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