rev 49504 : imported patch 8151171-renamings
rev 49506 : imported patch 8200234-g1concurrentmark-refactorings
rev 49510 : 8200255: Remove G1CMTask::_concurrent
Reviewed-by: sangheki, sjohanss
rev 49511 : 8200074: Remove G1ConcurrentMark::_concurrent_marking_in_progress
Reviewed-by: sjohanss, sangheki
rev 49513 : [mq]: 8200385-prev-bitmap-marks-left

   1 /*
   2  * Copyright (c) 2001, 2018, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
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  23  */
  24 
  25 #ifndef SHARE_VM_GC_G1_G1CONCURRENTMARK_HPP
  26 #define SHARE_VM_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 "memory/allocation.hpp"
  35 
  36 class ConcurrentGCTimer;
  37 class ConcurrentMarkThread;
  38 class G1CollectedHeap;
  39 class G1CMTask;
  40 class G1ConcurrentMark;
  41 class G1OldTracer;
  42 class G1RegionToSpaceMapper;
  43 class G1SurvivorRegions;
  44 
  45 #ifdef _MSC_VER
  46 #pragma warning(push)
  47 // warning C4522: multiple assignment operators specified
  48 #pragma warning(disable:4522)
  49 #endif
  50 
  51 // This is a container class for either an oop or a continuation address for
  52 // mark stack entries. Both are pushed onto the mark stack.
  53 class G1TaskQueueEntry {
  54 private:
  55   void* _holder;
  56 
  57   static const uintptr_t ArraySliceBit = 1;
  58 
  59   G1TaskQueueEntry(oop obj) : _holder(obj) {
  60     assert(_holder != NULL, "Not allowed to set NULL task queue element");
  61   }
  62   G1TaskQueueEntry(HeapWord* addr) : _holder((void*)((uintptr_t)addr | ArraySliceBit)) { }
  63 public:
  64   G1TaskQueueEntry(const G1TaskQueueEntry& other) { _holder = other._holder; }
  65   G1TaskQueueEntry() : _holder(NULL) { }
  66 
  67   static G1TaskQueueEntry from_slice(HeapWord* what) { return G1TaskQueueEntry(what); }
  68   static G1TaskQueueEntry from_oop(oop obj) { return G1TaskQueueEntry(obj); }
  69 
  70   G1TaskQueueEntry& operator=(const G1TaskQueueEntry& t) {
  71     _holder = t._holder;
  72     return *this;
  73   }
  74 
  75   volatile G1TaskQueueEntry& operator=(const volatile G1TaskQueueEntry& t) volatile {
  76     _holder = t._holder;
  77     return *this;
  78   }
  79 
  80   oop obj() const {
  81     assert(!is_array_slice(), "Trying to read array slice " PTR_FORMAT " as oop", p2i(_holder));
  82     return (oop)_holder;
  83   }
  84 
  85   HeapWord* slice() const {
  86     assert(is_array_slice(), "Trying to read oop " PTR_FORMAT " as array slice", p2i(_holder));
  87     return (HeapWord*)((uintptr_t)_holder & ~ArraySliceBit);
  88   }
  89 
  90   bool is_oop() const { return !is_array_slice(); }
  91   bool is_array_slice() const { return ((uintptr_t)_holder & ArraySliceBit) != 0; }
  92   bool is_null() const { return _holder == NULL; }
  93 };
  94 
  95 #ifdef _MSC_VER
  96 #pragma warning(pop)
  97 #endif
  98 
  99 typedef GenericTaskQueue<G1TaskQueueEntry, mtGC> G1CMTaskQueue;
 100 typedef GenericTaskQueueSet<G1CMTaskQueue, mtGC> G1CMTaskQueueSet;
 101 
 102 // Closure used by CM during concurrent reference discovery
 103 // and reference processing (during remarking) to determine
 104 // if a particular object is alive. It is primarily used
 105 // to determine if referents of discovered reference objects
 106 // are alive. An instance is also embedded into the
 107 // reference processor as the _is_alive_non_header field
 108 class G1CMIsAliveClosure : public BoolObjectClosure {
 109   G1CollectedHeap* _g1h;
 110  public:
 111   G1CMIsAliveClosure(G1CollectedHeap* g1) : _g1h(g1) { }
 112 
 113   bool do_object_b(oop obj);
 114 };
 115 
 116 // Represents the overflow mark stack used by concurrent marking.
 117 //
 118 // Stores oops in a huge buffer in virtual memory that is always fully committed.
 119 // Resizing may only happen during a STW pause when the stack is empty.
 120 //
 121 // Memory is allocated on a "chunk" basis, i.e. a set of oops. For this, the mark
 122 // stack memory is split into evenly sized chunks of oops. Users can only
 123 // add or remove entries on that basis.
 124 // Chunks are filled in increasing address order. Not completely filled chunks
 125 // have a NULL element as a terminating element.
 126 //
 127 // Every chunk has a header containing a single pointer element used for memory
 128 // management. This wastes some space, but is negligible (< .1% with current sizing).
 129 //
 130 // Memory management is done using a mix of tracking a high water-mark indicating
 131 // that all chunks at a lower address are valid chunks, and a singly linked free
 132 // list connecting all empty chunks.
 133 class G1CMMarkStack {
 134 public:
 135   // Number of TaskQueueEntries that can fit in a single chunk.
 136   static const size_t EntriesPerChunk = 1024 - 1 /* One reference for the next pointer */;
 137 private:
 138   struct TaskQueueEntryChunk {
 139     TaskQueueEntryChunk* next;
 140     G1TaskQueueEntry data[EntriesPerChunk];
 141   };
 142 
 143   size_t _max_chunk_capacity;    // Maximum number of TaskQueueEntryChunk elements on the stack.
 144 
 145   TaskQueueEntryChunk* _base;    // Bottom address of allocated memory area.
 146   size_t _chunk_capacity;        // Current maximum number of TaskQueueEntryChunk elements.
 147 
 148   char _pad0[DEFAULT_CACHE_LINE_SIZE];
 149   TaskQueueEntryChunk* volatile _free_list;  // Linked list of free chunks that can be allocated by users.
 150   char _pad1[DEFAULT_CACHE_LINE_SIZE - sizeof(TaskQueueEntryChunk*)];
 151   TaskQueueEntryChunk* volatile _chunk_list; // List of chunks currently containing data.
 152   volatile size_t _chunks_in_chunk_list;
 153   char _pad2[DEFAULT_CACHE_LINE_SIZE - sizeof(TaskQueueEntryChunk*) - sizeof(size_t)];
 154 
 155   volatile size_t _hwm;          // High water mark within the reserved space.
 156   char _pad4[DEFAULT_CACHE_LINE_SIZE - sizeof(size_t)];
 157 
 158   // Allocate a new chunk from the reserved memory, using the high water mark. Returns
 159   // NULL if out of memory.
 160   TaskQueueEntryChunk* allocate_new_chunk();
 161 
 162   // Atomically add the given chunk to the list.
 163   void add_chunk_to_list(TaskQueueEntryChunk* volatile* list, TaskQueueEntryChunk* elem);
 164   // Atomically remove and return a chunk from the given list. Returns NULL if the
 165   // list is empty.
 166   TaskQueueEntryChunk* remove_chunk_from_list(TaskQueueEntryChunk* volatile* list);
 167 
 168   void add_chunk_to_chunk_list(TaskQueueEntryChunk* elem);
 169   void add_chunk_to_free_list(TaskQueueEntryChunk* elem);
 170 
 171   TaskQueueEntryChunk* remove_chunk_from_chunk_list();
 172   TaskQueueEntryChunk* remove_chunk_from_free_list();
 173 
 174   // Resizes the mark stack to the given new capacity. Releases any previous
 175   // memory if successful.
 176   bool resize(size_t new_capacity);
 177 
 178  public:
 179   G1CMMarkStack();
 180   ~G1CMMarkStack();
 181 
 182   // Alignment and minimum capacity of this mark stack in number of oops.
 183   static size_t capacity_alignment();
 184 
 185   // Allocate and initialize the mark stack with the given number of oops.
 186   bool initialize(size_t initial_capacity, size_t max_capacity);
 187 
 188   // Pushes the given buffer containing at most EntriesPerChunk elements on the mark
 189   // stack. If less than EntriesPerChunk elements are to be pushed, the array must
 190   // be terminated with a NULL.
 191   // Returns whether the buffer contents were successfully pushed to the global mark
 192   // stack.
 193   bool par_push_chunk(G1TaskQueueEntry* buffer);
 194 
 195   // Pops a chunk from this mark stack, copying them into the given buffer. This
 196   // chunk may contain up to EntriesPerChunk elements. If there are less, the last
 197   // element in the array is a NULL pointer.
 198   bool par_pop_chunk(G1TaskQueueEntry* buffer);
 199 
 200   // Return whether the chunk list is empty. Racy due to unsynchronized access to
 201   // _chunk_list.
 202   bool is_empty() const { return _chunk_list == NULL; }
 203 
 204   size_t capacity() const  { return _chunk_capacity; }
 205 
 206   // Expand the stack, typically in response to an overflow condition
 207   void expand();
 208 
 209   // Return the approximate number of oops on this mark stack. Racy due to
 210   // unsynchronized access to _chunks_in_chunk_list.
 211   size_t size() const { return _chunks_in_chunk_list * EntriesPerChunk; }
 212 
 213   void set_empty();
 214 
 215   // Apply Fn to every oop on the mark stack. The mark stack must not
 216   // be modified while iterating.
 217   template<typename Fn> void iterate(Fn fn) const PRODUCT_RETURN;
 218 };
 219 
 220 // Root Regions are regions that are not empty at the beginning of a
 221 // marking cycle and which we might collect during an evacuation pause
 222 // while the cycle is active. Given that, during evacuation pauses, we
 223 // do not copy objects that are explicitly marked, what we have to do
 224 // for the root regions is to scan them and mark all objects reachable
 225 // from them. According to the SATB assumptions, we only need to visit
 226 // each object once during marking. So, as long as we finish this scan
 227 // before the next evacuation pause, we can copy the objects from the
 228 // root regions without having to mark them or do anything else to them.
 229 //
 230 // Currently, we only support root region scanning once (at the start
 231 // of the marking cycle) and the root regions are all the survivor
 232 // regions populated during the initial-mark pause.
 233 class G1CMRootRegions {
 234 private:
 235   const G1SurvivorRegions* _survivors;
 236   G1ConcurrentMark*        _cm;
 237 
 238   volatile bool            _scan_in_progress;
 239   volatile bool            _should_abort;
 240   volatile int             _claimed_survivor_index;
 241 
 242   void notify_scan_done();
 243 
 244 public:
 245   G1CMRootRegions();
 246   // We actually do most of the initialization in this method.
 247   void init(const G1SurvivorRegions* survivors, G1ConcurrentMark* cm);
 248 
 249   // Reset the claiming / scanning of the root regions.
 250   void prepare_for_scan();
 251 
 252   // Forces get_next() to return NULL so that the iteration aborts early.
 253   void abort() { _should_abort = true; }
 254 
 255   // Return true if the CM thread are actively scanning root regions,
 256   // false otherwise.
 257   bool scan_in_progress() { return _scan_in_progress; }
 258 
 259   // Claim the next root region to scan atomically, or return NULL if
 260   // all have been claimed.
 261   HeapRegion* claim_next();
 262 
 263   // The number of root regions to scan.
 264   uint num_root_regions() const;
 265 
 266   void cancel_scan();
 267 
 268   // Flag that we're done with root region scanning and notify anyone
 269   // who's waiting on it. If aborted is false, assume that all regions
 270   // have been claimed.
 271   void scan_finished();
 272 
 273   // If CM threads are still scanning root regions, wait until they
 274   // are done. Return true if we had to wait, false otherwise.
 275   bool wait_until_scan_finished();
 276 };
 277 
 278 // This class manages data structures and methods for doing liveness analysis in
 279 // G1's concurrent cycle.
 280 class G1ConcurrentMark : public CHeapObj<mtGC> {
 281   friend class ConcurrentMarkThread;
 282   friend class G1CMRefProcTaskProxy;
 283   friend class G1CMRefProcTaskExecutor;
 284   friend class G1CMKeepAliveAndDrainClosure;
 285   friend class G1CMDrainMarkingStackClosure;
 286   friend class G1CMBitMapClosure;
 287   friend class G1CMConcurrentMarkingTask;
 288   friend class G1CMRemarkTask;
 289   friend class G1CMTask;
 290 
 291   ConcurrentMarkThread*  _cm_thread;     // The thread doing the work
 292   G1CollectedHeap*       _g1h;           // The heap
 293   bool                   _completed_initialization; // Set to true when initialization is complete
 294 
 295   // Concurrent marking support structures
 296   G1CMBitMap             _mark_bitmap_1;
 297   G1CMBitMap             _mark_bitmap_2;
 298   G1CMBitMap*            _prev_mark_bitmap; // Completed mark bitmap
 299   G1CMBitMap*            _next_mark_bitmap; // Under-construction mark bitmap
 300 
 301   // Heap bounds
 302   MemRegion const        _heap;
 303 
 304   // Root region tracking and claiming
 305   G1CMRootRegions        _root_regions;
 306 
 307   // For grey objects
 308   G1CMMarkStack          _global_mark_stack; // Grey objects behind global finger
 309   HeapWord* volatile     _finger;            // The global finger, region aligned,
 310                                              // always pointing to the end of the
 311                                              // last claimed region
 312 
 313   uint                   _worker_id_offset;
 314   uint                   _max_num_tasks;    // Maximum number of marking tasks
 315   uint                   _num_active_tasks; // Number of tasks currently active
 316   G1CMTask**             _tasks;            // Task queue array (max_worker_id length)
 317 
 318   G1CMTaskQueueSet*      _task_queues;      // Task queue set
 319   ParallelTaskTerminator _terminator;       // For termination
 320 
 321   // Two sync barriers that are used to synchronize tasks when an
 322   // overflow occurs. The algorithm is the following. All tasks enter
 323   // the first one to ensure that they have all stopped manipulating
 324   // the global data structures. After they exit it, they re-initialize
 325   // their data structures and task 0 re-initializes the global data
 326   // structures. Then, they enter the second sync barrier. This
 327   // ensure, that no task starts doing work before all data
 328   // structures (local and global) have been re-initialized. When they
 329   // exit it, they are free to start working again.
 330   WorkGangBarrierSync    _first_overflow_barrier_sync;
 331   WorkGangBarrierSync    _second_overflow_barrier_sync;
 332 
 333   // This is set by any task, when an overflow on the global data
 334   // structures is detected
 335   volatile bool          _has_overflown;
 336   // True: marking is concurrent, false: we're in remark
 337   volatile bool          _concurrent;
 338   // Set at the end of a Full GC so that marking aborts
 339   volatile bool          _has_aborted;
 340 
 341   // Used when remark aborts due to an overflow to indicate that
 342   // another concurrent marking phase should start
 343   volatile bool          _restart_for_overflow;
 344 
 345   ConcurrentGCTimer*     _gc_timer_cm;
 346 
 347   G1OldTracer*           _gc_tracer_cm;
 348 
 349   // Timing statistics. All of them are in ms
 350   NumberSeq _init_times;
 351   NumberSeq _remark_times;
 352   NumberSeq _remark_mark_times;
 353   NumberSeq _remark_weak_ref_times;
 354   NumberSeq _cleanup_times;
 355   double    _total_cleanup_time;
 356 
 357   double*   _accum_task_vtime;   // Accumulated task vtime
 358 
 359   WorkGang* _concurrent_workers;
 360   uint      _num_concurrent_workers; // The number of marking worker threads we're using
 361   uint      _max_concurrent_workers; // Maximum number of marking worker threads
 362 
 363   void verify_during_pause(G1HeapVerifier::G1VerifyType type, VerifyOption vo, const char* caller);
 364 
 365   void finalize_marking();
 366 
 367   void weak_refs_work_parallel_part(BoolObjectClosure* is_alive, bool purged_classes);
 368   void weak_refs_work(bool clear_all_soft_refs);
 369 
 370   void report_object_count();
 371 
 372   void swap_mark_bitmaps();
 373 
 374   void reclaim_empty_regions();
 375 
 376   // Clear statistics gathered during the concurrent cycle for the given region after
 377   // it has been reclaimed.
 378   void clear_statistics(HeapRegion* r);
 379 
 380   // Resets the global marking data structures, as well as the
 381   // task local ones; should be called during initial mark.
 382   void reset();
 383 
 384   // Resets all the marking data structures. Called when we have to restart
 385   // marking or when marking completes (via set_non_marking_state below).
 386   void reset_marking_for_restart();
 387 
 388   // We do this after we're done with marking so that the marking data
 389   // structures are initialized to a sensible and predictable state.
 390   void reset_at_marking_complete();
 391 
 392   // Called to indicate how many threads are currently active.
 393   void set_concurrency(uint active_tasks);
 394 
 395   // Should be called to indicate which phase we're in (concurrent
 396   // mark or remark) and how many threads are currently active.
 397   void set_concurrency_and_phase(uint active_tasks, bool concurrent);
 398 
 399   // Prints all gathered CM-related statistics
 400   void print_stats();
 401 
 402   HeapWord*               finger()          { return _finger;   }
 403   bool                    concurrent()      { return _concurrent; }
 404   uint                    active_tasks()    { return _num_active_tasks; }
 405   ParallelTaskTerminator* terminator()      { return &_terminator; }
 406 
 407   // Claims the next available region to be scanned by a marking
 408   // task/thread. It might return NULL if the next region is empty or
 409   // we have run out of regions. In the latter case, out_of_regions()
 410   // determines whether we've really run out of regions or the task
 411   // should call claim_region() again. This might seem a bit
 412   // awkward. Originally, the code was written so that claim_region()
 413   // either successfully returned with a non-empty region or there
 414   // were no more regions to be claimed. The problem with this was
 415   // that, in certain circumstances, it iterated over large chunks of
 416   // the heap finding only empty regions and, while it was working, it
 417   // was preventing the calling task to call its regular clock
 418   // method. So, this way, each task will spend very little time in
 419   // claim_region() and is allowed to call the regular clock method
 420   // frequently.
 421   HeapRegion* claim_region(uint worker_id);
 422 
 423   // Determines whether we've run out of regions to scan. Note that
 424   // the finger can point past the heap end in case the heap was expanded
 425   // to satisfy an allocation without doing a GC. This is fine, because all
 426   // objects in those regions will be considered live anyway because of
 427   // SATB guarantees (i.e. their TAMS will be equal to bottom).
 428   bool out_of_regions() { return _finger >= _heap.end(); }
 429 
 430   // Returns the task with the given id
 431   G1CMTask* task(uint id) {
 432     // During initial mark we use the parallel gc threads to do some work, so
 433     // we can only compare against _max_num_tasks.
 434     assert(id < _max_num_tasks, "Task id %u not within bounds up to %u", id, _max_num_tasks);
 435     return _tasks[id];
 436   }
 437 
 438   // Access / manipulation of the overflow flag which is set to
 439   // indicate that the global stack has overflown
 440   bool has_overflown()           { return _has_overflown; }
 441   void set_has_overflown()       { _has_overflown = true; }
 442   void clear_has_overflown()     { _has_overflown = false; }
 443   bool restart_for_overflow()    { return _restart_for_overflow; }
 444 
 445   // Methods to enter the two overflow sync barriers
 446   void enter_first_sync_barrier(uint worker_id);
 447   void enter_second_sync_barrier(uint worker_id);
 448 
 449   // Clear the given bitmap in parallel using the given WorkGang. If may_yield is
 450   // true, periodically insert checks to see if this method should exit prematurely.
 451   void clear_bitmap(G1CMBitMap* bitmap, WorkGang* workers, bool may_yield);
 452 
 453   // Region statistics gathered during marking.
 454   G1RegionMarkStats* _region_mark_stats;
 455   // Top pointer for each region at the start of the rebuild remembered set process
 456   // for regions which remembered sets need to be rebuilt. A NULL for a given region
 457   // means that this region does not be scanned during the rebuilding remembered
 458   // set phase at all.
 459   HeapWord* volatile* _top_at_rebuild_starts;
 460 public:
 461   void add_to_liveness(uint worker_id, oop const obj, size_t size);
 462   // Liveness of the given region as determined by concurrent marking, i.e. the amount of
 463   // live words between bottom and nTAMS.
 464   size_t liveness(uint region)  { return _region_mark_stats[region]._live_words; }
 465 
 466   // Sets the internal top_at_region_start for the given region to current top of the region.
 467   inline void update_top_at_rebuild_start(HeapRegion* r);
 468   // TARS for the given region during remembered set rebuilding.
 469   inline HeapWord* top_at_rebuild_start(uint region) const;
 470 
 471   // Clear statistics gathered during the concurrent cycle for the given region after
 472   // it has been reclaimed.
 473   void clear_statistics_in_region(uint region_idx);
 474   // Notification for eagerly reclaimed regions to clean up.
 475   void humongous_object_eagerly_reclaimed(HeapRegion* r);
 476   // Manipulation of the global mark stack.
 477   // The push and pop operations are used by tasks for transfers
 478   // between task-local queues and the global mark stack.
 479   bool mark_stack_push(G1TaskQueueEntry* arr) {
 480     if (!_global_mark_stack.par_push_chunk(arr)) {
 481       set_has_overflown();
 482       return false;
 483     }
 484     return true;
 485   }
 486   bool mark_stack_pop(G1TaskQueueEntry* arr) {
 487     return _global_mark_stack.par_pop_chunk(arr);
 488   }
 489   size_t mark_stack_size() const                { return _global_mark_stack.size(); }
 490   size_t partial_mark_stack_size_target() const { return _global_mark_stack.capacity() / 3; }
 491   bool mark_stack_empty() const                 { return _global_mark_stack.is_empty(); }
 492 
 493   G1CMRootRegions* root_regions() { return &_root_regions; }
 494 
 495   void concurrent_cycle_start();
 496   // Abandon current marking iteration due to a Full GC.
 497   void concurrent_cycle_abort();
 498   void concurrent_cycle_end();
 499 
 500   void update_accum_task_vtime(int i, double vtime) {
 501     _accum_task_vtime[i] += vtime;
 502   }
 503 
 504   double all_task_accum_vtime() {
 505     double ret = 0.0;
 506     for (uint i = 0; i < _max_num_tasks; ++i)
 507       ret += _accum_task_vtime[i];
 508     return ret;
 509   }
 510 
 511   // Attempts to steal an object from the task queues of other tasks
 512   bool try_stealing(uint worker_id, int* hash_seed, G1TaskQueueEntry& task_entry);
 513 
 514   G1ConcurrentMark(G1CollectedHeap* g1h,
 515                    G1RegionToSpaceMapper* prev_bitmap_storage,
 516                    G1RegionToSpaceMapper* next_bitmap_storage);
 517   ~G1ConcurrentMark();
 518 
 519   ConcurrentMarkThread* cm_thread() { return _cm_thread; }
 520 
 521   const G1CMBitMap* const prev_mark_bitmap() const { return _prev_mark_bitmap; }
 522   G1CMBitMap* next_mark_bitmap() const { return _next_mark_bitmap; }
 523 
 524   // Calculates the number of concurrent GC threads to be used in the marking phase.
 525   uint calc_active_marking_workers();
 526 
 527   // Moves all per-task cached data into global state.
 528   void flush_all_task_caches();
 529   // Prepare internal data structures for the next mark cycle. This includes clearing
 530   // the next mark bitmap and some internal data structures. This method is intended
 531   // to be called concurrently to the mutator. It will yield to safepoint requests.
 532   void cleanup_for_next_mark();
 533 
 534   // Clear the previous marking bitmap during safepoint.
 535   void clear_prev_bitmap(WorkGang* workers);
 536 
 537   // Return whether the next mark bitmap has no marks set. To be used for assertions
 538   // only. Will not yield to pause requests.
 539   bool next_mark_bitmap_is_clear();
 540 
 541   // These two methods do the work that needs to be done at the start and end of the
 542   // initial mark pause.
 543   void pre_initial_mark();
 544   void post_initial_mark();
 545 
 546   // Scan all the root regions and mark everything reachable from
 547   // them.
 548   void scan_root_regions();
 549 
 550   // Scan a single root region and mark everything reachable from it.
 551   void scan_root_region(HeapRegion* hr, uint worker_id);
 552 
 553   // Do concurrent phase of marking, to a tentative transitive closure.
 554   void mark_from_roots();
 555 
 556   void remark();
 557 
 558   void cleanup();
 559   // Mark in the previous bitmap. Caution: the prev bitmap is usually read-only, so use
 560   // this carefully.
 561   inline void mark_in_prev_bitmap(oop p);
 562 
 563   // Clears marks for all objects in the given range, for the prev or
 564   // next bitmaps.  Caution: the previous bitmap is usually
 565   // read-only, so use this carefully!
 566   void clear_range_in_prev_bitmap(MemRegion mr);
 567 
 568   inline bool is_marked_in_prev_bitmap(oop p) const;
 569 
 570   // Verify that there are no collection set oops on the stacks (taskqueues /
 571   // global mark stack) and fingers (global / per-task).
 572   // If marking is not in progress, it's a no-op.
 573   void verify_no_cset_oops() PRODUCT_RETURN;
 574 
 575   inline bool do_yield_check();
 576 
 577   bool has_aborted()      { return _has_aborted; }
 578 
 579   void print_summary_info();
 580 
 581   void print_worker_threads_on(outputStream* st) const;
 582   void threads_do(ThreadClosure* tc) const;
 583 
 584   void print_on_error(outputStream* st) const;
 585 
 586   // Mark the given object on the next bitmap if it is below nTAMS.
 587   // If the passed obj_size is zero, it is recalculated from the given object if
 588   // needed. This is to be as lazy as possible with accessing the object's size.
 589   inline bool mark_in_next_bitmap(uint worker_id, HeapRegion* const hr, oop const obj, size_t const obj_size = 0);
 590   inline bool mark_in_next_bitmap(uint worker_id, oop const obj, size_t const obj_size = 0);
 591 
 592   inline bool is_marked_in_next_bitmap(oop p) const;
 593 
 594   // Returns true if initialization was successfully completed.
 595   bool completed_initialization() const {
 596     return _completed_initialization;
 597   }
 598 
 599   ConcurrentGCTimer* gc_timer_cm() const { return _gc_timer_cm; }
 600   G1OldTracer* gc_tracer_cm() const { return _gc_tracer_cm; }
 601 
 602 private:
 603   // Rebuilds the remembered sets for chosen regions in parallel and concurrently to the application.
 604   void rebuild_rem_set_concurrently();
 605 };
 606 
 607 // A class representing a marking task.
 608 class G1CMTask : public TerminatorTerminator {
 609 private:
 610   enum PrivateConstants {
 611     // The regular clock call is called once the scanned words reaches
 612     // this limit
 613     words_scanned_period          = 12*1024,
 614     // The regular clock call is called once the number of visited
 615     // references reaches this limit
 616     refs_reached_period           = 1024,
 617     // Initial value for the hash seed, used in the work stealing code
 618     init_hash_seed                = 17
 619   };
 620 
 621   // Number of entries in the per-task stats entry. This seems enough to have a very
 622   // low cache miss rate.
 623   static const uint RegionMarkStatsCacheSize = 1024;
 624 
 625   G1CMObjArrayProcessor       _objArray_processor;
 626 
 627   uint                        _worker_id;
 628   G1CollectedHeap*            _g1h;
 629   G1ConcurrentMark*           _cm;
 630   G1CMBitMap*                 _next_mark_bitmap;
 631   // the task queue of this task
 632   G1CMTaskQueue*              _task_queue;
 633 
 634   G1RegionMarkStatsCache      _mark_stats_cache;
 635   // Number of calls to this task
 636   uint                        _calls;
 637 
 638   // When the virtual timer reaches this time, the marking step should exit
 639   double                      _time_target_ms;
 640   // Start time of the current marking step
 641   double                      _start_time_ms;
 642 
 643   // Oop closure used for iterations over oops
 644   G1CMOopClosure*             _cm_oop_closure;
 645 
 646   // Region this task is scanning, NULL if we're not scanning any
 647   HeapRegion*                 _curr_region;
 648   // Local finger of this task, NULL if we're not scanning a region
 649   HeapWord*                   _finger;
 650   // Limit of the region this task is scanning, NULL if we're not scanning one
 651   HeapWord*                   _region_limit;
 652 
 653   // Number of words this task has scanned
 654   size_t                      _words_scanned;
 655   // When _words_scanned reaches this limit, the regular clock is
 656   // called. Notice that this might be decreased under certain
 657   // circumstances (i.e. when we believe that we did an expensive
 658   // operation).
 659   size_t                      _words_scanned_limit;
 660   // Initial value of _words_scanned_limit (i.e. what it was
 661   // before it was decreased).
 662   size_t                      _real_words_scanned_limit;
 663 
 664   // Number of references this task has visited
 665   size_t                      _refs_reached;
 666   // When _refs_reached reaches this limit, the regular clock is
 667   // called. Notice this this might be decreased under certain
 668   // circumstances (i.e. when we believe that we did an expensive
 669   // operation).
 670   size_t                      _refs_reached_limit;
 671   // Initial value of _refs_reached_limit (i.e. what it was before
 672   // it was decreased).
 673   size_t                      _real_refs_reached_limit;
 674 
 675   // Used by the work stealing
 676   int                         _hash_seed;
 677   // If true, then the task has aborted for some reason
 678   bool                        _has_aborted;
 679   // Set when the task aborts because it has met its time quota
 680   bool                        _has_timed_out;
 681   // True when we're draining SATB buffers; this avoids the task
 682   // aborting due to SATB buffers being available (as we're already
 683   // dealing with them)
 684   bool                        _draining_satb_buffers;
 685 
 686   // Number sequence of past step times
 687   NumberSeq                   _step_times_ms;
 688   // Elapsed time of this task
 689   double                      _elapsed_time_ms;
 690   // Termination time of this task
 691   double                      _termination_time_ms;
 692   // When this task got into the termination protocol
 693   double                      _termination_start_time_ms;
 694 
 695   TruncatedSeq                _marking_step_diffs_ms;
 696 
 697   // Updates the local fields after this task has claimed
 698   // a new region to scan
 699   void setup_for_region(HeapRegion* hr);
 700   // Makes the limit of the region up-to-date
 701   void update_region_limit();
 702 
 703   // Called when either the words scanned or the refs visited limit
 704   // has been reached
 705   void reached_limit();
 706   // Recalculates the words scanned and refs visited limits
 707   void recalculate_limits();
 708   // Decreases the words scanned and refs visited limits when we reach
 709   // an expensive operation
 710   void decrease_limits();
 711   // Checks whether the words scanned or refs visited reached their
 712   // respective limit and calls reached_limit() if they have
 713   void check_limits() {
 714     if (_words_scanned >= _words_scanned_limit ||
 715         _refs_reached >= _refs_reached_limit) {
 716       reached_limit();
 717     }
 718   }
 719   // Supposed to be called regularly during a marking step as
 720   // it checks a bunch of conditions that might cause the marking step
 721   // to abort
 722   void regular_clock_call();
 723 
 724   // Test whether obj might have already been passed over by the
 725   // mark bitmap scan, and so needs to be pushed onto the mark stack.
 726   bool is_below_finger(oop obj, HeapWord* global_finger) const;
 727 
 728   template<bool scan> void process_grey_task_entry(G1TaskQueueEntry task_entry);
 729 public:
 730   // Apply the closure on the given area of the objArray. Return the number of words
 731   // scanned.
 732   inline size_t scan_objArray(objArrayOop obj, MemRegion mr);
 733   // Resets the task; should be called right at the beginning of a marking phase.
 734   void reset(G1CMBitMap* next_mark_bitmap);
 735   // Clears all the fields that correspond to a claimed region.
 736   void clear_region_fields();
 737 
 738   // The main method of this class which performs a marking step
 739   // trying not to exceed the given duration. However, it might exit
 740   // prematurely, according to some conditions (i.e. SATB buffers are
 741   // available for processing).
 742   void do_marking_step(double target_ms,
 743                        bool do_termination,
 744                        bool is_serial);
 745 
 746   // These two calls start and stop the timer
 747   void record_start_time() {
 748     _elapsed_time_ms = os::elapsedTime() * 1000.0;
 749   }
 750   void record_end_time() {
 751     _elapsed_time_ms = os::elapsedTime() * 1000.0 - _elapsed_time_ms;
 752   }
 753 
 754   // Returns the worker ID associated with this task.
 755   uint worker_id() { return _worker_id; }
 756 
 757   // From TerminatorTerminator. It determines whether this task should
 758   // exit the termination protocol after it's entered it.
 759   virtual bool should_exit_termination();
 760 
 761   // Resets the local region fields after a task has finished scanning a
 762   // region; or when they have become stale as a result of the region
 763   // being evacuated.
 764   void giveup_current_region();
 765 
 766   HeapWord* finger()            { return _finger; }
 767 
 768   bool has_aborted()            { return _has_aborted; }
 769   void set_has_aborted()        { _has_aborted = true; }
 770   void clear_has_aborted()      { _has_aborted = false; }
 771 
 772   void set_cm_oop_closure(G1CMOopClosure* cm_oop_closure);
 773 
 774   // Increment the number of references this task has visited.
 775   void increment_refs_reached() { ++_refs_reached; }
 776 
 777   // Grey the object by marking it.  If not already marked, push it on
 778   // the local queue if below the finger.
 779   // obj is below its region's NTAMS.
 780   inline void make_reference_grey(oop obj);
 781 
 782   // Grey the object (by calling make_grey_reference) if required,
 783   // e.g. obj is below its containing region's NTAMS.
 784   // Precondition: obj is a valid heap object.
 785   template <class T>
 786   inline void deal_with_reference(T* p);
 787 
 788   // Scans an object and visits its children.
 789   inline void scan_task_entry(G1TaskQueueEntry task_entry);
 790 
 791   // Pushes an object on the local queue.
 792   inline void push(G1TaskQueueEntry task_entry);
 793 
 794   // Move entries to the global stack.
 795   void move_entries_to_global_stack();
 796   // Move entries from the global stack, return true if we were successful to do so.
 797   bool get_entries_from_global_stack();
 798 
 799   // Pops and scans objects from the local queue. If partially is
 800   // true, then it stops when the queue size is of a given limit. If
 801   // partially is false, then it stops when the queue is empty.
 802   void drain_local_queue(bool partially);
 803   // Moves entries from the global stack to the local queue and
 804   // drains the local queue. If partially is true, then it stops when
 805   // both the global stack and the local queue reach a given size. If
 806   // partially if false, it tries to empty them totally.
 807   void drain_global_stack(bool partially);
 808   // Keeps picking SATB buffers and processing them until no SATB
 809   // buffers are available.
 810   void drain_satb_buffers();
 811 
 812   // Moves the local finger to a new location
 813   inline void move_finger_to(HeapWord* new_finger) {
 814     assert(new_finger >= _finger && new_finger < _region_limit, "invariant");
 815     _finger = new_finger;
 816   }
 817 
 818   G1CMTask(uint worker_id,
 819            G1ConcurrentMark *cm,
 820            G1CMTaskQueue* task_queue,
 821            G1RegionMarkStats* mark_stats,
 822            uint max_regions);
 823 
 824   inline void update_liveness(oop const obj, size_t const obj_size);
 825 
 826   // Clear (without flushing) the mark cache entry for the given region.
 827   void clear_mark_stats_cache(uint region_idx);
 828   // Evict the whole statistics cache into the global statistics. Returns the
 829   // number of cache hits and misses so far.
 830   Pair<size_t, size_t> flush_mark_stats_cache();
 831   // Prints statistics associated with this task
 832   void print_stats();
 833 };
 834 
 835 // Class that's used to to print out per-region liveness
 836 // information. It's currently used at the end of marking and also
 837 // after we sort the old regions at the end of the cleanup operation.
 838 class G1PrintRegionLivenessInfoClosure : public HeapRegionClosure {
 839 private:
 840   // Accumulators for these values.
 841   size_t _total_used_bytes;
 842   size_t _total_capacity_bytes;
 843   size_t _total_prev_live_bytes;
 844   size_t _total_next_live_bytes;
 845 
 846   // Accumulator for the remembered set size
 847   size_t _total_remset_bytes;
 848 
 849   // Accumulator for strong code roots memory size
 850   size_t _total_strong_code_roots_bytes;
 851 
 852   static double bytes_to_mb(size_t val) {
 853     return (double) val / (double) M;
 854   }
 855 
 856 public:
 857   // The header and footer are printed in the constructor and
 858   // destructor respectively.
 859   G1PrintRegionLivenessInfoClosure(const char* phase_name);
 860   virtual bool do_heap_region(HeapRegion* r);
 861   ~G1PrintRegionLivenessInfoClosure();
 862 };
 863 
 864 #endif // SHARE_VM_GC_G1_G1CONCURRENTMARK_HPP
--- EOF ---