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