1 /*
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  24 
  25 #ifndef SHARE_VM_GC_CMS_CONCURRENTMARKSWEEPGENERATION_HPP
  26 #define SHARE_VM_GC_CMS_CONCURRENTMARKSWEEPGENERATION_HPP
  27 
  28 #include "gc/cms/cmsOopClosures.hpp"
  29 #include "gc/cms/gSpaceCounters.hpp"
  30 #include "gc/cms/yieldingWorkgroup.hpp"
  31 #include "gc/shared/cardGeneration.hpp"
  32 #include "gc/shared/gcHeapSummary.hpp"
  33 #include "gc/shared/gcStats.hpp"
  34 #include "gc/shared/gcWhen.hpp"
  35 #include "gc/shared/generationCounters.hpp"
  36 #include "gc/shared/space.hpp"
  37 #include "gc/shared/taskqueue.hpp"
  38 #include "logging/log.hpp"
  39 #include "memory/freeBlockDictionary.hpp"
  40 #include "memory/iterator.hpp"
  41 #include "memory/virtualspace.hpp"
  42 #include "runtime/mutexLocker.hpp"
  43 #include "services/memoryService.hpp"
  44 #include "utilities/bitMap.hpp"
  45 #include "utilities/stack.hpp"
  46 
  47 // ConcurrentMarkSweepGeneration is in support of a concurrent
  48 // mark-sweep old generation in the Detlefs-Printezis--Boehm-Demers-Schenker
  49 // style. We assume, for now, that this generation is always the
  50 // seniormost generation and for simplicity
  51 // in the first implementation, that this generation is a single compactible
  52 // space. Neither of these restrictions appears essential, and will be
  53 // relaxed in the future when more time is available to implement the
  54 // greater generality (and there's a need for it).
  55 //
  56 // Concurrent mode failures are currently handled by
  57 // means of a sliding mark-compact.
  58 
  59 class AdaptiveSizePolicy;
  60 class CMSCollector;
  61 class CMSConcMarkingTask;
  62 class CMSGCAdaptivePolicyCounters;
  63 class CMSTracer;
  64 class ConcurrentGCTimer;
  65 class ConcurrentMarkSweepGeneration;
  66 class ConcurrentMarkSweepPolicy;
  67 class ConcurrentMarkSweepThread;
  68 class CompactibleFreeListSpace;
  69 class FreeChunk;
  70 class ParNewGeneration;
  71 class PromotionInfo;
  72 class ScanMarkedObjectsAgainCarefullyClosure;
  73 class TenuredGeneration;
  74 class SerialOldTracer;
  75 
  76 // A generic CMS bit map. It's the basis for both the CMS marking bit map
  77 // as well as for the mod union table (in each case only a subset of the
  78 // methods are used). This is essentially a wrapper around the BitMap class,
  79 // with one bit per (1<<_shifter) HeapWords. (i.e. for the marking bit map,
  80 // we have _shifter == 0. and for the mod union table we have
  81 // shifter == CardTableModRefBS::card_shift - LogHeapWordSize.)
  82 // XXX 64-bit issues in BitMap?
  83 class CMSBitMap VALUE_OBJ_CLASS_SPEC {
  84   friend class VMStructs;
  85 
  86   HeapWord* _bmStartWord;   // base address of range covered by map
  87   size_t    _bmWordSize;    // map size (in #HeapWords covered)
  88   const int _shifter;       // shifts to convert HeapWord to bit position
  89   VirtualSpace _virtual_space; // underlying the bit map
  90   BitMap    _bm;            // the bit map itself
  91  public:
  92   Mutex* const _lock;       // mutex protecting _bm;
  93 
  94  public:
  95   // constructor
  96   CMSBitMap(int shifter, int mutex_rank, const char* mutex_name);
  97 
  98   // allocates the actual storage for the map
  99   bool allocate(MemRegion mr);
 100   // field getter
 101   Mutex* lock() const { return _lock; }
 102   // locking verifier convenience function
 103   void assert_locked() const PRODUCT_RETURN;
 104 
 105   // inquiries
 106   HeapWord* startWord()   const { return _bmStartWord; }
 107   size_t    sizeInWords() const { return _bmWordSize;  }
 108   size_t    sizeInBits()  const { return _bm.size();   }
 109   // the following is one past the last word in space
 110   HeapWord* endWord()     const { return _bmStartWord + _bmWordSize; }
 111 
 112   // reading marks
 113   bool isMarked(HeapWord* addr) const;
 114   bool par_isMarked(HeapWord* addr) const; // do not lock checks
 115   bool isUnmarked(HeapWord* addr) const;
 116   bool isAllClear() const;
 117 
 118   // writing marks
 119   void mark(HeapWord* addr);
 120   // For marking by parallel GC threads;
 121   // returns true if we did, false if another thread did
 122   bool par_mark(HeapWord* addr);
 123 
 124   void mark_range(MemRegion mr);
 125   void par_mark_range(MemRegion mr);
 126   void mark_large_range(MemRegion mr);
 127   void par_mark_large_range(MemRegion mr);
 128   void par_clear(HeapWord* addr); // For unmarking by parallel GC threads.
 129   void clear_range(MemRegion mr);
 130   void par_clear_range(MemRegion mr);
 131   void clear_large_range(MemRegion mr);
 132   void par_clear_large_range(MemRegion mr);
 133   void clear_all();
 134   void clear_all_incrementally();  // Not yet implemented!!
 135 
 136   NOT_PRODUCT(
 137     // checks the memory region for validity
 138     void region_invariant(MemRegion mr);
 139   )
 140 
 141   // iteration
 142   void iterate(BitMapClosure* cl) {
 143     _bm.iterate(cl);
 144   }
 145   void iterate(BitMapClosure* cl, HeapWord* left, HeapWord* right);
 146   void dirty_range_iterate_clear(MemRegionClosure* cl);
 147   void dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl);
 148 
 149   // auxiliary support for iteration
 150   HeapWord* getNextMarkedWordAddress(HeapWord* addr) const;
 151   HeapWord* getNextMarkedWordAddress(HeapWord* start_addr,
 152                                             HeapWord* end_addr) const;
 153   HeapWord* getNextUnmarkedWordAddress(HeapWord* addr) const;
 154   HeapWord* getNextUnmarkedWordAddress(HeapWord* start_addr,
 155                                               HeapWord* end_addr) const;
 156   MemRegion getAndClearMarkedRegion(HeapWord* addr);
 157   MemRegion getAndClearMarkedRegion(HeapWord* start_addr,
 158                                            HeapWord* end_addr);
 159 
 160   // conversion utilities
 161   HeapWord* offsetToHeapWord(size_t offset) const;
 162   size_t    heapWordToOffset(HeapWord* addr) const;
 163   size_t    heapWordDiffToOffsetDiff(size_t diff) const;
 164 
 165   void print_on_error(outputStream* st, const char* prefix) const;
 166 
 167   // debugging
 168   // is this address range covered by the bit-map?
 169   NOT_PRODUCT(
 170     bool covers(MemRegion mr) const;
 171     bool covers(HeapWord* start, size_t size = 0) const;
 172   )
 173   void verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) PRODUCT_RETURN;
 174 };
 175 
 176 // Represents a marking stack used by the CMS collector.
 177 // Ideally this should be GrowableArray<> just like MSC's marking stack(s).
 178 class CMSMarkStack: public CHeapObj<mtGC>  {
 179   friend class CMSCollector;   // To get at expansion stats further below.
 180 
 181   VirtualSpace _virtual_space;  // Space for the stack
 182   oop*   _base;      // Bottom of stack
 183   size_t _index;     // One more than last occupied index
 184   size_t _capacity;  // Max #elements
 185   Mutex  _par_lock;  // An advisory lock used in case of parallel access
 186   NOT_PRODUCT(size_t _max_depth;)  // Max depth plumbed during run
 187 
 188  protected:
 189   size_t _hit_limit;      // We hit max stack size limit
 190   size_t _failed_double;  // We failed expansion before hitting limit
 191 
 192  public:
 193   CMSMarkStack():
 194     _par_lock(Mutex::event, "CMSMarkStack._par_lock", true,
 195               Monitor::_safepoint_check_never),
 196     _hit_limit(0),
 197     _failed_double(0) {}
 198 
 199   bool allocate(size_t size);
 200 
 201   size_t capacity() const { return _capacity; }
 202 
 203   oop pop() {
 204     if (!isEmpty()) {
 205       return _base[--_index] ;
 206     }
 207     return NULL;
 208   }
 209 
 210   bool push(oop ptr) {
 211     if (isFull()) {
 212       return false;
 213     } else {
 214       _base[_index++] = ptr;
 215       NOT_PRODUCT(_max_depth = MAX2(_max_depth, _index));
 216       return true;
 217     }
 218   }
 219 
 220   bool isEmpty() const { return _index == 0; }
 221   bool isFull()  const {
 222     assert(_index <= _capacity, "buffer overflow");
 223     return _index == _capacity;
 224   }
 225 
 226   size_t length() { return _index; }
 227 
 228   // "Parallel versions" of some of the above
 229   oop par_pop() {
 230     // lock and pop
 231     MutexLockerEx x(&_par_lock, Mutex::_no_safepoint_check_flag);
 232     return pop();
 233   }
 234 
 235   bool par_push(oop ptr) {
 236     // lock and push
 237     MutexLockerEx x(&_par_lock, Mutex::_no_safepoint_check_flag);
 238     return push(ptr);
 239   }
 240 
 241   // Forcibly reset the stack, losing all of its contents.
 242   void reset() {
 243     _index = 0;
 244   }
 245 
 246   // Expand the stack, typically in response to an overflow condition.
 247   void expand();
 248 
 249   // Compute the least valued stack element.
 250   oop least_value(HeapWord* low) {
 251      oop least = (oop)low;
 252      for (size_t i = 0; i < _index; i++) {
 253        least = MIN2(least, _base[i]);
 254      }
 255      return least;
 256   }
 257 
 258   // Exposed here to allow stack expansion in || case.
 259   Mutex* par_lock() { return &_par_lock; }
 260 };
 261 
 262 class CardTableRS;
 263 class CMSParGCThreadState;
 264 
 265 class ModUnionClosure: public MemRegionClosure {
 266  protected:
 267   CMSBitMap* _t;
 268  public:
 269   ModUnionClosure(CMSBitMap* t): _t(t) { }
 270   void do_MemRegion(MemRegion mr);
 271 };
 272 
 273 class ModUnionClosurePar: public ModUnionClosure {
 274  public:
 275   ModUnionClosurePar(CMSBitMap* t): ModUnionClosure(t) { }
 276   void do_MemRegion(MemRegion mr);
 277 };
 278 
 279 // Survivor Chunk Array in support of parallelization of
 280 // Survivor Space rescan.
 281 class ChunkArray: public CHeapObj<mtGC> {
 282   size_t _index;
 283   size_t _capacity;
 284   size_t _overflows;
 285   HeapWord** _array;   // storage for array
 286 
 287  public:
 288   ChunkArray() : _index(0), _capacity(0), _overflows(0), _array(NULL) {}
 289   ChunkArray(HeapWord** a, size_t c):
 290     _index(0), _capacity(c), _overflows(0), _array(a) {}
 291 
 292   HeapWord** array() { return _array; }
 293   void set_array(HeapWord** a) { _array = a; }
 294 
 295   size_t capacity() { return _capacity; }
 296   void set_capacity(size_t c) { _capacity = c; }
 297 
 298   size_t end() {
 299     assert(_index <= capacity(),
 300            "_index (" SIZE_FORMAT ") > _capacity (" SIZE_FORMAT "): out of bounds",
 301            _index, _capacity);
 302     return _index;
 303   }  // exclusive
 304 
 305   HeapWord* nth(size_t n) {
 306     assert(n < end(), "Out of bounds access");
 307     return _array[n];
 308   }
 309 
 310   void reset() {
 311     _index = 0;
 312     if (_overflows > 0) {
 313       log_trace(gc)("CMS: ChunkArray[" SIZE_FORMAT "] overflowed " SIZE_FORMAT " times", _capacity, _overflows);
 314     }
 315     _overflows = 0;
 316   }
 317 
 318   void record_sample(HeapWord* p, size_t sz) {
 319     // For now we do not do anything with the size
 320     if (_index < _capacity) {
 321       _array[_index++] = p;
 322     } else {
 323       ++_overflows;
 324       assert(_index == _capacity,
 325              "_index (" SIZE_FORMAT ") > _capacity (" SIZE_FORMAT
 326              "): out of bounds at overflow#" SIZE_FORMAT,
 327              _index, _capacity, _overflows);
 328     }
 329   }
 330 };
 331 
 332 //
 333 // Timing, allocation and promotion statistics for gc scheduling and incremental
 334 // mode pacing.  Most statistics are exponential averages.
 335 //
 336 class CMSStats VALUE_OBJ_CLASS_SPEC {
 337  private:
 338   ConcurrentMarkSweepGeneration* const _cms_gen;   // The cms (old) gen.
 339 
 340   // The following are exponential averages with factor alpha:
 341   //   avg = (100 - alpha) * avg + alpha * cur_sample
 342   //
 343   //   The durations measure:  end_time[n] - start_time[n]
 344   //   The periods measure:    start_time[n] - start_time[n-1]
 345   //
 346   // The cms period and duration include only concurrent collections; time spent
 347   // in foreground cms collections due to System.gc() or because of a failure to
 348   // keep up are not included.
 349   //
 350   // There are 3 alphas to "bootstrap" the statistics.  The _saved_alpha is the
 351   // real value, but is used only after the first period.  A value of 100 is
 352   // used for the first sample so it gets the entire weight.
 353   unsigned int _saved_alpha; // 0-100
 354   unsigned int _gc0_alpha;
 355   unsigned int _cms_alpha;
 356 
 357   double _gc0_duration;
 358   double _gc0_period;
 359   size_t _gc0_promoted;         // bytes promoted per gc0
 360   double _cms_duration;
 361   double _cms_duration_pre_sweep; // time from initiation to start of sweep
 362   double _cms_period;
 363   size_t _cms_allocated;        // bytes of direct allocation per gc0 period
 364 
 365   // Timers.
 366   elapsedTimer _cms_timer;
 367   TimeStamp    _gc0_begin_time;
 368   TimeStamp    _cms_begin_time;
 369   TimeStamp    _cms_end_time;
 370 
 371   // Snapshots of the amount used in the CMS generation.
 372   size_t _cms_used_at_gc0_begin;
 373   size_t _cms_used_at_gc0_end;
 374   size_t _cms_used_at_cms_begin;
 375 
 376   // Used to prevent the duty cycle from being reduced in the middle of a cms
 377   // cycle.
 378   bool _allow_duty_cycle_reduction;
 379 
 380   enum {
 381     _GC0_VALID = 0x1,
 382     _CMS_VALID = 0x2,
 383     _ALL_VALID = _GC0_VALID | _CMS_VALID
 384   };
 385 
 386   unsigned int _valid_bits;
 387 
 388  protected:
 389   // In support of adjusting of cms trigger ratios based on history
 390   // of concurrent mode failure.
 391   double cms_free_adjustment_factor(size_t free) const;
 392   void   adjust_cms_free_adjustment_factor(bool fail, size_t free);
 393 
 394  public:
 395   CMSStats(ConcurrentMarkSweepGeneration* cms_gen,
 396            unsigned int alpha = CMSExpAvgFactor);
 397 
 398   // Whether or not the statistics contain valid data; higher level statistics
 399   // cannot be called until this returns true (they require at least one young
 400   // gen and one cms cycle to have completed).
 401   bool valid() const;
 402 
 403   // Record statistics.
 404   void record_gc0_begin();
 405   void record_gc0_end(size_t cms_gen_bytes_used);
 406   void record_cms_begin();
 407   void record_cms_end();
 408 
 409   // Allow management of the cms timer, which must be stopped/started around
 410   // yield points.
 411   elapsedTimer& cms_timer()     { return _cms_timer; }
 412   void start_cms_timer()        { _cms_timer.start(); }
 413   void stop_cms_timer()         { _cms_timer.stop(); }
 414 
 415   // Basic statistics; units are seconds or bytes.
 416   double gc0_period() const     { return _gc0_period; }
 417   double gc0_duration() const   { return _gc0_duration; }
 418   size_t gc0_promoted() const   { return _gc0_promoted; }
 419   double cms_period() const          { return _cms_period; }
 420   double cms_duration() const        { return _cms_duration; }
 421   size_t cms_allocated() const       { return _cms_allocated; }
 422 
 423   size_t cms_used_at_gc0_end() const { return _cms_used_at_gc0_end;}
 424 
 425   // Seconds since the last background cms cycle began or ended.
 426   double cms_time_since_begin() const;
 427   double cms_time_since_end() const;
 428 
 429   // Higher level statistics--caller must check that valid() returns true before
 430   // calling.
 431 
 432   // Returns bytes promoted per second of wall clock time.
 433   double promotion_rate() const;
 434 
 435   // Returns bytes directly allocated per second of wall clock time.
 436   double cms_allocation_rate() const;
 437 
 438   // Rate at which space in the cms generation is being consumed (sum of the
 439   // above two).
 440   double cms_consumption_rate() const;
 441 
 442   // Returns an estimate of the number of seconds until the cms generation will
 443   // fill up, assuming no collection work is done.
 444   double time_until_cms_gen_full() const;
 445 
 446   // Returns an estimate of the number of seconds remaining until
 447   // the cms generation collection should start.
 448   double time_until_cms_start() const;
 449 
 450   // End of higher level statistics.
 451 
 452   // Debugging.
 453   void print_on(outputStream* st) const PRODUCT_RETURN;
 454   void print() const { print_on(tty); }
 455 };
 456 
 457 // A closure related to weak references processing which
 458 // we embed in the CMSCollector, since we need to pass
 459 // it to the reference processor for secondary filtering
 460 // of references based on reachability of referent;
 461 // see role of _is_alive_non_header closure in the
 462 // ReferenceProcessor class.
 463 // For objects in the CMS generation, this closure checks
 464 // if the object is "live" (reachable). Used in weak
 465 // reference processing.
 466 class CMSIsAliveClosure: public BoolObjectClosure {
 467   const MemRegion  _span;
 468   const CMSBitMap* _bit_map;
 469 
 470   friend class CMSCollector;
 471  public:
 472   CMSIsAliveClosure(MemRegion span,
 473                     CMSBitMap* bit_map):
 474     _span(span),
 475     _bit_map(bit_map) {
 476     assert(!span.is_empty(), "Empty span could spell trouble");
 477   }
 478 
 479   bool do_object_b(oop obj);
 480 };
 481 
 482 
 483 // Implements AbstractRefProcTaskExecutor for CMS.
 484 class CMSRefProcTaskExecutor: public AbstractRefProcTaskExecutor {
 485 public:
 486 
 487   CMSRefProcTaskExecutor(CMSCollector& collector)
 488     : _collector(collector)
 489   { }
 490 
 491   // Executes a task using worker threads.
 492   virtual void execute(ProcessTask& task);
 493   virtual void execute(EnqueueTask& task);
 494 private:
 495   CMSCollector& _collector;
 496 };
 497 
 498 
 499 class CMSCollector: public CHeapObj<mtGC> {
 500   friend class VMStructs;
 501   friend class ConcurrentMarkSweepThread;
 502   friend class ConcurrentMarkSweepGeneration;
 503   friend class CompactibleFreeListSpace;
 504   friend class CMSParMarkTask;
 505   friend class CMSParInitialMarkTask;
 506   friend class CMSParRemarkTask;
 507   friend class CMSConcMarkingTask;
 508   friend class CMSRefProcTaskProxy;
 509   friend class CMSRefProcTaskExecutor;
 510   friend class ScanMarkedObjectsAgainCarefullyClosure;  // for sampling eden
 511   friend class SurvivorSpacePrecleanClosure;            // --- ditto -------
 512   friend class PushOrMarkClosure;             // to access _restart_addr
 513   friend class ParPushOrMarkClosure;          // to access _restart_addr
 514   friend class MarkFromRootsClosure;          //  -- ditto --
 515                                               // ... and for clearing cards
 516   friend class ParMarkFromRootsClosure;       //  to access _restart_addr
 517                                               // ... and for clearing cards
 518   friend class ParConcMarkingClosure;         //  to access _restart_addr etc.
 519   friend class MarkFromRootsVerifyClosure;    // to access _restart_addr
 520   friend class PushAndMarkVerifyClosure;      //  -- ditto --
 521   friend class MarkRefsIntoAndScanClosure;    // to access _overflow_list
 522   friend class PushAndMarkClosure;            //  -- ditto --
 523   friend class ParPushAndMarkClosure;         //  -- ditto --
 524   friend class CMSKeepAliveClosure;           //  -- ditto --
 525   friend class CMSDrainMarkingStackClosure;   //  -- ditto --
 526   friend class CMSInnerParMarkAndPushClosure; //  -- ditto --
 527   NOT_PRODUCT(friend class ScanMarkedObjectsAgainClosure;) //  assertion on _overflow_list
 528   friend class ReleaseForegroundGC;  // to access _foregroundGCShouldWait
 529   friend class VM_CMS_Operation;
 530   friend class VM_CMS_Initial_Mark;
 531   friend class VM_CMS_Final_Remark;
 532   friend class TraceCMSMemoryManagerStats;
 533 
 534  private:
 535   jlong _time_of_last_gc;
 536   void update_time_of_last_gc(jlong now) {
 537     _time_of_last_gc = now;
 538   }
 539 
 540   OopTaskQueueSet* _task_queues;
 541 
 542   // Overflow list of grey objects, threaded through mark-word
 543   // Manipulated with CAS in the parallel/multi-threaded case.
 544   oop _overflow_list;
 545   // The following array-pair keeps track of mark words
 546   // displaced for accommodating overflow list above.
 547   // This code will likely be revisited under RFE#4922830.
 548   Stack<oop, mtGC>     _preserved_oop_stack;
 549   Stack<markOop, mtGC> _preserved_mark_stack;
 550 
 551   int*             _hash_seed;
 552 
 553   // In support of multi-threaded concurrent phases
 554   YieldingFlexibleWorkGang* _conc_workers;
 555 
 556   // Performance Counters
 557   CollectorCounters* _gc_counters;
 558   CollectorCounters* _cgc_counters;
 559 
 560   // Initialization Errors
 561   bool _completed_initialization;
 562 
 563   // In support of ExplicitGCInvokesConcurrent
 564   static bool _full_gc_requested;
 565   static GCCause::Cause _full_gc_cause;
 566   unsigned int _collection_count_start;
 567 
 568   // Should we unload classes this concurrent cycle?
 569   bool _should_unload_classes;
 570   unsigned int  _concurrent_cycles_since_last_unload;
 571   unsigned int concurrent_cycles_since_last_unload() const {
 572     return _concurrent_cycles_since_last_unload;
 573   }
 574   // Did we (allow) unload classes in the previous concurrent cycle?
 575   bool unloaded_classes_last_cycle() const {
 576     return concurrent_cycles_since_last_unload() == 0;
 577   }
 578   // Root scanning options for perm gen
 579   int _roots_scanning_options;
 580   int roots_scanning_options() const      { return _roots_scanning_options; }
 581   void add_root_scanning_option(int o)    { _roots_scanning_options |= o;   }
 582   void remove_root_scanning_option(int o) { _roots_scanning_options &= ~o;  }
 583 
 584   // Verification support
 585   CMSBitMap     _verification_mark_bm;
 586   void verify_after_remark_work_1();
 587   void verify_after_remark_work_2();
 588 
 589   // True if any verification flag is on.
 590   bool _verifying;
 591   bool verifying() const { return _verifying; }
 592   void set_verifying(bool v) { _verifying = v; }
 593 
 594   // Collector policy
 595   ConcurrentMarkSweepPolicy* _collector_policy;
 596   ConcurrentMarkSweepPolicy* collector_policy() { return _collector_policy; }
 597 
 598   void set_did_compact(bool v);
 599 
 600   // XXX Move these to CMSStats ??? FIX ME !!!
 601   elapsedTimer _inter_sweep_timer;   // Time between sweeps
 602   elapsedTimer _intra_sweep_timer;   // Time _in_ sweeps
 603   // Padded decaying average estimates of the above
 604   AdaptivePaddedAverage _inter_sweep_estimate;
 605   AdaptivePaddedAverage _intra_sweep_estimate;
 606 
 607   CMSTracer* _gc_tracer_cm;
 608   ConcurrentGCTimer* _gc_timer_cm;
 609 
 610   bool _cms_start_registered;
 611 
 612   GCHeapSummary _last_heap_summary;
 613   MetaspaceSummary _last_metaspace_summary;
 614 
 615   void register_gc_start(GCCause::Cause cause);
 616   void register_gc_end();
 617   void save_heap_summary();
 618   void report_heap_summary(GCWhen::Type when);
 619 
 620  protected:
 621   ConcurrentMarkSweepGeneration* _cmsGen;  // Old gen (CMS)
 622   MemRegion                      _span;    // Span covering above two
 623   CardTableRS*                   _ct;      // Card table
 624 
 625   // CMS marking support structures
 626   CMSBitMap     _markBitMap;
 627   CMSBitMap     _modUnionTable;
 628   CMSMarkStack  _markStack;
 629 
 630   HeapWord*     _restart_addr; // In support of marking stack overflow
 631   void          lower_restart_addr(HeapWord* low);
 632 
 633   // Counters in support of marking stack / work queue overflow handling:
 634   // a non-zero value indicates certain types of overflow events during
 635   // the current CMS cycle and could lead to stack resizing efforts at
 636   // an opportune future time.
 637   size_t        _ser_pmc_preclean_ovflw;
 638   size_t        _ser_pmc_remark_ovflw;
 639   size_t        _par_pmc_remark_ovflw;
 640   size_t        _ser_kac_preclean_ovflw;
 641   size_t        _ser_kac_ovflw;
 642   size_t        _par_kac_ovflw;
 643   NOT_PRODUCT(ssize_t _num_par_pushes;)
 644 
 645   // ("Weak") Reference processing support.
 646   ReferenceProcessor*            _ref_processor;
 647   CMSIsAliveClosure              _is_alive_closure;
 648   // Keep this textually after _markBitMap and _span; c'tor dependency.
 649 
 650   ConcurrentMarkSweepThread*     _cmsThread;   // The thread doing the work
 651   ModUnionClosurePar _modUnionClosurePar;
 652 
 653   // CMS abstract state machine
 654   // initial_state: Idling
 655   // next_state(Idling)            = {Marking}
 656   // next_state(Marking)           = {Precleaning, Sweeping}
 657   // next_state(Precleaning)       = {AbortablePreclean, FinalMarking}
 658   // next_state(AbortablePreclean) = {FinalMarking}
 659   // next_state(FinalMarking)      = {Sweeping}
 660   // next_state(Sweeping)          = {Resizing}
 661   // next_state(Resizing)          = {Resetting}
 662   // next_state(Resetting)         = {Idling}
 663   // The numeric values below are chosen so that:
 664   // . _collectorState <= Idling ==  post-sweep && pre-mark
 665   // . _collectorState in (Idling, Sweeping) == {initial,final}marking ||
 666   //                                            precleaning || abortablePrecleanb
 667  public:
 668   enum CollectorState {
 669     Resizing            = 0,
 670     Resetting           = 1,
 671     Idling              = 2,
 672     InitialMarking      = 3,
 673     Marking             = 4,
 674     Precleaning         = 5,
 675     AbortablePreclean   = 6,
 676     FinalMarking        = 7,
 677     Sweeping            = 8
 678   };
 679  protected:
 680   static CollectorState _collectorState;
 681 
 682   // State related to prologue/epilogue invocation for my generations
 683   bool _between_prologue_and_epilogue;
 684 
 685   // Signaling/State related to coordination between fore- and background GC
 686   // Note: When the baton has been passed from background GC to foreground GC,
 687   // _foregroundGCIsActive is true and _foregroundGCShouldWait is false.
 688   static bool _foregroundGCIsActive;    // true iff foreground collector is active or
 689                                  // wants to go active
 690   static bool _foregroundGCShouldWait;  // true iff background GC is active and has not
 691                                  // yet passed the baton to the foreground GC
 692 
 693   // Support for CMSScheduleRemark (abortable preclean)
 694   bool _abort_preclean;
 695   bool _start_sampling;
 696 
 697   int    _numYields;
 698   size_t _numDirtyCards;
 699   size_t _sweep_count;
 700 
 701   // Occupancy used for bootstrapping stats
 702   double _bootstrap_occupancy;
 703 
 704   // Timer
 705   elapsedTimer _timer;
 706 
 707   // Timing, allocation and promotion statistics, used for scheduling.
 708   CMSStats      _stats;
 709 
 710   enum CMS_op_type {
 711     CMS_op_checkpointRootsInitial,
 712     CMS_op_checkpointRootsFinal
 713   };
 714 
 715   void do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause);
 716   bool stop_world_and_do(CMS_op_type op);
 717 
 718   OopTaskQueueSet* task_queues() { return _task_queues; }
 719   int*             hash_seed(int i) { return &_hash_seed[i]; }
 720   YieldingFlexibleWorkGang* conc_workers() { return _conc_workers; }
 721 
 722   // Support for parallelizing Eden rescan in CMS remark phase
 723   void sample_eden(); // ... sample Eden space top
 724 
 725  private:
 726   // Support for parallelizing young gen rescan in CMS remark phase
 727   ParNewGeneration* _young_gen;
 728 
 729   HeapWord** _top_addr;    // ... Top of Eden
 730   HeapWord** _end_addr;    // ... End of Eden
 731   Mutex*     _eden_chunk_lock;
 732   HeapWord** _eden_chunk_array; // ... Eden partitioning array
 733   size_t     _eden_chunk_index; // ... top (exclusive) of array
 734   size_t     _eden_chunk_capacity;  // ... max entries in array
 735 
 736   // Support for parallelizing survivor space rescan
 737   HeapWord** _survivor_chunk_array;
 738   size_t     _survivor_chunk_index;
 739   size_t     _survivor_chunk_capacity;
 740   size_t*    _cursor;
 741   ChunkArray* _survivor_plab_array;
 742 
 743   // Support for marking stack overflow handling
 744   bool take_from_overflow_list(size_t num, CMSMarkStack* to_stack);
 745   bool par_take_from_overflow_list(size_t num,
 746                                    OopTaskQueue* to_work_q,
 747                                    int no_of_gc_threads);
 748   void push_on_overflow_list(oop p);
 749   void par_push_on_overflow_list(oop p);
 750   // The following is, obviously, not, in general, "MT-stable"
 751   bool overflow_list_is_empty() const;
 752 
 753   void preserve_mark_if_necessary(oop p);
 754   void par_preserve_mark_if_necessary(oop p);
 755   void preserve_mark_work(oop p, markOop m);
 756   void restore_preserved_marks_if_any();
 757   NOT_PRODUCT(bool no_preserved_marks() const;)
 758   // In support of testing overflow code
 759   NOT_PRODUCT(int _overflow_counter;)
 760   NOT_PRODUCT(bool simulate_overflow();)       // Sequential
 761   NOT_PRODUCT(bool par_simulate_overflow();)   // MT version
 762 
 763   // CMS work methods
 764   void checkpointRootsInitialWork(); // Initial checkpoint work
 765 
 766   // A return value of false indicates failure due to stack overflow
 767   bool markFromRootsWork();  // Concurrent marking work
 768 
 769  public:   // FIX ME!!! only for testing
 770   bool do_marking_st();      // Single-threaded marking
 771   bool do_marking_mt();      // Multi-threaded  marking
 772 
 773  private:
 774 
 775   // Concurrent precleaning work
 776   size_t preclean_mod_union_table(ConcurrentMarkSweepGeneration* old_gen,
 777                                   ScanMarkedObjectsAgainCarefullyClosure* cl);
 778   size_t preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
 779                              ScanMarkedObjectsAgainCarefullyClosure* cl);
 780   // Does precleaning work, returning a quantity indicative of
 781   // the amount of "useful work" done.
 782   size_t preclean_work(bool clean_refs, bool clean_survivors);
 783   void preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock);
 784   void abortable_preclean(); // Preclean while looking for possible abort
 785   void initialize_sequential_subtasks_for_young_gen_rescan(int i);
 786   // Helper function for above; merge-sorts the per-thread plab samples
 787   void merge_survivor_plab_arrays(ContiguousSpace* surv, int no_of_gc_threads);
 788   // Resets (i.e. clears) the per-thread plab sample vectors
 789   void reset_survivor_plab_arrays();
 790 
 791   // Final (second) checkpoint work
 792   void checkpointRootsFinalWork();
 793   // Work routine for parallel version of remark
 794   void do_remark_parallel();
 795   // Work routine for non-parallel version of remark
 796   void do_remark_non_parallel();
 797   // Reference processing work routine (during second checkpoint)
 798   void refProcessingWork();
 799 
 800   // Concurrent sweeping work
 801   void sweepWork(ConcurrentMarkSweepGeneration* old_gen);
 802 
 803   // Concurrent resetting of support data structures
 804   void reset_concurrent();
 805   // Resetting of support data structures from a STW full GC
 806   void reset_stw();
 807 
 808   // Clear _expansion_cause fields of constituent generations
 809   void clear_expansion_cause();
 810 
 811   // An auxiliary method used to record the ends of
 812   // used regions of each generation to limit the extent of sweep
 813   void save_sweep_limits();
 814 
 815   // A work method used by the foreground collector to do
 816   // a mark-sweep-compact.
 817   void do_compaction_work(bool clear_all_soft_refs);
 818 
 819   // Work methods for reporting concurrent mode interruption or failure
 820   bool is_external_interruption();
 821   void report_concurrent_mode_interruption();
 822 
 823   // If the background GC is active, acquire control from the background
 824   // GC and do the collection.
 825   void acquire_control_and_collect(bool   full, bool clear_all_soft_refs);
 826 
 827   // For synchronizing passing of control from background to foreground
 828   // GC.  waitForForegroundGC() is called by the background
 829   // collector.  It if had to wait for a foreground collection,
 830   // it returns true and the background collection should assume
 831   // that the collection was finished by the foreground
 832   // collector.
 833   bool waitForForegroundGC();
 834 
 835   size_t block_size_using_printezis_bits(HeapWord* addr) const;
 836   size_t block_size_if_printezis_bits(HeapWord* addr) const;
 837   HeapWord* next_card_start_after_block(HeapWord* addr) const;
 838 
 839   void setup_cms_unloading_and_verification_state();
 840  public:
 841   CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
 842                CardTableRS*                   ct,
 843                ConcurrentMarkSweepPolicy*     cp);
 844   ConcurrentMarkSweepThread* cmsThread() { return _cmsThread; }
 845 
 846   ReferenceProcessor* ref_processor() { return _ref_processor; }
 847   void ref_processor_init();
 848 
 849   Mutex* bitMapLock()        const { return _markBitMap.lock();    }
 850   static CollectorState abstract_state() { return _collectorState;  }
 851 
 852   bool should_abort_preclean() const; // Whether preclean should be aborted.
 853   size_t get_eden_used() const;
 854   size_t get_eden_capacity() const;
 855 
 856   ConcurrentMarkSweepGeneration* cmsGen() { return _cmsGen; }
 857 
 858   // Locking checks
 859   NOT_PRODUCT(static bool have_cms_token();)
 860 
 861   bool shouldConcurrentCollect();
 862 
 863   void collect(bool   full,
 864                bool   clear_all_soft_refs,
 865                size_t size,
 866                bool   tlab);
 867   void collect_in_background(GCCause::Cause cause);
 868 
 869   // In support of ExplicitGCInvokesConcurrent
 870   static void request_full_gc(unsigned int full_gc_count, GCCause::Cause cause);
 871   // Should we unload classes in a particular concurrent cycle?
 872   bool should_unload_classes() const {
 873     return _should_unload_classes;
 874   }
 875   void update_should_unload_classes();
 876 
 877   void direct_allocated(HeapWord* start, size_t size);
 878 
 879   // Object is dead if not marked and current phase is sweeping.
 880   bool is_dead_obj(oop obj) const;
 881 
 882   // After a promotion (of "start"), do any necessary marking.
 883   // If "par", then it's being done by a parallel GC thread.
 884   // The last two args indicate if we need precise marking
 885   // and if so the size of the object so it can be dirtied
 886   // in its entirety.
 887   void promoted(bool par, HeapWord* start,
 888                 bool is_obj_array, size_t obj_size);
 889 
 890   void getFreelistLocks() const;
 891   void releaseFreelistLocks() const;
 892   bool haveFreelistLocks() const;
 893 
 894   // Adjust size of underlying generation
 895   void compute_new_size();
 896 
 897   // GC prologue and epilogue
 898   void gc_prologue(bool full);
 899   void gc_epilogue(bool full);
 900 
 901   jlong time_of_last_gc(jlong now) {
 902     if (_collectorState <= Idling) {
 903       // gc not in progress
 904       return _time_of_last_gc;
 905     } else {
 906       // collection in progress
 907       return now;
 908     }
 909   }
 910 
 911   // Support for parallel remark of survivor space
 912   void* get_data_recorder(int thr_num);
 913   void sample_eden_chunk();
 914 
 915   CMSBitMap* markBitMap()  { return &_markBitMap; }
 916   void directAllocated(HeapWord* start, size_t size);
 917 
 918   // Main CMS steps and related support
 919   void checkpointRootsInitial();
 920   bool markFromRoots();  // a return value of false indicates failure
 921                          // due to stack overflow
 922   void preclean();
 923   void checkpointRootsFinal();
 924   void sweep();
 925 
 926   // Check that the currently executing thread is the expected
 927   // one (foreground collector or background collector).
 928   static void check_correct_thread_executing() PRODUCT_RETURN;
 929 
 930   NOT_PRODUCT(bool is_cms_reachable(HeapWord* addr);)
 931 
 932   // Performance Counter Support
 933   CollectorCounters* counters()    { return _gc_counters; }
 934   CollectorCounters* cgc_counters()    { return _cgc_counters; }
 935 
 936   // Timer stuff
 937   void    startTimer() { assert(!_timer.is_active(), "Error"); _timer.start();   }
 938   void    stopTimer()  { assert( _timer.is_active(), "Error"); _timer.stop();    }
 939   void    resetTimer() { assert(!_timer.is_active(), "Error"); _timer.reset();   }
 940   jlong   timerTicks() { assert(!_timer.is_active(), "Error"); return _timer.ticks(); }
 941 
 942   int  yields()          { return _numYields; }
 943   void resetYields()     { _numYields = 0;    }
 944   void incrementYields() { _numYields++;      }
 945   void resetNumDirtyCards()               { _numDirtyCards = 0; }
 946   void incrementNumDirtyCards(size_t num) { _numDirtyCards += num; }
 947   size_t  numDirtyCards()                 { return _numDirtyCards; }
 948 
 949   static bool foregroundGCShouldWait() { return _foregroundGCShouldWait; }
 950   static void set_foregroundGCShouldWait(bool v) { _foregroundGCShouldWait = v; }
 951   static bool foregroundGCIsActive() { return _foregroundGCIsActive; }
 952   static void set_foregroundGCIsActive(bool v) { _foregroundGCIsActive = v; }
 953   size_t sweep_count() const             { return _sweep_count; }
 954   void   increment_sweep_count()         { _sweep_count++; }
 955 
 956   // Timers/stats for gc scheduling and incremental mode pacing.
 957   CMSStats& stats() { return _stats; }
 958 
 959   // Adaptive size policy
 960   AdaptiveSizePolicy* size_policy();
 961 
 962   static void print_on_error(outputStream* st);
 963 
 964   // Debugging
 965   void verify();
 966   bool verify_after_remark();
 967   void verify_ok_to_terminate() const PRODUCT_RETURN;
 968   void verify_work_stacks_empty() const PRODUCT_RETURN;
 969   void verify_overflow_empty() const PRODUCT_RETURN;
 970 
 971   // Convenience methods in support of debugging
 972   static const size_t skip_header_HeapWords() PRODUCT_RETURN0;
 973   HeapWord* block_start(const void* p) const PRODUCT_RETURN0;
 974 
 975   // Accessors
 976   CMSMarkStack* verification_mark_stack() { return &_markStack; }
 977   CMSBitMap*    verification_mark_bm()    { return &_verification_mark_bm; }
 978 
 979   // Initialization errors
 980   bool completed_initialization() { return _completed_initialization; }
 981 
 982   void print_eden_and_survivor_chunk_arrays();
 983 
 984   ConcurrentGCTimer* gc_timer_cm() const { return _gc_timer_cm; }
 985 };
 986 
 987 class CMSExpansionCause : public AllStatic  {
 988  public:
 989   enum Cause {
 990     _no_expansion,
 991     _satisfy_free_ratio,
 992     _satisfy_promotion,
 993     _satisfy_allocation,
 994     _allocate_par_lab,
 995     _allocate_par_spooling_space,
 996     _adaptive_size_policy
 997   };
 998   // Return a string describing the cause of the expansion.
 999   static const char* to_string(CMSExpansionCause::Cause cause);
1000 };
1001 
1002 class ConcurrentMarkSweepGeneration: public CardGeneration {
1003   friend class VMStructs;
1004   friend class ConcurrentMarkSweepThread;
1005   friend class ConcurrentMarkSweep;
1006   friend class CMSCollector;
1007  protected:
1008   static CMSCollector*       _collector; // the collector that collects us
1009   CompactibleFreeListSpace*  _cmsSpace;  // underlying space (only one for now)
1010 
1011   // Performance Counters
1012   GenerationCounters*      _gen_counters;
1013   GSpaceCounters*          _space_counters;
1014 
1015   // Words directly allocated, used by CMSStats.
1016   size_t _direct_allocated_words;
1017 
1018   // Non-product stat counters
1019   NOT_PRODUCT(
1020     size_t _numObjectsPromoted;
1021     size_t _numWordsPromoted;
1022     size_t _numObjectsAllocated;
1023     size_t _numWordsAllocated;
1024   )
1025 
1026   // Used for sizing decisions
1027   bool _incremental_collection_failed;
1028   bool incremental_collection_failed() {
1029     return _incremental_collection_failed;
1030   }
1031   void set_incremental_collection_failed() {
1032     _incremental_collection_failed = true;
1033   }
1034   void clear_incremental_collection_failed() {
1035     _incremental_collection_failed = false;
1036   }
1037 
1038   // accessors
1039   void set_expansion_cause(CMSExpansionCause::Cause v) { _expansion_cause = v;}
1040   CMSExpansionCause::Cause expansion_cause() const { return _expansion_cause; }
1041 
1042   // Accessing spaces
1043   CompactibleSpace* space() const { return (CompactibleSpace*)_cmsSpace; }
1044 
1045  private:
1046   // For parallel young-gen GC support.
1047   CMSParGCThreadState** _par_gc_thread_states;
1048 
1049   // Reason generation was expanded
1050   CMSExpansionCause::Cause _expansion_cause;
1051 
1052   // In support of MinChunkSize being larger than min object size
1053   const double _dilatation_factor;
1054 
1055   // True if a compacting collection was done.
1056   bool _did_compact;
1057   bool did_compact() { return _did_compact; }
1058 
1059   // Fraction of current occupancy at which to start a CMS collection which
1060   // will collect this generation (at least).
1061   double _initiating_occupancy;
1062 
1063  protected:
1064   // Shrink generation by specified size (returns false if unable to shrink)
1065   void shrink_free_list_by(size_t bytes);
1066 
1067   // Update statistics for GC
1068   virtual void update_gc_stats(Generation* current_generation, bool full);
1069 
1070   // Maximum available space in the generation (including uncommitted)
1071   // space.
1072   size_t max_available() const;
1073 
1074   // getter and initializer for _initiating_occupancy field.
1075   double initiating_occupancy() const { return _initiating_occupancy; }
1076   void   init_initiating_occupancy(intx io, uintx tr);
1077 
1078   void expand_for_gc_cause(size_t bytes, size_t expand_bytes, CMSExpansionCause::Cause cause);
1079 
1080   void assert_correct_size_change_locking();
1081 
1082  public:
1083   ConcurrentMarkSweepGeneration(ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct);
1084 
1085   // Accessors
1086   CMSCollector* collector() const { return _collector; }
1087   static void set_collector(CMSCollector* collector) {
1088     assert(_collector == NULL, "already set");
1089     _collector = collector;
1090   }
1091   CompactibleFreeListSpace*  cmsSpace() const { return _cmsSpace;  }
1092 
1093   Mutex* freelistLock() const;
1094 
1095   virtual Generation::Name kind() { return Generation::ConcurrentMarkSweep; }
1096 
1097   void set_did_compact(bool v) { _did_compact = v; }
1098 
1099   bool refs_discovery_is_atomic() const { return false; }
1100   bool refs_discovery_is_mt()     const {
1101     // Note: CMS does MT-discovery during the parallel-remark
1102     // phases. Use ReferenceProcessorMTMutator to make refs
1103     // discovery MT-safe during such phases or other parallel
1104     // discovery phases in the future. This may all go away
1105     // if/when we decide that refs discovery is sufficiently
1106     // rare that the cost of the CAS's involved is in the
1107     // noise. That's a measurement that should be done, and
1108     // the code simplified if that turns out to be the case.
1109     return ConcGCThreads > 1;
1110   }
1111 
1112   // Override
1113   virtual void ref_processor_init();
1114 
1115   void clear_expansion_cause() { _expansion_cause = CMSExpansionCause::_no_expansion; }
1116 
1117   // Space enquiries
1118   double occupancy() const { return ((double)used())/((double)capacity()); }
1119   size_t contiguous_available() const;
1120   size_t unsafe_max_alloc_nogc() const;
1121 
1122   // over-rides
1123   MemRegion used_region_at_save_marks() const;
1124 
1125   // Adjust quantities in the generation affected by
1126   // the compaction.
1127   void reset_after_compaction();
1128 
1129   // Allocation support
1130   HeapWord* allocate(size_t size, bool tlab);
1131   HeapWord* have_lock_and_allocate(size_t size, bool tlab);
1132   oop       promote(oop obj, size_t obj_size);
1133   HeapWord* par_allocate(size_t size, bool tlab) {
1134     return allocate(size, tlab);
1135   }
1136 
1137 
1138   // Used by CMSStats to track direct allocation.  The value is sampled and
1139   // reset after each young gen collection.
1140   size_t direct_allocated_words() const { return _direct_allocated_words; }
1141   void reset_direct_allocated_words()   { _direct_allocated_words = 0; }
1142 
1143   // Overrides for parallel promotion.
1144   virtual oop par_promote(int thread_num,
1145                           oop obj, markOop m, size_t word_sz);
1146   virtual void par_promote_alloc_done(int thread_num);
1147   virtual void par_oop_since_save_marks_iterate_done(int thread_num);
1148 
1149   virtual bool promotion_attempt_is_safe(size_t promotion_in_bytes) const;
1150 
1151   // Inform this (old) generation that a promotion failure was
1152   // encountered during a collection of the young generation.
1153   virtual void promotion_failure_occurred();
1154 
1155   bool should_collect(bool full, size_t size, bool tlab);
1156   virtual bool should_concurrent_collect() const;
1157   virtual bool is_too_full() const;
1158   void collect(bool   full,
1159                bool   clear_all_soft_refs,
1160                size_t size,
1161                bool   tlab);
1162 
1163   HeapWord* expand_and_allocate(size_t word_size,
1164                                 bool tlab,
1165                                 bool parallel = false);
1166 
1167   // GC prologue and epilogue
1168   void gc_prologue(bool full);
1169   void gc_prologue_work(bool full, bool registerClosure,
1170                         ModUnionClosure* modUnionClosure);
1171   void gc_epilogue(bool full);
1172   void gc_epilogue_work(bool full);
1173 
1174   // Time since last GC of this generation
1175   jlong time_of_last_gc(jlong now) {
1176     return collector()->time_of_last_gc(now);
1177   }
1178   void update_time_of_last_gc(jlong now) {
1179     collector()-> update_time_of_last_gc(now);
1180   }
1181 
1182   // Allocation failure
1183   void shrink(size_t bytes);
1184   HeapWord* expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz);
1185   bool expand_and_ensure_spooling_space(PromotionInfo* promo);
1186 
1187   // Iteration support and related enquiries
1188   void save_marks();
1189   bool no_allocs_since_save_marks();
1190 
1191   // Iteration support specific to CMS generations
1192   void save_sweep_limit();
1193 
1194   // More iteration support
1195   virtual void oop_iterate(ExtendedOopClosure* cl);
1196   virtual void safe_object_iterate(ObjectClosure* cl);
1197   virtual void object_iterate(ObjectClosure* cl);
1198 
1199   // Need to declare the full complement of closures, whether we'll
1200   // override them or not, or get message from the compiler:
1201   //   oop_since_save_marks_iterate_nv hides virtual function...
1202   #define CMS_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix) \
1203     void oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl);
1204   ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DECL)
1205 
1206   // Smart allocation  XXX -- move to CFLSpace?
1207   void setNearLargestChunk();
1208   bool isNearLargestChunk(HeapWord* addr);
1209 
1210   // Get the chunk at the end of the space.  Delegates to
1211   // the space.
1212   FreeChunk* find_chunk_at_end();
1213 
1214   void post_compact();
1215 
1216   // Debugging
1217   void prepare_for_verify();
1218   void verify();
1219   void print_statistics()               PRODUCT_RETURN;
1220 
1221   // Performance Counters support
1222   virtual void update_counters();
1223   virtual void update_counters(size_t used);
1224   void initialize_performance_counters();
1225   CollectorCounters* counters()  { return collector()->counters(); }
1226 
1227   // Support for parallel remark of survivor space
1228   void* get_data_recorder(int thr_num) {
1229     //Delegate to collector
1230     return collector()->get_data_recorder(thr_num);
1231   }
1232   void sample_eden_chunk() {
1233     //Delegate to collector
1234     return collector()->sample_eden_chunk();
1235   }
1236 
1237   // Printing
1238   const char* name() const;
1239   virtual const char* short_name() const { return "CMS"; }
1240   void        print() const;
1241 
1242   // Resize the generation after a compacting GC.  The
1243   // generation can be treated as a contiguous space
1244   // after the compaction.
1245   virtual void compute_new_size();
1246   // Resize the generation after a non-compacting
1247   // collection.
1248   void compute_new_size_free_list();
1249 };
1250 
1251 //
1252 // Closures of various sorts used by CMS to accomplish its work
1253 //
1254 
1255 // This closure is used to do concurrent marking from the roots
1256 // following the first checkpoint.
1257 class MarkFromRootsClosure: public BitMapClosure {
1258   CMSCollector*  _collector;
1259   MemRegion      _span;
1260   CMSBitMap*     _bitMap;
1261   CMSBitMap*     _mut;
1262   CMSMarkStack*  _markStack;
1263   bool           _yield;
1264   int            _skipBits;
1265   HeapWord*      _finger;
1266   HeapWord*      _threshold;
1267   DEBUG_ONLY(bool _verifying;)
1268 
1269  public:
1270   MarkFromRootsClosure(CMSCollector* collector, MemRegion span,
1271                        CMSBitMap* bitMap,
1272                        CMSMarkStack*  markStack,
1273                        bool should_yield, bool verifying = false);
1274   bool do_bit(size_t offset);
1275   void reset(HeapWord* addr);
1276   inline void do_yield_check();
1277 
1278  private:
1279   void scanOopsInOop(HeapWord* ptr);
1280   void do_yield_work();
1281 };
1282 
1283 // This closure is used to do concurrent multi-threaded
1284 // marking from the roots following the first checkpoint.
1285 // XXX This should really be a subclass of The serial version
1286 // above, but i have not had the time to refactor things cleanly.
1287 class ParMarkFromRootsClosure: public BitMapClosure {
1288   CMSCollector*  _collector;
1289   MemRegion      _whole_span;
1290   MemRegion      _span;
1291   CMSBitMap*     _bit_map;
1292   CMSBitMap*     _mut;
1293   OopTaskQueue*  _work_queue;
1294   CMSMarkStack*  _overflow_stack;
1295   int            _skip_bits;
1296   HeapWord*      _finger;
1297   HeapWord*      _threshold;
1298   CMSConcMarkingTask* _task;
1299  public:
1300   ParMarkFromRootsClosure(CMSConcMarkingTask* task, CMSCollector* collector,
1301                           MemRegion span,
1302                           CMSBitMap* bit_map,
1303                           OopTaskQueue* work_queue,
1304                           CMSMarkStack*  overflow_stack);
1305   bool do_bit(size_t offset);
1306   inline void do_yield_check();
1307 
1308  private:
1309   void scan_oops_in_oop(HeapWord* ptr);
1310   void do_yield_work();
1311   bool get_work_from_overflow_stack();
1312 };
1313 
1314 // The following closures are used to do certain kinds of verification of
1315 // CMS marking.
1316 class PushAndMarkVerifyClosure: public MetadataAwareOopClosure {
1317   CMSCollector*    _collector;
1318   MemRegion        _span;
1319   CMSBitMap*       _verification_bm;
1320   CMSBitMap*       _cms_bm;
1321   CMSMarkStack*    _mark_stack;
1322  protected:
1323   void do_oop(oop p);
1324   template <class T> inline void do_oop_work(T *p) {
1325     oop obj = oopDesc::load_decode_heap_oop(p);
1326     do_oop(obj);
1327   }
1328  public:
1329   PushAndMarkVerifyClosure(CMSCollector* cms_collector,
1330                            MemRegion span,
1331                            CMSBitMap* verification_bm,
1332                            CMSBitMap* cms_bm,
1333                            CMSMarkStack*  mark_stack);
1334   void do_oop(oop* p);
1335   void do_oop(narrowOop* p);
1336 
1337   // Deal with a stack overflow condition
1338   void handle_stack_overflow(HeapWord* lost);
1339 };
1340 
1341 class MarkFromRootsVerifyClosure: public BitMapClosure {
1342   CMSCollector*  _collector;
1343   MemRegion      _span;
1344   CMSBitMap*     _verification_bm;
1345   CMSBitMap*     _cms_bm;
1346   CMSMarkStack*  _mark_stack;
1347   HeapWord*      _finger;
1348   PushAndMarkVerifyClosure _pam_verify_closure;
1349  public:
1350   MarkFromRootsVerifyClosure(CMSCollector* collector, MemRegion span,
1351                              CMSBitMap* verification_bm,
1352                              CMSBitMap* cms_bm,
1353                              CMSMarkStack*  mark_stack);
1354   bool do_bit(size_t offset);
1355   void reset(HeapWord* addr);
1356 };
1357 
1358 
1359 // This closure is used to check that a certain set of bits is
1360 // "empty" (i.e. the bit vector doesn't have any 1-bits).
1361 class FalseBitMapClosure: public BitMapClosure {
1362  public:
1363   bool do_bit(size_t offset) {
1364     guarantee(false, "Should not have a 1 bit");
1365     return true;
1366   }
1367 };
1368 
1369 // A version of ObjectClosure with "memory" (see _previous_address below)
1370 class UpwardsObjectClosure: public BoolObjectClosure {
1371   HeapWord* _previous_address;
1372  public:
1373   UpwardsObjectClosure() : _previous_address(NULL) { }
1374   void set_previous(HeapWord* addr) { _previous_address = addr; }
1375   HeapWord* previous()              { return _previous_address; }
1376   // A return value of "true" can be used by the caller to decide
1377   // if this object's end should *NOT* be recorded in
1378   // _previous_address above.
1379   virtual bool do_object_bm(oop obj, MemRegion mr) = 0;
1380 };
1381 
1382 // This closure is used during the second checkpointing phase
1383 // to rescan the marked objects on the dirty cards in the mod
1384 // union table and the card table proper. It's invoked via
1385 // MarkFromDirtyCardsClosure below. It uses either
1386 // [Par_]MarkRefsIntoAndScanClosure (Par_ in the parallel case)
1387 // declared in genOopClosures.hpp to accomplish some of its work.
1388 // In the parallel case the bitMap is shared, so access to
1389 // it needs to be suitably synchronized for updates by embedded
1390 // closures that update it; however, this closure itself only
1391 // reads the bit_map and because it is idempotent, is immune to
1392 // reading stale values.
1393 class ScanMarkedObjectsAgainClosure: public UpwardsObjectClosure {
1394   #ifdef ASSERT
1395     CMSCollector*          _collector;
1396     MemRegion              _span;
1397     union {
1398       CMSMarkStack*        _mark_stack;
1399       OopTaskQueue*        _work_queue;
1400     };
1401   #endif // ASSERT
1402   bool                       _parallel;
1403   CMSBitMap*                 _bit_map;
1404   union {
1405     MarkRefsIntoAndScanClosure*    _scan_closure;
1406     ParMarkRefsIntoAndScanClosure* _par_scan_closure;
1407   };
1408 
1409  public:
1410   ScanMarkedObjectsAgainClosure(CMSCollector* collector,
1411                                 MemRegion span,
1412                                 ReferenceProcessor* rp,
1413                                 CMSBitMap* bit_map,
1414                                 CMSMarkStack*  mark_stack,
1415                                 MarkRefsIntoAndScanClosure* cl):
1416     #ifdef ASSERT
1417       _collector(collector),
1418       _span(span),
1419       _mark_stack(mark_stack),
1420     #endif // ASSERT
1421     _parallel(false),
1422     _bit_map(bit_map),
1423     _scan_closure(cl) { }
1424 
1425   ScanMarkedObjectsAgainClosure(CMSCollector* collector,
1426                                 MemRegion span,
1427                                 ReferenceProcessor* rp,
1428                                 CMSBitMap* bit_map,
1429                                 OopTaskQueue* work_queue,
1430                                 ParMarkRefsIntoAndScanClosure* cl):
1431     #ifdef ASSERT
1432       _collector(collector),
1433       _span(span),
1434       _work_queue(work_queue),
1435     #endif // ASSERT
1436     _parallel(true),
1437     _bit_map(bit_map),
1438     _par_scan_closure(cl) { }
1439 
1440   bool do_object_b(oop obj) {
1441     guarantee(false, "Call do_object_b(oop, MemRegion) form instead");
1442     return false;
1443   }
1444   bool do_object_bm(oop p, MemRegion mr);
1445 };
1446 
1447 // This closure is used during the second checkpointing phase
1448 // to rescan the marked objects on the dirty cards in the mod
1449 // union table and the card table proper. It invokes
1450 // ScanMarkedObjectsAgainClosure above to accomplish much of its work.
1451 // In the parallel case, the bit map is shared and requires
1452 // synchronized access.
1453 class MarkFromDirtyCardsClosure: public MemRegionClosure {
1454   CompactibleFreeListSpace*      _space;
1455   ScanMarkedObjectsAgainClosure  _scan_cl;
1456   size_t                         _num_dirty_cards;
1457 
1458  public:
1459   MarkFromDirtyCardsClosure(CMSCollector* collector,
1460                             MemRegion span,
1461                             CompactibleFreeListSpace* space,
1462                             CMSBitMap* bit_map,
1463                             CMSMarkStack* mark_stack,
1464                             MarkRefsIntoAndScanClosure* cl):
1465     _space(space),
1466     _num_dirty_cards(0),
1467     _scan_cl(collector, span, collector->ref_processor(), bit_map,
1468                  mark_stack, cl) { }
1469 
1470   MarkFromDirtyCardsClosure(CMSCollector* collector,
1471                             MemRegion span,
1472                             CompactibleFreeListSpace* space,
1473                             CMSBitMap* bit_map,
1474                             OopTaskQueue* work_queue,
1475                             ParMarkRefsIntoAndScanClosure* cl):
1476     _space(space),
1477     _num_dirty_cards(0),
1478     _scan_cl(collector, span, collector->ref_processor(), bit_map,
1479              work_queue, cl) { }
1480 
1481   void do_MemRegion(MemRegion mr);
1482   void set_space(CompactibleFreeListSpace* space) { _space = space; }
1483   size_t num_dirty_cards() { return _num_dirty_cards; }
1484 };
1485 
1486 // This closure is used in the non-product build to check
1487 // that there are no MemRegions with a certain property.
1488 class FalseMemRegionClosure: public MemRegionClosure {
1489   void do_MemRegion(MemRegion mr) {
1490     guarantee(!mr.is_empty(), "Shouldn't be empty");
1491     guarantee(false, "Should never be here");
1492   }
1493 };
1494 
1495 // This closure is used during the precleaning phase
1496 // to "carefully" rescan marked objects on dirty cards.
1497 // It uses MarkRefsIntoAndScanClosure declared in genOopClosures.hpp
1498 // to accomplish some of its work.
1499 class ScanMarkedObjectsAgainCarefullyClosure: public ObjectClosureCareful {
1500   CMSCollector*                  _collector;
1501   MemRegion                      _span;
1502   bool                           _yield;
1503   Mutex*                         _freelistLock;
1504   CMSBitMap*                     _bitMap;
1505   CMSMarkStack*                  _markStack;
1506   MarkRefsIntoAndScanClosure*    _scanningClosure;
1507 
1508  public:
1509   ScanMarkedObjectsAgainCarefullyClosure(CMSCollector* collector,
1510                                          MemRegion     span,
1511                                          CMSBitMap* bitMap,
1512                                          CMSMarkStack*  markStack,
1513                                          MarkRefsIntoAndScanClosure* cl,
1514                                          bool should_yield):
1515     _collector(collector),
1516     _span(span),
1517     _yield(should_yield),
1518     _bitMap(bitMap),
1519     _markStack(markStack),
1520     _scanningClosure(cl) {
1521   }
1522 
1523   void do_object(oop p) {
1524     guarantee(false, "call do_object_careful instead");
1525   }
1526 
1527   size_t      do_object_careful(oop p) {
1528     guarantee(false, "Unexpected caller");
1529     return 0;
1530   }
1531 
1532   size_t      do_object_careful_m(oop p, MemRegion mr);
1533 
1534   void setFreelistLock(Mutex* m) {
1535     _freelistLock = m;
1536     _scanningClosure->set_freelistLock(m);
1537   }
1538 
1539  private:
1540   inline bool do_yield_check();
1541 
1542   void do_yield_work();
1543 };
1544 
1545 class SurvivorSpacePrecleanClosure: public ObjectClosureCareful {
1546   CMSCollector*                  _collector;
1547   MemRegion                      _span;
1548   bool                           _yield;
1549   CMSBitMap*                     _bit_map;
1550   CMSMarkStack*                  _mark_stack;
1551   PushAndMarkClosure*            _scanning_closure;
1552   unsigned int                   _before_count;
1553 
1554  public:
1555   SurvivorSpacePrecleanClosure(CMSCollector* collector,
1556                                MemRegion     span,
1557                                CMSBitMap*    bit_map,
1558                                CMSMarkStack* mark_stack,
1559                                PushAndMarkClosure* cl,
1560                                unsigned int  before_count,
1561                                bool          should_yield):
1562     _collector(collector),
1563     _span(span),
1564     _yield(should_yield),
1565     _bit_map(bit_map),
1566     _mark_stack(mark_stack),
1567     _scanning_closure(cl),
1568     _before_count(before_count)
1569   { }
1570 
1571   void do_object(oop p) {
1572     guarantee(false, "call do_object_careful instead");
1573   }
1574 
1575   size_t      do_object_careful(oop p);
1576 
1577   size_t      do_object_careful_m(oop p, MemRegion mr) {
1578     guarantee(false, "Unexpected caller");
1579     return 0;
1580   }
1581 
1582  private:
1583   inline void do_yield_check();
1584   void do_yield_work();
1585 };
1586 
1587 // This closure is used to accomplish the sweeping work
1588 // after the second checkpoint but before the concurrent reset
1589 // phase.
1590 //
1591 // Terminology
1592 //   left hand chunk (LHC) - block of one or more chunks currently being
1593 //     coalesced.  The LHC is available for coalescing with a new chunk.
1594 //   right hand chunk (RHC) - block that is currently being swept that is
1595 //     free or garbage that can be coalesced with the LHC.
1596 // _inFreeRange is true if there is currently a LHC
1597 // _lastFreeRangeCoalesced is true if the LHC consists of more than one chunk.
1598 // _freeRangeInFreeLists is true if the LHC is in the free lists.
1599 // _freeFinger is the address of the current LHC
1600 class SweepClosure: public BlkClosureCareful {
1601   CMSCollector*                  _collector;  // collector doing the work
1602   ConcurrentMarkSweepGeneration* _g;    // Generation being swept
1603   CompactibleFreeListSpace*      _sp;   // Space being swept
1604   HeapWord*                      _limit;// the address at or above which the sweep should stop
1605                                         // because we do not expect newly garbage blocks
1606                                         // eligible for sweeping past that address.
1607   Mutex*                         _freelistLock; // Free list lock (in space)
1608   CMSBitMap*                     _bitMap;       // Marking bit map (in
1609                                                 // generation)
1610   bool                           _inFreeRange;  // Indicates if we are in the
1611                                                 // midst of a free run
1612   bool                           _freeRangeInFreeLists;
1613                                         // Often, we have just found
1614                                         // a free chunk and started
1615                                         // a new free range; we do not
1616                                         // eagerly remove this chunk from
1617                                         // the free lists unless there is
1618                                         // a possibility of coalescing.
1619                                         // When true, this flag indicates
1620                                         // that the _freeFinger below
1621                                         // points to a potentially free chunk
1622                                         // that may still be in the free lists
1623   bool                           _lastFreeRangeCoalesced;
1624                                         // free range contains chunks
1625                                         // coalesced
1626   bool                           _yield;
1627                                         // Whether sweeping should be
1628                                         // done with yields. For instance
1629                                         // when done by the foreground
1630                                         // collector we shouldn't yield.
1631   HeapWord*                      _freeFinger;   // When _inFreeRange is set, the
1632                                                 // pointer to the "left hand
1633                                                 // chunk"
1634   size_t                         _freeRangeSize;
1635                                         // When _inFreeRange is set, this
1636                                         // indicates the accumulated size
1637                                         // of the "left hand chunk"
1638   NOT_PRODUCT(
1639     size_t                       _numObjectsFreed;
1640     size_t                       _numWordsFreed;
1641     size_t                       _numObjectsLive;
1642     size_t                       _numWordsLive;
1643     size_t                       _numObjectsAlreadyFree;
1644     size_t                       _numWordsAlreadyFree;
1645     FreeChunk*                   _last_fc;
1646   )
1647  private:
1648   // Code that is common to a free chunk or garbage when
1649   // encountered during sweeping.
1650   void do_post_free_or_garbage_chunk(FreeChunk *fc, size_t chunkSize);
1651   // Process a free chunk during sweeping.
1652   void do_already_free_chunk(FreeChunk *fc);
1653   // Work method called when processing an already free or a
1654   // freshly garbage chunk to do a lookahead and possibly a
1655   // preemptive flush if crossing over _limit.
1656   void lookahead_and_flush(FreeChunk* fc, size_t chunkSize);
1657   // Process a garbage chunk during sweeping.
1658   size_t do_garbage_chunk(FreeChunk *fc);
1659   // Process a live chunk during sweeping.
1660   size_t do_live_chunk(FreeChunk* fc);
1661 
1662   // Accessors.
1663   HeapWord* freeFinger() const          { return _freeFinger; }
1664   void set_freeFinger(HeapWord* v)      { _freeFinger = v; }
1665   bool inFreeRange()    const           { return _inFreeRange; }
1666   void set_inFreeRange(bool v)          { _inFreeRange = v; }
1667   bool lastFreeRangeCoalesced() const    { return _lastFreeRangeCoalesced; }
1668   void set_lastFreeRangeCoalesced(bool v) { _lastFreeRangeCoalesced = v; }
1669   bool freeRangeInFreeLists() const     { return _freeRangeInFreeLists; }
1670   void set_freeRangeInFreeLists(bool v) { _freeRangeInFreeLists = v; }
1671 
1672   // Initialize a free range.
1673   void initialize_free_range(HeapWord* freeFinger, bool freeRangeInFreeLists);
1674   // Return this chunk to the free lists.
1675   void flush_cur_free_chunk(HeapWord* chunk, size_t size);
1676 
1677   // Check if we should yield and do so when necessary.
1678   inline void do_yield_check(HeapWord* addr);
1679 
1680   // Yield
1681   void do_yield_work(HeapWord* addr);
1682 
1683   // Debugging/Printing
1684   void print_free_block_coalesced(FreeChunk* fc) const;
1685 
1686  public:
1687   SweepClosure(CMSCollector* collector, ConcurrentMarkSweepGeneration* g,
1688                CMSBitMap* bitMap, bool should_yield);
1689   ~SweepClosure() PRODUCT_RETURN;
1690 
1691   size_t       do_blk_careful(HeapWord* addr);
1692   void         print() const { print_on(tty); }
1693   void         print_on(outputStream *st) const;
1694 };
1695 
1696 // Closures related to weak references processing
1697 
1698 // During CMS' weak reference processing, this is a
1699 // work-routine/closure used to complete transitive
1700 // marking of objects as live after a certain point
1701 // in which an initial set has been completely accumulated.
1702 // This closure is currently used both during the final
1703 // remark stop-world phase, as well as during the concurrent
1704 // precleaning of the discovered reference lists.
1705 class CMSDrainMarkingStackClosure: public VoidClosure {
1706   CMSCollector*        _collector;
1707   MemRegion            _span;
1708   CMSMarkStack*        _mark_stack;
1709   CMSBitMap*           _bit_map;
1710   CMSKeepAliveClosure* _keep_alive;
1711   bool                 _concurrent_precleaning;
1712  public:
1713   CMSDrainMarkingStackClosure(CMSCollector* collector, MemRegion span,
1714                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
1715                       CMSKeepAliveClosure* keep_alive,
1716                       bool cpc):
1717     _collector(collector),
1718     _span(span),
1719     _bit_map(bit_map),
1720     _mark_stack(mark_stack),
1721     _keep_alive(keep_alive),
1722     _concurrent_precleaning(cpc) {
1723     assert(_concurrent_precleaning == _keep_alive->concurrent_precleaning(),
1724            "Mismatch");
1725   }
1726 
1727   void do_void();
1728 };
1729 
1730 // A parallel version of CMSDrainMarkingStackClosure above.
1731 class CMSParDrainMarkingStackClosure: public VoidClosure {
1732   CMSCollector*           _collector;
1733   MemRegion               _span;
1734   OopTaskQueue*           _work_queue;
1735   CMSBitMap*              _bit_map;
1736   CMSInnerParMarkAndPushClosure _mark_and_push;
1737 
1738  public:
1739   CMSParDrainMarkingStackClosure(CMSCollector* collector,
1740                                  MemRegion span, CMSBitMap* bit_map,
1741                                  OopTaskQueue* work_queue):
1742     _collector(collector),
1743     _span(span),
1744     _bit_map(bit_map),
1745     _work_queue(work_queue),
1746     _mark_and_push(collector, span, bit_map, work_queue) { }
1747 
1748  public:
1749   void trim_queue(uint max);
1750   void do_void();
1751 };
1752 
1753 // Allow yielding or short-circuiting of reference list
1754 // precleaning work.
1755 class CMSPrecleanRefsYieldClosure: public YieldClosure {
1756   CMSCollector* _collector;
1757   void do_yield_work();
1758  public:
1759   CMSPrecleanRefsYieldClosure(CMSCollector* collector):
1760     _collector(collector) {}
1761   virtual bool should_return();
1762 };
1763 
1764 
1765 // Convenience class that locks free list locks for given CMS collector
1766 class FreelistLocker: public StackObj {
1767  private:
1768   CMSCollector* _collector;
1769  public:
1770   FreelistLocker(CMSCollector* collector):
1771     _collector(collector) {
1772     _collector->getFreelistLocks();
1773   }
1774 
1775   ~FreelistLocker() {
1776     _collector->releaseFreelistLocks();
1777   }
1778 };
1779 
1780 // Mark all dead objects in a given space.
1781 class MarkDeadObjectsClosure: public BlkClosure {
1782   const CMSCollector*             _collector;
1783   const CompactibleFreeListSpace* _sp;
1784   CMSBitMap*                      _live_bit_map;
1785   CMSBitMap*                      _dead_bit_map;
1786 public:
1787   MarkDeadObjectsClosure(const CMSCollector* collector,
1788                          const CompactibleFreeListSpace* sp,
1789                          CMSBitMap *live_bit_map,
1790                          CMSBitMap *dead_bit_map) :
1791     _collector(collector),
1792     _sp(sp),
1793     _live_bit_map(live_bit_map),
1794     _dead_bit_map(dead_bit_map) {}
1795   size_t do_blk(HeapWord* addr);
1796 };
1797 
1798 class TraceCMSMemoryManagerStats : public TraceMemoryManagerStats {
1799 
1800  public:
1801   TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause);
1802 };
1803 
1804 
1805 #endif // SHARE_VM_GC_CMS_CONCURRENTMARKSWEEPGENERATION_HPP