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.
  22  *
  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 G1ConcurrentMarkThread;
  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* g1h) : _g1h(g1h) { }
 112   bool do_object_b(oop obj);
 113 };
 114 
 115 class G1CMSubjectToDiscoveryClosure : public BoolObjectClosure {
 116   G1CollectedHeap* _g1h;
 117 public:
 118   G1CMSubjectToDiscoveryClosure(G1CollectedHeap* g1h) : _g1h(g1h) { }
 119   bool do_object_b(oop obj);
 120 };
 121 
 122 // Represents the overflow mark stack used by concurrent marking.
 123 //
 124 // Stores oops in a huge buffer in virtual memory that is always fully committed.
 125 // Resizing may only happen during a STW pause when the stack is empty.
 126 //
 127 // Memory is allocated on a "chunk" basis, i.e. a set of oops. For this, the mark
 128 // stack memory is split into evenly sized chunks of oops. Users can only
 129 // add or remove entries on that basis.
 130 // Chunks are filled in increasing address order. Not completely filled chunks
 131 // have a NULL element as a terminating element.
 132 //
 133 // Every chunk has a header containing a single pointer element used for memory
 134 // management. This wastes some space, but is negligible (< .1% with current sizing).
 135 //
 136 // Memory management is done using a mix of tracking a high water-mark indicating
 137 // that all chunks at a lower address are valid chunks, and a singly linked free
 138 // list connecting all empty chunks.
 139 class G1CMMarkStack {
 140 public:
 141   // Number of TaskQueueEntries that can fit in a single chunk.
 142   static const size_t EntriesPerChunk = 1024 - 1 /* One reference for the next pointer */;
 143 private:
 144   struct TaskQueueEntryChunk {
 145     TaskQueueEntryChunk* next;
 146     G1TaskQueueEntry data[EntriesPerChunk];
 147   };
 148 
 149   size_t _max_chunk_capacity;    // Maximum number of TaskQueueEntryChunk elements on the stack.
 150 
 151   TaskQueueEntryChunk* _base;    // Bottom address of allocated memory area.
 152   size_t _chunk_capacity;        // Current maximum number of TaskQueueEntryChunk elements.
 153 
 154   char _pad0[DEFAULT_CACHE_LINE_SIZE];
 155   TaskQueueEntryChunk* volatile _free_list;  // Linked list of free chunks that can be allocated by users.
 156   char _pad1[DEFAULT_CACHE_LINE_SIZE - sizeof(TaskQueueEntryChunk*)];
 157   TaskQueueEntryChunk* volatile _chunk_list; // List of chunks currently containing data.
 158   volatile size_t _chunks_in_chunk_list;
 159   char _pad2[DEFAULT_CACHE_LINE_SIZE - sizeof(TaskQueueEntryChunk*) - sizeof(size_t)];
 160 
 161   volatile size_t _hwm;          // High water mark within the reserved space.
 162   char _pad4[DEFAULT_CACHE_LINE_SIZE - sizeof(size_t)];
 163 
 164   // Allocate a new chunk from the reserved memory, using the high water mark. Returns
 165   // NULL if out of memory.
 166   TaskQueueEntryChunk* allocate_new_chunk();
 167 
 168   // Atomically add the given chunk to the list.
 169   void add_chunk_to_list(TaskQueueEntryChunk* volatile* list, TaskQueueEntryChunk* elem);
 170   // Atomically remove and return a chunk from the given list. Returns NULL if the
 171   // list is empty.
 172   TaskQueueEntryChunk* remove_chunk_from_list(TaskQueueEntryChunk* volatile* list);
 173 
 174   void add_chunk_to_chunk_list(TaskQueueEntryChunk* elem);
 175   void add_chunk_to_free_list(TaskQueueEntryChunk* elem);
 176 
 177   TaskQueueEntryChunk* remove_chunk_from_chunk_list();
 178   TaskQueueEntryChunk* remove_chunk_from_free_list();
 179 
 180   // Resizes the mark stack to the given new capacity. Releases any previous
 181   // memory if successful.
 182   bool resize(size_t new_capacity);
 183 
 184  public:
 185   G1CMMarkStack();
 186   ~G1CMMarkStack();
 187 
 188   // Alignment and minimum capacity of this mark stack in number of oops.
 189   static size_t capacity_alignment();
 190 
 191   // Allocate and initialize the mark stack with the given number of oops.
 192   bool initialize(size_t initial_capacity, size_t max_capacity);
 193 
 194   // Pushes the given buffer containing at most EntriesPerChunk elements on the mark
 195   // stack. If less than EntriesPerChunk elements are to be pushed, the array must
 196   // be terminated with a NULL.
 197   // Returns whether the buffer contents were successfully pushed to the global mark
 198   // stack.
 199   bool par_push_chunk(G1TaskQueueEntry* buffer);
 200 
 201   // Pops a chunk from this mark stack, copying them into the given buffer. This
 202   // chunk may contain up to EntriesPerChunk elements. If there are less, the last
 203   // element in the array is a NULL pointer.
 204   bool par_pop_chunk(G1TaskQueueEntry* buffer);
 205 
 206   // Return whether the chunk list is empty. Racy due to unsynchronized access to
 207   // _chunk_list.
 208   bool is_empty() const { return _chunk_list == NULL; }
 209 
 210   size_t capacity() const  { return _chunk_capacity; }
 211 
 212   // Expand the stack, typically in response to an overflow condition
 213   void expand();
 214 
 215   // Return the approximate number of oops on this mark stack. Racy due to
 216   // unsynchronized access to _chunks_in_chunk_list.
 217   size_t size() const { return _chunks_in_chunk_list * EntriesPerChunk; }
 218 
 219   void set_empty();
 220 
 221   // Apply Fn to every oop on the mark stack. The mark stack must not
 222   // be modified while iterating.
 223   template<typename Fn> void iterate(Fn fn) const PRODUCT_RETURN;
 224 };
 225 
 226 // Root Regions are regions that are not empty at the beginning of a
 227 // marking cycle and which we might collect during an evacuation pause
 228 // while the cycle is active. Given that, during evacuation pauses, we
 229 // do not copy objects that are explicitly marked, what we have to do
 230 // for the root regions is to scan them and mark all objects reachable
 231 // from them. According to the SATB assumptions, we only need to visit
 232 // each object once during marking. So, as long as we finish this scan
 233 // before the next evacuation pause, we can copy the objects from the
 234 // root regions without having to mark them or do anything else to them.
 235 //
 236 // Currently, we only support root region scanning once (at the start
 237 // of the marking cycle) and the root regions are all the survivor
 238 // regions populated during the initial-mark pause.
 239 class G1CMRootRegions {
 240 private:
 241   const G1SurvivorRegions* _survivors;
 242   G1ConcurrentMark*        _cm;
 243 
 244   volatile bool            _scan_in_progress;
 245   volatile bool            _should_abort;
 246   volatile int             _claimed_survivor_index;
 247 
 248   void notify_scan_done();
 249 
 250 public:
 251   G1CMRootRegions();
 252   // We actually do most of the initialization in this method.
 253   void init(const G1SurvivorRegions* survivors, G1ConcurrentMark* cm);
 254 
 255   // Reset the claiming / scanning of the root regions.
 256   void prepare_for_scan();
 257 
 258   // Forces get_next() to return NULL so that the iteration aborts early.
 259   void abort() { _should_abort = true; }
 260 
 261   // Return true if the CM thread are actively scanning root regions,
 262   // false otherwise.
 263   bool scan_in_progress() { return _scan_in_progress; }
 264 
 265   // Claim the next root region to scan atomically, or return NULL if
 266   // all have been claimed.
 267   HeapRegion* claim_next();
 268 
 269   // The number of root regions to scan.
 270   uint num_root_regions() const;
 271 
 272   void cancel_scan();
 273 
 274   // Flag that we're done with root region scanning and notify anyone
 275   // who's waiting on it. If aborted is false, assume that all regions
 276   // have been claimed.
 277   void scan_finished();
 278 
 279   // If CM threads are still scanning root regions, wait until they
 280   // are done. Return true if we had to wait, false otherwise.
 281   bool wait_until_scan_finished();
 282 };
 283 
 284 // This class manages data structures and methods for doing liveness analysis in
 285 // G1's concurrent cycle.
 286 class G1ConcurrentMark : public CHeapObj<mtGC> {
 287   friend class G1ConcurrentMarkThread;
 288   friend class G1CMRefProcTaskProxy;
 289   friend class G1CMRefProcTaskExecutor;
 290   friend class G1CMKeepAliveAndDrainClosure;
 291   friend class G1CMDrainMarkingStackClosure;
 292   friend class G1CMBitMapClosure;
 293   friend class G1CMConcurrentMarkingTask;
 294   friend class G1CMRemarkTask;
 295   friend class G1CMTask;
 296 
 297   G1ConcurrentMarkThread* _cm_thread;     // The thread doing the work
 298   G1CollectedHeap*        _g1h;           // The heap
 299   bool                    _completed_initialization; // Set to true when initialization is complete
 300 
 301   // Concurrent marking support structures
 302   G1CMBitMap              _mark_bitmap_1;
 303   G1CMBitMap              _mark_bitmap_2;
 304   G1CMBitMap*             _prev_mark_bitmap; // Completed mark bitmap
 305   G1CMBitMap*             _next_mark_bitmap; // Under-construction mark bitmap
 306 
 307   // Heap bounds
 308   MemRegion const         _heap;
 309 
 310   // Root region tracking and claiming
 311   G1CMRootRegions         _root_regions;
 312 
 313   // For grey objects
 314   G1CMMarkStack           _global_mark_stack; // Grey objects behind global finger
 315   HeapWord* volatile      _finger;            // The global finger, region aligned,
 316                                               // always pointing to the end of the
 317                                               // last claimed region
 318 
 319   uint                    _worker_id_offset;
 320   uint                    _max_num_tasks;    // Maximum number of marking tasks
 321   uint                    _num_active_tasks; // Number of tasks currently active
 322   G1CMTask**              _tasks;            // Task queue array (max_worker_id length)
 323 
 324   G1CMTaskQueueSet*       _task_queues;      // Task queue set
 325   ParallelTaskTerminator  _terminator;       // For termination
 326 
 327   // Two sync barriers that are used to synchronize tasks when an
 328   // overflow occurs. The algorithm is the following. All tasks enter
 329   // the first one to ensure that they have all stopped manipulating
 330   // the global data structures. After they exit it, they re-initialize
 331   // their data structures and task 0 re-initializes the global data
 332   // structures. Then, they enter the second sync barrier. This
 333   // ensure, that no task starts doing work before all data
 334   // structures (local and global) have been re-initialized. When they
 335   // exit it, they are free to start working again.
 336   WorkGangBarrierSync     _first_overflow_barrier_sync;
 337   WorkGangBarrierSync     _second_overflow_barrier_sync;
 338 
 339   // This is set by any task, when an overflow on the global data
 340   // structures is detected
 341   volatile bool           _has_overflown;
 342   // True: marking is concurrent, false: we're in remark
 343   volatile bool           _concurrent;
 344   // Set at the end of a Full GC so that marking aborts
 345   volatile bool           _has_aborted;
 346 
 347   // Used when remark aborts due to an overflow to indicate that
 348   // another concurrent marking phase should start
 349   volatile bool           _restart_for_overflow;
 350 
 351   ConcurrentGCTimer*      _gc_timer_cm;
 352 
 353   G1OldTracer*            _gc_tracer_cm;
 354 
 355   // Timing statistics. All of them are in ms
 356   NumberSeq _init_times;
 357   NumberSeq _remark_times;
 358   NumberSeq _remark_mark_times;
 359   NumberSeq _remark_weak_ref_times;
 360   NumberSeq _cleanup_times;
 361   double    _total_cleanup_time;
 362 
 363   double*   _accum_task_vtime;   // Accumulated task vtime
 364 
 365   WorkGang* _concurrent_workers;
 366   uint      _num_concurrent_workers; // The number of marking worker threads we're using
 367   uint      _max_concurrent_workers; // Maximum number of marking worker threads
 368 
 369   void verify_during_pause(G1HeapVerifier::G1VerifyType type, VerifyOption vo, const char* caller);
 370 
 371   void finalize_marking();
 372 
 373   void weak_refs_work_parallel_part(BoolObjectClosure* is_alive, bool purged_classes);
 374   void weak_refs_work(bool clear_all_soft_refs);
 375 
 376   void report_object_count(bool mark_completed);
 377 
 378   void swap_mark_bitmaps();
 379 
 380   void reclaim_empty_regions();
 381 
 382   // After reclaiming empty regions, update heap sizes.
 383   void compute_new_sizes();
 384 
 385   // Clear statistics gathered during the concurrent cycle for the given region after
 386   // it has been reclaimed.
 387   void clear_statistics(HeapRegion* r);
 388 
 389   // Resets the global marking data structures, as well as the
 390   // task local ones; should be called during initial mark.
 391   void reset();
 392 
 393   // Resets all the marking data structures. Called when we have to restart
 394   // marking or when marking completes (via set_non_marking_state below).
 395   void reset_marking_for_restart();
 396 
 397   // We do this after we're done with marking so that the marking data
 398   // structures are initialized to a sensible and predictable state.
 399   void reset_at_marking_complete();
 400 
 401   // Called to indicate how many threads are currently active.
 402   void set_concurrency(uint active_tasks);
 403 
 404   // Should be called to indicate which phase we're in (concurrent
 405   // mark or remark) and how many threads are currently active.
 406   void set_concurrency_and_phase(uint active_tasks, bool concurrent);
 407 
 408   // Prints all gathered CM-related statistics
 409   void print_stats();
 410 
 411   HeapWord*               finger()          { return _finger;   }
 412   bool                    concurrent()      { return _concurrent; }
 413   uint                    active_tasks()    { return _num_active_tasks; }
 414   ParallelTaskTerminator* terminator()      { return &_terminator; }
 415 
 416   // Claims the next available region to be scanned by a marking
 417   // task/thread. It might return NULL if the next region is empty or
 418   // we have run out of regions. In the latter case, out_of_regions()
 419   // determines whether we've really run out of regions or the task
 420   // should call claim_region() again. This might seem a bit
 421   // awkward. Originally, the code was written so that claim_region()
 422   // either successfully returned with a non-empty region or there
 423   // were no more regions to be claimed. The problem with this was
 424   // that, in certain circumstances, it iterated over large chunks of
 425   // the heap finding only empty regions and, while it was working, it
 426   // was preventing the calling task to call its regular clock
 427   // method. So, this way, each task will spend very little time in
 428   // claim_region() and is allowed to call the regular clock method
 429   // frequently.
 430   HeapRegion* claim_region(uint worker_id);
 431 
 432   // Determines whether we've run out of regions to scan. Note that
 433   // the finger can point past the heap end in case the heap was expanded
 434   // to satisfy an allocation without doing a GC. This is fine, because all
 435   // objects in those regions will be considered live anyway because of
 436   // SATB guarantees (i.e. their TAMS will be equal to bottom).
 437   bool out_of_regions() { return _finger >= _heap.end(); }
 438 
 439   // Returns the task with the given id
 440   G1CMTask* task(uint id) {
 441     // During initial mark we use the parallel gc threads to do some work, so
 442     // we can only compare against _max_num_tasks.
 443     assert(id < _max_num_tasks, "Task id %u not within bounds up to %u", id, _max_num_tasks);
 444     return _tasks[id];
 445   }
 446 
 447   // Access / manipulation of the overflow flag which is set to
 448   // indicate that the global stack has overflown
 449   bool has_overflown()           { return _has_overflown; }
 450   void set_has_overflown()       { _has_overflown = true; }
 451   void clear_has_overflown()     { _has_overflown = false; }
 452   bool restart_for_overflow()    { return _restart_for_overflow; }
 453 
 454   // Methods to enter the two overflow sync barriers
 455   void enter_first_sync_barrier(uint worker_id);
 456   void enter_second_sync_barrier(uint worker_id);
 457 
 458   // Clear the given bitmap in parallel using the given WorkGang. If may_yield is
 459   // true, periodically insert checks to see if this method should exit prematurely.
 460   void clear_bitmap(G1CMBitMap* bitmap, WorkGang* workers, bool may_yield);
 461 
 462   // Region statistics gathered during marking.
 463   G1RegionMarkStats* _region_mark_stats;
 464   // Top pointer for each region at the start of the rebuild remembered set process
 465   // for regions which remembered sets need to be rebuilt. A NULL for a given region
 466   // means that this region does not be scanned during the rebuilding remembered
 467   // set phase at all.
 468   HeapWord* volatile* _top_at_rebuild_starts;
 469 public:
 470   void add_to_liveness(uint worker_id, oop const obj, size_t size);
 471   // Liveness of the given region as determined by concurrent marking, i.e. the amount of
 472   // live words between bottom and nTAMS.
 473   size_t liveness(uint region) const { return _region_mark_stats[region]._live_words; }
 474 
 475   // Sets the internal top_at_region_start for the given region to current top of the region.
 476   inline void update_top_at_rebuild_start(HeapRegion* r);
 477   // TARS for the given region during remembered set rebuilding.
 478   inline HeapWord* top_at_rebuild_start(uint region) const;
 479 
 480   // Clear statistics gathered during the concurrent cycle for the given region after
 481   // it has been reclaimed.
 482   void clear_statistics_in_region(uint region_idx);
 483   // Notification for eagerly reclaimed regions to clean up.
 484   void humongous_object_eagerly_reclaimed(HeapRegion* r);
 485   // Manipulation of the global mark stack.
 486   // The push and pop operations are used by tasks for transfers
 487   // between task-local queues and the global mark stack.
 488   bool mark_stack_push(G1TaskQueueEntry* arr) {
 489     if (!_global_mark_stack.par_push_chunk(arr)) {
 490       set_has_overflown();
 491       return false;
 492     }
 493     return true;
 494   }
 495   bool mark_stack_pop(G1TaskQueueEntry* arr) {
 496     return _global_mark_stack.par_pop_chunk(arr);
 497   }
 498   size_t mark_stack_size() const                { return _global_mark_stack.size(); }
 499   size_t partial_mark_stack_size_target() const { return _global_mark_stack.capacity() / 3; }
 500   bool mark_stack_empty() const                 { return _global_mark_stack.is_empty(); }
 501 
 502   G1CMRootRegions* root_regions() { return &_root_regions; }
 503 
 504   void concurrent_cycle_start();
 505   // Abandon current marking iteration due to a Full GC.
 506   void concurrent_cycle_abort();
 507   void concurrent_cycle_end();
 508 
 509   void update_accum_task_vtime(int i, double vtime) {
 510     _accum_task_vtime[i] += vtime;
 511   }
 512 
 513   double all_task_accum_vtime() {
 514     double ret = 0.0;
 515     for (uint i = 0; i < _max_num_tasks; ++i)
 516       ret += _accum_task_vtime[i];
 517     return ret;
 518   }
 519 
 520   // Attempts to steal an object from the task queues of other tasks
 521   bool try_stealing(uint worker_id, int* hash_seed, G1TaskQueueEntry& task_entry);
 522 
 523   G1ConcurrentMark(G1CollectedHeap* g1h,
 524                    G1RegionToSpaceMapper* prev_bitmap_storage,
 525                    G1RegionToSpaceMapper* next_bitmap_storage);
 526   ~G1ConcurrentMark();
 527 
 528   G1ConcurrentMarkThread* cm_thread() { return _cm_thread; }
 529 
 530   const G1CMBitMap* const prev_mark_bitmap() const { return _prev_mark_bitmap; }
 531   G1CMBitMap* next_mark_bitmap() const { return _next_mark_bitmap; }
 532 
 533   // Calculates the number of concurrent GC threads to be used in the marking phase.
 534   uint calc_active_marking_workers();
 535 
 536   // Moves all per-task cached data into global state.
 537   void flush_all_task_caches();
 538   // Prepare internal data structures for the next mark cycle. This includes clearing
 539   // the next mark bitmap and some internal data structures. This method is intended
 540   // to be called concurrently to the mutator. It will yield to safepoint requests.
 541   void cleanup_for_next_mark();
 542 
 543   // Clear the previous marking bitmap during safepoint.
 544   void clear_prev_bitmap(WorkGang* workers);
 545 
 546   // Return whether the next mark bitmap has no marks set. To be used for assertions
 547   // only. Will not yield to pause requests.
 548   bool next_mark_bitmap_is_clear();
 549 
 550   // These two methods do the work that needs to be done at the start and end of the
 551   // initial mark pause.
 552   void pre_initial_mark();
 553   void post_initial_mark();
 554 
 555   // Scan all the root regions and mark everything reachable from
 556   // them.
 557   void scan_root_regions();
 558 
 559   // Scan a single root region and mark everything reachable from it.
 560   void scan_root_region(HeapRegion* hr, uint worker_id);
 561 
 562   // Do concurrent phase of marking, to a tentative transitive closure.
 563   void mark_from_roots();
 564 
 565   // Do concurrent preclean work.
 566   void preclean();
 567 
 568   void remark();
 569 
 570   void cleanup();
 571   // Mark in the previous bitmap. Caution: the prev bitmap is usually read-only, so use
 572   // this carefully.
 573   inline void mark_in_prev_bitmap(oop p);
 574 
 575   // Clears marks for all objects in the given range, for the prev or
 576   // next bitmaps.  Caution: the previous bitmap is usually
 577   // read-only, so use this carefully!
 578   void clear_range_in_prev_bitmap(MemRegion mr);
 579 
 580   inline bool is_marked_in_prev_bitmap(oop p) const;
 581 
 582   // Verify that there are no collection set oops on the stacks (taskqueues /
 583   // global mark stack) and fingers (global / per-task).
 584   // If marking is not in progress, it's a no-op.
 585   void verify_no_cset_oops() PRODUCT_RETURN;
 586 
 587   inline bool do_yield_check();
 588 
 589   bool has_aborted()      { return _has_aborted; }
 590 
 591   void print_summary_info();
 592 
 593   void print_worker_threads_on(outputStream* st) const;
 594   void threads_do(ThreadClosure* tc) const;
 595 
 596   void print_on_error(outputStream* st) const;
 597 
 598   // Mark the given object on the next bitmap if it is below nTAMS.
 599   // If the passed obj_size is zero, it is recalculated from the given object if
 600   // needed. This is to be as lazy as possible with accessing the object's size.
 601   inline bool mark_in_next_bitmap(uint worker_id, HeapRegion* const hr, oop const obj, size_t const obj_size = 0);
 602   inline bool mark_in_next_bitmap(uint worker_id, oop const obj, size_t const obj_size = 0);
 603 
 604   inline bool is_marked_in_next_bitmap(oop p) const;
 605 
 606   // Returns true if initialization was successfully completed.
 607   bool completed_initialization() const {
 608     return _completed_initialization;
 609   }
 610 
 611   ConcurrentGCTimer* gc_timer_cm() const { return _gc_timer_cm; }
 612   G1OldTracer* gc_tracer_cm() const { return _gc_tracer_cm; }
 613 
 614 private:
 615   // Rebuilds the remembered sets for chosen regions in parallel and concurrently to the application.
 616   void rebuild_rem_set_concurrently();
 617 };
 618 
 619 // A class representing a marking task.
 620 class G1CMTask : public TerminatorTerminator {
 621 private:
 622   enum PrivateConstants {
 623     // The regular clock call is called once the scanned words reaches
 624     // this limit
 625     words_scanned_period          = 12*1024,
 626     // The regular clock call is called once the number of visited
 627     // references reaches this limit
 628     refs_reached_period           = 1024,
 629     // Initial value for the hash seed, used in the work stealing code
 630     init_hash_seed                = 17
 631   };
 632 
 633   // Number of entries in the per-task stats entry. This seems enough to have a very
 634   // low cache miss rate.
 635   static const uint RegionMarkStatsCacheSize = 1024;
 636 
 637   G1CMObjArrayProcessor       _objArray_processor;
 638 
 639   uint                        _worker_id;
 640   G1CollectedHeap*            _g1h;
 641   G1ConcurrentMark*           _cm;
 642   G1CMBitMap*                 _next_mark_bitmap;
 643   // the task queue of this task
 644   G1CMTaskQueue*              _task_queue;
 645 
 646   G1RegionMarkStatsCache      _mark_stats_cache;
 647   // Number of calls to this task
 648   uint                        _calls;
 649 
 650   // When the virtual timer reaches this time, the marking step should exit
 651   double                      _time_target_ms;
 652   // Start time of the current marking step
 653   double                      _start_time_ms;
 654 
 655   // Oop closure used for iterations over oops
 656   G1CMOopClosure*             _cm_oop_closure;
 657 
 658   // Region this task is scanning, NULL if we're not scanning any
 659   HeapRegion*                 _curr_region;
 660   // Local finger of this task, NULL if we're not scanning a region
 661   HeapWord*                   _finger;
 662   // Limit of the region this task is scanning, NULL if we're not scanning one
 663   HeapWord*                   _region_limit;
 664 
 665   // Number of words this task has scanned
 666   size_t                      _words_scanned;
 667   // When _words_scanned reaches this limit, the regular clock is
 668   // called. Notice that this might be decreased under certain
 669   // circumstances (i.e. when we believe that we did an expensive
 670   // operation).
 671   size_t                      _words_scanned_limit;
 672   // Initial value of _words_scanned_limit (i.e. what it was
 673   // before it was decreased).
 674   size_t                      _real_words_scanned_limit;
 675 
 676   // Number of references this task has visited
 677   size_t                      _refs_reached;
 678   // When _refs_reached reaches this limit, the regular clock is
 679   // called. Notice this this might be decreased under certain
 680   // circumstances (i.e. when we believe that we did an expensive
 681   // operation).
 682   size_t                      _refs_reached_limit;
 683   // Initial value of _refs_reached_limit (i.e. what it was before
 684   // it was decreased).
 685   size_t                      _real_refs_reached_limit;
 686 
 687   // Used by the work stealing
 688   int                         _hash_seed;
 689   // If true, then the task has aborted for some reason
 690   bool                        _has_aborted;
 691   // Set when the task aborts because it has met its time quota
 692   bool                        _has_timed_out;
 693   // True when we're draining SATB buffers; this avoids the task
 694   // aborting due to SATB buffers being available (as we're already
 695   // dealing with them)
 696   bool                        _draining_satb_buffers;
 697 
 698   // Number sequence of past step times
 699   NumberSeq                   _step_times_ms;
 700   // Elapsed time of this task
 701   double                      _elapsed_time_ms;
 702   // Termination time of this task
 703   double                      _termination_time_ms;
 704   // When this task got into the termination protocol
 705   double                      _termination_start_time_ms;
 706 
 707   TruncatedSeq                _marking_step_diffs_ms;
 708 
 709   // Updates the local fields after this task has claimed
 710   // a new region to scan
 711   void setup_for_region(HeapRegion* hr);
 712   // Makes the limit of the region up-to-date
 713   void update_region_limit();
 714 
 715   // Called when either the words scanned or the refs visited limit
 716   // has been reached
 717   void reached_limit();
 718   // Recalculates the words scanned and refs visited limits
 719   void recalculate_limits();
 720   // Decreases the words scanned and refs visited limits when we reach
 721   // an expensive operation
 722   void decrease_limits();
 723   // Checks whether the words scanned or refs visited reached their
 724   // respective limit and calls reached_limit() if they have
 725   void check_limits() {
 726     if (_words_scanned >= _words_scanned_limit ||
 727         _refs_reached >= _refs_reached_limit) {
 728       reached_limit();
 729     }
 730   }
 731   // Supposed to be called regularly during a marking step as
 732   // it checks a bunch of conditions that might cause the marking step
 733   // to abort
 734   void regular_clock_call();
 735 
 736   // Test whether obj might have already been passed over by the
 737   // mark bitmap scan, and so needs to be pushed onto the mark stack.
 738   bool is_below_finger(oop obj, HeapWord* global_finger) const;
 739 
 740   template<bool scan> void process_grey_task_entry(G1TaskQueueEntry task_entry);
 741 public:
 742   // Apply the closure on the given area of the objArray. Return the number of words
 743   // scanned.
 744   inline size_t scan_objArray(objArrayOop obj, MemRegion mr);
 745   // Resets the task; should be called right at the beginning of a marking phase.
 746   void reset(G1CMBitMap* next_mark_bitmap);
 747   // Clears all the fields that correspond to a claimed region.
 748   void clear_region_fields();
 749 
 750   // The main method of this class which performs a marking step
 751   // trying not to exceed the given duration. However, it might exit
 752   // prematurely, according to some conditions (i.e. SATB buffers are
 753   // available for processing).
 754   void do_marking_step(double target_ms,
 755                        bool do_termination,
 756                        bool is_serial);
 757 
 758   // These two calls start and stop the timer
 759   void record_start_time() {
 760     _elapsed_time_ms = os::elapsedTime() * 1000.0;
 761   }
 762   void record_end_time() {
 763     _elapsed_time_ms = os::elapsedTime() * 1000.0 - _elapsed_time_ms;
 764   }
 765 
 766   // Returns the worker ID associated with this task.
 767   uint worker_id() { return _worker_id; }
 768 
 769   // From TerminatorTerminator. It determines whether this task should
 770   // exit the termination protocol after it's entered it.
 771   virtual bool should_exit_termination();
 772 
 773   // Resets the local region fields after a task has finished scanning a
 774   // region; or when they have become stale as a result of the region
 775   // being evacuated.
 776   void giveup_current_region();
 777 
 778   HeapWord* finger()            { return _finger; }
 779 
 780   bool has_aborted()            { return _has_aborted; }
 781   void set_has_aborted()        { _has_aborted = true; }
 782   void clear_has_aborted()      { _has_aborted = false; }
 783 
 784   void set_cm_oop_closure(G1CMOopClosure* cm_oop_closure);
 785 
 786   // Increment the number of references this task has visited.
 787   void increment_refs_reached() { ++_refs_reached; }
 788 
 789   // Grey the object by marking it.  If not already marked, push it on
 790   // the local queue if below the finger. obj is required to be below its region's NTAMS.
 791   // Returns whether there has been a mark to the bitmap.
 792   inline bool make_reference_grey(oop obj);
 793 
 794   // Grey the object (by calling make_grey_reference) if required,
 795   // e.g. obj is below its containing region's NTAMS.
 796   // Precondition: obj is a valid heap object.
 797   // Returns true if the reference caused a mark to be set in the next bitmap.
 798   template <class T>
 799   inline bool deal_with_reference(T* p);
 800 
 801   // Scans an object and visits its children.
 802   inline void scan_task_entry(G1TaskQueueEntry task_entry);
 803 
 804   // Pushes an object on the local queue.
 805   inline void push(G1TaskQueueEntry task_entry);
 806 
 807   // Move entries to the global stack.
 808   void move_entries_to_global_stack();
 809   // Move entries from the global stack, return true if we were successful to do so.
 810   bool get_entries_from_global_stack();
 811 
 812   // Pops and scans objects from the local queue. If partially is
 813   // true, then it stops when the queue size is of a given limit. If
 814   // partially is false, then it stops when the queue is empty.
 815   void drain_local_queue(bool partially);
 816   // Moves entries from the global stack to the local queue and
 817   // drains the local queue. If partially is true, then it stops when
 818   // both the global stack and the local queue reach a given size. If
 819   // partially if false, it tries to empty them totally.
 820   void drain_global_stack(bool partially);
 821   // Keeps picking SATB buffers and processing them until no SATB
 822   // buffers are available.
 823   void drain_satb_buffers();
 824 
 825   // Moves the local finger to a new location
 826   inline void move_finger_to(HeapWord* new_finger) {
 827     assert(new_finger >= _finger && new_finger < _region_limit, "invariant");
 828     _finger = new_finger;
 829   }
 830 
 831   G1CMTask(uint worker_id,
 832            G1ConcurrentMark *cm,
 833            G1CMTaskQueue* task_queue,
 834            G1RegionMarkStats* mark_stats,
 835            uint max_regions);
 836 
 837   inline void update_liveness(oop const obj, size_t const obj_size);
 838 
 839   // Clear (without flushing) the mark cache entry for the given region.
 840   void clear_mark_stats_cache(uint region_idx);
 841   // Evict the whole statistics cache into the global statistics. Returns the
 842   // number of cache hits and misses so far.
 843   Pair<size_t, size_t> flush_mark_stats_cache();
 844   // Prints statistics associated with this task
 845   void print_stats();
 846 };
 847 
 848 // Class that's used to to print out per-region liveness
 849 // information. It's currently used at the end of marking and also
 850 // after we sort the old regions at the end of the cleanup operation.
 851 class G1PrintRegionLivenessInfoClosure : public HeapRegionClosure {
 852   // Accumulators for these values.
 853   size_t _total_used_bytes;
 854   size_t _total_capacity_bytes;
 855   size_t _total_prev_live_bytes;
 856   size_t _total_next_live_bytes;
 857 
 858   // Accumulator for the remembered set size
 859   size_t _total_remset_bytes;
 860 
 861   // Accumulator for strong code roots memory size
 862   size_t _total_strong_code_roots_bytes;
 863 
 864   static double bytes_to_mb(size_t val) {
 865     return (double) val / (double) M;
 866   }
 867 
 868 public:
 869   // The header and footer are printed in the constructor and
 870   // destructor respectively.
 871   G1PrintRegionLivenessInfoClosure(const char* phase_name);
 872   virtual bool do_heap_region(HeapRegion* r);
 873   ~G1PrintRegionLivenessInfoClosure();
 874 };
 875 
 876 #endif // SHARE_VM_GC_G1_G1CONCURRENTMARK_HPP