1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   6  * under the terms of the GNU General Public License version 2 only, as
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  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
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  24 
  25 #ifndef SHARE_VM_GC_G1_CONCURRENTMARK_HPP
  26 #define SHARE_VM_GC_G1_CONCURRENTMARK_HPP
  27 
  28 #include "classfile/javaClasses.hpp"
  29 #include "gc/g1/g1RegionToSpaceMapper.hpp"
  30 #include "gc/g1/heapRegionSet.hpp"
  31 #include "gc/shared/gcId.hpp"
  32 #include "gc/shared/taskqueue.hpp"
  33 
  34 class G1CollectedHeap;
  35 class CMBitMap;
  36 class CMTask;
  37 class ConcurrentMark;
  38 typedef GenericTaskQueue<oop, mtGC>            CMTaskQueue;
  39 typedef GenericTaskQueueSet<CMTaskQueue, mtGC> CMTaskQueueSet;
  40 
  41 // Closure used by CM during concurrent reference discovery
  42 // and reference processing (during remarking) to determine
  43 // if a particular object is alive. It is primarily used
  44 // to determine if referents of discovered reference objects
  45 // are alive. An instance is also embedded into the
  46 // reference processor as the _is_alive_non_header field
  47 class G1CMIsAliveClosure: public BoolObjectClosure {
  48   G1CollectedHeap* _g1;
  49  public:
  50   G1CMIsAliveClosure(G1CollectedHeap* g1) : _g1(g1) { }
  51 
  52   bool do_object_b(oop obj);
  53 };
  54 
  55 // A generic CM bit map.  This is essentially a wrapper around the BitMap
  56 // class, with one bit per (1<<_shifter) HeapWords.
  57 
  58 class CMBitMapRO VALUE_OBJ_CLASS_SPEC {
  59  protected:
  60   HeapWord* _bmStartWord;      // base address of range covered by map
  61   size_t    _bmWordSize;       // map size (in #HeapWords covered)
  62   const int _shifter;          // map to char or bit
  63   BitMap    _bm;               // the bit map itself
  64 
  65  public:
  66   // constructor
  67   CMBitMapRO(int shifter);
  68 
  69   enum { do_yield = true };
  70 
  71   // inquiries
  72   HeapWord* startWord()   const { return _bmStartWord; }
  73   size_t    sizeInWords() const { return _bmWordSize;  }
  74   // the following is one past the last word in space
  75   HeapWord* endWord()     const { return _bmStartWord + _bmWordSize; }
  76 
  77   // read marks
  78 
  79   bool isMarked(HeapWord* addr) const {
  80     assert(_bmStartWord <= addr && addr < (_bmStartWord + _bmWordSize),
  81            "outside underlying space?");
  82     return _bm.at(heapWordToOffset(addr));
  83   }
  84 
  85   // iteration
  86   inline bool iterate(BitMapClosure* cl, MemRegion mr);
  87   inline bool iterate(BitMapClosure* cl);
  88 
  89   // Return the address corresponding to the next marked bit at or after
  90   // "addr", and before "limit", if "limit" is non-NULL.  If there is no
  91   // such bit, returns "limit" if that is non-NULL, or else "endWord()".
  92   HeapWord* getNextMarkedWordAddress(const HeapWord* addr,
  93                                      const HeapWord* limit = NULL) const;
  94   // Return the address corresponding to the next unmarked bit at or after
  95   // "addr", and before "limit", if "limit" is non-NULL.  If there is no
  96   // such bit, returns "limit" if that is non-NULL, or else "endWord()".
  97   HeapWord* getNextUnmarkedWordAddress(const HeapWord* addr,
  98                                        const HeapWord* limit = NULL) const;
  99 
 100   // conversion utilities
 101   HeapWord* offsetToHeapWord(size_t offset) const {
 102     return _bmStartWord + (offset << _shifter);
 103   }
 104   size_t heapWordToOffset(const HeapWord* addr) const {
 105     return pointer_delta(addr, _bmStartWord) >> _shifter;
 106   }
 107   int heapWordDiffToOffsetDiff(size_t diff) const;
 108 
 109   // The argument addr should be the start address of a valid object
 110   HeapWord* nextObject(HeapWord* addr) {
 111     oop obj = (oop) addr;
 112     HeapWord* res =  addr + obj->size();
 113     assert(offsetToHeapWord(heapWordToOffset(res)) == res, "sanity");
 114     return res;
 115   }
 116 
 117   void print_on_error(outputStream* st, const char* prefix) const;
 118 
 119   // debugging
 120   NOT_PRODUCT(bool covers(MemRegion rs) const;)
 121 };
 122 
 123 class CMBitMapMappingChangedListener : public G1MappingChangedListener {
 124  private:
 125   CMBitMap* _bm;
 126  public:
 127   CMBitMapMappingChangedListener() : _bm(NULL) {}
 128 
 129   void set_bitmap(CMBitMap* bm) { _bm = bm; }
 130 
 131   virtual void on_commit(uint start_idx, size_t num_regions, bool zero_filled);
 132 };
 133 
 134 class CMBitMap : public CMBitMapRO {
 135  private:
 136   CMBitMapMappingChangedListener _listener;
 137 
 138  public:
 139   static size_t compute_size(size_t heap_size);
 140   // Returns the amount of bytes on the heap between two marks in the bitmap.
 141   static size_t mark_distance();
 142   // Returns how many bytes (or bits) of the heap a single byte (or bit) of the
 143   // mark bitmap corresponds to. This is the same as the mark distance above.
 144   static size_t heap_map_factor() {
 145     return mark_distance();
 146   }
 147 
 148   CMBitMap() : CMBitMapRO(LogMinObjAlignment), _listener() { _listener.set_bitmap(this); }
 149 
 150   // Initializes the underlying BitMap to cover the given area.
 151   void initialize(MemRegion heap, G1RegionToSpaceMapper* storage);
 152 
 153   // Write marks.
 154   inline void mark(HeapWord* addr);
 155   inline void clear(HeapWord* addr);
 156   inline bool parMark(HeapWord* addr);
 157   inline bool parClear(HeapWord* addr);
 158 
 159   void markRange(MemRegion mr);
 160   void clearRange(MemRegion mr);
 161 
 162   // Starting at the bit corresponding to "addr" (inclusive), find the next
 163   // "1" bit, if any.  This bit starts some run of consecutive "1"'s; find
 164   // the end of this run (stopping at "end_addr").  Return the MemRegion
 165   // covering from the start of the region corresponding to the first bit
 166   // of the run to the end of the region corresponding to the last bit of
 167   // the run.  If there is no "1" bit at or after "addr", return an empty
 168   // MemRegion.
 169   MemRegion getAndClearMarkedRegion(HeapWord* addr, HeapWord* end_addr);
 170 
 171   // Clear the whole mark bitmap.
 172   void clearAll();
 173 };
 174 
 175 // Represents a marking stack used by ConcurrentMarking in the G1 collector.
 176 class CMMarkStack VALUE_OBJ_CLASS_SPEC {
 177   VirtualSpace _virtual_space;   // Underlying backing store for actual stack
 178   ConcurrentMark* _cm;
 179   oop* _base;        // bottom of stack
 180   jint _index;       // one more than last occupied index
 181   jint _capacity;    // max #elements
 182   jint _saved_index; // value of _index saved at start of GC
 183 
 184   bool  _overflow;
 185   bool  _should_expand;
 186   DEBUG_ONLY(bool _drain_in_progress;)
 187   DEBUG_ONLY(bool _drain_in_progress_yields;)
 188 
 189   oop pop() {
 190     if (!isEmpty()) {
 191       return _base[--_index] ;
 192     }
 193     return NULL;
 194   }
 195 
 196  public:
 197   CMMarkStack(ConcurrentMark* cm);
 198   ~CMMarkStack();
 199 
 200   bool allocate(size_t capacity);
 201 
 202   // Pushes the first "n" elements of "ptr_arr" on the stack.
 203   // Locking impl: concurrency is allowed only with
 204   // "par_push_arr" and/or "par_pop_arr" operations, which use the same
 205   // locking strategy.
 206   void par_push_arr(oop* ptr_arr, int n);
 207 
 208   // If returns false, the array was empty.  Otherwise, removes up to "max"
 209   // elements from the stack, and transfers them to "ptr_arr" in an
 210   // unspecified order.  The actual number transferred is given in "n" ("n
 211   // == 0" is deliberately redundant with the return value.)  Locking impl:
 212   // concurrency is allowed only with "par_push_arr" and/or "par_pop_arr"
 213   // operations, which use the same locking strategy.
 214   bool par_pop_arr(oop* ptr_arr, int max, int* n);
 215 
 216   // Drain the mark stack, applying the given closure to all fields of
 217   // objects on the stack.  (That is, continue until the stack is empty,
 218   // even if closure applications add entries to the stack.)  The "bm"
 219   // argument, if non-null, may be used to verify that only marked objects
 220   // are on the mark stack.  If "yield_after" is "true", then the
 221   // concurrent marker performing the drain offers to yield after
 222   // processing each object.  If a yield occurs, stops the drain operation
 223   // and returns false.  Otherwise, returns true.
 224   template<class OopClosureClass>
 225   bool drain(OopClosureClass* cl, CMBitMap* bm, bool yield_after = false);
 226 
 227   bool isEmpty()    { return _index == 0; }
 228   int  maxElems()   { return _capacity; }
 229 
 230   bool overflow() { return _overflow; }
 231   void clear_overflow() { _overflow = false; }
 232 
 233   bool should_expand() const { return _should_expand; }
 234   void set_should_expand();
 235 
 236   // Expand the stack, typically in response to an overflow condition
 237   void expand();
 238 
 239   int  size() { return _index; }
 240 
 241   void setEmpty()   { _index = 0; clear_overflow(); }
 242 
 243   // Record the current index.
 244   void note_start_of_gc();
 245 
 246   // Make sure that we have not added any entries to the stack during GC.
 247   void note_end_of_gc();
 248 
 249   // Apply fn to each oop in the mark stack, up to the bound recorded
 250   // via one of the above "note" functions.  The mark stack must not
 251   // be modified while iterating.
 252   template<typename Fn> void iterate(Fn fn);
 253 };
 254 
 255 class ForceOverflowSettings VALUE_OBJ_CLASS_SPEC {
 256 private:
 257 #ifndef PRODUCT
 258   uintx _num_remaining;
 259   bool _force;
 260 #endif // !defined(PRODUCT)
 261 
 262 public:
 263   void init() PRODUCT_RETURN;
 264   void update() PRODUCT_RETURN;
 265   bool should_force() PRODUCT_RETURN_( return false; );
 266 };
 267 
 268 // this will enable a variety of different statistics per GC task
 269 #define _MARKING_STATS_       0
 270 // this will enable the higher verbose levels
 271 #define _MARKING_VERBOSE_     0
 272 
 273 #if _MARKING_STATS_
 274 #define statsOnly(statement)  \
 275 do {                          \
 276   statement ;                 \
 277 } while (0)
 278 #else // _MARKING_STATS_
 279 #define statsOnly(statement)  \
 280 do {                          \
 281 } while (0)
 282 #endif // _MARKING_STATS_
 283 
 284 typedef enum {
 285   no_verbose  = 0,   // verbose turned off
 286   stats_verbose,     // only prints stats at the end of marking
 287   low_verbose,       // low verbose, mostly per region and per major event
 288   medium_verbose,    // a bit more detailed than low
 289   high_verbose       // per object verbose
 290 } CMVerboseLevel;
 291 
 292 class YoungList;
 293 
 294 // Root Regions are regions that are not empty at the beginning of a
 295 // marking cycle and which we might collect during an evacuation pause
 296 // while the cycle is active. Given that, during evacuation pauses, we
 297 // do not copy objects that are explicitly marked, what we have to do
 298 // for the root regions is to scan them and mark all objects reachable
 299 // from them. According to the SATB assumptions, we only need to visit
 300 // each object once during marking. So, as long as we finish this scan
 301 // before the next evacuation pause, we can copy the objects from the
 302 // root regions without having to mark them or do anything else to them.
 303 //
 304 // Currently, we only support root region scanning once (at the start
 305 // of the marking cycle) and the root regions are all the survivor
 306 // regions populated during the initial-mark pause.
 307 class CMRootRegions VALUE_OBJ_CLASS_SPEC {
 308 private:
 309   YoungList*           _young_list;
 310   ConcurrentMark*      _cm;
 311 
 312   volatile bool        _scan_in_progress;
 313   volatile bool        _should_abort;
 314   HeapRegion* volatile _next_survivor;
 315 
 316 public:
 317   CMRootRegions();
 318   // We actually do most of the initialization in this method.
 319   void init(G1CollectedHeap* g1h, ConcurrentMark* cm);
 320 
 321   // Reset the claiming / scanning of the root regions.
 322   void prepare_for_scan();
 323 
 324   // Forces get_next() to return NULL so that the iteration aborts early.
 325   void abort() { _should_abort = true; }
 326 
 327   // Return true if the CM thread are actively scanning root regions,
 328   // false otherwise.
 329   bool scan_in_progress() { return _scan_in_progress; }
 330 
 331   // Claim the next root region to scan atomically, or return NULL if
 332   // all have been claimed.
 333   HeapRegion* claim_next();
 334 
 335   // Flag that we're done with root region scanning and notify anyone
 336   // who's waiting on it. If aborted is false, assume that all regions
 337   // have been claimed.
 338   void scan_finished();
 339 
 340   // If CM threads are still scanning root regions, wait until they
 341   // are done. Return true if we had to wait, false otherwise.
 342   bool wait_until_scan_finished();
 343 };
 344 
 345 class ConcurrentMarkThread;
 346 
 347 class ConcurrentMark: public CHeapObj<mtGC> {
 348   friend class CMMarkStack;
 349   friend class ConcurrentMarkThread;
 350   friend class CMTask;
 351   friend class CMBitMapClosure;
 352   friend class CMRemarkTask;
 353   friend class CMConcurrentMarkingTask;
 354   friend class G1ParNoteEndTask;
 355   friend class CalcLiveObjectsClosure;
 356   friend class G1CMRefProcTaskProxy;
 357   friend class G1CMRefProcTaskExecutor;
 358   friend class G1CMKeepAliveAndDrainClosure;
 359   friend class G1CMDrainMarkingStackClosure;
 360 
 361 protected:
 362   ConcurrentMarkThread* _cmThread;   // The thread doing the work
 363   G1CollectedHeap*      _g1h;        // The heap
 364   uint                  _parallel_marking_threads; // The number of marking
 365                                                    // threads we're using
 366   uint                  _max_parallel_marking_threads; // Max number of marking
 367                                                        // threads we'll ever use
 368   double                _sleep_factor; // How much we have to sleep, with
 369                                        // respect to the work we just did, to
 370                                        // meet the marking overhead goal
 371   double                _marking_task_overhead; // Marking target overhead for
 372                                                 // a single task
 373 
 374   // Same as the two above, but for the cleanup task
 375   double                _cleanup_sleep_factor;
 376   double                _cleanup_task_overhead;
 377 
 378   FreeRegionList        _cleanup_list;
 379 
 380   // Concurrent marking support structures
 381   CMBitMap                _markBitMap1;
 382   CMBitMap                _markBitMap2;
 383   CMBitMapRO*             _prevMarkBitMap; // Completed mark bitmap
 384   CMBitMap*               _nextMarkBitMap; // Under-construction mark bitmap
 385 
 386   BitMap                  _region_bm;
 387   BitMap                  _card_bm;
 388 
 389   // Heap bounds
 390   HeapWord*               _heap_start;
 391   HeapWord*               _heap_end;
 392 
 393   // Root region tracking and claiming
 394   CMRootRegions           _root_regions;
 395 
 396   // For gray objects
 397   CMMarkStack             _markStack; // Grey objects behind global finger
 398   HeapWord* volatile      _finger;  // The global finger, region aligned,
 399                                     // always points to the end of the
 400                                     // last claimed region
 401 
 402   // Marking tasks
 403   uint                    _max_worker_id;// Maximum worker id
 404   uint                    _active_tasks; // Task num currently active
 405   CMTask**                _tasks;        // Task queue array (max_worker_id len)
 406   CMTaskQueueSet*         _task_queues;  // Task queue set
 407   ParallelTaskTerminator  _terminator;   // For termination
 408 
 409   // Two sync barriers that are used to synchronize tasks when an
 410   // overflow occurs. The algorithm is the following. All tasks enter
 411   // the first one to ensure that they have all stopped manipulating
 412   // the global data structures. After they exit it, they re-initialize
 413   // their data structures and task 0 re-initializes the global data
 414   // structures. Then, they enter the second sync barrier. This
 415   // ensure, that no task starts doing work before all data
 416   // structures (local and global) have been re-initialized. When they
 417   // exit it, they are free to start working again.
 418   WorkGangBarrierSync     _first_overflow_barrier_sync;
 419   WorkGangBarrierSync     _second_overflow_barrier_sync;
 420 
 421   // This is set by any task, when an overflow on the global data
 422   // structures is detected
 423   volatile bool           _has_overflown;
 424   // True: marking is concurrent, false: we're in remark
 425   volatile bool           _concurrent;
 426   // Set at the end of a Full GC so that marking aborts
 427   volatile bool           _has_aborted;
 428   GCId                    _aborted_gc_id;
 429 
 430   // Used when remark aborts due to an overflow to indicate that
 431   // another concurrent marking phase should start
 432   volatile bool           _restart_for_overflow;
 433 
 434   // This is true from the very start of concurrent marking until the
 435   // point when all the tasks complete their work. It is really used
 436   // to determine the points between the end of concurrent marking and
 437   // time of remark.
 438   volatile bool           _concurrent_marking_in_progress;
 439 
 440   // Verbose level
 441   CMVerboseLevel          _verbose_level;
 442 
 443   // All of these times are in ms
 444   NumberSeq _init_times;
 445   NumberSeq _remark_times;
 446   NumberSeq _remark_mark_times;
 447   NumberSeq _remark_weak_ref_times;
 448   NumberSeq _cleanup_times;
 449   double    _total_counting_time;
 450   double    _total_rs_scrub_time;
 451 
 452   double*   _accum_task_vtime;   // Accumulated task vtime
 453 
 454   WorkGang* _parallel_workers;
 455 
 456   ForceOverflowSettings _force_overflow_conc;
 457   ForceOverflowSettings _force_overflow_stw;
 458 
 459   void weakRefsWorkParallelPart(BoolObjectClosure* is_alive, bool purged_classes);
 460   void weakRefsWork(bool clear_all_soft_refs);
 461 
 462   void swapMarkBitMaps();
 463 
 464   // It resets the global marking data structures, as well as the
 465   // task local ones; should be called during initial mark.
 466   void reset();
 467 
 468   // Resets all the marking data structures. Called when we have to restart
 469   // marking or when marking completes (via set_non_marking_state below).
 470   void reset_marking_state(bool clear_overflow = true);
 471 
 472   // We do this after we're done with marking so that the marking data
 473   // structures are initialized to a sensible and predictable state.
 474   void set_non_marking_state();
 475 
 476   // Called to indicate how many threads are currently active.
 477   void set_concurrency(uint active_tasks);
 478 
 479   // It should be called to indicate which phase we're in (concurrent
 480   // mark or remark) and how many threads are currently active.
 481   void set_concurrency_and_phase(uint active_tasks, bool concurrent);
 482 
 483   // Prints all gathered CM-related statistics
 484   void print_stats();
 485 
 486   bool cleanup_list_is_empty() {
 487     return _cleanup_list.is_empty();
 488   }
 489 
 490   // Accessor methods
 491   uint parallel_marking_threads() const     { return _parallel_marking_threads; }
 492   uint max_parallel_marking_threads() const { return _max_parallel_marking_threads;}
 493   double sleep_factor()                     { return _sleep_factor; }
 494   double marking_task_overhead()            { return _marking_task_overhead;}
 495   double cleanup_sleep_factor()             { return _cleanup_sleep_factor; }
 496   double cleanup_task_overhead()            { return _cleanup_task_overhead;}
 497 
 498   HeapWord*               finger()          { return _finger;   }
 499   bool                    concurrent()      { return _concurrent; }
 500   uint                    active_tasks()    { return _active_tasks; }
 501   ParallelTaskTerminator* terminator()      { return &_terminator; }
 502 
 503   // It claims the next available region to be scanned by a marking
 504   // task/thread. It might return NULL if the next region is empty or
 505   // we have run out of regions. In the latter case, out_of_regions()
 506   // determines whether we've really run out of regions or the task
 507   // should call claim_region() again. This might seem a bit
 508   // awkward. Originally, the code was written so that claim_region()
 509   // either successfully returned with a non-empty region or there
 510   // were no more regions to be claimed. The problem with this was
 511   // that, in certain circumstances, it iterated over large chunks of
 512   // the heap finding only empty regions and, while it was working, it
 513   // was preventing the calling task to call its regular clock
 514   // method. So, this way, each task will spend very little time in
 515   // claim_region() and is allowed to call the regular clock method
 516   // frequently.
 517   HeapRegion* claim_region(uint worker_id);
 518 
 519   // It determines whether we've run out of regions to scan. Note that
 520   // the finger can point past the heap end in case the heap was expanded
 521   // to satisfy an allocation without doing a GC. This is fine, because all
 522   // objects in those regions will be considered live anyway because of
 523   // SATB guarantees (i.e. their TAMS will be equal to bottom).
 524   bool        out_of_regions() { return _finger >= _heap_end; }
 525 
 526   // Returns the task with the given id
 527   CMTask* task(int id) {
 528     assert(0 <= id && id < (int) _active_tasks,
 529            "task id not within active bounds");
 530     return _tasks[id];
 531   }
 532 
 533   // Returns the task queue with the given id
 534   CMTaskQueue* task_queue(int id) {
 535     assert(0 <= id && id < (int) _active_tasks,
 536            "task queue id not within active bounds");
 537     return (CMTaskQueue*) _task_queues->queue(id);
 538   }
 539 
 540   // Returns the task queue set
 541   CMTaskQueueSet* task_queues()  { return _task_queues; }
 542 
 543   // Access / manipulation of the overflow flag which is set to
 544   // indicate that the global stack has overflown
 545   bool has_overflown()           { return _has_overflown; }
 546   void set_has_overflown()       { _has_overflown = true; }
 547   void clear_has_overflown()     { _has_overflown = false; }
 548   bool restart_for_overflow()    { return _restart_for_overflow; }
 549 
 550   // Methods to enter the two overflow sync barriers
 551   void enter_first_sync_barrier(uint worker_id);
 552   void enter_second_sync_barrier(uint worker_id);
 553 
 554   ForceOverflowSettings* force_overflow_conc() {
 555     return &_force_overflow_conc;
 556   }
 557 
 558   ForceOverflowSettings* force_overflow_stw() {
 559     return &_force_overflow_stw;
 560   }
 561 
 562   ForceOverflowSettings* force_overflow() {
 563     if (concurrent()) {
 564       return force_overflow_conc();
 565     } else {
 566       return force_overflow_stw();
 567     }
 568   }
 569 
 570   // Live Data Counting data structures...
 571   // These data structures are initialized at the start of
 572   // marking. They are written to while marking is active.
 573   // They are aggregated during remark; the aggregated values
 574   // are then used to populate the _region_bm, _card_bm, and
 575   // the total live bytes, which are then subsequently updated
 576   // during cleanup.
 577 
 578   // An array of bitmaps (one bit map per task). Each bitmap
 579   // is used to record the cards spanned by the live objects
 580   // marked by that task/worker.
 581   BitMap*  _count_card_bitmaps;
 582 
 583   // Used to record the number of marked live bytes
 584   // (for each region, by worker thread).
 585   size_t** _count_marked_bytes;
 586 
 587   // Card index of the bottom of the G1 heap. Used for biasing indices into
 588   // the card bitmaps.
 589   intptr_t _heap_bottom_card_num;
 590 
 591   // Set to true when initialization is complete
 592   bool _completed_initialization;
 593 
 594 public:
 595   // Manipulation of the global mark stack.
 596   // The push and pop operations are used by tasks for transfers
 597   // between task-local queues and the global mark stack, and use
 598   // locking for concurrency safety.
 599   bool mark_stack_push(oop* arr, int n) {
 600     _markStack.par_push_arr(arr, n);
 601     if (_markStack.overflow()) {
 602       set_has_overflown();
 603       return false;
 604     }
 605     return true;
 606   }
 607   void mark_stack_pop(oop* arr, int max, int* n) {
 608     _markStack.par_pop_arr(arr, max, n);
 609   }
 610   size_t mark_stack_size()                { return _markStack.size(); }
 611   size_t partial_mark_stack_size_target() { return _markStack.maxElems()/3; }
 612   bool mark_stack_overflow()              { return _markStack.overflow(); }
 613   bool mark_stack_empty()                 { return _markStack.isEmpty(); }
 614 
 615   CMRootRegions* root_regions() { return &_root_regions; }
 616 
 617   bool concurrent_marking_in_progress() {
 618     return _concurrent_marking_in_progress;
 619   }
 620   void set_concurrent_marking_in_progress() {
 621     _concurrent_marking_in_progress = true;
 622   }
 623   void clear_concurrent_marking_in_progress() {
 624     _concurrent_marking_in_progress = false;
 625   }
 626 
 627   void update_accum_task_vtime(int i, double vtime) {
 628     _accum_task_vtime[i] += vtime;
 629   }
 630 
 631   double all_task_accum_vtime() {
 632     double ret = 0.0;
 633     for (uint i = 0; i < _max_worker_id; ++i)
 634       ret += _accum_task_vtime[i];
 635     return ret;
 636   }
 637 
 638   // Attempts to steal an object from the task queues of other tasks
 639   bool try_stealing(uint worker_id, int* hash_seed, oop& obj);
 640 
 641   ConcurrentMark(G1CollectedHeap* g1h,
 642                  G1RegionToSpaceMapper* prev_bitmap_storage,
 643                  G1RegionToSpaceMapper* next_bitmap_storage);
 644   ~ConcurrentMark();
 645 
 646   ConcurrentMarkThread* cmThread() { return _cmThread; }
 647 
 648   CMBitMapRO* prevMarkBitMap() const { return _prevMarkBitMap; }
 649   CMBitMap*   nextMarkBitMap() const { return _nextMarkBitMap; }
 650 
 651   // Returns the number of GC threads to be used in a concurrent
 652   // phase based on the number of GC threads being used in a STW
 653   // phase.
 654   uint scale_parallel_threads(uint n_par_threads);
 655 
 656   // Calculates the number of GC threads to be used in a concurrent phase.
 657   uint calc_parallel_marking_threads();
 658 
 659   // The following three are interaction between CM and
 660   // G1CollectedHeap
 661 
 662   // This notifies CM that a root during initial-mark needs to be
 663   // grayed. It is MT-safe. word_size is the size of the object in
 664   // words. It is passed explicitly as sometimes we cannot calculate
 665   // it from the given object because it might be in an inconsistent
 666   // state (e.g., in to-space and being copied). So the caller is
 667   // responsible for dealing with this issue (e.g., get the size from
 668   // the from-space image when the to-space image might be
 669   // inconsistent) and always passing the size. hr is the region that
 670   // contains the object and it's passed optionally from callers who
 671   // might already have it (no point in recalculating it).
 672   inline void grayRoot(oop obj,
 673                        size_t word_size,
 674                        uint worker_id,
 675                        HeapRegion* hr = NULL);
 676 
 677   // It iterates over the heap and for each object it comes across it
 678   // will dump the contents of its reference fields, as well as
 679   // liveness information for the object and its referents. The dump
 680   // will be written to a file with the following name:
 681   // G1PrintReachableBaseFile + "." + str.
 682   // vo decides whether the prev (vo == UsePrevMarking), the next
 683   // (vo == UseNextMarking) marking information, or the mark word
 684   // (vo == UseMarkWord) will be used to determine the liveness of
 685   // each object / referent.
 686   // If all is true, all objects in the heap will be dumped, otherwise
 687   // only the live ones. In the dump the following symbols / breviations
 688   // are used:
 689   //   M : an explicitly live object (its bitmap bit is set)
 690   //   > : an implicitly live object (over tams)
 691   //   O : an object outside the G1 heap (typically: in the perm gen)
 692   //   NOT : a reference field whose referent is not live
 693   //   AND MARKED : indicates that an object is both explicitly and
 694   //   implicitly live (it should be one or the other, not both)
 695   void print_reachable(const char* str,
 696                        VerifyOption vo,
 697                        bool all) PRODUCT_RETURN;
 698 
 699   // Clear the next marking bitmap (will be called concurrently).
 700   void clearNextBitmap();
 701 
 702   // Return whether the next mark bitmap has no marks set. To be used for assertions
 703   // only. Will not yield to pause requests.
 704   bool nextMarkBitmapIsClear();
 705 
 706   // These two do the work that needs to be done before and after the
 707   // initial root checkpoint. Since this checkpoint can be done at two
 708   // different points (i.e. an explicit pause or piggy-backed on a
 709   // young collection), then it's nice to be able to easily share the
 710   // pre/post code. It might be the case that we can put everything in
 711   // the post method. TP
 712   void checkpointRootsInitialPre();
 713   void checkpointRootsInitialPost();
 714 
 715   // Scan all the root regions and mark everything reachable from
 716   // them.
 717   void scanRootRegions();
 718 
 719   // Scan a single root region and mark everything reachable from it.
 720   void scanRootRegion(HeapRegion* hr, uint worker_id);
 721 
 722   // Do concurrent phase of marking, to a tentative transitive closure.
 723   void markFromRoots();
 724 
 725   void checkpointRootsFinal(bool clear_all_soft_refs);
 726   void checkpointRootsFinalWork();
 727   void cleanup();
 728   void completeCleanup();
 729 
 730   // Mark in the previous bitmap.  NB: this is usually read-only, so use
 731   // this carefully!
 732   inline void markPrev(oop p);
 733 
 734   // Clears marks for all objects in the given range, for the prev or
 735   // next bitmaps.  NB: the previous bitmap is usually
 736   // read-only, so use this carefully!
 737   void clearRangePrevBitmap(MemRegion mr);
 738   void clearRangeNextBitmap(MemRegion mr);
 739 
 740   // Notify data structures that a GC has started.
 741   void note_start_of_gc() {
 742     _markStack.note_start_of_gc();
 743   }
 744 
 745   // Notify data structures that a GC is finished.
 746   void note_end_of_gc() {
 747     _markStack.note_end_of_gc();
 748   }
 749 
 750   // Verify that there are no CSet oops on the stacks (taskqueues /
 751   // global mark stack) and fingers (global / per-task).
 752   // If marking is not in progress, it's a no-op.
 753   void verify_no_cset_oops() PRODUCT_RETURN;
 754 
 755   bool isPrevMarked(oop p) const {
 756     assert(p != NULL && p->is_oop(), "expected an oop");
 757     HeapWord* addr = (HeapWord*)p;
 758     assert(addr >= _prevMarkBitMap->startWord() ||
 759            addr < _prevMarkBitMap->endWord(), "in a region");
 760 
 761     return _prevMarkBitMap->isMarked(addr);
 762   }
 763 
 764   inline bool do_yield_check(uint worker_i = 0);
 765 
 766   // Called to abort the marking cycle after a Full GC takes place.
 767   void abort();
 768 
 769   bool has_aborted()      { return _has_aborted; }
 770 
 771   const GCId& concurrent_gc_id();
 772 
 773   // This prints the global/local fingers. It is used for debugging.
 774   NOT_PRODUCT(void print_finger();)
 775 
 776   void print_summary_info();
 777 
 778   void print_worker_threads_on(outputStream* st) const;
 779 
 780   void print_on_error(outputStream* st) const;
 781 
 782   // The following indicate whether a given verbose level has been
 783   // set. Notice that anything above stats is conditional to
 784   // _MARKING_VERBOSE_ having been set to 1
 785   bool verbose_stats() {
 786     return _verbose_level >= stats_verbose;
 787   }
 788   bool verbose_low() {
 789     return _MARKING_VERBOSE_ && _verbose_level >= low_verbose;
 790   }
 791   bool verbose_medium() {
 792     return _MARKING_VERBOSE_ && _verbose_level >= medium_verbose;
 793   }
 794   bool verbose_high() {
 795     return _MARKING_VERBOSE_ && _verbose_level >= high_verbose;
 796   }
 797 
 798   // Liveness counting
 799 
 800   // Utility routine to set an exclusive range of cards on the given
 801   // card liveness bitmap
 802   inline void set_card_bitmap_range(BitMap* card_bm,
 803                                     BitMap::idx_t start_idx,
 804                                     BitMap::idx_t end_idx,
 805                                     bool is_par);
 806 
 807   // Returns the card number of the bottom of the G1 heap.
 808   // Used in biasing indices into accounting card bitmaps.
 809   intptr_t heap_bottom_card_num() const {
 810     return _heap_bottom_card_num;
 811   }
 812 
 813   // Returns the card bitmap for a given task or worker id.
 814   BitMap* count_card_bitmap_for(uint worker_id) {
 815     assert(worker_id < _max_worker_id, "oob");
 816     assert(_count_card_bitmaps != NULL, "uninitialized");
 817     BitMap* task_card_bm = &_count_card_bitmaps[worker_id];
 818     assert(task_card_bm->size() == _card_bm.size(), "size mismatch");
 819     return task_card_bm;
 820   }
 821 
 822   // Returns the array containing the marked bytes for each region,
 823   // for the given worker or task id.
 824   size_t* count_marked_bytes_array_for(uint worker_id) {
 825     assert(worker_id < _max_worker_id, "oob");
 826     assert(_count_marked_bytes != NULL, "uninitialized");
 827     size_t* marked_bytes_array = _count_marked_bytes[worker_id];
 828     assert(marked_bytes_array != NULL, "uninitialized");
 829     return marked_bytes_array;
 830   }
 831 
 832   // Returns the index in the liveness accounting card table bitmap
 833   // for the given address
 834   inline BitMap::idx_t card_bitmap_index_for(HeapWord* addr);
 835 
 836   // Counts the size of the given memory region in the the given
 837   // marked_bytes array slot for the given HeapRegion.
 838   // Sets the bits in the given card bitmap that are associated with the
 839   // cards that are spanned by the memory region.
 840   inline void count_region(MemRegion mr,
 841                            HeapRegion* hr,
 842                            size_t* marked_bytes_array,
 843                            BitMap* task_card_bm);
 844 
 845   // Counts the given memory region in the task/worker counting
 846   // data structures for the given worker id.
 847   inline void count_region(MemRegion mr, HeapRegion* hr, uint worker_id);
 848 
 849   // Counts the given object in the given task/worker counting
 850   // data structures.
 851   inline void count_object(oop obj,
 852                            HeapRegion* hr,
 853                            size_t* marked_bytes_array,
 854                            BitMap* task_card_bm);
 855 
 856   // Attempts to mark the given object and, if successful, counts
 857   // the object in the given task/worker counting structures.
 858   inline bool par_mark_and_count(oop obj,
 859                                  HeapRegion* hr,
 860                                  size_t* marked_bytes_array,
 861                                  BitMap* task_card_bm);
 862 
 863   // Attempts to mark the given object and, if successful, counts
 864   // the object in the task/worker counting structures for the
 865   // given worker id.
 866   inline bool par_mark_and_count(oop obj,
 867                                  size_t word_size,
 868                                  HeapRegion* hr,
 869                                  uint worker_id);
 870 
 871   // Returns true if initialization was successfully completed.
 872   bool completed_initialization() const {
 873     return _completed_initialization;
 874   }
 875 
 876 protected:
 877   // Clear all the per-task bitmaps and arrays used to store the
 878   // counting data.
 879   void clear_all_count_data();
 880 
 881   // Aggregates the counting data for each worker/task
 882   // that was constructed while marking. Also sets
 883   // the amount of marked bytes for each region and
 884   // the top at concurrent mark count.
 885   void aggregate_count_data();
 886 
 887   // Verification routine
 888   void verify_count_data();
 889 };
 890 
 891 // A class representing a marking task.
 892 class CMTask : public TerminatorTerminator {
 893 private:
 894   enum PrivateConstants {
 895     // the regular clock call is called once the scanned words reaches
 896     // this limit
 897     words_scanned_period          = 12*1024,
 898     // the regular clock call is called once the number of visited
 899     // references reaches this limit
 900     refs_reached_period           = 384,
 901     // initial value for the hash seed, used in the work stealing code
 902     init_hash_seed                = 17,
 903     // how many entries will be transferred between global stack and
 904     // local queues
 905     global_stack_transfer_size    = 16
 906   };
 907 
 908   uint                        _worker_id;
 909   G1CollectedHeap*            _g1h;
 910   ConcurrentMark*             _cm;
 911   CMBitMap*                   _nextMarkBitMap;
 912   // the task queue of this task
 913   CMTaskQueue*                _task_queue;
 914 private:
 915   // the task queue set---needed for stealing
 916   CMTaskQueueSet*             _task_queues;
 917   // indicates whether the task has been claimed---this is only  for
 918   // debugging purposes
 919   bool                        _claimed;
 920 
 921   // number of calls to this task
 922   int                         _calls;
 923 
 924   // when the virtual timer reaches this time, the marking step should
 925   // exit
 926   double                      _time_target_ms;
 927   // the start time of the current marking step
 928   double                      _start_time_ms;
 929 
 930   // the oop closure used for iterations over oops
 931   G1CMOopClosure*             _cm_oop_closure;
 932 
 933   // the region this task is scanning, NULL if we're not scanning any
 934   HeapRegion*                 _curr_region;
 935   // the local finger of this task, NULL if we're not scanning a region
 936   HeapWord*                   _finger;
 937   // limit of the region this task is scanning, NULL if we're not scanning one
 938   HeapWord*                   _region_limit;
 939 
 940   // the number of words this task has scanned
 941   size_t                      _words_scanned;
 942   // When _words_scanned reaches this limit, the regular clock is
 943   // called. Notice that this might be decreased under certain
 944   // circumstances (i.e. when we believe that we did an expensive
 945   // operation).
 946   size_t                      _words_scanned_limit;
 947   // the initial value of _words_scanned_limit (i.e. what it was
 948   // before it was decreased).
 949   size_t                      _real_words_scanned_limit;
 950 
 951   // the number of references this task has visited
 952   size_t                      _refs_reached;
 953   // When _refs_reached reaches this limit, the regular clock is
 954   // called. Notice this this might be decreased under certain
 955   // circumstances (i.e. when we believe that we did an expensive
 956   // operation).
 957   size_t                      _refs_reached_limit;
 958   // the initial value of _refs_reached_limit (i.e. what it was before
 959   // it was decreased).
 960   size_t                      _real_refs_reached_limit;
 961 
 962   // used by the work stealing stuff
 963   int                         _hash_seed;
 964   // if this is true, then the task has aborted for some reason
 965   bool                        _has_aborted;
 966   // set when the task aborts because it has met its time quota
 967   bool                        _has_timed_out;
 968   // true when we're draining SATB buffers; this avoids the task
 969   // aborting due to SATB buffers being available (as we're already
 970   // dealing with them)
 971   bool                        _draining_satb_buffers;
 972 
 973   // number sequence of past step times
 974   NumberSeq                   _step_times_ms;
 975   // elapsed time of this task
 976   double                      _elapsed_time_ms;
 977   // termination time of this task
 978   double                      _termination_time_ms;
 979   // when this task got into the termination protocol
 980   double                      _termination_start_time_ms;
 981 
 982   // true when the task is during a concurrent phase, false when it is
 983   // in the remark phase (so, in the latter case, we do not have to
 984   // check all the things that we have to check during the concurrent
 985   // phase, i.e. SATB buffer availability...)
 986   bool                        _concurrent;
 987 
 988   TruncatedSeq                _marking_step_diffs_ms;
 989 
 990   // Counting data structures. Embedding the task's marked_bytes_array
 991   // and card bitmap into the actual task saves having to go through
 992   // the ConcurrentMark object.
 993   size_t*                     _marked_bytes_array;
 994   BitMap*                     _card_bm;
 995 
 996   // LOTS of statistics related with this task
 997 #if _MARKING_STATS_
 998   NumberSeq                   _all_clock_intervals_ms;
 999   double                      _interval_start_time_ms;
1000 
1001   size_t                      _aborted;
1002   size_t                      _aborted_overflow;
1003   size_t                      _aborted_cm_aborted;
1004   size_t                      _aborted_yield;
1005   size_t                      _aborted_timed_out;
1006   size_t                      _aborted_satb;
1007   size_t                      _aborted_termination;
1008 
1009   size_t                      _steal_attempts;
1010   size_t                      _steals;
1011 
1012   size_t                      _clock_due_to_marking;
1013   size_t                      _clock_due_to_scanning;
1014 
1015   size_t                      _local_pushes;
1016   size_t                      _local_pops;
1017   size_t                      _local_max_size;
1018   size_t                      _objs_scanned;
1019 
1020   size_t                      _global_pushes;
1021   size_t                      _global_pops;
1022   size_t                      _global_max_size;
1023 
1024   size_t                      _global_transfers_to;
1025   size_t                      _global_transfers_from;
1026 
1027   size_t                      _regions_claimed;
1028   size_t                      _objs_found_on_bitmap;
1029 
1030   size_t                      _satb_buffers_processed;
1031 #endif // _MARKING_STATS_
1032 
1033   // it updates the local fields after this task has claimed
1034   // a new region to scan
1035   void setup_for_region(HeapRegion* hr);
1036   // it brings up-to-date the limit of the region
1037   void update_region_limit();
1038 
1039   // called when either the words scanned or the refs visited limit
1040   // has been reached
1041   void reached_limit();
1042   // recalculates the words scanned and refs visited limits
1043   void recalculate_limits();
1044   // decreases the words scanned and refs visited limits when we reach
1045   // an expensive operation
1046   void decrease_limits();
1047   // it checks whether the words scanned or refs visited reached their
1048   // respective limit and calls reached_limit() if they have
1049   void check_limits() {
1050     if (_words_scanned >= _words_scanned_limit ||
1051         _refs_reached >= _refs_reached_limit) {
1052       reached_limit();
1053     }
1054   }
1055   // this is supposed to be called regularly during a marking step as
1056   // it checks a bunch of conditions that might cause the marking step
1057   // to abort
1058   void regular_clock_call();
1059   bool concurrent() { return _concurrent; }
1060 
1061   // Test whether obj might have already been passed over by the
1062   // mark bitmap scan, and so needs to be pushed onto the mark stack.
1063   bool is_below_finger(oop obj, HeapWord* global_finger) const;
1064 
1065   template<bool scan> void process_grey_object(oop obj);
1066 
1067 public:
1068   // It resets the task; it should be called right at the beginning of
1069   // a marking phase.
1070   void reset(CMBitMap* _nextMarkBitMap);
1071   // it clears all the fields that correspond to a claimed region.
1072   void clear_region_fields();
1073 
1074   void set_concurrent(bool concurrent) { _concurrent = concurrent; }
1075 
1076   // The main method of this class which performs a marking step
1077   // trying not to exceed the given duration. However, it might exit
1078   // prematurely, according to some conditions (i.e. SATB buffers are
1079   // available for processing).
1080   void do_marking_step(double target_ms,
1081                        bool do_termination,
1082                        bool is_serial);
1083 
1084   // These two calls start and stop the timer
1085   void record_start_time() {
1086     _elapsed_time_ms = os::elapsedTime() * 1000.0;
1087   }
1088   void record_end_time() {
1089     _elapsed_time_ms = os::elapsedTime() * 1000.0 - _elapsed_time_ms;
1090   }
1091 
1092   // returns the worker ID associated with this task.
1093   uint worker_id() { return _worker_id; }
1094 
1095   // From TerminatorTerminator. It determines whether this task should
1096   // exit the termination protocol after it's entered it.
1097   virtual bool should_exit_termination();
1098 
1099   // Resets the local region fields after a task has finished scanning a
1100   // region; or when they have become stale as a result of the region
1101   // being evacuated.
1102   void giveup_current_region();
1103 
1104   HeapWord* finger()            { return _finger; }
1105 
1106   bool has_aborted()            { return _has_aborted; }
1107   void set_has_aborted()        { _has_aborted = true; }
1108   void clear_has_aborted()      { _has_aborted = false; }
1109   bool has_timed_out()          { return _has_timed_out; }
1110   bool claimed()                { return _claimed; }
1111 
1112   void set_cm_oop_closure(G1CMOopClosure* cm_oop_closure);
1113 
1114   // Increment the number of references this task has visited.
1115   void increment_refs_reached() { ++_refs_reached; }
1116 
1117   // Grey the object by marking it.  If not already marked, push it on
1118   // the local queue if below the finger.
1119   // Precondition: obj is in region.
1120   // Precondition: obj is below region's NTAMS.
1121   inline void make_reference_grey(oop obj, HeapRegion* region);
1122 
1123   // Grey the object (by calling make_grey_reference) if required,
1124   // e.g. obj is below its containing region's NTAMS.
1125   // Precondition: obj is a valid heap object.
1126   inline void deal_with_reference(oop obj);
1127 
1128   // It scans an object and visits its children.
1129   inline void scan_object(oop obj);
1130 
1131   // It pushes an object on the local queue.
1132   inline void push(oop obj);
1133 
1134   // These two move entries to/from the global stack.
1135   void move_entries_to_global_stack();
1136   void get_entries_from_global_stack();
1137 
1138   // It pops and scans objects from the local queue. If partially is
1139   // true, then it stops when the queue size is of a given limit. If
1140   // partially is false, then it stops when the queue is empty.
1141   void drain_local_queue(bool partially);
1142   // It moves entries from the global stack to the local queue and
1143   // drains the local queue. If partially is true, then it stops when
1144   // both the global stack and the local queue reach a given size. If
1145   // partially if false, it tries to empty them totally.
1146   void drain_global_stack(bool partially);
1147   // It keeps picking SATB buffers and processing them until no SATB
1148   // buffers are available.
1149   void drain_satb_buffers();
1150 
1151   // moves the local finger to a new location
1152   inline void move_finger_to(HeapWord* new_finger) {
1153     assert(new_finger >= _finger && new_finger < _region_limit, "invariant");
1154     _finger = new_finger;
1155   }
1156 
1157   CMTask(uint worker_id,
1158          ConcurrentMark *cm,
1159          size_t* marked_bytes,
1160          BitMap* card_bm,
1161          CMTaskQueue* task_queue,
1162          CMTaskQueueSet* task_queues);
1163 
1164   // it prints statistics associated with this task
1165   void print_stats();
1166 
1167 #if _MARKING_STATS_
1168   void increase_objs_found_on_bitmap() { ++_objs_found_on_bitmap; }
1169 #endif // _MARKING_STATS_
1170 };
1171 
1172 // Class that's used to to print out per-region liveness
1173 // information. It's currently used at the end of marking and also
1174 // after we sort the old regions at the end of the cleanup operation.
1175 class G1PrintRegionLivenessInfoClosure: public HeapRegionClosure {
1176 private:
1177   outputStream* _out;
1178 
1179   // Accumulators for these values.
1180   size_t _total_used_bytes;
1181   size_t _total_capacity_bytes;
1182   size_t _total_prev_live_bytes;
1183   size_t _total_next_live_bytes;
1184 
1185   // These are set up when we come across a "stars humongous" region
1186   // (as this is where most of this information is stored, not in the
1187   // subsequent "continues humongous" regions). After that, for every
1188   // region in a given humongous region series we deduce the right
1189   // values for it by simply subtracting the appropriate amount from
1190   // these fields. All these values should reach 0 after we've visited
1191   // the last region in the series.
1192   size_t _hum_used_bytes;
1193   size_t _hum_capacity_bytes;
1194   size_t _hum_prev_live_bytes;
1195   size_t _hum_next_live_bytes;
1196 
1197   // Accumulator for the remembered set size
1198   size_t _total_remset_bytes;
1199 
1200   // Accumulator for strong code roots memory size
1201   size_t _total_strong_code_roots_bytes;
1202 
1203   static double perc(size_t val, size_t total) {
1204     if (total == 0) {
1205       return 0.0;
1206     } else {
1207       return 100.0 * ((double) val / (double) total);
1208     }
1209   }
1210 
1211   static double bytes_to_mb(size_t val) {
1212     return (double) val / (double) M;
1213   }
1214 
1215   // See the .cpp file.
1216   size_t get_hum_bytes(size_t* hum_bytes);
1217   void get_hum_bytes(size_t* used_bytes, size_t* capacity_bytes,
1218                      size_t* prev_live_bytes, size_t* next_live_bytes);
1219 
1220 public:
1221   // The header and footer are printed in the constructor and
1222   // destructor respectively.
1223   G1PrintRegionLivenessInfoClosure(outputStream* out, const char* phase_name);
1224   virtual bool doHeapRegion(HeapRegion* r);
1225   ~G1PrintRegionLivenessInfoClosure();
1226 };
1227 
1228 #endif // SHARE_VM_GC_G1_CONCURRENTMARK_HPP