rev 55281 : [mq]: 8225478-cmrootregions-cleanup

   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_GC_G1_G1CONCURRENTMARK_HPP
  26 #define SHARE_GC_G1_G1CONCURRENTMARK_HPP
  27 
  28 #include "gc/g1/g1ConcurrentMarkBitMap.hpp"
  29 #include "gc/g1/g1ConcurrentMarkObjArrayProcessor.hpp"
  30 #include "gc/g1/g1HeapVerifier.hpp"
  31 #include "gc/g1/g1RegionMarkStatsCache.hpp"
  32 #include "gc/g1/heapRegionSet.hpp"
  33 #include "gc/shared/taskqueue.hpp"
  34 #include "gc/shared/verifyOption.hpp"
  35 #include "memory/allocation.hpp"
  36 #include "utilities/compilerWarnings.hpp"
  37 
  38 class ConcurrentGCTimer;
  39 class G1ConcurrentMarkThread;
  40 class G1CollectedHeap;
  41 class G1CMOopClosure;
  42 class G1CMTask;
  43 class G1ConcurrentMark;
  44 class G1OldTracer;
  45 class G1RegionToSpaceMapper;
  46 class G1SurvivorRegions;
  47 
  48 PRAGMA_DIAG_PUSH
  49 // warning C4522: multiple assignment operators specified
  50 PRAGMA_DISABLE_MSVC_WARNING(4522)
  51 
  52 // This is a container class for either an oop or a continuation address for
  53 // mark stack entries. Both are pushed onto the mark stack.
  54 class G1TaskQueueEntry {
  55 private:
  56   void* _holder;
  57 
  58   static const uintptr_t ArraySliceBit = 1;
  59 
  60   G1TaskQueueEntry(oop obj) : _holder(obj) {
  61     assert(_holder != NULL, "Not allowed to set NULL task queue element");
  62   }
  63   G1TaskQueueEntry(HeapWord* addr) : _holder((void*)((uintptr_t)addr | ArraySliceBit)) { }
  64 public:
  65   G1TaskQueueEntry(const G1TaskQueueEntry& other) { _holder = other._holder; }
  66   G1TaskQueueEntry() : _holder(NULL) { }
  67 
  68   static G1TaskQueueEntry from_slice(HeapWord* what) { return G1TaskQueueEntry(what); }
  69   static G1TaskQueueEntry from_oop(oop obj) { return G1TaskQueueEntry(obj); }
  70 
  71   G1TaskQueueEntry& operator=(const G1TaskQueueEntry& t) {
  72     _holder = t._holder;
  73     return *this;
  74   }
  75 
  76   volatile G1TaskQueueEntry& operator=(const volatile G1TaskQueueEntry& t) volatile {
  77     _holder = t._holder;
  78     return *this;
  79   }
  80 
  81   oop obj() const {
  82     assert(!is_array_slice(), "Trying to read array slice " PTR_FORMAT " as oop", p2i(_holder));
  83     return (oop)_holder;
  84   }
  85 
  86   HeapWord* slice() const {
  87     assert(is_array_slice(), "Trying to read oop " PTR_FORMAT " as array slice", p2i(_holder));
  88     return (HeapWord*)((uintptr_t)_holder & ~ArraySliceBit);
  89   }
  90 
  91   bool is_oop() const { return !is_array_slice(); }
  92   bool is_array_slice() const { return ((uintptr_t)_holder & ArraySliceBit) != 0; }
  93   bool is_null() const { return _holder == NULL; }
  94 };
  95 
  96 PRAGMA_DIAG_POP
  97 
  98 typedef GenericTaskQueue<G1TaskQueueEntry, mtGC> G1CMTaskQueue;
  99 typedef GenericTaskQueueSet<G1CMTaskQueue, mtGC> G1CMTaskQueueSet;
 100 
 101 // Closure used by CM during concurrent reference discovery
 102 // and reference processing (during remarking) to determine
 103 // if a particular object is alive. It is primarily used
 104 // to determine if referents of discovered reference objects
 105 // are alive. An instance is also embedded into the
 106 // reference processor as the _is_alive_non_header field
 107 class G1CMIsAliveClosure : public BoolObjectClosure {
 108   G1CollectedHeap* _g1h;
 109 public:
 110   G1CMIsAliveClosure(G1CollectedHeap* g1h) : _g1h(g1h) { }
 111   bool do_object_b(oop obj);
 112 };
 113 
 114 class G1CMSubjectToDiscoveryClosure : public BoolObjectClosure {
 115   G1CollectedHeap* _g1h;
 116 public:
 117   G1CMSubjectToDiscoveryClosure(G1CollectedHeap* g1h) : _g1h(g1h) { }
 118   bool do_object_b(oop obj);
 119 };
 120 
 121 // Represents the overflow mark stack used by concurrent marking.
 122 //
 123 // Stores oops in a huge buffer in virtual memory that is always fully committed.
 124 // Resizing may only happen during a STW pause when the stack is empty.
 125 //
 126 // Memory is allocated on a "chunk" basis, i.e. a set of oops. For this, the mark
 127 // stack memory is split into evenly sized chunks of oops. Users can only
 128 // add or remove entries on that basis.
 129 // Chunks are filled in increasing address order. Not completely filled chunks
 130 // have a NULL element as a terminating element.
 131 //
 132 // Every chunk has a header containing a single pointer element used for memory
 133 // management. This wastes some space, but is negligible (< .1% with current sizing).
 134 //
 135 // Memory management is done using a mix of tracking a high water-mark indicating
 136 // that all chunks at a lower address are valid chunks, and a singly linked free
 137 // list connecting all empty chunks.
 138 class G1CMMarkStack {
 139 public:
 140   // Number of TaskQueueEntries that can fit in a single chunk.
 141   static const size_t EntriesPerChunk = 1024 - 1 /* One reference for the next pointer */;
 142 private:
 143   struct TaskQueueEntryChunk {
 144     TaskQueueEntryChunk* next;
 145     G1TaskQueueEntry data[EntriesPerChunk];
 146   };
 147 
 148   size_t _max_chunk_capacity;    // Maximum number of TaskQueueEntryChunk elements on the stack.
 149 
 150   TaskQueueEntryChunk* _base;    // Bottom address of allocated memory area.
 151   size_t _chunk_capacity;        // Current maximum number of TaskQueueEntryChunk elements.
 152 
 153   char _pad0[DEFAULT_CACHE_LINE_SIZE];
 154   TaskQueueEntryChunk* volatile _free_list;  // Linked list of free chunks that can be allocated by users.
 155   char _pad1[DEFAULT_CACHE_LINE_SIZE - sizeof(TaskQueueEntryChunk*)];
 156   TaskQueueEntryChunk* volatile _chunk_list; // List of chunks currently containing data.
 157   volatile size_t _chunks_in_chunk_list;
 158   char _pad2[DEFAULT_CACHE_LINE_SIZE - sizeof(TaskQueueEntryChunk*) - sizeof(size_t)];
 159 
 160   volatile size_t _hwm;          // High water mark within the reserved space.
 161   char _pad4[DEFAULT_CACHE_LINE_SIZE - sizeof(size_t)];
 162 
 163   // Allocate a new chunk from the reserved memory, using the high water mark. Returns
 164   // NULL if out of memory.
 165   TaskQueueEntryChunk* allocate_new_chunk();
 166 
 167   // Atomically add the given chunk to the list.
 168   void add_chunk_to_list(TaskQueueEntryChunk* volatile* list, TaskQueueEntryChunk* elem);
 169   // Atomically remove and return a chunk from the given list. Returns NULL if the
 170   // list is empty.
 171   TaskQueueEntryChunk* remove_chunk_from_list(TaskQueueEntryChunk* volatile* list);
 172 
 173   void add_chunk_to_chunk_list(TaskQueueEntryChunk* elem);
 174   void add_chunk_to_free_list(TaskQueueEntryChunk* elem);
 175 
 176   TaskQueueEntryChunk* remove_chunk_from_chunk_list();
 177   TaskQueueEntryChunk* remove_chunk_from_free_list();
 178 
 179   // Resizes the mark stack to the given new capacity. Releases any previous
 180   // memory if successful.
 181   bool resize(size_t new_capacity);
 182 
 183  public:
 184   G1CMMarkStack();
 185   ~G1CMMarkStack();
 186 
 187   // Alignment and minimum capacity of this mark stack in number of oops.
 188   static size_t capacity_alignment();
 189 
 190   // Allocate and initialize the mark stack with the given number of oops.
 191   bool initialize(size_t initial_capacity, size_t max_capacity);
 192 
 193   // Pushes the given buffer containing at most EntriesPerChunk elements on the mark
 194   // stack. If less than EntriesPerChunk elements are to be pushed, the array must
 195   // be terminated with a NULL.
 196   // Returns whether the buffer contents were successfully pushed to the global mark
 197   // stack.
 198   bool par_push_chunk(G1TaskQueueEntry* buffer);
 199 
 200   // Pops a chunk from this mark stack, copying them into the given buffer. This
 201   // chunk may contain up to EntriesPerChunk elements. If there are less, the last
 202   // element in the array is a NULL pointer.
 203   bool par_pop_chunk(G1TaskQueueEntry* buffer);
 204 
 205   // Return whether the chunk list is empty. Racy due to unsynchronized access to
 206   // _chunk_list.
 207   bool is_empty() const { return _chunk_list == NULL; }
 208 
 209   size_t capacity() const  { return _chunk_capacity; }
 210 
 211   // Expand the stack, typically in response to an overflow condition
 212   void expand();
 213 
 214   // Return the approximate number of oops on this mark stack. Racy due to
 215   // unsynchronized access to _chunks_in_chunk_list.
 216   size_t size() const { return _chunks_in_chunk_list * EntriesPerChunk; }
 217 
 218   void set_empty();
 219 
 220   // Apply Fn to every oop on the mark stack. The mark stack must not
 221   // be modified while iterating.
 222   template<typename Fn> void iterate(Fn fn) const PRODUCT_RETURN;
 223 };
 224 
 225 // Root Regions are regions that contain objects from nTAMS to top. These are roots
 226 // for marking, i.e. their referenced objects must be kept alive to maintain the
 227 // SATB invariant.
 228 // We could scan and mark them through during the initial-mark pause, but for

 229 // pause time reasons we move this work to the concurrent phase.
 230 // We need to complete this procedure before the next GC because it might determine
 231 // that some of these "root objects" are dead, potentially dropping some required
 232 // references.
 233 // Root regions comprise of the complete contents of survivor regions, and any
 234 // objects copied into old gen during GC.
 235 class G1CMRootRegions {
 236   HeapRegion** _root_regions;

 237   size_t const _max_regions;
 238 
 239   volatile size_t _num_root_regions; // Actual number of root regions.
 240 
 241   volatile size_t _claimed_root_regions; // Number of root regions currently claimed.
 242 
 243   volatile bool _scan_in_progress;
 244   volatile bool _should_abort;
 245 
 246   void notify_scan_done();
 247 
 248 public:
 249   G1CMRootRegions(uint const max_regions);
 250   ~G1CMRootRegions();
 251 
 252   // Reset the data structure to allow addition of new root regions.
 253   void reset();
 254 
 255   void add(HeapRegion* hr);
 256 
 257   // Reset the claiming / scanning of the root regions.
 258   void prepare_for_scan();
 259 
 260   // Forces get_next() to return NULL so that the iteration aborts early.
 261   void abort() { _should_abort = true; }
 262 
 263   // Return true if the CM thread are actively scanning root regions,
 264   // false otherwise.
 265   bool scan_in_progress() { return _scan_in_progress; }
 266 
 267   // Claim the next root region to scan atomically, or return NULL if
 268   // all have been claimed.
 269   HeapRegion* claim_next();
 270 
 271   // The number of root regions to scan.
 272   uint num_root_regions() const;
 273 
 274   void cancel_scan();
 275 
 276   // Flag that we're done with root region scanning and notify anyone
 277   // who's waiting on it. If aborted is false, assume that all regions
 278   // have been claimed.
 279   void scan_finished();
 280 
 281   // If CM threads are still scanning root regions, wait until they
 282   // are done. Return true if we had to wait, false otherwise.
 283   bool wait_until_scan_finished();
 284 };
 285 
 286 // This class manages data structures and methods for doing liveness analysis in
 287 // G1's concurrent cycle.
 288 class G1ConcurrentMark : public CHeapObj<mtGC> {
 289   friend class G1ConcurrentMarkThread;
 290   friend class G1CMRefProcTaskProxy;
 291   friend class G1CMRefProcTaskExecutor;
 292   friend class G1CMKeepAliveAndDrainClosure;
 293   friend class G1CMDrainMarkingStackClosure;
 294   friend class G1CMBitMapClosure;
 295   friend class G1CMConcurrentMarkingTask;
 296   friend class G1CMRemarkTask;
 297   friend class G1CMTask;
 298 
 299   G1ConcurrentMarkThread* _cm_thread;     // The thread doing the work
 300   G1CollectedHeap*        _g1h;           // The heap
 301   bool                    _completed_initialization; // Set to true when initialization is complete
 302 
 303   // Concurrent marking support structures
 304   G1CMBitMap              _mark_bitmap_1;
 305   G1CMBitMap              _mark_bitmap_2;
 306   G1CMBitMap*             _prev_mark_bitmap; // Completed mark bitmap
 307   G1CMBitMap*             _next_mark_bitmap; // Under-construction mark bitmap
 308 
 309   // Heap bounds
 310   MemRegion const         _heap;
 311 
 312   // Root region tracking and claiming
 313   G1CMRootRegions         _root_regions;
 314 
 315   // For grey objects
 316   G1CMMarkStack           _global_mark_stack; // Grey objects behind global finger
 317   HeapWord* volatile      _finger;            // The global finger, region aligned,
 318                                               // always pointing to the end of the
 319                                               // last claimed region
 320 
 321   uint                    _worker_id_offset;
 322   uint                    _max_num_tasks;    // Maximum number of marking tasks
 323   uint                    _num_active_tasks; // Number of tasks currently active
 324   G1CMTask**              _tasks;            // Task queue array (max_worker_id length)
 325 
 326   G1CMTaskQueueSet*       _task_queues; // Task queue set
 327   TaskTerminator          _terminator;  // For termination
 328 
 329   // Two sync barriers that are used to synchronize tasks when an
 330   // overflow occurs. The algorithm is the following. All tasks enter
 331   // the first one to ensure that they have all stopped manipulating
 332   // the global data structures. After they exit it, they re-initialize
 333   // their data structures and task 0 re-initializes the global data
 334   // structures. Then, they enter the second sync barrier. This
 335   // ensure, that no task starts doing work before all data
 336   // structures (local and global) have been re-initialized. When they
 337   // exit it, they are free to start working again.
 338   WorkGangBarrierSync     _first_overflow_barrier_sync;
 339   WorkGangBarrierSync     _second_overflow_barrier_sync;
 340 
 341   // This is set by any task, when an overflow on the global data
 342   // structures is detected
 343   volatile bool           _has_overflown;
 344   // True: marking is concurrent, false: we're in remark
 345   volatile bool           _concurrent;
 346   // Set at the end of a Full GC so that marking aborts
 347   volatile bool           _has_aborted;
 348 
 349   // Used when remark aborts due to an overflow to indicate that
 350   // another concurrent marking phase should start
 351   volatile bool           _restart_for_overflow;
 352 
 353   ConcurrentGCTimer*      _gc_timer_cm;
 354 
 355   G1OldTracer*            _gc_tracer_cm;
 356 
 357   // Timing statistics. All of them are in ms
 358   NumberSeq _init_times;
 359   NumberSeq _remark_times;
 360   NumberSeq _remark_mark_times;
 361   NumberSeq _remark_weak_ref_times;
 362   NumberSeq _cleanup_times;
 363   double    _total_cleanup_time;
 364 
 365   double*   _accum_task_vtime;   // Accumulated task vtime
 366 
 367   WorkGang* _concurrent_workers;
 368   uint      _num_concurrent_workers; // The number of marking worker threads we're using
 369   uint      _max_concurrent_workers; // Maximum number of marking worker threads
 370 
 371   void verify_during_pause(G1HeapVerifier::G1VerifyType type, VerifyOption vo, const char* caller);
 372 
 373   void finalize_marking();
 374 
 375   void weak_refs_work_parallel_part(BoolObjectClosure* is_alive, bool purged_classes);
 376   void weak_refs_work(bool clear_all_soft_refs);
 377 
 378   void report_object_count(bool mark_completed);
 379 
 380   void swap_mark_bitmaps();
 381 
 382   void reclaim_empty_regions();
 383 
 384   // After reclaiming empty regions, update heap sizes.
 385   void compute_new_sizes();
 386 
 387   // Clear statistics gathered during the concurrent cycle for the given region after
 388   // it has been reclaimed.
 389   void clear_statistics(HeapRegion* r);
 390 
 391   // Resets the global marking data structures, as well as the
 392   // task local ones; should be called during initial mark.
 393   void reset();
 394 
 395   // Resets all the marking data structures. Called when we have to restart
 396   // marking or when marking completes (via set_non_marking_state below).
 397   void reset_marking_for_restart();
 398 
 399   // We do this after we're done with marking so that the marking data
 400   // structures are initialized to a sensible and predictable state.
 401   void reset_at_marking_complete();
 402 
 403   // Called to indicate how many threads are currently active.
 404   void set_concurrency(uint active_tasks);
 405 
 406   // Should be called to indicate which phase we're in (concurrent
 407   // mark or remark) and how many threads are currently active.
 408   void set_concurrency_and_phase(uint active_tasks, bool concurrent);
 409 
 410   // Prints all gathered CM-related statistics
 411   void print_stats();
 412 
 413   HeapWord*               finger()           { return _finger;   }
 414   bool                    concurrent()       { return _concurrent; }
 415   uint                    active_tasks()     { return _num_active_tasks; }
 416   ParallelTaskTerminator* terminator() const { return _terminator.terminator(); }
 417 
 418   // Claims the next available region to be scanned by a marking
 419   // task/thread. It might return NULL if the next region is empty or
 420   // we have run out of regions. In the latter case, out_of_regions()
 421   // determines whether we've really run out of regions or the task
 422   // should call claim_region() again. This might seem a bit
 423   // awkward. Originally, the code was written so that claim_region()
 424   // either successfully returned with a non-empty region or there
 425   // were no more regions to be claimed. The problem with this was
 426   // that, in certain circumstances, it iterated over large chunks of
 427   // the heap finding only empty regions and, while it was working, it
 428   // was preventing the calling task to call its regular clock
 429   // method. So, this way, each task will spend very little time in
 430   // claim_region() and is allowed to call the regular clock method
 431   // frequently.
 432   HeapRegion* claim_region(uint worker_id);
 433 
 434   // Determines whether we've run out of regions to scan. Note that
 435   // the finger can point past the heap end in case the heap was expanded
 436   // to satisfy an allocation without doing a GC. This is fine, because all
 437   // objects in those regions will be considered live anyway because of
 438   // SATB guarantees (i.e. their TAMS will be equal to bottom).
 439   bool out_of_regions() { return _finger >= _heap.end(); }
 440 
 441   // Returns the task with the given id
 442   G1CMTask* task(uint id) {
 443     // During initial mark we use the parallel gc threads to do some work, so
 444     // we can only compare against _max_num_tasks.
 445     assert(id < _max_num_tasks, "Task id %u not within bounds up to %u", id, _max_num_tasks);
 446     return _tasks[id];
 447   }
 448 
 449   // Access / manipulation of the overflow flag which is set to
 450   // indicate that the global stack has overflown
 451   bool has_overflown()           { return _has_overflown; }
 452   void set_has_overflown()       { _has_overflown = true; }
 453   void clear_has_overflown()     { _has_overflown = false; }
 454   bool restart_for_overflow()    { return _restart_for_overflow; }
 455 
 456   // Methods to enter the two overflow sync barriers
 457   void enter_first_sync_barrier(uint worker_id);
 458   void enter_second_sync_barrier(uint worker_id);
 459 
 460   // Clear the given bitmap in parallel using the given WorkGang. If may_yield is
 461   // true, periodically insert checks to see if this method should exit prematurely.
 462   void clear_bitmap(G1CMBitMap* bitmap, WorkGang* workers, bool may_yield);
 463 
 464   // Region statistics gathered during marking.
 465   G1RegionMarkStats* _region_mark_stats;
 466   // Top pointer for each region at the start of the rebuild remembered set process
 467   // for regions which remembered sets need to be rebuilt. A NULL for a given region
 468   // means that this region does not be scanned during the rebuilding remembered
 469   // set phase at all.
 470   HeapWord* volatile* _top_at_rebuild_starts;
 471 public:
 472   void add_to_liveness(uint worker_id, oop const obj, size_t size);
 473   // Liveness of the given region as determined by concurrent marking, i.e. the amount of
 474   // live words between bottom and nTAMS.
 475   size_t liveness(uint region) const { return _region_mark_stats[region]._live_words; }
 476 
 477   // Sets the internal top_at_region_start for the given region to current top of the region.
 478   inline void update_top_at_rebuild_start(HeapRegion* r);
 479   // TARS for the given region during remembered set rebuilding.
 480   inline HeapWord* top_at_rebuild_start(uint region) const;
 481 
 482   // Clear statistics gathered during the concurrent cycle for the given region after
 483   // it has been reclaimed.
 484   void clear_statistics_in_region(uint region_idx);
 485   // Notification for eagerly reclaimed regions to clean up.
 486   void humongous_object_eagerly_reclaimed(HeapRegion* r);
 487   // Manipulation of the global mark stack.
 488   // The push and pop operations are used by tasks for transfers
 489   // between task-local queues and the global mark stack.
 490   bool mark_stack_push(G1TaskQueueEntry* arr) {
 491     if (!_global_mark_stack.par_push_chunk(arr)) {
 492       set_has_overflown();
 493       return false;
 494     }
 495     return true;
 496   }
 497   bool mark_stack_pop(G1TaskQueueEntry* arr) {
 498     return _global_mark_stack.par_pop_chunk(arr);
 499   }
 500   size_t mark_stack_size() const                { return _global_mark_stack.size(); }
 501   size_t partial_mark_stack_size_target() const { return _global_mark_stack.capacity() / 3; }
 502   bool mark_stack_empty() const                 { return _global_mark_stack.is_empty(); }
 503 
 504   G1CMRootRegions* root_regions() { return &_root_regions; }
 505 
 506   void concurrent_cycle_start();
 507   // Abandon current marking iteration due to a Full GC.
 508   void concurrent_cycle_abort();
 509   void concurrent_cycle_end();
 510 
 511   void update_accum_task_vtime(int i, double vtime) {
 512     _accum_task_vtime[i] += vtime;
 513   }
 514 
 515   double all_task_accum_vtime() {
 516     double ret = 0.0;
 517     for (uint i = 0; i < _max_num_tasks; ++i)
 518       ret += _accum_task_vtime[i];
 519     return ret;
 520   }
 521 
 522   // Attempts to steal an object from the task queues of other tasks
 523   bool try_stealing(uint worker_id, G1TaskQueueEntry& task_entry);
 524 
 525   G1ConcurrentMark(G1CollectedHeap* g1h,
 526                    G1RegionToSpaceMapper* prev_bitmap_storage,
 527                    G1RegionToSpaceMapper* next_bitmap_storage);
 528   ~G1ConcurrentMark();
 529 
 530   G1ConcurrentMarkThread* cm_thread() { return _cm_thread; }
 531 
 532   const G1CMBitMap* const prev_mark_bitmap() const { return _prev_mark_bitmap; }
 533   G1CMBitMap* next_mark_bitmap() const { return _next_mark_bitmap; }
 534 
 535   // Calculates the number of concurrent GC threads to be used in the marking phase.
 536   uint calc_active_marking_workers();
 537 
 538   // Moves all per-task cached data into global state.
 539   void flush_all_task_caches();
 540   // Prepare internal data structures for the next mark cycle. This includes clearing
 541   // the next mark bitmap and some internal data structures. This method is intended
 542   // to be called concurrently to the mutator. It will yield to safepoint requests.
 543   void cleanup_for_next_mark();
 544 
 545   // Clear the previous marking bitmap during safepoint.
 546   void clear_prev_bitmap(WorkGang* workers);
 547 
 548   // These two methods do the work that needs to be done at the start and end of the
 549   // initial mark pause.
 550   void pre_initial_mark();
 551   void post_initial_mark();
 552 
 553   // Scan all the root regions and mark everything reachable from
 554   // them.
 555   void scan_root_regions();
 556 
 557   // Scan a single root region from nTAMS to top and mark everything reachable from it.
 558   void scan_root_region(HeapRegion* hr, uint worker_id);
 559 
 560   // Do concurrent phase of marking, to a tentative transitive closure.
 561   void mark_from_roots();
 562 
 563   // Do concurrent preclean work.
 564   void preclean();
 565 
 566   void remark();
 567 
 568   void cleanup();
 569   // Mark in the previous bitmap. Caution: the prev bitmap is usually read-only, so use
 570   // this carefully.
 571   inline void mark_in_prev_bitmap(oop p);
 572 
 573   // Clears marks for all objects in the given range, for the prev or
 574   // next bitmaps.  Caution: the previous bitmap is usually
 575   // read-only, so use this carefully!
 576   void clear_range_in_prev_bitmap(MemRegion mr);
 577 
 578   inline bool is_marked_in_prev_bitmap(oop p) const;
 579 
 580   // Verify that there are no collection set oops on the stacks (taskqueues /
 581   // global mark stack) and fingers (global / per-task).
 582   // If marking is not in progress, it's a no-op.
 583   void verify_no_collection_set_oops() PRODUCT_RETURN;
 584 
 585   inline bool do_yield_check();
 586 
 587   bool has_aborted()      { return _has_aborted; }
 588 
 589   void print_summary_info();
 590 
 591   void print_worker_threads_on(outputStream* st) const;
 592   void threads_do(ThreadClosure* tc) const;
 593 
 594   void print_on_error(outputStream* st) const;
 595 
 596   // Mark the given object on the next bitmap if it is below nTAMS.
 597   inline bool mark_in_next_bitmap(uint worker_id, HeapRegion* const hr, oop const obj);
 598   inline bool mark_in_next_bitmap(uint worker_id, oop const obj);
 599 
 600   inline bool is_marked_in_next_bitmap(oop p) const;
 601 
 602   // Returns true if initialization was successfully completed.
 603   bool completed_initialization() const {
 604     return _completed_initialization;
 605   }
 606 
 607   ConcurrentGCTimer* gc_timer_cm() const { return _gc_timer_cm; }
 608   G1OldTracer* gc_tracer_cm() const { return _gc_tracer_cm; }
 609 
 610 private:
 611   // Rebuilds the remembered sets for chosen regions in parallel and concurrently to the application.
 612   void rebuild_rem_set_concurrently();
 613 };
 614 
 615 // A class representing a marking task.
 616 class G1CMTask : public TerminatorTerminator {
 617 private:
 618   enum PrivateConstants {
 619     // The regular clock call is called once the scanned words reaches
 620     // this limit
 621     words_scanned_period          = 12*1024,
 622     // The regular clock call is called once the number of visited
 623     // references reaches this limit
 624     refs_reached_period           = 1024,
 625     // Initial value for the hash seed, used in the work stealing code
 626     init_hash_seed                = 17
 627   };
 628 
 629   // Number of entries in the per-task stats entry. This seems enough to have a very
 630   // low cache miss rate.
 631   static const uint RegionMarkStatsCacheSize = 1024;
 632 
 633   G1CMObjArrayProcessor       _objArray_processor;
 634 
 635   uint                        _worker_id;
 636   G1CollectedHeap*            _g1h;
 637   G1ConcurrentMark*           _cm;
 638   G1CMBitMap*                 _next_mark_bitmap;
 639   // the task queue of this task
 640   G1CMTaskQueue*              _task_queue;
 641 
 642   G1RegionMarkStatsCache      _mark_stats_cache;
 643   // Number of calls to this task
 644   uint                        _calls;
 645 
 646   // When the virtual timer reaches this time, the marking step should exit
 647   double                      _time_target_ms;
 648   // Start time of the current marking step
 649   double                      _start_time_ms;
 650 
 651   // Oop closure used for iterations over oops
 652   G1CMOopClosure*             _cm_oop_closure;
 653 
 654   // Region this task is scanning, NULL if we're not scanning any
 655   HeapRegion*                 _curr_region;
 656   // Local finger of this task, NULL if we're not scanning a region
 657   HeapWord*                   _finger;
 658   // Limit of the region this task is scanning, NULL if we're not scanning one
 659   HeapWord*                   _region_limit;
 660 
 661   // Number of words this task has scanned
 662   size_t                      _words_scanned;
 663   // When _words_scanned reaches this limit, the regular clock is
 664   // called. Notice that this might be decreased under certain
 665   // circumstances (i.e. when we believe that we did an expensive
 666   // operation).
 667   size_t                      _words_scanned_limit;
 668   // Initial value of _words_scanned_limit (i.e. what it was
 669   // before it was decreased).
 670   size_t                      _real_words_scanned_limit;
 671 
 672   // Number of references this task has visited
 673   size_t                      _refs_reached;
 674   // When _refs_reached reaches this limit, the regular clock is
 675   // called. Notice this this might be decreased under certain
 676   // circumstances (i.e. when we believe that we did an expensive
 677   // operation).
 678   size_t                      _refs_reached_limit;
 679   // Initial value of _refs_reached_limit (i.e. what it was before
 680   // it was decreased).
 681   size_t                      _real_refs_reached_limit;
 682 
 683   // If true, then the task has aborted for some reason
 684   bool                        _has_aborted;
 685   // Set when the task aborts because it has met its time quota
 686   bool                        _has_timed_out;
 687   // True when we're draining SATB buffers; this avoids the task
 688   // aborting due to SATB buffers being available (as we're already
 689   // dealing with them)
 690   bool                        _draining_satb_buffers;
 691 
 692   // Number sequence of past step times
 693   NumberSeq                   _step_times_ms;
 694   // Elapsed time of this task
 695   double                      _elapsed_time_ms;
 696   // Termination time of this task
 697   double                      _termination_time_ms;
 698   // When this task got into the termination protocol
 699   double                      _termination_start_time_ms;
 700 
 701   TruncatedSeq                _marking_step_diffs_ms;
 702 
 703   // Updates the local fields after this task has claimed
 704   // a new region to scan
 705   void setup_for_region(HeapRegion* hr);
 706   // Makes the limit of the region up-to-date
 707   void update_region_limit();
 708 
 709   // Called when either the words scanned or the refs visited limit
 710   // has been reached
 711   void reached_limit();
 712   // Recalculates the words scanned and refs visited limits
 713   void recalculate_limits();
 714   // Decreases the words scanned and refs visited limits when we reach
 715   // an expensive operation
 716   void decrease_limits();
 717   // Checks whether the words scanned or refs visited reached their
 718   // respective limit and calls reached_limit() if they have
 719   void check_limits() {
 720     if (_words_scanned >= _words_scanned_limit ||
 721         _refs_reached >= _refs_reached_limit) {
 722       reached_limit();
 723     }
 724   }
 725   // Supposed to be called regularly during a marking step as
 726   // it checks a bunch of conditions that might cause the marking step
 727   // to abort
 728   // Return true if the marking step should continue. Otherwise, return false to abort
 729   bool regular_clock_call();
 730 
 731   // Set abort flag if regular_clock_call() check fails
 732   inline void abort_marking_if_regular_check_fail();
 733 
 734   // Test whether obj might have already been passed over by the
 735   // mark bitmap scan, and so needs to be pushed onto the mark stack.
 736   bool is_below_finger(oop obj, HeapWord* global_finger) const;
 737 
 738   template<bool scan> void process_grey_task_entry(G1TaskQueueEntry task_entry);
 739 public:
 740   // Apply the closure on the given area of the objArray. Return the number of words
 741   // scanned.
 742   inline size_t scan_objArray(objArrayOop obj, MemRegion mr);
 743   // Resets the task; should be called right at the beginning of a marking phase.
 744   void reset(G1CMBitMap* next_mark_bitmap);
 745   // Clears all the fields that correspond to a claimed region.
 746   void clear_region_fields();
 747 
 748   // The main method of this class which performs a marking step
 749   // trying not to exceed the given duration. However, it might exit
 750   // prematurely, according to some conditions (i.e. SATB buffers are
 751   // available for processing).
 752   void do_marking_step(double target_ms,
 753                        bool do_termination,
 754                        bool is_serial);
 755 
 756   // These two calls start and stop the timer
 757   void record_start_time() {
 758     _elapsed_time_ms = os::elapsedTime() * 1000.0;
 759   }
 760   void record_end_time() {
 761     _elapsed_time_ms = os::elapsedTime() * 1000.0 - _elapsed_time_ms;
 762   }
 763 
 764   // Returns the worker ID associated with this task.
 765   uint worker_id() { return _worker_id; }
 766 
 767   // From TerminatorTerminator. It determines whether this task should
 768   // exit the termination protocol after it's entered it.
 769   virtual bool should_exit_termination();
 770 
 771   // Resets the local region fields after a task has finished scanning a
 772   // region; or when they have become stale as a result of the region
 773   // being evacuated.
 774   void giveup_current_region();
 775 
 776   HeapWord* finger()            { return _finger; }
 777 
 778   bool has_aborted()            { return _has_aborted; }
 779   void set_has_aborted()        { _has_aborted = true; }
 780   void clear_has_aborted()      { _has_aborted = false; }
 781 
 782   void set_cm_oop_closure(G1CMOopClosure* cm_oop_closure);
 783 
 784   // Increment the number of references this task has visited.
 785   void increment_refs_reached() { ++_refs_reached; }
 786 
 787   // Grey the object by marking it.  If not already marked, push it on
 788   // the local queue if below the finger. obj is required to be below its region's NTAMS.
 789   // Returns whether there has been a mark to the bitmap.
 790   inline bool make_reference_grey(oop obj);
 791 
 792   // Grey the object (by calling make_grey_reference) if required,
 793   // e.g. obj is below its containing region's NTAMS.
 794   // Precondition: obj is a valid heap object.
 795   // Returns true if the reference caused a mark to be set in the next bitmap.
 796   template <class T>
 797   inline bool deal_with_reference(T* p);
 798 
 799   // Scans an object and visits its children.
 800   inline void scan_task_entry(G1TaskQueueEntry task_entry);
 801 
 802   // Pushes an object on the local queue.
 803   inline void push(G1TaskQueueEntry task_entry);
 804 
 805   // Move entries to the global stack.
 806   void move_entries_to_global_stack();
 807   // Move entries from the global stack, return true if we were successful to do so.
 808   bool get_entries_from_global_stack();
 809 
 810   // Pops and scans objects from the local queue. If partially is
 811   // true, then it stops when the queue size is of a given limit. If
 812   // partially is false, then it stops when the queue is empty.
 813   void drain_local_queue(bool partially);
 814   // Moves entries from the global stack to the local queue and
 815   // drains the local queue. If partially is true, then it stops when
 816   // both the global stack and the local queue reach a given size. If
 817   // partially if false, it tries to empty them totally.
 818   void drain_global_stack(bool partially);
 819   // Keeps picking SATB buffers and processing them until no SATB
 820   // buffers are available.
 821   void drain_satb_buffers();
 822 
 823   // Moves the local finger to a new location
 824   inline void move_finger_to(HeapWord* new_finger) {
 825     assert(new_finger >= _finger && new_finger < _region_limit, "invariant");
 826     _finger = new_finger;
 827   }
 828 
 829   G1CMTask(uint worker_id,
 830            G1ConcurrentMark *cm,
 831            G1CMTaskQueue* task_queue,
 832            G1RegionMarkStats* mark_stats,
 833            uint max_regions);
 834 
 835   inline void update_liveness(oop const obj, size_t const obj_size);
 836 
 837   // Clear (without flushing) the mark cache entry for the given region.
 838   void clear_mark_stats_cache(uint region_idx);
 839   // Evict the whole statistics cache into the global statistics. Returns the
 840   // number of cache hits and misses so far.
 841   Pair<size_t, size_t> flush_mark_stats_cache();
 842   // Prints statistics associated with this task
 843   void print_stats();
 844 };
 845 
 846 // Class that's used to to print out per-region liveness
 847 // information. It's currently used at the end of marking and also
 848 // after we sort the old regions at the end of the cleanup operation.
 849 class G1PrintRegionLivenessInfoClosure : public HeapRegionClosure {
 850   // Accumulators for these values.
 851   size_t _total_used_bytes;
 852   size_t _total_capacity_bytes;
 853   size_t _total_prev_live_bytes;
 854   size_t _total_next_live_bytes;
 855 
 856   // Accumulator for the remembered set size
 857   size_t _total_remset_bytes;
 858 
 859   // Accumulator for strong code roots memory size
 860   size_t _total_strong_code_roots_bytes;
 861 
 862   static double bytes_to_mb(size_t val) {
 863     return (double) val / (double) M;
 864   }
 865 
 866 public:
 867   // The header and footer are printed in the constructor and
 868   // destructor respectively.
 869   G1PrintRegionLivenessInfoClosure(const char* phase_name);
 870   virtual bool do_heap_region(HeapRegion* r);
 871   ~G1PrintRegionLivenessInfoClosure();
 872 };
 873 
 874 #endif // SHARE_GC_G1_G1CONCURRENTMARK_HPP
--- EOF ---