 687   // Grow generation to reserved size.
 688   virtual bool grow_to_reserved();
 689   // Shrink generation with specified size (returns false if unable to shrink)
 690   void shrink_by(size_t bytes);
 691 
 692   // Allocation failure
 693   virtual bool expand(size_t bytes, size_t expand_bytes);
 694   void shrink(size_t bytes);
 695 
 696   // Accessing spaces
 697   ContiguousSpace* the_space() const { return _the_space; }
 698 
 699  public:
 700   OneContigSpaceCardGeneration(ReservedSpace rs, size_t initial_byte_size,
 701                                int level, GenRemSet* remset,
 702                                ContiguousSpace* space) :
 703     CardGeneration(rs, initial_byte_size, level, remset),
 704     _the_space(space)
 705   {}
 706 
 707   inline bool is_in(const void* p) const;
 708 
 709   // Space enquiries
 710   size_t capacity() const;
 711   size_t used() const;
 712   size_t free() const;
 713 
 714   MemRegion used_region() const;
 715 
 716   size_t unsafe_max_alloc_nogc() const;
 717   size_t contiguous_available() const;
 718 
 719   // Iteration
 720   void object_iterate(ObjectClosure* blk);
 721   void space_iterate(SpaceClosure* blk, bool usedOnly = false);
 722 
 723   void younger_refs_iterate(OopsInGenClosure* blk);
 724 
 725   inline CompactibleSpace* first_compaction_space() const;
 726 
 727   virtual inline HeapWord* allocate(size_t word_size, bool is_tlab);
 728   virtual inline HeapWord* par_allocate(size_t word_size, bool is_tlab);
 729 
 730   // Accessing marks
 731   inline WaterMark top_mark();
 732   inline WaterMark bottom_mark();
 733 
 734 #define OneContig_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix)      \
 735   void oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl);
 736   OneContig_SINCE_SAVE_MARKS_DECL(OopsInGenClosure,_v)
 737   SPECIALIZED_SINCE_SAVE_MARKS_CLOSURES(OneContig_SINCE_SAVE_MARKS_DECL)
 738 
 739   void save_marks();
 740   void reset_saved_marks();
 741   bool no_allocs_since_save_marks();
 742 
 743   inline size_t block_size(const HeapWord* addr) const;
 744 
 745   inline bool block_is_obj(const HeapWord* addr) const;
 746 
 747   virtual void collect(bool full,
 748                        bool clear_all_soft_refs,
 749                        size_t size,
 750                        bool is_tlab);
 751   HeapWord* expand_and_allocate(size_t size,
 752                                 bool is_tlab,
 753                                 bool parallel = false);
 754 
 755   virtual void prepare_for_verify();
 756 
 757   virtual void gc_epilogue(bool full);
 758 
 759   virtual void record_spaces_top();
 760 
 761   virtual void verify();
 762   virtual void print_on(outputStream* st) const;
 763 };
 764 
 765 #endif // SHARE_VM_MEMORY_GENERATION_HPP