1 /*
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   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.
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   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  *
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  24 
  25 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_HEAPREGION_HPP
  26 #define SHARE_VM_GC_IMPLEMENTATION_G1_HEAPREGION_HPP
  27 
  28 #include "gc_implementation/g1/g1BlockOffsetTable.inline.hpp"
  29 #include "gc_implementation/g1/g1_specialized_oop_closures.hpp"
  30 #include "gc_implementation/g1/survRateGroup.hpp"
  31 #include "gc_implementation/shared/ageTable.hpp"
  32 #include "gc_implementation/shared/spaceDecorator.hpp"
  33 #include "memory/space.inline.hpp"
  34 #include "memory/watermark.hpp"
  35 
  36 #ifndef SERIALGC
  37 
  38 // A HeapRegion is the smallest piece of a G1CollectedHeap that
  39 // can be collected independently.
  40 
  41 // NOTE: Although a HeapRegion is a Space, its
  42 // Space::initDirtyCardClosure method must not be called.
  43 // The problem is that the existence of this method breaks
  44 // the independence of barrier sets from remembered sets.
  45 // The solution is to remove this method from the definition
  46 // of a Space.
  47 
  48 class CompactibleSpace;
  49 class ContiguousSpace;
  50 class HeapRegionRemSet;
  51 class HeapRegionRemSetIterator;
  52 class HeapRegion;
  53 class HeapRegionSetBase;
  54 
  55 #define HR_FORMAT SIZE_FORMAT":(%s)["PTR_FORMAT","PTR_FORMAT","PTR_FORMAT"]"
  56 #define HR_FORMAT_PARAMS(_hr_) \
  57                 (_hr_)->hrs_index(), \
  58                 (_hr_)->is_survivor() ? "S" : (_hr_)->is_young() ? "E" : "-", \
  59                 (_hr_)->bottom(), (_hr_)->top(), (_hr_)->end()
  60 
  61 // A dirty card to oop closure for heap regions. It
  62 // knows how to get the G1 heap and how to use the bitmap
  63 // in the concurrent marker used by G1 to filter remembered
  64 // sets.
  65 
  66 class HeapRegionDCTOC : public ContiguousSpaceDCTOC {
  67 public:
  68   // Specification of possible DirtyCardToOopClosure filtering.
  69   enum FilterKind {
  70     NoFilterKind,
  71     IntoCSFilterKind,
  72     OutOfRegionFilterKind
  73   };
  74 
  75 protected:
  76   HeapRegion* _hr;
  77   FilterKind _fk;
  78   G1CollectedHeap* _g1;
  79 
  80   void walk_mem_region_with_cl(MemRegion mr,
  81                                HeapWord* bottom, HeapWord* top,
  82                                OopClosure* cl);
  83 
  84   // We don't specialize this for FilteringClosure; filtering is handled by
  85   // the "FilterKind" mechanism.  But we provide this to avoid a compiler
  86   // warning.
  87   void walk_mem_region_with_cl(MemRegion mr,
  88                                HeapWord* bottom, HeapWord* top,
  89                                FilteringClosure* cl) {
  90     HeapRegionDCTOC::walk_mem_region_with_cl(mr, bottom, top,
  91                                                        (OopClosure*)cl);
  92   }
  93 
  94   // Get the actual top of the area on which the closure will
  95   // operate, given where the top is assumed to be (the end of the
  96   // memory region passed to do_MemRegion) and where the object
  97   // at the top is assumed to start. For example, an object may
  98   // start at the top but actually extend past the assumed top,
  99   // in which case the top becomes the end of the object.
 100   HeapWord* get_actual_top(HeapWord* top, HeapWord* top_obj) {
 101     return ContiguousSpaceDCTOC::get_actual_top(top, top_obj);
 102   }
 103 
 104   // Walk the given memory region from bottom to (actual) top
 105   // looking for objects and applying the oop closure (_cl) to
 106   // them. The base implementation of this treats the area as
 107   // blocks, where a block may or may not be an object. Sub-
 108   // classes should override this to provide more accurate
 109   // or possibly more efficient walking.
 110   void walk_mem_region(MemRegion mr, HeapWord* bottom, HeapWord* top) {
 111     Filtering_DCTOC::walk_mem_region(mr, bottom, top);
 112   }
 113 
 114 public:
 115   HeapRegionDCTOC(G1CollectedHeap* g1,
 116                   HeapRegion* hr, OopClosure* cl,
 117                   CardTableModRefBS::PrecisionStyle precision,
 118                   FilterKind fk);
 119 };
 120 
 121 // The complicating factor is that BlockOffsetTable diverged
 122 // significantly, and we need functionality that is only in the G1 version.
 123 // So I copied that code, which led to an alternate G1 version of
 124 // OffsetTableContigSpace.  If the two versions of BlockOffsetTable could
 125 // be reconciled, then G1OffsetTableContigSpace could go away.
 126 
 127 // The idea behind time stamps is the following. Doing a save_marks on
 128 // all regions at every GC pause is time consuming (if I remember
 129 // well, 10ms or so). So, we would like to do that only for regions
 130 // that are GC alloc regions. To achieve this, we use time
 131 // stamps. For every evacuation pause, G1CollectedHeap generates a
 132 // unique time stamp (essentially a counter that gets
 133 // incremented). Every time we want to call save_marks on a region,
 134 // we set the saved_mark_word to top and also copy the current GC
 135 // time stamp to the time stamp field of the space. Reading the
 136 // saved_mark_word involves checking the time stamp of the
 137 // region. If it is the same as the current GC time stamp, then we
 138 // can safely read the saved_mark_word field, as it is valid. If the
 139 // time stamp of the region is not the same as the current GC time
 140 // stamp, then we instead read top, as the saved_mark_word field is
 141 // invalid. Time stamps (on the regions and also on the
 142 // G1CollectedHeap) are reset at every cleanup (we iterate over
 143 // the regions anyway) and at the end of a Full GC. The current scheme
 144 // that uses sequential unsigned ints will fail only if we have 4b
 145 // evacuation pauses between two cleanups, which is _highly_ unlikely.
 146 
 147 class G1OffsetTableContigSpace: public ContiguousSpace {
 148   friend class VMStructs;
 149  protected:
 150   G1BlockOffsetArrayContigSpace _offsets;
 151   Mutex _par_alloc_lock;
 152   volatile unsigned _gc_time_stamp;
 153   // When we need to retire an allocation region, while other threads
 154   // are also concurrently trying to allocate into it, we typically
 155   // allocate a dummy object at the end of the region to ensure that
 156   // no more allocations can take place in it. However, sometimes we
 157   // want to know where the end of the last "real" object we allocated
 158   // into the region was and this is what this keeps track.
 159   HeapWord* _pre_dummy_top;
 160 
 161  public:
 162   // Constructor.  If "is_zeroed" is true, the MemRegion "mr" may be
 163   // assumed to contain zeros.
 164   G1OffsetTableContigSpace(G1BlockOffsetSharedArray* sharedOffsetArray,
 165                            MemRegion mr, bool is_zeroed = false);
 166 
 167   void set_bottom(HeapWord* value);
 168   void set_end(HeapWord* value);
 169 
 170   virtual HeapWord* saved_mark_word() const;
 171   virtual void set_saved_mark();
 172   void reset_gc_time_stamp() { _gc_time_stamp = 0; }
 173 
 174   // See the comment above in the declaration of _pre_dummy_top for an
 175   // explanation of what it is.
 176   void set_pre_dummy_top(HeapWord* pre_dummy_top) {
 177     assert(is_in(pre_dummy_top) && pre_dummy_top <= top(), "pre-condition");
 178     _pre_dummy_top = pre_dummy_top;
 179   }
 180   HeapWord* pre_dummy_top() {
 181     return (_pre_dummy_top == NULL) ? top() : _pre_dummy_top;
 182   }
 183   void reset_pre_dummy_top() { _pre_dummy_top = NULL; }
 184 
 185   virtual void initialize(MemRegion mr, bool clear_space, bool mangle_space);
 186   virtual void clear(bool mangle_space);
 187 
 188   HeapWord* block_start(const void* p);
 189   HeapWord* block_start_const(const void* p) const;
 190 
 191   // Add offset table update.
 192   virtual HeapWord* allocate(size_t word_size);
 193   HeapWord* par_allocate(size_t word_size);
 194 
 195   // MarkSweep support phase3
 196   virtual HeapWord* initialize_threshold();
 197   virtual HeapWord* cross_threshold(HeapWord* start, HeapWord* end);
 198 
 199   virtual void print() const;
 200 
 201   void reset_bot() {
 202     _offsets.zero_bottom_entry();
 203     _offsets.initialize_threshold();
 204   }
 205 
 206   void update_bot_for_object(HeapWord* start, size_t word_size) {
 207     _offsets.alloc_block(start, word_size);
 208   }
 209 
 210   void print_bot_on(outputStream* out) {
 211     _offsets.print_on(out);
 212   }
 213 };
 214 
 215 class HeapRegion: public G1OffsetTableContigSpace {
 216   friend class VMStructs;
 217  private:
 218 
 219   enum HumongousType {
 220     NotHumongous = 0,
 221     StartsHumongous,
 222     ContinuesHumongous
 223   };
 224 
 225   // Requires that the region "mr" be dense with objects, and begin and end
 226   // with an object.
 227   void oops_in_mr_iterate(MemRegion mr, OopClosure* cl);
 228 
 229   // The remembered set for this region.
 230   // (Might want to make this "inline" later, to avoid some alloc failure
 231   // issues.)
 232   HeapRegionRemSet* _rem_set;
 233 
 234   G1BlockOffsetArrayContigSpace* offsets() { return &_offsets; }
 235 
 236  protected:
 237   // The index of this region in the heap region sequence.
 238   size_t  _hrs_index;
 239 
 240   HumongousType _humongous_type;
 241   // For a humongous region, region in which it starts.
 242   HeapRegion* _humongous_start_region;
 243   // For the start region of a humongous sequence, it's original end().
 244   HeapWord* _orig_end;
 245 
 246   // True iff the region is in current collection_set.
 247   bool _in_collection_set;
 248 
 249   // True iff an attempt to evacuate an object in the region failed.
 250   bool _evacuation_failed;
 251 
 252   // A heap region may be a member one of a number of special subsets, each
 253   // represented as linked lists through the field below.  Currently, these
 254   // sets include:
 255   //   The collection set.
 256   //   The set of allocation regions used in a collection pause.
 257   //   Spaces that may contain gray objects.
 258   HeapRegion* _next_in_special_set;
 259 
 260   // next region in the young "generation" region set
 261   HeapRegion* _next_young_region;
 262 
 263   // Next region whose cards need cleaning
 264   HeapRegion* _next_dirty_cards_region;
 265 
 266   // Fields used by the HeapRegionSetBase class and subclasses.
 267   HeapRegion* _next;
 268 #ifdef ASSERT
 269   HeapRegionSetBase* _containing_set;
 270 #endif // ASSERT
 271   bool _pending_removal;
 272 
 273   // For parallel heapRegion traversal.
 274   jint _claimed;
 275 
 276   // We use concurrent marking to determine the amount of live data
 277   // in each heap region.
 278   size_t _prev_marked_bytes;    // Bytes known to be live via last completed marking.
 279   size_t _next_marked_bytes;    // Bytes known to be live via in-progress marking.
 280 
 281   // See "sort_index" method.  -1 means is not in the array.
 282   int _sort_index;
 283 
 284   // <PREDICTION>
 285   double _gc_efficiency;
 286   // </PREDICTION>
 287 
 288   enum YoungType {
 289     NotYoung,                   // a region is not young
 290     Young,                      // a region is young
 291     Survivor                    // a region is young and it contains survivors
 292   };
 293 
 294   volatile YoungType _young_type;
 295   int  _young_index_in_cset;
 296   SurvRateGroup* _surv_rate_group;
 297   int  _age_index;
 298 
 299   // The start of the unmarked area. The unmarked area extends from this
 300   // word until the top and/or end of the region, and is the part
 301   // of the region for which no marking was done, i.e. objects may
 302   // have been allocated in this part since the last mark phase.
 303   // "prev" is the top at the start of the last completed marking.
 304   // "next" is the top at the start of the in-progress marking (if any.)
 305   HeapWord* _prev_top_at_mark_start;
 306   HeapWord* _next_top_at_mark_start;
 307   // If a collection pause is in progress, this is the top at the start
 308   // of that pause.
 309 
 310   // We've counted the marked bytes of objects below here.
 311   HeapWord* _top_at_conc_mark_count;
 312 
 313   void init_top_at_mark_start() {
 314     assert(_prev_marked_bytes == 0 &&
 315            _next_marked_bytes == 0,
 316            "Must be called after zero_marked_bytes.");
 317     HeapWord* bot = bottom();
 318     _prev_top_at_mark_start = bot;
 319     _next_top_at_mark_start = bot;
 320     _top_at_conc_mark_count = bot;
 321   }
 322 
 323   void set_young_type(YoungType new_type) {
 324     //assert(_young_type != new_type, "setting the same type" );
 325     // TODO: add more assertions here
 326     _young_type = new_type;
 327   }
 328 
 329   // Cached attributes used in the collection set policy information
 330 
 331   // The RSet length that was added to the total value
 332   // for the collection set.
 333   size_t _recorded_rs_length;
 334 
 335   // The predicted elapsed time that was added to total value
 336   // for the collection set.
 337   double _predicted_elapsed_time_ms;
 338 
 339   // The predicted number of bytes to copy that was added to
 340   // the total value for the collection set.
 341   size_t _predicted_bytes_to_copy;
 342 
 343  public:
 344   // If "is_zeroed" is "true", the region "mr" can be assumed to contain zeros.
 345   HeapRegion(size_t hrs_index,
 346              G1BlockOffsetSharedArray* sharedOffsetArray,
 347              MemRegion mr, bool is_zeroed);
 348 
 349   static int    LogOfHRGrainBytes;
 350   static int    LogOfHRGrainWords;
 351 
 352   static size_t GrainBytes;
 353   static size_t GrainWords;
 354   static size_t CardsPerRegion;
 355 
 356   static size_t align_up_to_region_byte_size(size_t sz) {
 357     return (sz + (size_t) GrainBytes - 1) &
 358                                       ~((1 << (size_t) LogOfHRGrainBytes) - 1);
 359   }
 360 
 361   // It sets up the heap region size (GrainBytes / GrainWords), as
 362   // well as other related fields that are based on the heap region
 363   // size (LogOfHRGrainBytes / LogOfHRGrainWords /
 364   // CardsPerRegion). All those fields are considered constant
 365   // throughout the JVM's execution, therefore they should only be set
 366   // up once during initialization time.
 367   static void setup_heap_region_size(uintx min_heap_size);
 368 
 369   enum ClaimValues {
 370     InitialClaimValue     = 0,
 371     FinalCountClaimValue  = 1,
 372     NoteEndClaimValue     = 2,
 373     ScrubRemSetClaimValue = 3,
 374     ParVerifyClaimValue   = 4,
 375     RebuildRSClaimValue   = 5
 376   };
 377 
 378   inline HeapWord* par_allocate_no_bot_updates(size_t word_size) {
 379     assert(is_young(), "we can only skip BOT updates on young regions");
 380     return ContiguousSpace::par_allocate(word_size);
 381   }
 382   inline HeapWord* allocate_no_bot_updates(size_t word_size) {
 383     assert(is_young(), "we can only skip BOT updates on young regions");
 384     return ContiguousSpace::allocate(word_size);
 385   }
 386 
 387   // If this region is a member of a HeapRegionSeq, the index in that
 388   // sequence, otherwise -1.
 389   size_t hrs_index() const { return _hrs_index; }
 390 
 391   // The number of bytes marked live in the region in the last marking phase.
 392   size_t marked_bytes()    { return _prev_marked_bytes; }
 393   size_t live_bytes() {
 394     return (top() - prev_top_at_mark_start()) * HeapWordSize + marked_bytes();
 395   }
 396 
 397   // The number of bytes counted in the next marking.
 398   size_t next_marked_bytes() { return _next_marked_bytes; }
 399   // The number of bytes live wrt the next marking.
 400   size_t next_live_bytes() {
 401     return
 402       (top() - next_top_at_mark_start()) * HeapWordSize + next_marked_bytes();
 403   }
 404 
 405   // A lower bound on the amount of garbage bytes in the region.
 406   size_t garbage_bytes() {
 407     size_t used_at_mark_start_bytes =
 408       (prev_top_at_mark_start() - bottom()) * HeapWordSize;
 409     assert(used_at_mark_start_bytes >= marked_bytes(),
 410            "Can't mark more than we have.");
 411     return used_at_mark_start_bytes - marked_bytes();
 412   }
 413 
 414   // An upper bound on the number of live bytes in the region.
 415   size_t max_live_bytes() { return used() - garbage_bytes(); }
 416 
 417   void add_to_marked_bytes(size_t incr_bytes) {
 418     _next_marked_bytes = _next_marked_bytes + incr_bytes;
 419     guarantee( _next_marked_bytes <= used(), "invariant" );
 420   }
 421 
 422   void zero_marked_bytes()      {
 423     _prev_marked_bytes = _next_marked_bytes = 0;
 424   }
 425 
 426   bool isHumongous() const { return _humongous_type != NotHumongous; }
 427   bool startsHumongous() const { return _humongous_type == StartsHumongous; }
 428   bool continuesHumongous() const { return _humongous_type == ContinuesHumongous; }
 429   // For a humongous region, region in which it starts.
 430   HeapRegion* humongous_start_region() const {
 431     return _humongous_start_region;
 432   }
 433 
 434   // Same as Space::is_in_reserved, but will use the actual size of a humongous start
 435   // region rather than the end of the humongous object.
 436   bool is_in_reserved_raw(const void* p) const {
 437     if (startsHumongous()) {
 438       return _bottom <= p && p < _orig_end;
 439     } else {
 440       return Space::is_in_reserved(p);
 441     }
 442   }
 443 
 444   // Makes the current region be a "starts humongous" region, i.e.,
 445   // the first region in a series of one or more contiguous regions
 446   // that will contain a single "humongous" object. The two parameters
 447   // are as follows:
 448   //
 449   // new_top : The new value of the top field of this region which
 450   // points to the end of the humongous object that's being
 451   // allocated. If there is more than one region in the series, top
 452   // will lie beyond this region's original end field and on the last
 453   // region in the series.
 454   //
 455   // new_end : The new value of the end field of this region which
 456   // points to the end of the last region in the series. If there is
 457   // one region in the series (namely: this one) end will be the same
 458   // as the original end of this region.
 459   //
 460   // Updating top and end as described above makes this region look as
 461   // if it spans the entire space taken up by all the regions in the
 462   // series and an single allocation moved its top to new_top. This
 463   // ensures that the space (capacity / allocated) taken up by all
 464   // humongous regions can be calculated by just looking at the
 465   // "starts humongous" regions and by ignoring the "continues
 466   // humongous" regions.
 467   void set_startsHumongous(HeapWord* new_top, HeapWord* new_end);
 468 
 469   // Makes the current region be a "continues humongous'
 470   // region. first_hr is the "start humongous" region of the series
 471   // which this region will be part of.
 472   void set_continuesHumongous(HeapRegion* first_hr);
 473 
 474   // Unsets the humongous-related fields on the region.
 475   void set_notHumongous();
 476 
 477   // If the region has a remembered set, return a pointer to it.
 478   HeapRegionRemSet* rem_set() const {
 479     return _rem_set;
 480   }
 481 
 482   // True iff the region is in current collection_set.
 483   bool in_collection_set() const {
 484     return _in_collection_set;
 485   }
 486   void set_in_collection_set(bool b) {
 487     _in_collection_set = b;
 488   }
 489   HeapRegion* next_in_collection_set() {
 490     assert(in_collection_set(), "should only invoke on member of CS.");
 491     assert(_next_in_special_set == NULL ||
 492            _next_in_special_set->in_collection_set(),
 493            "Malformed CS.");
 494     return _next_in_special_set;
 495   }
 496   void set_next_in_collection_set(HeapRegion* r) {
 497     assert(in_collection_set(), "should only invoke on member of CS.");
 498     assert(r == NULL || r->in_collection_set(), "Malformed CS.");
 499     _next_in_special_set = r;
 500   }
 501 
 502   // Methods used by the HeapRegionSetBase class and subclasses.
 503 
 504   // Getter and setter for the next field used to link regions into
 505   // linked lists.
 506   HeapRegion* next()              { return _next; }
 507 
 508   void set_next(HeapRegion* next) { _next = next; }
 509 
 510   // Every region added to a set is tagged with a reference to that
 511   // set. This is used for doing consistency checking to make sure that
 512   // the contents of a set are as they should be and it's only
 513   // available in non-product builds.
 514 #ifdef ASSERT
 515   void set_containing_set(HeapRegionSetBase* containing_set) {
 516     assert((containing_set == NULL && _containing_set != NULL) ||
 517            (containing_set != NULL && _containing_set == NULL),
 518            err_msg("containing_set: "PTR_FORMAT" "
 519                    "_containing_set: "PTR_FORMAT,
 520                    containing_set, _containing_set));
 521 
 522     _containing_set = containing_set;
 523   }
 524 
 525   HeapRegionSetBase* containing_set() { return _containing_set; }
 526 #else // ASSERT
 527   void set_containing_set(HeapRegionSetBase* containing_set) { }
 528 
 529   // containing_set() is only used in asserts so there's no reason
 530   // to provide a dummy version of it.
 531 #endif // ASSERT
 532 
 533   // If we want to remove regions from a list in bulk we can simply tag
 534   // them with the pending_removal tag and call the
 535   // remove_all_pending() method on the list.
 536 
 537   bool pending_removal() { return _pending_removal; }
 538 
 539   void set_pending_removal(bool pending_removal) {
 540     if (pending_removal) {
 541       assert(!_pending_removal && containing_set() != NULL,
 542              "can only set pending removal to true if it's false and "
 543              "the region belongs to a region set");
 544     } else {
 545       assert( _pending_removal && containing_set() == NULL,
 546               "can only set pending removal to false if it's true and "
 547               "the region does not belong to a region set");
 548     }
 549 
 550     _pending_removal = pending_removal;
 551   }
 552 
 553   HeapRegion* get_next_young_region() { return _next_young_region; }
 554   void set_next_young_region(HeapRegion* hr) {
 555     _next_young_region = hr;
 556   }
 557 
 558   HeapRegion* get_next_dirty_cards_region() const { return _next_dirty_cards_region; }
 559   HeapRegion** next_dirty_cards_region_addr() { return &_next_dirty_cards_region; }
 560   void set_next_dirty_cards_region(HeapRegion* hr) { _next_dirty_cards_region = hr; }
 561   bool is_on_dirty_cards_region_list() const { return get_next_dirty_cards_region() != NULL; }
 562 
 563   HeapWord* orig_end() { return _orig_end; }
 564 
 565   // Allows logical separation between objects allocated before and after.
 566   void save_marks();
 567 
 568   // Reset HR stuff to default values.
 569   void hr_clear(bool par, bool clear_space);
 570   void par_clear();
 571 
 572   void initialize(MemRegion mr, bool clear_space, bool mangle_space);
 573 
 574   // Get the start of the unmarked area in this region.
 575   HeapWord* prev_top_at_mark_start() const { return _prev_top_at_mark_start; }
 576   HeapWord* next_top_at_mark_start() const { return _next_top_at_mark_start; }
 577 
 578   // Apply "cl->do_oop" to (the addresses of) all reference fields in objects
 579   // allocated in the current region before the last call to "save_mark".
 580   void oop_before_save_marks_iterate(OopClosure* cl);
 581 
 582   DirtyCardToOopClosure*
 583   new_dcto_closure(OopClosure* cl,
 584                    CardTableModRefBS::PrecisionStyle precision,
 585                    HeapRegionDCTOC::FilterKind fk);
 586 
 587   // Note the start or end of marking. This tells the heap region
 588   // that the collector is about to start or has finished (concurrently)
 589   // marking the heap.
 590 
 591   // Note the start of a marking phase. Record the
 592   // start of the unmarked area of the region here.
 593   void note_start_of_marking(bool during_initial_mark) {
 594     init_top_at_conc_mark_count();
 595     _next_marked_bytes = 0;
 596     if (during_initial_mark && is_young() && !is_survivor())
 597       _next_top_at_mark_start = bottom();
 598     else
 599       _next_top_at_mark_start = top();
 600   }
 601 
 602   // Note the end of a marking phase. Install the start of
 603   // the unmarked area that was captured at start of marking.
 604   void note_end_of_marking() {
 605     _prev_top_at_mark_start = _next_top_at_mark_start;
 606     _prev_marked_bytes = _next_marked_bytes;
 607     _next_marked_bytes = 0;
 608 
 609     guarantee(_prev_marked_bytes <=
 610               (size_t) (prev_top_at_mark_start() - bottom()) * HeapWordSize,
 611               "invariant");
 612   }
 613 
 614   // After an evacuation, we need to update _next_top_at_mark_start
 615   // to be the current top.  Note this is only valid if we have only
 616   // ever evacuated into this region.  If we evacuate, allocate, and
 617   // then evacuate we are in deep doodoo.
 618   void note_end_of_copying() {
 619     assert(top() >= _next_top_at_mark_start, "Increase only");
 620     _next_top_at_mark_start = top();
 621   }
 622 
 623   // Returns "false" iff no object in the region was allocated when the
 624   // last mark phase ended.
 625   bool is_marked() { return _prev_top_at_mark_start != bottom(); }
 626 
 627   // If "is_marked()" is true, then this is the index of the region in
 628   // an array constructed at the end of marking of the regions in a
 629   // "desirability" order.
 630   int sort_index() {
 631     return _sort_index;
 632   }
 633   void set_sort_index(int i) {
 634     _sort_index = i;
 635   }
 636 
 637   void init_top_at_conc_mark_count() {
 638     _top_at_conc_mark_count = bottom();
 639   }
 640 
 641   void set_top_at_conc_mark_count(HeapWord *cur) {
 642     assert(bottom() <= cur && cur <= end(), "Sanity.");
 643     _top_at_conc_mark_count = cur;
 644   }
 645 
 646   HeapWord* top_at_conc_mark_count() {
 647     return _top_at_conc_mark_count;
 648   }
 649 
 650   void reset_during_compaction() {
 651     guarantee( isHumongous() && startsHumongous(),
 652                "should only be called for humongous regions");
 653 
 654     zero_marked_bytes();
 655     init_top_at_mark_start();
 656   }
 657 
 658   // <PREDICTION>
 659   void calc_gc_efficiency(void);
 660   double gc_efficiency() { return _gc_efficiency;}
 661   // </PREDICTION>
 662 
 663   bool is_young() const     { return _young_type != NotYoung; }
 664   bool is_survivor() const  { return _young_type == Survivor; }
 665 
 666   int  young_index_in_cset() const { return _young_index_in_cset; }
 667   void set_young_index_in_cset(int index) {
 668     assert( (index == -1) || is_young(), "pre-condition" );
 669     _young_index_in_cset = index;
 670   }
 671 
 672   int age_in_surv_rate_group() {
 673     assert( _surv_rate_group != NULL, "pre-condition" );
 674     assert( _age_index > -1, "pre-condition" );
 675     return _surv_rate_group->age_in_group(_age_index);
 676   }
 677 
 678   void record_surv_words_in_group(size_t words_survived) {
 679     assert( _surv_rate_group != NULL, "pre-condition" );
 680     assert( _age_index > -1, "pre-condition" );
 681     int age_in_group = age_in_surv_rate_group();
 682     _surv_rate_group->record_surviving_words(age_in_group, words_survived);
 683   }
 684 
 685   int age_in_surv_rate_group_cond() {
 686     if (_surv_rate_group != NULL)
 687       return age_in_surv_rate_group();
 688     else
 689       return -1;
 690   }
 691 
 692   SurvRateGroup* surv_rate_group() {
 693     return _surv_rate_group;
 694   }
 695 
 696   void install_surv_rate_group(SurvRateGroup* surv_rate_group) {
 697     assert( surv_rate_group != NULL, "pre-condition" );
 698     assert( _surv_rate_group == NULL, "pre-condition" );
 699     assert( is_young(), "pre-condition" );
 700 
 701     _surv_rate_group = surv_rate_group;
 702     _age_index = surv_rate_group->next_age_index();
 703   }
 704 
 705   void uninstall_surv_rate_group() {
 706     if (_surv_rate_group != NULL) {
 707       assert( _age_index > -1, "pre-condition" );
 708       assert( is_young(), "pre-condition" );
 709 
 710       _surv_rate_group = NULL;
 711       _age_index = -1;
 712     } else {
 713       assert( _age_index == -1, "pre-condition" );
 714     }
 715   }
 716 
 717   void set_young() { set_young_type(Young); }
 718 
 719   void set_survivor() { set_young_type(Survivor); }
 720 
 721   void set_not_young() { set_young_type(NotYoung); }
 722 
 723   // Determine if an object has been allocated since the last
 724   // mark performed by the collector. This returns true iff the object
 725   // is within the unmarked area of the region.
 726   bool obj_allocated_since_prev_marking(oop obj) const {
 727     return (HeapWord *) obj >= prev_top_at_mark_start();
 728   }
 729   bool obj_allocated_since_next_marking(oop obj) const {
 730     return (HeapWord *) obj >= next_top_at_mark_start();
 731   }
 732 
 733   // For parallel heapRegion traversal.
 734   bool claimHeapRegion(int claimValue);
 735   jint claim_value() { return _claimed; }
 736   // Use this carefully: only when you're sure no one is claiming...
 737   void set_claim_value(int claimValue) { _claimed = claimValue; }
 738 
 739   // Returns the "evacuation_failed" property of the region.
 740   bool evacuation_failed() { return _evacuation_failed; }
 741 
 742   // Sets the "evacuation_failed" property of the region.
 743   void set_evacuation_failed(bool b) {
 744     _evacuation_failed = b;
 745 
 746     if (b) {
 747       init_top_at_conc_mark_count();
 748       _next_marked_bytes = 0;
 749     }
 750   }
 751 
 752   // Requires that "mr" be entirely within the region.
 753   // Apply "cl->do_object" to all objects that intersect with "mr".
 754   // If the iteration encounters an unparseable portion of the region,
 755   // or if "cl->abort()" is true after a closure application,
 756   // terminate the iteration and return the address of the start of the
 757   // subregion that isn't done.  (The two can be distinguished by querying
 758   // "cl->abort()".)  Return of "NULL" indicates that the iteration
 759   // completed.
 760   HeapWord*
 761   object_iterate_mem_careful(MemRegion mr, ObjectClosure* cl);
 762 
 763   // filter_young: if true and the region is a young region then we
 764   // skip the iteration.
 765   // card_ptr: if not NULL, and we decide that the card is not young
 766   // and we iterate over it, we'll clean the card before we start the
 767   // iteration.
 768   HeapWord*
 769   oops_on_card_seq_iterate_careful(MemRegion mr,
 770                                    FilterOutOfRegionClosure* cl,
 771                                    bool filter_young,
 772                                    jbyte* card_ptr);
 773 
 774   // A version of block start that is guaranteed to find *some* block
 775   // boundary at or before "p", but does not object iteration, and may
 776   // therefore be used safely when the heap is unparseable.
 777   HeapWord* block_start_careful(const void* p) const {
 778     return _offsets.block_start_careful(p);
 779   }
 780 
 781   // Requires that "addr" is within the region.  Returns the start of the
 782   // first ("careful") block that starts at or after "addr", or else the
 783   // "end" of the region if there is no such block.
 784   HeapWord* next_block_start_careful(HeapWord* addr);
 785 
 786   size_t recorded_rs_length() const        { return _recorded_rs_length; }
 787   double predicted_elapsed_time_ms() const { return _predicted_elapsed_time_ms; }
 788   size_t predicted_bytes_to_copy() const   { return _predicted_bytes_to_copy; }
 789 
 790   void set_recorded_rs_length(size_t rs_length) {
 791     _recorded_rs_length = rs_length;
 792   }
 793 
 794   void set_predicted_elapsed_time_ms(double ms) {
 795     _predicted_elapsed_time_ms = ms;
 796   }
 797 
 798   void set_predicted_bytes_to_copy(size_t bytes) {
 799     _predicted_bytes_to_copy = bytes;
 800   }
 801 
 802 #define HeapRegion_OOP_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix)  \
 803   virtual void oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl);
 804   SPECIALIZED_SINCE_SAVE_MARKS_CLOSURES(HeapRegion_OOP_SINCE_SAVE_MARKS_DECL)
 805 
 806   CompactibleSpace* next_compaction_space() const;
 807 
 808   virtual void reset_after_compaction();
 809 
 810   void print() const;
 811   void print_on(outputStream* st) const;
 812 
 813   // vo == UsePrevMarking  -> use "prev" marking information,
 814   // vo == UseNextMarking -> use "next" marking information
 815   // vo == UseMarkWord    -> use the mark word in the object header
 816   //
 817   // NOTE: Only the "prev" marking information is guaranteed to be
 818   // consistent most of the time, so most calls to this should use
 819   // vo == UsePrevMarking.
 820   // Currently, there is only one case where this is called with
 821   // vo == UseNextMarking, which is to verify the "next" marking
 822   // information at the end of remark.
 823   // Currently there is only one place where this is called with
 824   // vo == UseMarkWord, which is to verify the marking during a
 825   // full GC.
 826   void verify(bool allow_dirty, VerifyOption vo, bool *failures) const;
 827 
 828   // Override; it uses the "prev" marking information
 829   virtual void verify(bool allow_dirty) const;
 830 };
 831 
 832 // HeapRegionClosure is used for iterating over regions.
 833 // Terminates the iteration when the "doHeapRegion" method returns "true".
 834 class HeapRegionClosure : public StackObj {
 835   friend class HeapRegionSeq;
 836   friend class G1CollectedHeap;
 837 
 838   bool _complete;
 839   void incomplete() { _complete = false; }
 840 
 841  public:
 842   HeapRegionClosure(): _complete(true) {}
 843 
 844   // Typically called on each region until it returns true.
 845   virtual bool doHeapRegion(HeapRegion* r) = 0;
 846 
 847   // True after iteration if the closure was applied to all heap regions
 848   // and returned "false" in all cases.
 849   bool complete() { return _complete; }
 850 };
 851 
 852 #endif // SERIALGC
 853 
 854 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_HEAPREGION_HPP