1 /*
   2  * Copyright (c) 2001, 2019, 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 #include "precompiled.hpp"
  26 #include "classfile/classLoaderDataGraph.hpp"
  27 #include "code/codeCache.hpp"
  28 #include "gc/g1/g1BarrierSet.hpp"
  29 #include "gc/g1/g1CollectedHeap.inline.hpp"
  30 #include "gc/g1/g1CollectorState.hpp"
  31 #include "gc/g1/g1ConcurrentMark.inline.hpp"
  32 #include "gc/g1/g1ConcurrentMarkThread.inline.hpp"
  33 #include "gc/g1/g1DirtyCardQueue.hpp"
  34 #include "gc/g1/g1HeapVerifier.hpp"
  35 #include "gc/g1/g1OopClosures.inline.hpp"
  36 #include "gc/g1/g1Policy.hpp"
  37 #include "gc/g1/g1RegionMarkStatsCache.inline.hpp"
  38 #include "gc/g1/g1StringDedup.hpp"
  39 #include "gc/g1/g1ThreadLocalData.hpp"
  40 #include "gc/g1/heapRegion.inline.hpp"
  41 #include "gc/g1/heapRegionRemSet.hpp"
  42 #include "gc/g1/heapRegionSet.inline.hpp"
  43 #include "gc/shared/gcId.hpp"
  44 #include "gc/shared/gcTimer.hpp"
  45 #include "gc/shared/gcTrace.hpp"
  46 #include "gc/shared/gcTraceTime.inline.hpp"
  47 #include "gc/shared/gcVMOperations.hpp"
  48 #include "gc/shared/genOopClosures.inline.hpp"
  49 #include "gc/shared/referencePolicy.hpp"
  50 #include "gc/shared/strongRootsScope.hpp"
  51 #include "gc/shared/suspendibleThreadSet.hpp"
  52 #include "gc/shared/taskqueue.inline.hpp"
  53 #include "gc/shared/weakProcessor.inline.hpp"
  54 #include "gc/shared/workerPolicy.hpp"
  55 #include "include/jvm.h"
  56 #include "logging/log.hpp"
  57 #include "memory/allocation.hpp"
  58 #include "memory/resourceArea.hpp"
  59 #include "oops/access.inline.hpp"
  60 #include "oops/oop.inline.hpp"
  61 #include "runtime/atomic.hpp"
  62 #include "runtime/handles.inline.hpp"
  63 #include "runtime/java.hpp"
  64 #include "runtime/prefetch.inline.hpp"
  65 #include "services/memTracker.hpp"
  66 #include "utilities/align.hpp"
  67 #include "utilities/growableArray.hpp"
  68 
  69 bool G1CMBitMapClosure::do_addr(HeapWord* const addr) {
  70   assert(addr < _cm->finger(), "invariant");
  71   assert(addr >= _task->finger(), "invariant");
  72 
  73   // We move that task's local finger along.
  74   _task->move_finger_to(addr);
  75 
  76   _task->scan_task_entry(G1TaskQueueEntry::from_oop(oop(addr)));
  77   // we only partially drain the local queue and global stack
  78   _task->drain_local_queue(true);
  79   _task->drain_global_stack(true);
  80 
  81   // if the has_aborted flag has been raised, we need to bail out of
  82   // the iteration
  83   return !_task->has_aborted();
  84 }
  85 
  86 G1CMMarkStack::G1CMMarkStack() :
  87   _max_chunk_capacity(0),
  88   _base(NULL),
  89   _chunk_capacity(0) {
  90   set_empty();
  91 }
  92 
  93 bool G1CMMarkStack::resize(size_t new_capacity) {
  94   assert(is_empty(), "Only resize when stack is empty.");
  95   assert(new_capacity <= _max_chunk_capacity,
  96          "Trying to resize stack to " SIZE_FORMAT " chunks when the maximum is " SIZE_FORMAT, new_capacity, _max_chunk_capacity);
  97 
  98   TaskQueueEntryChunk* new_base = MmapArrayAllocator<TaskQueueEntryChunk>::allocate_or_null(new_capacity, mtGC);
  99 
 100   if (new_base == NULL) {
 101     log_warning(gc)("Failed to reserve memory for new overflow mark stack with " SIZE_FORMAT " chunks and size " SIZE_FORMAT "B.", new_capacity, new_capacity * sizeof(TaskQueueEntryChunk));
 102     return false;
 103   }
 104   // Release old mapping.
 105   if (_base != NULL) {
 106     MmapArrayAllocator<TaskQueueEntryChunk>::free(_base, _chunk_capacity);
 107   }
 108 
 109   _base = new_base;
 110   _chunk_capacity = new_capacity;
 111   set_empty();
 112 
 113   return true;
 114 }
 115 
 116 size_t G1CMMarkStack::capacity_alignment() {
 117   return (size_t)lcm(os::vm_allocation_granularity(), sizeof(TaskQueueEntryChunk)) / sizeof(G1TaskQueueEntry);
 118 }
 119 
 120 bool G1CMMarkStack::initialize(size_t initial_capacity, size_t max_capacity) {
 121   guarantee(_max_chunk_capacity == 0, "G1CMMarkStack already initialized.");
 122 
 123   size_t const TaskEntryChunkSizeInVoidStar = sizeof(TaskQueueEntryChunk) / sizeof(G1TaskQueueEntry);
 124 
 125   _max_chunk_capacity = align_up(max_capacity, capacity_alignment()) / TaskEntryChunkSizeInVoidStar;
 126   size_t initial_chunk_capacity = align_up(initial_capacity, capacity_alignment()) / TaskEntryChunkSizeInVoidStar;
 127 
 128   guarantee(initial_chunk_capacity <= _max_chunk_capacity,
 129             "Maximum chunk capacity " SIZE_FORMAT " smaller than initial capacity " SIZE_FORMAT,
 130             _max_chunk_capacity,
 131             initial_chunk_capacity);
 132 
 133   log_debug(gc)("Initialize mark stack with " SIZE_FORMAT " chunks, maximum " SIZE_FORMAT,
 134                 initial_chunk_capacity, _max_chunk_capacity);
 135 
 136   return resize(initial_chunk_capacity);
 137 }
 138 
 139 void G1CMMarkStack::expand() {
 140   if (_chunk_capacity == _max_chunk_capacity) {
 141     log_debug(gc)("Can not expand overflow mark stack further, already at maximum capacity of " SIZE_FORMAT " chunks.", _chunk_capacity);
 142     return;
 143   }
 144   size_t old_capacity = _chunk_capacity;
 145   // Double capacity if possible
 146   size_t new_capacity = MIN2(old_capacity * 2, _max_chunk_capacity);
 147 
 148   if (resize(new_capacity)) {
 149     log_debug(gc)("Expanded mark stack capacity from " SIZE_FORMAT " to " SIZE_FORMAT " chunks",
 150                   old_capacity, new_capacity);
 151   } else {
 152     log_warning(gc)("Failed to expand mark stack capacity from " SIZE_FORMAT " to " SIZE_FORMAT " chunks",
 153                     old_capacity, new_capacity);
 154   }
 155 }
 156 
 157 G1CMMarkStack::~G1CMMarkStack() {
 158   if (_base != NULL) {
 159     MmapArrayAllocator<TaskQueueEntryChunk>::free(_base, _chunk_capacity);
 160   }
 161 }
 162 
 163 void G1CMMarkStack::add_chunk_to_list(TaskQueueEntryChunk* volatile* list, TaskQueueEntryChunk* elem) {
 164   elem->next = *list;
 165   *list = elem;
 166 }
 167 
 168 void G1CMMarkStack::add_chunk_to_chunk_list(TaskQueueEntryChunk* elem) {
 169   MutexLockerEx x(MarkStackChunkList_lock, Mutex::_no_safepoint_check_flag);
 170   add_chunk_to_list(&_chunk_list, elem);
 171   _chunks_in_chunk_list++;
 172 }
 173 
 174 void G1CMMarkStack::add_chunk_to_free_list(TaskQueueEntryChunk* elem) {
 175   MutexLockerEx x(MarkStackFreeList_lock, Mutex::_no_safepoint_check_flag);
 176   add_chunk_to_list(&_free_list, elem);
 177 }
 178 
 179 G1CMMarkStack::TaskQueueEntryChunk* G1CMMarkStack::remove_chunk_from_list(TaskQueueEntryChunk* volatile* list) {
 180   TaskQueueEntryChunk* result = *list;
 181   if (result != NULL) {
 182     *list = (*list)->next;
 183   }
 184   return result;
 185 }
 186 
 187 G1CMMarkStack::TaskQueueEntryChunk* G1CMMarkStack::remove_chunk_from_chunk_list() {
 188   MutexLockerEx x(MarkStackChunkList_lock, Mutex::_no_safepoint_check_flag);
 189   TaskQueueEntryChunk* result = remove_chunk_from_list(&_chunk_list);
 190   if (result != NULL) {
 191     _chunks_in_chunk_list--;
 192   }
 193   return result;
 194 }
 195 
 196 G1CMMarkStack::TaskQueueEntryChunk* G1CMMarkStack::remove_chunk_from_free_list() {
 197   MutexLockerEx x(MarkStackFreeList_lock, Mutex::_no_safepoint_check_flag);
 198   return remove_chunk_from_list(&_free_list);
 199 }
 200 
 201 G1CMMarkStack::TaskQueueEntryChunk* G1CMMarkStack::allocate_new_chunk() {
 202   // This dirty read of _hwm is okay because we only ever increase the _hwm in parallel code.
 203   // Further this limits _hwm to a value of _chunk_capacity + #threads, avoiding
 204   // wraparound of _hwm.
 205   if (_hwm >= _chunk_capacity) {
 206     return NULL;
 207   }
 208 
 209   size_t cur_idx = Atomic::add(1u, &_hwm) - 1;
 210   if (cur_idx >= _chunk_capacity) {
 211     return NULL;
 212   }
 213 
 214   TaskQueueEntryChunk* result = ::new (&_base[cur_idx]) TaskQueueEntryChunk;
 215   result->next = NULL;
 216   return result;
 217 }
 218 
 219 bool G1CMMarkStack::par_push_chunk(G1TaskQueueEntry* ptr_arr) {
 220   // Get a new chunk.
 221   TaskQueueEntryChunk* new_chunk = remove_chunk_from_free_list();
 222 
 223   if (new_chunk == NULL) {
 224     // Did not get a chunk from the free list. Allocate from backing memory.
 225     new_chunk = allocate_new_chunk();
 226 
 227     if (new_chunk == NULL) {
 228       return false;
 229     }
 230   }
 231 
 232   Copy::conjoint_memory_atomic(ptr_arr, new_chunk->data, EntriesPerChunk * sizeof(G1TaskQueueEntry));
 233 
 234   add_chunk_to_chunk_list(new_chunk);
 235 
 236   return true;
 237 }
 238 
 239 bool G1CMMarkStack::par_pop_chunk(G1TaskQueueEntry* ptr_arr) {
 240   TaskQueueEntryChunk* cur = remove_chunk_from_chunk_list();
 241 
 242   if (cur == NULL) {
 243     return false;
 244   }
 245 
 246   Copy::conjoint_memory_atomic(cur->data, ptr_arr, EntriesPerChunk * sizeof(G1TaskQueueEntry));
 247 
 248   add_chunk_to_free_list(cur);
 249   return true;
 250 }
 251 
 252 void G1CMMarkStack::set_empty() {
 253   _chunks_in_chunk_list = 0;
 254   _hwm = 0;
 255   _chunk_list = NULL;
 256   _free_list = NULL;
 257 }
 258 
 259 G1CMRootRegions::G1CMRootRegions(uint const max_regions) :
 260   _root_regions(NEW_C_HEAP_ARRAY(HeapRegion*, max_regions, mtGC)),
 261   _max_regions(max_regions),
 262   _num_root_regions(0),
 263   _claimed_root_regions(0),
 264   _scan_in_progress(false),
 265   _should_abort(false) { }
 266 
 267 G1CMRootRegions::~G1CMRootRegions() {
 268   FREE_C_HEAP_ARRAY(HeapRegion*, _max_regions);
 269 }
 270 
 271 void G1CMRootRegions::reset() {
 272   _num_root_regions = 0;
 273 }
 274 
 275 void G1CMRootRegions::add(HeapRegion* hr) {
 276   assert_at_safepoint();
 277   size_t idx = Atomic::add((size_t)1, &_num_root_regions) - 1;
 278   assert(idx < _max_regions, "Trying to add more root regions than there is space " SIZE_FORMAT, _max_regions);
 279   _root_regions[idx] = hr;
 280 }
 281 
 282 void G1CMRootRegions::prepare_for_scan() {
 283   assert(!scan_in_progress(), "pre-condition");
 284 
 285   _scan_in_progress = _num_root_regions > 0;
 286 
 287   _claimed_root_regions = 0;
 288   _should_abort = false;
 289 }
 290 
 291 HeapRegion* G1CMRootRegions::claim_next() {
 292   if (_should_abort) {
 293     // If someone has set the should_abort flag, we return NULL to
 294     // force the caller to bail out of their loop.
 295     return NULL;
 296   }
 297 
 298   if (_claimed_root_regions >= _num_root_regions) {
 299     return NULL;
 300   }
 301 
 302   size_t claimed_index = Atomic::add((size_t)1, &_claimed_root_regions) - 1;
 303   if (claimed_index < _num_root_regions) {
 304     return _root_regions[claimed_index];
 305   }
 306   return NULL;
 307 }
 308 
 309 uint G1CMRootRegions::num_root_regions() const {
 310   return (uint)_num_root_regions;
 311 }
 312 
 313 void G1CMRootRegions::notify_scan_done() {
 314   MutexLockerEx x(RootRegionScan_lock, Mutex::_no_safepoint_check_flag);
 315   _scan_in_progress = false;
 316   RootRegionScan_lock->notify_all();
 317 }
 318 
 319 void G1CMRootRegions::cancel_scan() {
 320   notify_scan_done();
 321 }
 322 
 323 void G1CMRootRegions::scan_finished() {
 324   assert(scan_in_progress(), "pre-condition");
 325 
 326   if (!_should_abort) {
 327     assert(_claimed_root_regions >= num_root_regions(),
 328            "we should have claimed all root regions, claimed " SIZE_FORMAT ", length = %u",
 329            _claimed_root_regions, num_root_regions());
 330   }
 331 
 332   notify_scan_done();
 333 }
 334 
 335 bool G1CMRootRegions::wait_until_scan_finished() {
 336   if (!scan_in_progress()) {
 337     return false;
 338   }
 339 
 340   {
 341     MutexLockerEx x(RootRegionScan_lock, Mutex::_no_safepoint_check_flag);
 342     while (scan_in_progress()) {
 343       RootRegionScan_lock->wait(Mutex::_no_safepoint_check_flag);
 344     }
 345   }
 346   return true;
 347 }
 348 
 349 // Returns the maximum number of workers to be used in a concurrent
 350 // phase based on the number of GC workers being used in a STW
 351 // phase.
 352 static uint scale_concurrent_worker_threads(uint num_gc_workers) {
 353   return MAX2((num_gc_workers + 2) / 4, 1U);
 354 }
 355 
 356 G1ConcurrentMark::G1ConcurrentMark(G1CollectedHeap* g1h,
 357                                    G1RegionToSpaceMapper* prev_bitmap_storage,
 358                                    G1RegionToSpaceMapper* next_bitmap_storage) :
 359   // _cm_thread set inside the constructor
 360   _g1h(g1h),
 361   _completed_initialization(false),
 362 
 363   _mark_bitmap_1(),
 364   _mark_bitmap_2(),
 365   _prev_mark_bitmap(&_mark_bitmap_1),
 366   _next_mark_bitmap(&_mark_bitmap_2),
 367 
 368   _heap(_g1h->reserved_region()),
 369 
 370   _root_regions(_g1h->max_regions()),
 371 
 372   _global_mark_stack(),
 373 
 374   // _finger set in set_non_marking_state
 375 
 376   _worker_id_offset(G1DirtyCardQueueSet::num_par_ids() + G1ConcRefinementThreads),
 377   _max_num_tasks(ParallelGCThreads),
 378   // _num_active_tasks set in set_non_marking_state()
 379   // _tasks set inside the constructor
 380 
 381   _task_queues(new G1CMTaskQueueSet((int) _max_num_tasks)),
 382   _terminator((int) _max_num_tasks, _task_queues),
 383 
 384   _first_overflow_barrier_sync(),
 385   _second_overflow_barrier_sync(),
 386 
 387   _has_overflown(false),
 388   _concurrent(false),
 389   _has_aborted(false),
 390   _restart_for_overflow(false),
 391   _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
 392   _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) G1OldTracer()),
 393 
 394   // _verbose_level set below
 395 
 396   _init_times(),
 397   _remark_times(),
 398   _remark_mark_times(),
 399   _remark_weak_ref_times(),
 400   _cleanup_times(),
 401   _total_cleanup_time(0.0),
 402 
 403   _accum_task_vtime(NULL),
 404 
 405   _concurrent_workers(NULL),
 406   _num_concurrent_workers(0),
 407   _max_concurrent_workers(0),
 408 
 409   _region_mark_stats(NEW_C_HEAP_ARRAY(G1RegionMarkStats, _g1h->max_regions(), mtGC)),
 410   _top_at_rebuild_starts(NEW_C_HEAP_ARRAY(HeapWord*, _g1h->max_regions(), mtGC))
 411 {
 412   _mark_bitmap_1.initialize(g1h->reserved_region(), prev_bitmap_storage);
 413   _mark_bitmap_2.initialize(g1h->reserved_region(), next_bitmap_storage);
 414 
 415   // Create & start ConcurrentMark thread.
 416   _cm_thread = new G1ConcurrentMarkThread(this);
 417   if (_cm_thread->osthread() == NULL) {
 418     vm_shutdown_during_initialization("Could not create ConcurrentMarkThread");
 419   }
 420 
 421   assert(CGC_lock != NULL, "CGC_lock must be initialized");
 422 
 423   if (FLAG_IS_DEFAULT(ConcGCThreads) || ConcGCThreads == 0) {
 424     // Calculate the number of concurrent worker threads by scaling
 425     // the number of parallel GC threads.
 426     uint marking_thread_num = scale_concurrent_worker_threads(ParallelGCThreads);
 427     FLAG_SET_ERGO(uint, ConcGCThreads, marking_thread_num);
 428   }
 429 
 430   assert(ConcGCThreads > 0, "ConcGCThreads have been set.");
 431   if (ConcGCThreads > ParallelGCThreads) {
 432     log_warning(gc)("More ConcGCThreads (%u) than ParallelGCThreads (%u).",
 433                     ConcGCThreads, ParallelGCThreads);
 434     return;
 435   }
 436 
 437   log_debug(gc)("ConcGCThreads: %u offset %u", ConcGCThreads, _worker_id_offset);
 438   log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads);
 439 
 440   _num_concurrent_workers = ConcGCThreads;
 441   _max_concurrent_workers = _num_concurrent_workers;
 442 
 443   _concurrent_workers = new WorkGang("G1 Conc", _max_concurrent_workers, false, true);
 444   _concurrent_workers->initialize_workers();
 445 
 446   if (FLAG_IS_DEFAULT(MarkStackSize)) {
 447     size_t mark_stack_size =
 448       MIN2(MarkStackSizeMax,
 449           MAX2(MarkStackSize, (size_t) (_max_concurrent_workers * TASKQUEUE_SIZE)));
 450     // Verify that the calculated value for MarkStackSize is in range.
 451     // It would be nice to use the private utility routine from Arguments.
 452     if (!(mark_stack_size >= 1 && mark_stack_size <= MarkStackSizeMax)) {
 453       log_warning(gc)("Invalid value calculated for MarkStackSize (" SIZE_FORMAT "): "
 454                       "must be between 1 and " SIZE_FORMAT,
 455                       mark_stack_size, MarkStackSizeMax);
 456       return;
 457     }
 458     FLAG_SET_ERGO(size_t, MarkStackSize, mark_stack_size);
 459   } else {
 460     // Verify MarkStackSize is in range.
 461     if (FLAG_IS_CMDLINE(MarkStackSize)) {
 462       if (FLAG_IS_DEFAULT(MarkStackSizeMax)) {
 463         if (!(MarkStackSize >= 1 && MarkStackSize <= MarkStackSizeMax)) {
 464           log_warning(gc)("Invalid value specified for MarkStackSize (" SIZE_FORMAT "): "
 465                           "must be between 1 and " SIZE_FORMAT,
 466                           MarkStackSize, MarkStackSizeMax);
 467           return;
 468         }
 469       } else if (FLAG_IS_CMDLINE(MarkStackSizeMax)) {
 470         if (!(MarkStackSize >= 1 && MarkStackSize <= MarkStackSizeMax)) {
 471           log_warning(gc)("Invalid value specified for MarkStackSize (" SIZE_FORMAT ")"
 472                           " or for MarkStackSizeMax (" SIZE_FORMAT ")",
 473                           MarkStackSize, MarkStackSizeMax);
 474           return;
 475         }
 476       }
 477     }
 478   }
 479 
 480   if (!_global_mark_stack.initialize(MarkStackSize, MarkStackSizeMax)) {
 481     vm_exit_during_initialization("Failed to allocate initial concurrent mark overflow mark stack.");
 482   }
 483 
 484   _tasks = NEW_C_HEAP_ARRAY(G1CMTask*, _max_num_tasks, mtGC);
 485   _accum_task_vtime = NEW_C_HEAP_ARRAY(double, _max_num_tasks, mtGC);
 486 
 487   // so that the assertion in MarkingTaskQueue::task_queue doesn't fail
 488   _num_active_tasks = _max_num_tasks;
 489 
 490   for (uint i = 0; i < _max_num_tasks; ++i) {
 491     G1CMTaskQueue* task_queue = new G1CMTaskQueue();
 492     task_queue->initialize();
 493     _task_queues->register_queue(i, task_queue);
 494 
 495     _tasks[i] = new G1CMTask(i, this, task_queue, _region_mark_stats, _g1h->max_regions());
 496 
 497     _accum_task_vtime[i] = 0.0;
 498   }
 499 
 500   reset_at_marking_complete();
 501   _completed_initialization = true;
 502 }
 503 
 504 void G1ConcurrentMark::reset() {
 505   _has_aborted = false;
 506 
 507   reset_marking_for_restart();
 508 
 509   // Reset all tasks, since different phases will use different number of active
 510   // threads. So, it's easiest to have all of them ready.
 511   for (uint i = 0; i < _max_num_tasks; ++i) {
 512     _tasks[i]->reset(_next_mark_bitmap);
 513   }
 514 
 515   uint max_regions = _g1h->max_regions();
 516   for (uint i = 0; i < max_regions; i++) {
 517     _top_at_rebuild_starts[i] = NULL;
 518     _region_mark_stats[i].clear();
 519   }
 520 }
 521 
 522 void G1ConcurrentMark::clear_statistics_in_region(uint region_idx) {
 523   for (uint j = 0; j < _max_num_tasks; ++j) {
 524     _tasks[j]->clear_mark_stats_cache(region_idx);
 525   }
 526   _top_at_rebuild_starts[region_idx] = NULL;
 527   _region_mark_stats[region_idx].clear();
 528 }
 529 
 530 void G1ConcurrentMark::clear_statistics(HeapRegion* r) {
 531   uint const region_idx = r->hrm_index();
 532   if (r->is_humongous()) {
 533     assert(r->is_starts_humongous(), "Got humongous continues region here");
 534     uint const size_in_regions = (uint)_g1h->humongous_obj_size_in_regions(oop(r->humongous_start_region()->bottom())->size());
 535     for (uint j = region_idx; j < (region_idx + size_in_regions); j++) {
 536       clear_statistics_in_region(j);
 537     }
 538   } else {
 539     clear_statistics_in_region(region_idx);
 540   }
 541 }
 542 
 543 static void clear_mark_if_set(G1CMBitMap* bitmap, HeapWord* addr) {
 544   if (bitmap->is_marked(addr)) {
 545     bitmap->clear(addr);
 546   }
 547 }
 548 
 549 void G1ConcurrentMark::humongous_object_eagerly_reclaimed(HeapRegion* r) {
 550   assert_at_safepoint_on_vm_thread();
 551 
 552   // Need to clear all mark bits of the humongous object.
 553   clear_mark_if_set(_prev_mark_bitmap, r->bottom());
 554   clear_mark_if_set(_next_mark_bitmap, r->bottom());
 555 
 556   if (!_g1h->collector_state()->mark_or_rebuild_in_progress()) {
 557     return;
 558   }
 559 
 560   // Clear any statistics about the region gathered so far.
 561   clear_statistics(r);
 562 }
 563 
 564 void G1ConcurrentMark::reset_marking_for_restart() {
 565   _global_mark_stack.set_empty();
 566 
 567   // Expand the marking stack, if we have to and if we can.
 568   if (has_overflown()) {
 569     _global_mark_stack.expand();
 570 
 571     uint max_regions = _g1h->max_regions();
 572     for (uint i = 0; i < max_regions; i++) {
 573       _region_mark_stats[i].clear_during_overflow();
 574     }
 575   }
 576 
 577   clear_has_overflown();
 578   _finger = _heap.start();
 579 
 580   for (uint i = 0; i < _max_num_tasks; ++i) {
 581     G1CMTaskQueue* queue = _task_queues->queue(i);
 582     queue->set_empty();
 583   }
 584 }
 585 
 586 void G1ConcurrentMark::set_concurrency(uint active_tasks) {
 587   assert(active_tasks <= _max_num_tasks, "we should not have more");
 588 
 589   _num_active_tasks = active_tasks;
 590   // Need to update the three data structures below according to the
 591   // number of active threads for this phase.
 592   _terminator.terminator()->reset_for_reuse((int) active_tasks);
 593   _first_overflow_barrier_sync.set_n_workers((int) active_tasks);
 594   _second_overflow_barrier_sync.set_n_workers((int) active_tasks);
 595 }
 596 
 597 void G1ConcurrentMark::set_concurrency_and_phase(uint active_tasks, bool concurrent) {
 598   set_concurrency(active_tasks);
 599 
 600   _concurrent = concurrent;
 601 
 602   if (!concurrent) {
 603     // At this point we should be in a STW phase, and completed marking.
 604     assert_at_safepoint_on_vm_thread();
 605     assert(out_of_regions(),
 606            "only way to get here: _finger: " PTR_FORMAT ", _heap_end: " PTR_FORMAT,
 607            p2i(_finger), p2i(_heap.end()));
 608   }
 609 }
 610 
 611 void G1ConcurrentMark::reset_at_marking_complete() {
 612   // We set the global marking state to some default values when we're
 613   // not doing marking.
 614   reset_marking_for_restart();
 615   _num_active_tasks = 0;
 616 }
 617 
 618 G1ConcurrentMark::~G1ConcurrentMark() {
 619   FREE_C_HEAP_ARRAY(HeapWord*, _top_at_rebuild_starts);
 620   FREE_C_HEAP_ARRAY(G1RegionMarkStats, _region_mark_stats);
 621   // The G1ConcurrentMark instance is never freed.
 622   ShouldNotReachHere();
 623 }
 624 
 625 class G1ClearBitMapTask : public AbstractGangTask {
 626 public:
 627   static size_t chunk_size() { return M; }
 628 
 629 private:
 630   // Heap region closure used for clearing the given mark bitmap.
 631   class G1ClearBitmapHRClosure : public HeapRegionClosure {
 632   private:
 633     G1CMBitMap* _bitmap;
 634     G1ConcurrentMark* _cm;
 635   public:
 636     G1ClearBitmapHRClosure(G1CMBitMap* bitmap, G1ConcurrentMark* cm) : HeapRegionClosure(), _bitmap(bitmap), _cm(cm) {
 637     }
 638 
 639     virtual bool do_heap_region(HeapRegion* r) {
 640       size_t const chunk_size_in_words = G1ClearBitMapTask::chunk_size() / HeapWordSize;
 641 
 642       HeapWord* cur = r->bottom();
 643       HeapWord* const end = r->end();
 644 
 645       while (cur < end) {
 646         MemRegion mr(cur, MIN2(cur + chunk_size_in_words, end));
 647         _bitmap->clear_range(mr);
 648 
 649         cur += chunk_size_in_words;
 650 
 651         // Abort iteration if after yielding the marking has been aborted.
 652         if (_cm != NULL && _cm->do_yield_check() && _cm->has_aborted()) {
 653           return true;
 654         }
 655         // Repeat the asserts from before the start of the closure. We will do them
 656         // as asserts here to minimize their overhead on the product. However, we
 657         // will have them as guarantees at the beginning / end of the bitmap
 658         // clearing to get some checking in the product.
 659         assert(_cm == NULL || _cm->cm_thread()->during_cycle(), "invariant");
 660         assert(_cm == NULL || !G1CollectedHeap::heap()->collector_state()->mark_or_rebuild_in_progress(), "invariant");
 661       }
 662       assert(cur == end, "Must have completed iteration over the bitmap for region %u.", r->hrm_index());
 663 
 664       return false;
 665     }
 666   };
 667 
 668   G1ClearBitmapHRClosure _cl;
 669   HeapRegionClaimer _hr_claimer;
 670   bool _suspendible; // If the task is suspendible, workers must join the STS.
 671 
 672 public:
 673   G1ClearBitMapTask(G1CMBitMap* bitmap, G1ConcurrentMark* cm, uint n_workers, bool suspendible) :
 674     AbstractGangTask("G1 Clear Bitmap"),
 675     _cl(bitmap, suspendible ? cm : NULL),
 676     _hr_claimer(n_workers),
 677     _suspendible(suspendible)
 678   { }
 679 
 680   void work(uint worker_id) {
 681     SuspendibleThreadSetJoiner sts_join(_suspendible);
 682     G1CollectedHeap::heap()->heap_region_par_iterate_from_worker_offset(&_cl, &_hr_claimer, worker_id);
 683   }
 684 
 685   bool is_complete() {
 686     return _cl.is_complete();
 687   }
 688 };
 689 
 690 void G1ConcurrentMark::clear_bitmap(G1CMBitMap* bitmap, WorkGang* workers, bool may_yield) {
 691   assert(may_yield || SafepointSynchronize::is_at_safepoint(), "Non-yielding bitmap clear only allowed at safepoint.");
 692 
 693   size_t const num_bytes_to_clear = (HeapRegion::GrainBytes * _g1h->num_regions()) / G1CMBitMap::heap_map_factor();
 694   size_t const num_chunks = align_up(num_bytes_to_clear, G1ClearBitMapTask::chunk_size()) / G1ClearBitMapTask::chunk_size();
 695 
 696   uint const num_workers = (uint)MIN2(num_chunks, (size_t)workers->active_workers());
 697 
 698   G1ClearBitMapTask cl(bitmap, this, num_workers, may_yield);
 699 
 700   log_debug(gc, ergo)("Running %s with %u workers for " SIZE_FORMAT " work units.", cl.name(), num_workers, num_chunks);
 701   workers->run_task(&cl, num_workers);
 702   guarantee(!may_yield || cl.is_complete(), "Must have completed iteration when not yielding.");
 703 }
 704 
 705 void G1ConcurrentMark::cleanup_for_next_mark() {
 706   // Make sure that the concurrent mark thread looks to still be in
 707   // the current cycle.
 708   guarantee(cm_thread()->during_cycle(), "invariant");
 709 
 710   // We are finishing up the current cycle by clearing the next
 711   // marking bitmap and getting it ready for the next cycle. During
 712   // this time no other cycle can start. So, let's make sure that this
 713   // is the case.
 714   guarantee(!_g1h->collector_state()->mark_or_rebuild_in_progress(), "invariant");
 715 
 716   clear_bitmap(_next_mark_bitmap, _concurrent_workers, true);
 717 
 718   // Repeat the asserts from above.
 719   guarantee(cm_thread()->during_cycle(), "invariant");
 720   guarantee(!_g1h->collector_state()->mark_or_rebuild_in_progress(), "invariant");
 721 }
 722 
 723 void G1ConcurrentMark::clear_prev_bitmap(WorkGang* workers) {
 724   assert_at_safepoint_on_vm_thread();
 725   clear_bitmap(_prev_mark_bitmap, workers, false);
 726 }
 727 
 728 class NoteStartOfMarkHRClosure : public HeapRegionClosure {
 729 public:
 730   bool do_heap_region(HeapRegion* r) {
 731     r->note_start_of_marking();
 732     return false;
 733   }
 734 };
 735 
 736 void G1ConcurrentMark::pre_initial_mark() {
 737   assert_at_safepoint_on_vm_thread();
 738 
 739   // Reset marking state.
 740   reset();
 741 
 742   // For each region note start of marking.
 743   NoteStartOfMarkHRClosure startcl;
 744   _g1h->heap_region_iterate(&startcl);
 745 
 746   _root_regions.reset();
 747 }
 748 
 749 
 750 void G1ConcurrentMark::post_initial_mark() {
 751   // Start Concurrent Marking weak-reference discovery.
 752   ReferenceProcessor* rp = _g1h->ref_processor_cm();
 753   // enable ("weak") refs discovery
 754   rp->enable_discovery();
 755   rp->setup_policy(false); // snapshot the soft ref policy to be used in this cycle
 756 
 757   SATBMarkQueueSet& satb_mq_set = G1BarrierSet::satb_mark_queue_set();
 758   // This is the start of  the marking cycle, we're expected all
 759   // threads to have SATB queues with active set to false.
 760   satb_mq_set.set_active_all_threads(true, /* new active value */
 761                                      false /* expected_active */);
 762 
 763   _root_regions.prepare_for_scan();
 764 
 765   // update_g1_committed() will be called at the end of an evac pause
 766   // when marking is on. So, it's also called at the end of the
 767   // initial-mark pause to update the heap end, if the heap expands
 768   // during it. No need to call it here.
 769 }
 770 
 771 /*
 772  * Notice that in the next two methods, we actually leave the STS
 773  * during the barrier sync and join it immediately afterwards. If we
 774  * do not do this, the following deadlock can occur: one thread could
 775  * be in the barrier sync code, waiting for the other thread to also
 776  * sync up, whereas another one could be trying to yield, while also
 777  * waiting for the other threads to sync up too.
 778  *
 779  * Note, however, that this code is also used during remark and in
 780  * this case we should not attempt to leave / enter the STS, otherwise
 781  * we'll either hit an assert (debug / fastdebug) or deadlock
 782  * (product). So we should only leave / enter the STS if we are
 783  * operating concurrently.
 784  *
 785  * Because the thread that does the sync barrier has left the STS, it
 786  * is possible to be suspended for a Full GC or an evacuation pause
 787  * could occur. This is actually safe, since the entering the sync
 788  * barrier is one of the last things do_marking_step() does, and it
 789  * doesn't manipulate any data structures afterwards.
 790  */
 791 
 792 void G1ConcurrentMark::enter_first_sync_barrier(uint worker_id) {
 793   bool barrier_aborted;
 794   {
 795     SuspendibleThreadSetLeaver sts_leave(concurrent());
 796     barrier_aborted = !_first_overflow_barrier_sync.enter();
 797   }
 798 
 799   // at this point everyone should have synced up and not be doing any
 800   // more work
 801 
 802   if (barrier_aborted) {
 803     // If the barrier aborted we ignore the overflow condition and
 804     // just abort the whole marking phase as quickly as possible.
 805     return;
 806   }
 807 }
 808 
 809 void G1ConcurrentMark::enter_second_sync_barrier(uint worker_id) {
 810   SuspendibleThreadSetLeaver sts_leave(concurrent());
 811   _second_overflow_barrier_sync.enter();
 812 
 813   // at this point everything should be re-initialized and ready to go
 814 }
 815 
 816 class G1CMConcurrentMarkingTask : public AbstractGangTask {
 817   G1ConcurrentMark*     _cm;
 818 
 819 public:
 820   void work(uint worker_id) {
 821     assert(Thread::current()->is_ConcurrentGC_thread(), "Not a concurrent GC thread");
 822     ResourceMark rm;
 823 
 824     double start_vtime = os::elapsedVTime();
 825 
 826     {
 827       SuspendibleThreadSetJoiner sts_join;
 828 
 829       assert(worker_id < _cm->active_tasks(), "invariant");
 830 
 831       G1CMTask* task = _cm->task(worker_id);
 832       task->record_start_time();
 833       if (!_cm->has_aborted()) {
 834         do {
 835           task->do_marking_step(G1ConcMarkStepDurationMillis,
 836                                 true  /* do_termination */,
 837                                 false /* is_serial*/);
 838 
 839           _cm->do_yield_check();
 840         } while (!_cm->has_aborted() && task->has_aborted());
 841       }
 842       task->record_end_time();
 843       guarantee(!task->has_aborted() || _cm->has_aborted(), "invariant");
 844     }
 845 
 846     double end_vtime = os::elapsedVTime();
 847     _cm->update_accum_task_vtime(worker_id, end_vtime - start_vtime);
 848   }
 849 
 850   G1CMConcurrentMarkingTask(G1ConcurrentMark* cm) :
 851       AbstractGangTask("Concurrent Mark"), _cm(cm) { }
 852 
 853   ~G1CMConcurrentMarkingTask() { }
 854 };
 855 
 856 uint G1ConcurrentMark::calc_active_marking_workers() {
 857   uint result = 0;
 858   if (!UseDynamicNumberOfGCThreads ||
 859       (!FLAG_IS_DEFAULT(ConcGCThreads) &&
 860        !ForceDynamicNumberOfGCThreads)) {
 861     result = _max_concurrent_workers;
 862   } else {
 863     result =
 864       WorkerPolicy::calc_default_active_workers(_max_concurrent_workers,
 865                                                 1, /* Minimum workers */
 866                                                 _num_concurrent_workers,
 867                                                 Threads::number_of_non_daemon_threads());
 868     // Don't scale the result down by scale_concurrent_workers() because
 869     // that scaling has already gone into "_max_concurrent_workers".
 870   }
 871   assert(result > 0 && result <= _max_concurrent_workers,
 872          "Calculated number of marking workers must be larger than zero and at most the maximum %u, but is %u",
 873          _max_concurrent_workers, result);
 874   return result;
 875 }
 876 
 877 void G1ConcurrentMark::scan_root_region(HeapRegion* hr, uint worker_id) {
 878   assert(hr->is_old() || (hr->is_survivor() && hr->next_top_at_mark_start() == hr->bottom()),
 879          "Root regions must be old or survivor but region %u is %s", hr->hrm_index(), hr->get_type_str());
 880   G1RootRegionScanClosure cl(_g1h, this, worker_id);
 881 
 882   const uintx interval = PrefetchScanIntervalInBytes;
 883   HeapWord* curr = hr->next_top_at_mark_start();
 884   const HeapWord* end = hr->top();
 885   while (curr < end) {
 886     Prefetch::read(curr, interval);
 887     oop obj = oop(curr);
 888     int size = obj->oop_iterate_size(&cl);
 889     assert(size == obj->size(), "sanity");
 890     curr += size;
 891   }
 892 }
 893 
 894 class G1CMRootRegionScanTask : public AbstractGangTask {
 895   G1ConcurrentMark* _cm;
 896 public:
 897   G1CMRootRegionScanTask(G1ConcurrentMark* cm) :
 898     AbstractGangTask("G1 Root Region Scan"), _cm(cm) { }
 899 
 900   void work(uint worker_id) {
 901     assert(Thread::current()->is_ConcurrentGC_thread(),
 902            "this should only be done by a conc GC thread");
 903 
 904     G1CMRootRegions* root_regions = _cm->root_regions();
 905     HeapRegion* hr = root_regions->claim_next();
 906     while (hr != NULL) {
 907       _cm->scan_root_region(hr, worker_id);
 908       hr = root_regions->claim_next();
 909     }
 910   }
 911 };
 912 
 913 void G1ConcurrentMark::scan_root_regions() {
 914   // scan_in_progress() will have been set to true only if there was
 915   // at least one root region to scan. So, if it's false, we
 916   // should not attempt to do any further work.
 917   if (root_regions()->scan_in_progress()) {
 918     assert(!has_aborted(), "Aborting before root region scanning is finished not supported.");
 919 
 920     _num_concurrent_workers = MIN2(calc_active_marking_workers(),
 921                                    // We distribute work on a per-region basis, so starting
 922                                    // more threads than that is useless.
 923                                    root_regions()->num_root_regions());
 924     assert(_num_concurrent_workers <= _max_concurrent_workers,
 925            "Maximum number of marking threads exceeded");
 926 
 927     G1CMRootRegionScanTask task(this);
 928     log_debug(gc, ergo)("Running %s using %u workers for %u work units.",
 929                         task.name(), _num_concurrent_workers, root_regions()->num_root_regions());
 930     _concurrent_workers->run_task(&task, _num_concurrent_workers);
 931 
 932     // It's possible that has_aborted() is true here without actually
 933     // aborting the survivor scan earlier. This is OK as it's
 934     // mainly used for sanity checking.
 935     root_regions()->scan_finished();
 936   }
 937 }
 938 
 939 void G1ConcurrentMark::concurrent_cycle_start() {
 940   _gc_timer_cm->register_gc_start();
 941 
 942   _gc_tracer_cm->report_gc_start(GCCause::_no_gc /* first parameter is not used */, _gc_timer_cm->gc_start());
 943 
 944   _g1h->trace_heap_before_gc(_gc_tracer_cm);
 945 }
 946 
 947 void G1ConcurrentMark::concurrent_cycle_end() {
 948   _g1h->collector_state()->set_clearing_next_bitmap(false);
 949 
 950   _g1h->trace_heap_after_gc(_gc_tracer_cm);
 951 
 952   if (has_aborted()) {
 953     log_info(gc, marking)("Concurrent Mark Abort");
 954     _gc_tracer_cm->report_concurrent_mode_failure();
 955   }
 956 
 957   _gc_timer_cm->register_gc_end();
 958 
 959   _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
 960 }
 961 
 962 void G1ConcurrentMark::mark_from_roots() {
 963   _restart_for_overflow = false;
 964 
 965   _num_concurrent_workers = calc_active_marking_workers();
 966 
 967   uint active_workers = MAX2(1U, _num_concurrent_workers);
 968 
 969   // Setting active workers is not guaranteed since fewer
 970   // worker threads may currently exist and more may not be
 971   // available.
 972   active_workers = _concurrent_workers->update_active_workers(active_workers);
 973   log_info(gc, task)("Using %u workers of %u for marking", active_workers, _concurrent_workers->total_workers());
 974 
 975   // Parallel task terminator is set in "set_concurrency_and_phase()"
 976   set_concurrency_and_phase(active_workers, true /* concurrent */);
 977 
 978   G1CMConcurrentMarkingTask marking_task(this);
 979   _concurrent_workers->run_task(&marking_task);
 980   print_stats();
 981 }
 982 
 983 void G1ConcurrentMark::verify_during_pause(G1HeapVerifier::G1VerifyType type, VerifyOption vo, const char* caller) {
 984   G1HeapVerifier* verifier = _g1h->verifier();
 985 
 986   verifier->verify_region_sets_optional();
 987 
 988   if (VerifyDuringGC) {
 989     GCTraceTime(Debug, gc, phases) debug(caller, _gc_timer_cm);
 990 
 991     size_t const BufLen = 512;
 992     char buffer[BufLen];
 993 
 994     jio_snprintf(buffer, BufLen, "During GC (%s)", caller);
 995     verifier->verify(type, vo, buffer);
 996   }
 997 
 998   verifier->check_bitmaps(caller);
 999 }
1000 
1001 class G1UpdateRemSetTrackingBeforeRebuildTask : public AbstractGangTask {
1002   G1CollectedHeap* _g1h;
1003   G1ConcurrentMark* _cm;
1004   HeapRegionClaimer _hrclaimer;
1005   uint volatile _total_selected_for_rebuild;
1006 
1007   G1PrintRegionLivenessInfoClosure _cl;
1008 
1009   class G1UpdateRemSetTrackingBeforeRebuild : public HeapRegionClosure {
1010     G1CollectedHeap* _g1h;
1011     G1ConcurrentMark* _cm;
1012 
1013     G1PrintRegionLivenessInfoClosure* _cl;
1014 
1015     uint _num_regions_selected_for_rebuild;  // The number of regions actually selected for rebuild.
1016 
1017     void update_remset_before_rebuild(HeapRegion* hr) {
1018       G1RemSetTrackingPolicy* tracking_policy = _g1h->policy()->remset_tracker();
1019 
1020       bool selected_for_rebuild;
1021       if (hr->is_humongous()) {
1022         bool const is_live = _cm->liveness(hr->humongous_start_region()->hrm_index()) > 0;
1023         selected_for_rebuild = tracking_policy->update_humongous_before_rebuild(hr, is_live);
1024       } else {
1025         size_t const live_bytes = _cm->liveness(hr->hrm_index());
1026         selected_for_rebuild = tracking_policy->update_before_rebuild(hr, live_bytes);
1027       }
1028       if (selected_for_rebuild) {
1029         _num_regions_selected_for_rebuild++;
1030       }
1031       _cm->update_top_at_rebuild_start(hr);
1032     }
1033 
1034     // Distribute the given words across the humongous object starting with hr and
1035     // note end of marking.
1036     void distribute_marked_bytes(HeapRegion* hr, size_t marked_words) {
1037       uint const region_idx = hr->hrm_index();
1038       size_t const obj_size_in_words = (size_t)oop(hr->bottom())->size();
1039       uint const num_regions_in_humongous = (uint)G1CollectedHeap::humongous_obj_size_in_regions(obj_size_in_words);
1040 
1041       // "Distributing" zero words means that we only note end of marking for these
1042       // regions.
1043       assert(marked_words == 0 || obj_size_in_words == marked_words,
1044              "Marked words should either be 0 or the same as humongous object (" SIZE_FORMAT ") but is " SIZE_FORMAT,
1045              obj_size_in_words, marked_words);
1046 
1047       for (uint i = region_idx; i < (region_idx + num_regions_in_humongous); i++) {
1048         HeapRegion* const r = _g1h->region_at(i);
1049         size_t const words_to_add = MIN2(HeapRegion::GrainWords, marked_words);
1050 
1051         log_trace(gc, marking)("Adding " SIZE_FORMAT " words to humongous region %u (%s)",
1052                                words_to_add, i, r->get_type_str());
1053         add_marked_bytes_and_note_end(r, words_to_add * HeapWordSize);
1054         marked_words -= words_to_add;
1055       }
1056       assert(marked_words == 0,
1057              SIZE_FORMAT " words left after distributing space across %u regions",
1058              marked_words, num_regions_in_humongous);
1059     }
1060 
1061     void update_marked_bytes(HeapRegion* hr) {
1062       uint const region_idx = hr->hrm_index();
1063       size_t const marked_words = _cm->liveness(region_idx);
1064       // The marking attributes the object's size completely to the humongous starts
1065       // region. We need to distribute this value across the entire set of regions a
1066       // humongous object spans.
1067       if (hr->is_humongous()) {
1068         assert(hr->is_starts_humongous() || marked_words == 0,
1069                "Should not have marked words " SIZE_FORMAT " in non-starts humongous region %u (%s)",
1070                marked_words, region_idx, hr->get_type_str());
1071         if (hr->is_starts_humongous()) {
1072           distribute_marked_bytes(hr, marked_words);
1073         }
1074       } else {
1075         log_trace(gc, marking)("Adding " SIZE_FORMAT " words to region %u (%s)", marked_words, region_idx, hr->get_type_str());
1076         add_marked_bytes_and_note_end(hr, marked_words * HeapWordSize);
1077       }
1078     }
1079 
1080     void add_marked_bytes_and_note_end(HeapRegion* hr, size_t marked_bytes) {
1081       hr->add_to_marked_bytes(marked_bytes);
1082       _cl->do_heap_region(hr);
1083       hr->note_end_of_marking();
1084     }
1085 
1086   public:
1087     G1UpdateRemSetTrackingBeforeRebuild(G1CollectedHeap* g1h, G1ConcurrentMark* cm, G1PrintRegionLivenessInfoClosure* cl) :
1088       _g1h(g1h), _cm(cm), _cl(cl), _num_regions_selected_for_rebuild(0) { }
1089 
1090     virtual bool do_heap_region(HeapRegion* r) {
1091       update_remset_before_rebuild(r);
1092       update_marked_bytes(r);
1093 
1094       return false;
1095     }
1096 
1097     uint num_selected_for_rebuild() const { return _num_regions_selected_for_rebuild; }
1098   };
1099 
1100 public:
1101   G1UpdateRemSetTrackingBeforeRebuildTask(G1CollectedHeap* g1h, G1ConcurrentMark* cm, uint num_workers) :
1102     AbstractGangTask("G1 Update RemSet Tracking Before Rebuild"),
1103     _g1h(g1h), _cm(cm), _hrclaimer(num_workers), _total_selected_for_rebuild(0), _cl("Post-Marking") { }
1104 
1105   virtual void work(uint worker_id) {
1106     G1UpdateRemSetTrackingBeforeRebuild update_cl(_g1h, _cm, &_cl);
1107     _g1h->heap_region_par_iterate_from_worker_offset(&update_cl, &_hrclaimer, worker_id);
1108     Atomic::add(update_cl.num_selected_for_rebuild(), &_total_selected_for_rebuild);
1109   }
1110 
1111   uint total_selected_for_rebuild() const { return _total_selected_for_rebuild; }
1112 
1113   // Number of regions for which roughly one thread should be spawned for this work.
1114   static const uint RegionsPerThread = 384;
1115 };
1116 
1117 class G1UpdateRemSetTrackingAfterRebuild : public HeapRegionClosure {
1118   G1CollectedHeap* _g1h;
1119 public:
1120   G1UpdateRemSetTrackingAfterRebuild(G1CollectedHeap* g1h) : _g1h(g1h) { }
1121 
1122   virtual bool do_heap_region(HeapRegion* r) {
1123     _g1h->policy()->remset_tracker()->update_after_rebuild(r);
1124     return false;
1125   }
1126 };
1127 
1128 void G1ConcurrentMark::remark() {
1129   assert_at_safepoint_on_vm_thread();
1130 
1131   // If a full collection has happened, we should not continue. However we might
1132   // have ended up here as the Remark VM operation has been scheduled already.
1133   if (has_aborted()) {
1134     return;
1135   }
1136 
1137   G1Policy* policy = _g1h->policy();
1138   policy->record_concurrent_mark_remark_start();
1139 
1140   double start = os::elapsedTime();
1141 
1142   verify_during_pause(G1HeapVerifier::G1VerifyRemark, VerifyOption_G1UsePrevMarking, "Remark before");
1143 
1144   {
1145     GCTraceTime(Debug, gc, phases) debug("Finalize Marking", _gc_timer_cm);
1146     finalize_marking();
1147   }
1148 
1149   double mark_work_end = os::elapsedTime();
1150 
1151   bool const mark_finished = !has_overflown();
1152   if (mark_finished) {
1153     weak_refs_work(false /* clear_all_soft_refs */);
1154 
1155     SATBMarkQueueSet& satb_mq_set = G1BarrierSet::satb_mark_queue_set();
1156     // We're done with marking.
1157     // This is the end of the marking cycle, we're expected all
1158     // threads to have SATB queues with active set to true.
1159     satb_mq_set.set_active_all_threads(false, /* new active value */
1160                                        true /* expected_active */);
1161 
1162     {
1163       GCTraceTime(Debug, gc, phases) debug("Flush Task Caches", _gc_timer_cm);
1164       flush_all_task_caches();
1165     }
1166 
1167     // Install newly created mark bitmap as "prev".
1168     swap_mark_bitmaps();
1169     {
1170       GCTraceTime(Debug, gc, phases) debug("Update Remembered Set Tracking Before Rebuild", _gc_timer_cm);
1171 
1172       uint const workers_by_capacity = (_g1h->num_regions() + G1UpdateRemSetTrackingBeforeRebuildTask::RegionsPerThread - 1) /
1173                                        G1UpdateRemSetTrackingBeforeRebuildTask::RegionsPerThread;
1174       uint const num_workers = MIN2(_g1h->workers()->active_workers(), workers_by_capacity);
1175 
1176       G1UpdateRemSetTrackingBeforeRebuildTask cl(_g1h, this, num_workers);
1177       log_debug(gc,ergo)("Running %s using %u workers for %u regions in heap", cl.name(), num_workers, _g1h->num_regions());
1178       _g1h->workers()->run_task(&cl, num_workers);
1179 
1180       log_debug(gc, remset, tracking)("Remembered Set Tracking update regions total %u, selected %u",
1181                                       _g1h->num_regions(), cl.total_selected_for_rebuild());
1182     }
1183     {
1184       GCTraceTime(Debug, gc, phases) debug("Reclaim Empty Regions", _gc_timer_cm);
1185       reclaim_empty_regions();
1186     }
1187 
1188     // Clean out dead classes
1189     if (ClassUnloadingWithConcurrentMark) {
1190       GCTraceTime(Debug, gc, phases) debug("Purge Metaspace", _gc_timer_cm);
1191       ClassLoaderDataGraph::purge();
1192     }
1193 
1194     _g1h->resize_heap_if_necessary();
1195 
1196     compute_new_sizes();
1197 
1198     verify_during_pause(G1HeapVerifier::G1VerifyRemark, VerifyOption_G1UsePrevMarking, "Remark after");
1199 
1200     assert(!restart_for_overflow(), "sanity");
1201     // Completely reset the marking state since marking completed
1202     reset_at_marking_complete();
1203   } else {
1204     // We overflowed.  Restart concurrent marking.
1205     _restart_for_overflow = true;
1206 
1207     verify_during_pause(G1HeapVerifier::G1VerifyRemark, VerifyOption_G1UsePrevMarking, "Remark overflow");
1208 
1209     // Clear the marking state because we will be restarting
1210     // marking due to overflowing the global mark stack.
1211     reset_marking_for_restart();
1212   }
1213 
1214   {
1215     GCTraceTime(Debug, gc, phases) debug("Report Object Count", _gc_timer_cm);
1216     report_object_count(mark_finished);
1217   }
1218 
1219   // Statistics
1220   double now = os::elapsedTime();
1221   _remark_mark_times.add((mark_work_end - start) * 1000.0);
1222   _remark_weak_ref_times.add((now - mark_work_end) * 1000.0);
1223   _remark_times.add((now - start) * 1000.0);
1224 
1225   policy->record_concurrent_mark_remark_end();
1226 }
1227 
1228 class G1ReclaimEmptyRegionsTask : public AbstractGangTask {
1229   // Per-region work during the Cleanup pause.
1230   class G1ReclaimEmptyRegionsClosure : public HeapRegionClosure {
1231     G1CollectedHeap* _g1h;
1232     size_t _freed_bytes;
1233     FreeRegionList* _local_cleanup_list;
1234     uint _old_regions_removed;
1235     uint _humongous_regions_removed;
1236 
1237   public:
1238     G1ReclaimEmptyRegionsClosure(G1CollectedHeap* g1h,
1239                                  FreeRegionList* local_cleanup_list) :
1240       _g1h(g1h),
1241       _freed_bytes(0),
1242       _local_cleanup_list(local_cleanup_list),
1243       _old_regions_removed(0),
1244       _humongous_regions_removed(0) { }
1245 
1246     size_t freed_bytes() { return _freed_bytes; }
1247     const uint old_regions_removed() { return _old_regions_removed; }
1248     const uint humongous_regions_removed() { return _humongous_regions_removed; }
1249 
1250     bool do_heap_region(HeapRegion *hr) {
1251       if (hr->used() > 0 && hr->max_live_bytes() == 0 && !hr->is_young() && !hr->is_archive()) {
1252         _freed_bytes += hr->used();
1253         hr->set_containing_set(NULL);
1254         if (hr->is_humongous()) {
1255           _humongous_regions_removed++;
1256           _g1h->free_humongous_region(hr, _local_cleanup_list);
1257         } else {
1258           _old_regions_removed++;
1259           _g1h->free_region(hr, _local_cleanup_list, false /* skip_remset */, false /* skip_hcc */, true /* locked */);
1260         }
1261         hr->clear_cardtable();
1262         _g1h->concurrent_mark()->clear_statistics_in_region(hr->hrm_index());
1263         log_trace(gc)("Reclaimed empty region %u (%s) bot " PTR_FORMAT, hr->hrm_index(), hr->get_short_type_str(), p2i(hr->bottom()));
1264       }
1265 
1266       return false;
1267     }
1268   };
1269 
1270   G1CollectedHeap* _g1h;
1271   FreeRegionList* _cleanup_list;
1272   HeapRegionClaimer _hrclaimer;
1273 
1274 public:
1275   G1ReclaimEmptyRegionsTask(G1CollectedHeap* g1h, FreeRegionList* cleanup_list, uint n_workers) :
1276     AbstractGangTask("G1 Cleanup"),
1277     _g1h(g1h),
1278     _cleanup_list(cleanup_list),
1279     _hrclaimer(n_workers) {
1280   }
1281 
1282   void work(uint worker_id) {
1283     FreeRegionList local_cleanup_list("Local Cleanup List");
1284     G1ReclaimEmptyRegionsClosure cl(_g1h, &local_cleanup_list);
1285     _g1h->heap_region_par_iterate_from_worker_offset(&cl, &_hrclaimer, worker_id);
1286     assert(cl.is_complete(), "Shouldn't have aborted!");
1287 
1288     // Now update the old/humongous region sets
1289     _g1h->remove_from_old_sets(cl.old_regions_removed(), cl.humongous_regions_removed());
1290     {
1291       MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
1292       _g1h->decrement_summary_bytes(cl.freed_bytes());
1293 
1294       _cleanup_list->add_ordered(&local_cleanup_list);
1295       assert(local_cleanup_list.is_empty(), "post-condition");
1296     }
1297   }
1298 };
1299 
1300 void G1ConcurrentMark::reclaim_empty_regions() {
1301   WorkGang* workers = _g1h->workers();
1302   FreeRegionList empty_regions_list("Empty Regions After Mark List");
1303 
1304   G1ReclaimEmptyRegionsTask cl(_g1h, &empty_regions_list, workers->active_workers());
1305   workers->run_task(&cl);
1306 
1307   if (!empty_regions_list.is_empty()) {
1308     log_debug(gc)("Reclaimed %u empty regions", empty_regions_list.length());
1309     // Now print the empty regions list.
1310     G1HRPrinter* hrp = _g1h->hr_printer();
1311     if (hrp->is_active()) {
1312       FreeRegionListIterator iter(&empty_regions_list);
1313       while (iter.more_available()) {
1314         HeapRegion* hr = iter.get_next();
1315         hrp->cleanup(hr);
1316       }
1317     }
1318     // And actually make them available.
1319     _g1h->prepend_to_freelist(&empty_regions_list);
1320   }
1321 }
1322 
1323 void G1ConcurrentMark::compute_new_sizes() {
1324   MetaspaceGC::compute_new_size();
1325 
1326   // Cleanup will have freed any regions completely full of garbage.
1327   // Update the soft reference policy with the new heap occupancy.
1328   Universe::update_heap_info_at_gc();
1329 
1330   // We reclaimed old regions so we should calculate the sizes to make
1331   // sure we update the old gen/space data.
1332   _g1h->g1mm()->update_sizes();
1333 }
1334 
1335 void G1ConcurrentMark::cleanup() {
1336   assert_at_safepoint_on_vm_thread();
1337 
1338   // If a full collection has happened, we shouldn't do this.
1339   if (has_aborted()) {
1340     return;
1341   }
1342 
1343   G1Policy* policy = _g1h->policy();
1344   policy->record_concurrent_mark_cleanup_start();
1345 
1346   double start = os::elapsedTime();
1347 
1348   verify_during_pause(G1HeapVerifier::G1VerifyCleanup, VerifyOption_G1UsePrevMarking, "Cleanup before");
1349 
1350   {
1351     GCTraceTime(Debug, gc, phases) debug("Update Remembered Set Tracking After Rebuild", _gc_timer_cm);
1352     G1UpdateRemSetTrackingAfterRebuild cl(_g1h);
1353     _g1h->heap_region_iterate(&cl);
1354   }
1355 
1356   if (log_is_enabled(Trace, gc, liveness)) {
1357     G1PrintRegionLivenessInfoClosure cl("Post-Cleanup");
1358     _g1h->heap_region_iterate(&cl);
1359   }
1360 
1361   verify_during_pause(G1HeapVerifier::G1VerifyCleanup, VerifyOption_G1UsePrevMarking, "Cleanup after");
1362 
1363   // We need to make this be a "collection" so any collection pause that
1364   // races with it goes around and waits for Cleanup to finish.
1365   _g1h->increment_total_collections();
1366 
1367   // Local statistics
1368   double recent_cleanup_time = (os::elapsedTime() - start);
1369   _total_cleanup_time += recent_cleanup_time;
1370   _cleanup_times.add(recent_cleanup_time);
1371 
1372   {
1373     GCTraceTime(Debug, gc, phases) debug("Finalize Concurrent Mark Cleanup", _gc_timer_cm);
1374     policy->record_concurrent_mark_cleanup_end();
1375   }
1376 }
1377 
1378 // 'Keep Alive' oop closure used by both serial parallel reference processing.
1379 // Uses the G1CMTask associated with a worker thread (for serial reference
1380 // processing the G1CMTask for worker 0 is used) to preserve (mark) and
1381 // trace referent objects.
1382 //
1383 // Using the G1CMTask and embedded local queues avoids having the worker
1384 // threads operating on the global mark stack. This reduces the risk
1385 // of overflowing the stack - which we would rather avoid at this late
1386 // state. Also using the tasks' local queues removes the potential
1387 // of the workers interfering with each other that could occur if
1388 // operating on the global stack.
1389 
1390 class G1CMKeepAliveAndDrainClosure : public OopClosure {
1391   G1ConcurrentMark* _cm;
1392   G1CMTask*         _task;
1393   uint              _ref_counter_limit;
1394   uint              _ref_counter;
1395   bool              _is_serial;
1396 public:
1397   G1CMKeepAliveAndDrainClosure(G1ConcurrentMark* cm, G1CMTask* task, bool is_serial) :
1398     _cm(cm), _task(task), _ref_counter_limit(G1RefProcDrainInterval),
1399     _ref_counter(_ref_counter_limit), _is_serial(is_serial) {
1400     assert(!_is_serial || _task->worker_id() == 0, "only task 0 for serial code");
1401   }
1402 
1403   virtual void do_oop(narrowOop* p) { do_oop_work(p); }
1404   virtual void do_oop(      oop* p) { do_oop_work(p); }
1405 
1406   template <class T> void do_oop_work(T* p) {
1407     if (_cm->has_overflown()) {
1408       return;
1409     }
1410     if (!_task->deal_with_reference(p)) {
1411       // We did not add anything to the mark bitmap (or mark stack), so there is
1412       // no point trying to drain it.
1413       return;
1414     }
1415     _ref_counter--;
1416 
1417     if (_ref_counter == 0) {
1418       // We have dealt with _ref_counter_limit references, pushing them
1419       // and objects reachable from them on to the local stack (and
1420       // possibly the global stack). Call G1CMTask::do_marking_step() to
1421       // process these entries.
1422       //
1423       // We call G1CMTask::do_marking_step() in a loop, which we'll exit if
1424       // there's nothing more to do (i.e. we're done with the entries that
1425       // were pushed as a result of the G1CMTask::deal_with_reference() calls
1426       // above) or we overflow.
1427       //
1428       // Note: G1CMTask::do_marking_step() can set the G1CMTask::has_aborted()
1429       // flag while there may still be some work to do. (See the comment at
1430       // the beginning of G1CMTask::do_marking_step() for those conditions -
1431       // one of which is reaching the specified time target.) It is only
1432       // when G1CMTask::do_marking_step() returns without setting the
1433       // has_aborted() flag that the marking step has completed.
1434       do {
1435         double mark_step_duration_ms = G1ConcMarkStepDurationMillis;
1436         _task->do_marking_step(mark_step_duration_ms,
1437                                false      /* do_termination */,
1438                                _is_serial);
1439       } while (_task->has_aborted() && !_cm->has_overflown());
1440       _ref_counter = _ref_counter_limit;
1441     }
1442   }
1443 };
1444 
1445 // 'Drain' oop closure used by both serial and parallel reference processing.
1446 // Uses the G1CMTask associated with a given worker thread (for serial
1447 // reference processing the G1CMtask for worker 0 is used). Calls the
1448 // do_marking_step routine, with an unbelievably large timeout value,
1449 // to drain the marking data structures of the remaining entries
1450 // added by the 'keep alive' oop closure above.
1451 
1452 class G1CMDrainMarkingStackClosure : public VoidClosure {
1453   G1ConcurrentMark* _cm;
1454   G1CMTask*         _task;
1455   bool              _is_serial;
1456  public:
1457   G1CMDrainMarkingStackClosure(G1ConcurrentMark* cm, G1CMTask* task, bool is_serial) :
1458     _cm(cm), _task(task), _is_serial(is_serial) {
1459     assert(!_is_serial || _task->worker_id() == 0, "only task 0 for serial code");
1460   }
1461 
1462   void do_void() {
1463     do {
1464       // We call G1CMTask::do_marking_step() to completely drain the local
1465       // and global marking stacks of entries pushed by the 'keep alive'
1466       // oop closure (an instance of G1CMKeepAliveAndDrainClosure above).
1467       //
1468       // G1CMTask::do_marking_step() is called in a loop, which we'll exit
1469       // if there's nothing more to do (i.e. we've completely drained the
1470       // entries that were pushed as a a result of applying the 'keep alive'
1471       // closure to the entries on the discovered ref lists) or we overflow
1472       // the global marking stack.
1473       //
1474       // Note: G1CMTask::do_marking_step() can set the G1CMTask::has_aborted()
1475       // flag while there may still be some work to do. (See the comment at
1476       // the beginning of G1CMTask::do_marking_step() for those conditions -
1477       // one of which is reaching the specified time target.) It is only
1478       // when G1CMTask::do_marking_step() returns without setting the
1479       // has_aborted() flag that the marking step has completed.
1480 
1481       _task->do_marking_step(1000000000.0 /* something very large */,
1482                              true         /* do_termination */,
1483                              _is_serial);
1484     } while (_task->has_aborted() && !_cm->has_overflown());
1485   }
1486 };
1487 
1488 // Implementation of AbstractRefProcTaskExecutor for parallel
1489 // reference processing at the end of G1 concurrent marking
1490 
1491 class G1CMRefProcTaskExecutor : public AbstractRefProcTaskExecutor {
1492 private:
1493   G1CollectedHeap*  _g1h;
1494   G1ConcurrentMark* _cm;
1495   WorkGang*         _workers;
1496   uint              _active_workers;
1497 
1498 public:
1499   G1CMRefProcTaskExecutor(G1CollectedHeap* g1h,
1500                           G1ConcurrentMark* cm,
1501                           WorkGang* workers,
1502                           uint n_workers) :
1503     _g1h(g1h), _cm(cm),
1504     _workers(workers), _active_workers(n_workers) { }
1505 
1506   virtual void execute(ProcessTask& task, uint ergo_workers);
1507 };
1508 
1509 class G1CMRefProcTaskProxy : public AbstractGangTask {
1510   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
1511   ProcessTask&      _proc_task;
1512   G1CollectedHeap*  _g1h;
1513   G1ConcurrentMark* _cm;
1514 
1515 public:
1516   G1CMRefProcTaskProxy(ProcessTask& proc_task,
1517                        G1CollectedHeap* g1h,
1518                        G1ConcurrentMark* cm) :
1519     AbstractGangTask("Process reference objects in parallel"),
1520     _proc_task(proc_task), _g1h(g1h), _cm(cm) {
1521     ReferenceProcessor* rp = _g1h->ref_processor_cm();
1522     assert(rp->processing_is_mt(), "shouldn't be here otherwise");
1523   }
1524 
1525   virtual void work(uint worker_id) {
1526     ResourceMark rm;
1527     HandleMark hm;
1528     G1CMTask* task = _cm->task(worker_id);
1529     G1CMIsAliveClosure g1_is_alive(_g1h);
1530     G1CMKeepAliveAndDrainClosure g1_par_keep_alive(_cm, task, false /* is_serial */);
1531     G1CMDrainMarkingStackClosure g1_par_drain(_cm, task, false /* is_serial */);
1532 
1533     _proc_task.work(worker_id, g1_is_alive, g1_par_keep_alive, g1_par_drain);
1534   }
1535 };
1536 
1537 void G1CMRefProcTaskExecutor::execute(ProcessTask& proc_task, uint ergo_workers) {
1538   assert(_workers != NULL, "Need parallel worker threads.");
1539   assert(_g1h->ref_processor_cm()->processing_is_mt(), "processing is not MT");
1540   assert(_workers->active_workers() >= ergo_workers,
1541          "Ergonomically chosen workers(%u) should be less than or equal to active workers(%u)",
1542          ergo_workers, _workers->active_workers());
1543 
1544   G1CMRefProcTaskProxy proc_task_proxy(proc_task, _g1h, _cm);
1545 
1546   // We need to reset the concurrency level before each
1547   // proxy task execution, so that the termination protocol
1548   // and overflow handling in G1CMTask::do_marking_step() knows
1549   // how many workers to wait for.
1550   _cm->set_concurrency(ergo_workers);
1551   _workers->run_task(&proc_task_proxy, ergo_workers);
1552 }
1553 
1554 void G1ConcurrentMark::weak_refs_work(bool clear_all_soft_refs) {
1555   ResourceMark rm;
1556   HandleMark   hm;
1557 
1558   // Is alive closure.
1559   G1CMIsAliveClosure g1_is_alive(_g1h);
1560 
1561   // Inner scope to exclude the cleaning of the string table
1562   // from the displayed time.
1563   {
1564     GCTraceTime(Debug, gc, phases) debug("Reference Processing", _gc_timer_cm);
1565 
1566     ReferenceProcessor* rp = _g1h->ref_processor_cm();
1567 
1568     // See the comment in G1CollectedHeap::ref_processing_init()
1569     // about how reference processing currently works in G1.
1570 
1571     // Set the soft reference policy
1572     rp->setup_policy(clear_all_soft_refs);
1573     assert(_global_mark_stack.is_empty(), "mark stack should be empty");
1574 
1575     // Instances of the 'Keep Alive' and 'Complete GC' closures used
1576     // in serial reference processing. Note these closures are also
1577     // used for serially processing (by the the current thread) the
1578     // JNI references during parallel reference processing.
1579     //
1580     // These closures do not need to synchronize with the worker
1581     // threads involved in parallel reference processing as these
1582     // instances are executed serially by the current thread (e.g.
1583     // reference processing is not multi-threaded and is thus
1584     // performed by the current thread instead of a gang worker).
1585     //
1586     // The gang tasks involved in parallel reference processing create
1587     // their own instances of these closures, which do their own
1588     // synchronization among themselves.
1589     G1CMKeepAliveAndDrainClosure g1_keep_alive(this, task(0), true /* is_serial */);
1590     G1CMDrainMarkingStackClosure g1_drain_mark_stack(this, task(0), true /* is_serial */);
1591 
1592     // We need at least one active thread. If reference processing
1593     // is not multi-threaded we use the current (VMThread) thread,
1594     // otherwise we use the work gang from the G1CollectedHeap and
1595     // we utilize all the worker threads we can.
1596     bool processing_is_mt = rp->processing_is_mt();
1597     uint active_workers = (processing_is_mt ? _g1h->workers()->active_workers() : 1U);
1598     active_workers = MAX2(MIN2(active_workers, _max_num_tasks), 1U);
1599 
1600     // Parallel processing task executor.
1601     G1CMRefProcTaskExecutor par_task_executor(_g1h, this,
1602                                               _g1h->workers(), active_workers);
1603     AbstractRefProcTaskExecutor* executor = (processing_is_mt ? &par_task_executor : NULL);
1604 
1605     // Set the concurrency level. The phase was already set prior to
1606     // executing the remark task.
1607     set_concurrency(active_workers);
1608 
1609     // Set the degree of MT processing here.  If the discovery was done MT,
1610     // the number of threads involved during discovery could differ from
1611     // the number of active workers.  This is OK as long as the discovered
1612     // Reference lists are balanced (see balance_all_queues() and balance_queues()).
1613     rp->set_active_mt_degree(active_workers);
1614 
1615     ReferenceProcessorPhaseTimes pt(_gc_timer_cm, rp->max_num_queues());
1616 
1617     // Process the weak references.
1618     const ReferenceProcessorStats& stats =
1619         rp->process_discovered_references(&g1_is_alive,
1620                                           &g1_keep_alive,
1621                                           &g1_drain_mark_stack,
1622                                           executor,
1623                                           &pt);
1624     _gc_tracer_cm->report_gc_reference_stats(stats);
1625     pt.print_all_references();
1626 
1627     // The do_oop work routines of the keep_alive and drain_marking_stack
1628     // oop closures will set the has_overflown flag if we overflow the
1629     // global marking stack.
1630 
1631     assert(has_overflown() || _global_mark_stack.is_empty(),
1632            "Mark stack should be empty (unless it has overflown)");
1633 
1634     assert(rp->num_queues() == active_workers, "why not");
1635 
1636     rp->verify_no_references_recorded();
1637     assert(!rp->discovery_enabled(), "Post condition");
1638   }
1639 
1640   if (has_overflown()) {
1641     // We can not trust g1_is_alive and the contents of the heap if the marking stack
1642     // overflowed while processing references. Exit the VM.
1643     fatal("Overflow during reference processing, can not continue. Please "
1644           "increase MarkStackSizeMax (current value: " SIZE_FORMAT ") and "
1645           "restart.", MarkStackSizeMax);
1646     return;
1647   }
1648 
1649   assert(_global_mark_stack.is_empty(), "Marking should have completed");
1650 
1651   {
1652     GCTraceTime(Debug, gc, phases) debug("Weak Processing", _gc_timer_cm);
1653     WeakProcessor::weak_oops_do(_g1h->workers(), &g1_is_alive, &do_nothing_cl, 1);
1654   }
1655 
1656   // Unload Klasses, String, Code Cache, etc.
1657   if (ClassUnloadingWithConcurrentMark) {
1658     GCTraceTime(Debug, gc, phases) debug("Class Unloading", _gc_timer_cm);
1659     bool purged_classes = SystemDictionary::do_unloading(_gc_timer_cm);
1660     _g1h->complete_cleaning(&g1_is_alive, purged_classes);
1661   } else if (StringDedup::is_enabled()) {
1662     GCTraceTime(Debug, gc, phases) debug("String Deduplication", _gc_timer_cm);
1663     _g1h->string_dedup_cleaning(&g1_is_alive, NULL);
1664   }
1665 }
1666 
1667 class G1PrecleanYieldClosure : public YieldClosure {
1668   G1ConcurrentMark* _cm;
1669 
1670 public:
1671   G1PrecleanYieldClosure(G1ConcurrentMark* cm) : _cm(cm) { }
1672 
1673   virtual bool should_return() {
1674     return _cm->has_aborted();
1675   }
1676 
1677   virtual bool should_return_fine_grain() {
1678     _cm->do_yield_check();
1679     return _cm->has_aborted();
1680   }
1681 };
1682 
1683 void G1ConcurrentMark::preclean() {
1684   assert(G1UseReferencePrecleaning, "Precleaning must be enabled.");
1685 
1686   SuspendibleThreadSetJoiner joiner;
1687 
1688   G1CMKeepAliveAndDrainClosure keep_alive(this, task(0), true /* is_serial */);
1689   G1CMDrainMarkingStackClosure drain_mark_stack(this, task(0), true /* is_serial */);
1690 
1691   set_concurrency_and_phase(1, true);
1692 
1693   G1PrecleanYieldClosure yield_cl(this);
1694 
1695   ReferenceProcessor* rp = _g1h->ref_processor_cm();
1696   // Precleaning is single threaded. Temporarily disable MT discovery.
1697   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
1698   rp->preclean_discovered_references(rp->is_alive_non_header(),
1699                                      &keep_alive,
1700                                      &drain_mark_stack,
1701                                      &yield_cl,
1702                                      _gc_timer_cm);
1703 }
1704 
1705 // When sampling object counts, we already swapped the mark bitmaps, so we need to use
1706 // the prev bitmap determining liveness.
1707 class G1ObjectCountIsAliveClosure: public BoolObjectClosure {
1708   G1CollectedHeap* _g1h;
1709 public:
1710   G1ObjectCountIsAliveClosure(G1CollectedHeap* g1h) : _g1h(g1h) { }
1711 
1712   bool do_object_b(oop obj) {
1713     HeapWord* addr = (HeapWord*)obj;
1714     return addr != NULL &&
1715            (!_g1h->is_in_g1_reserved(addr) || !_g1h->is_obj_dead(obj));
1716   }
1717 };
1718 
1719 void G1ConcurrentMark::report_object_count(bool mark_completed) {
1720   // Depending on the completion of the marking liveness needs to be determined
1721   // using either the next or prev bitmap.
1722   if (mark_completed) {
1723     G1ObjectCountIsAliveClosure is_alive(_g1h);
1724     _gc_tracer_cm->report_object_count_after_gc(&is_alive);
1725   } else {
1726     G1CMIsAliveClosure is_alive(_g1h);
1727     _gc_tracer_cm->report_object_count_after_gc(&is_alive);
1728   }
1729 }
1730 
1731 
1732 void G1ConcurrentMark::swap_mark_bitmaps() {
1733   G1CMBitMap* temp = _prev_mark_bitmap;
1734   _prev_mark_bitmap = _next_mark_bitmap;
1735   _next_mark_bitmap = temp;
1736   _g1h->collector_state()->set_clearing_next_bitmap(true);
1737 }
1738 
1739 // Closure for marking entries in SATB buffers.
1740 class G1CMSATBBufferClosure : public SATBBufferClosure {
1741 private:
1742   G1CMTask* _task;
1743   G1CollectedHeap* _g1h;
1744 
1745   // This is very similar to G1CMTask::deal_with_reference, but with
1746   // more relaxed requirements for the argument, so this must be more
1747   // circumspect about treating the argument as an object.
1748   void do_entry(void* entry) const {
1749     _task->increment_refs_reached();
1750     oop const obj = static_cast<oop>(entry);
1751     _task->make_reference_grey(obj);
1752   }
1753 
1754 public:
1755   G1CMSATBBufferClosure(G1CMTask* task, G1CollectedHeap* g1h)
1756     : _task(task), _g1h(g1h) { }
1757 
1758   virtual void do_buffer(void** buffer, size_t size) {
1759     for (size_t i = 0; i < size; ++i) {
1760       do_entry(buffer[i]);
1761     }
1762   }
1763 };
1764 
1765 class G1RemarkThreadsClosure : public ThreadClosure {
1766   G1CMSATBBufferClosure _cm_satb_cl;
1767   G1CMOopClosure _cm_cl;
1768   MarkingCodeBlobClosure _code_cl;
1769   uintx _claim_token;
1770 
1771  public:
1772   G1RemarkThreadsClosure(G1CollectedHeap* g1h, G1CMTask* task) :
1773     _cm_satb_cl(task, g1h),
1774     _cm_cl(g1h, task),
1775     _code_cl(&_cm_cl, !CodeBlobToOopClosure::FixRelocations),
1776     _claim_token(Threads::thread_claim_token()) {}
1777 
1778   void do_thread(Thread* thread) {
1779     if (thread->claim_threads_do(true, _claim_token)) {
1780       SATBMarkQueue& queue = G1ThreadLocalData::satb_mark_queue(thread);
1781       queue.apply_closure_and_empty(&_cm_satb_cl);
1782       if (thread->is_Java_thread()) {
1783         // In theory it should not be neccessary to explicitly walk the nmethods to find roots for concurrent marking
1784         // however the liveness of oops reachable from nmethods have very complex lifecycles:
1785         // * Alive if on the stack of an executing method
1786         // * Weakly reachable otherwise
1787         // Some objects reachable from nmethods, such as the class loader (or klass_holder) of the receiver should be
1788         // live by the SATB invariant but other oops recorded in nmethods may behave differently.
1789         JavaThread* jt = (JavaThread*)thread;
1790         jt->nmethods_do(&_code_cl);
1791       }
1792     }
1793   }
1794 };
1795 
1796 class G1CMRemarkTask : public AbstractGangTask {
1797   G1ConcurrentMark* _cm;
1798 public:
1799   void work(uint worker_id) {
1800     G1CMTask* task = _cm->task(worker_id);
1801     task->record_start_time();
1802     {
1803       ResourceMark rm;
1804       HandleMark hm;
1805 
1806       G1RemarkThreadsClosure threads_f(G1CollectedHeap::heap(), task);
1807       Threads::threads_do(&threads_f);
1808     }
1809 
1810     do {
1811       task->do_marking_step(1000000000.0 /* something very large */,
1812                             true         /* do_termination       */,
1813                             false        /* is_serial            */);
1814     } while (task->has_aborted() && !_cm->has_overflown());
1815     // If we overflow, then we do not want to restart. We instead
1816     // want to abort remark and do concurrent marking again.
1817     task->record_end_time();
1818   }
1819 
1820   G1CMRemarkTask(G1ConcurrentMark* cm, uint active_workers) :
1821     AbstractGangTask("Par Remark"), _cm(cm) {
1822     _cm->terminator()->reset_for_reuse(active_workers);
1823   }
1824 };
1825 
1826 void G1ConcurrentMark::finalize_marking() {
1827   ResourceMark rm;
1828   HandleMark   hm;
1829 
1830   _g1h->ensure_parsability(false);
1831 
1832   // this is remark, so we'll use up all active threads
1833   uint active_workers = _g1h->workers()->active_workers();
1834   set_concurrency_and_phase(active_workers, false /* concurrent */);
1835   // Leave _parallel_marking_threads at it's
1836   // value originally calculated in the G1ConcurrentMark
1837   // constructor and pass values of the active workers
1838   // through the gang in the task.
1839 
1840   {
1841     StrongRootsScope srs(active_workers);
1842 
1843     G1CMRemarkTask remarkTask(this, active_workers);
1844     // We will start all available threads, even if we decide that the
1845     // active_workers will be fewer. The extra ones will just bail out
1846     // immediately.
1847     _g1h->workers()->run_task(&remarkTask);
1848   }
1849 
1850   SATBMarkQueueSet& satb_mq_set = G1BarrierSet::satb_mark_queue_set();
1851   guarantee(has_overflown() ||
1852             satb_mq_set.completed_buffers_num() == 0,
1853             "Invariant: has_overflown = %s, num buffers = " SIZE_FORMAT,
1854             BOOL_TO_STR(has_overflown()),
1855             satb_mq_set.completed_buffers_num());
1856 
1857   print_stats();
1858 }
1859 
1860 void G1ConcurrentMark::flush_all_task_caches() {
1861   size_t hits = 0;
1862   size_t misses = 0;
1863   for (uint i = 0; i < _max_num_tasks; i++) {
1864     Pair<size_t, size_t> stats = _tasks[i]->flush_mark_stats_cache();
1865     hits += stats.first;
1866     misses += stats.second;
1867   }
1868   size_t sum = hits + misses;
1869   log_debug(gc, stats)("Mark stats cache hits " SIZE_FORMAT " misses " SIZE_FORMAT " ratio %1.3lf",
1870                        hits, misses, percent_of(hits, sum));
1871 }
1872 
1873 void G1ConcurrentMark::clear_range_in_prev_bitmap(MemRegion mr) {
1874   _prev_mark_bitmap->clear_range(mr);
1875 }
1876 
1877 HeapRegion*
1878 G1ConcurrentMark::claim_region(uint worker_id) {
1879   // "checkpoint" the finger
1880   HeapWord* finger = _finger;
1881 
1882   while (finger < _heap.end()) {
1883     assert(_g1h->is_in_g1_reserved(finger), "invariant");
1884 
1885     HeapRegion* curr_region = _g1h->heap_region_containing(finger);
1886     // Make sure that the reads below do not float before loading curr_region.
1887     OrderAccess::loadload();
1888     // Above heap_region_containing may return NULL as we always scan claim
1889     // until the end of the heap. In this case, just jump to the next region.
1890     HeapWord* end = curr_region != NULL ? curr_region->end() : finger + HeapRegion::GrainWords;
1891 
1892     // Is the gap between reading the finger and doing the CAS too long?
1893     HeapWord* res = Atomic::cmpxchg(end, &_finger, finger);
1894     if (res == finger && curr_region != NULL) {
1895       // we succeeded
1896       HeapWord*   bottom        = curr_region->bottom();
1897       HeapWord*   limit         = curr_region->next_top_at_mark_start();
1898 
1899       // notice that _finger == end cannot be guaranteed here since,
1900       // someone else might have moved the finger even further
1901       assert(_finger >= end, "the finger should have moved forward");
1902 
1903       if (limit > bottom) {
1904         return curr_region;
1905       } else {
1906         assert(limit == bottom,
1907                "the region limit should be at bottom");
1908         // we return NULL and the caller should try calling
1909         // claim_region() again.
1910         return NULL;
1911       }
1912     } else {
1913       assert(_finger > finger, "the finger should have moved forward");
1914       // read it again
1915       finger = _finger;
1916     }
1917   }
1918 
1919   return NULL;
1920 }
1921 
1922 #ifndef PRODUCT
1923 class VerifyNoCSetOops {
1924   G1CollectedHeap* _g1h;
1925   const char* _phase;
1926   int _info;
1927 
1928 public:
1929   VerifyNoCSetOops(const char* phase, int info = -1) :
1930     _g1h(G1CollectedHeap::heap()),
1931     _phase(phase),
1932     _info(info)
1933   { }
1934 
1935   void operator()(G1TaskQueueEntry task_entry) const {
1936     if (task_entry.is_array_slice()) {
1937       guarantee(_g1h->is_in_reserved(task_entry.slice()), "Slice " PTR_FORMAT " must be in heap.", p2i(task_entry.slice()));
1938       return;
1939     }
1940     guarantee(oopDesc::is_oop(task_entry.obj()),
1941               "Non-oop " PTR_FORMAT ", phase: %s, info: %d",
1942               p2i(task_entry.obj()), _phase, _info);
1943     guarantee(!_g1h->is_in_cset(task_entry.obj()),
1944               "obj: " PTR_FORMAT " in CSet, phase: %s, info: %d",
1945               p2i(task_entry.obj()), _phase, _info);
1946   }
1947 };
1948 
1949 void G1ConcurrentMark::verify_no_collection_set_oops() {
1950   assert(SafepointSynchronize::is_at_safepoint(), "should be at a safepoint");
1951   if (!_g1h->collector_state()->mark_or_rebuild_in_progress()) {
1952     return;
1953   }
1954 
1955   // Verify entries on the global mark stack
1956   _global_mark_stack.iterate(VerifyNoCSetOops("Stack"));
1957 
1958   // Verify entries on the task queues
1959   for (uint i = 0; i < _max_num_tasks; ++i) {
1960     G1CMTaskQueue* queue = _task_queues->queue(i);
1961     queue->iterate(VerifyNoCSetOops("Queue", i));
1962   }
1963 
1964   // Verify the global finger
1965   HeapWord* global_finger = finger();
1966   if (global_finger != NULL && global_finger < _heap.end()) {
1967     // Since we always iterate over all regions, we might get a NULL HeapRegion
1968     // here.
1969     HeapRegion* global_hr = _g1h->heap_region_containing(global_finger);
1970     guarantee(global_hr == NULL || global_finger == global_hr->bottom(),
1971               "global finger: " PTR_FORMAT " region: " HR_FORMAT,
1972               p2i(global_finger), HR_FORMAT_PARAMS(global_hr));
1973   }
1974 
1975   // Verify the task fingers
1976   assert(_num_concurrent_workers <= _max_num_tasks, "sanity");
1977   for (uint i = 0; i < _num_concurrent_workers; ++i) {
1978     G1CMTask* task = _tasks[i];
1979     HeapWord* task_finger = task->finger();
1980     if (task_finger != NULL && task_finger < _heap.end()) {
1981       // See above note on the global finger verification.
1982       HeapRegion* task_hr = _g1h->heap_region_containing(task_finger);
1983       guarantee(task_hr == NULL || task_finger == task_hr->bottom() ||
1984                 !task_hr->in_collection_set(),
1985                 "task finger: " PTR_FORMAT " region: " HR_FORMAT,
1986                 p2i(task_finger), HR_FORMAT_PARAMS(task_hr));
1987     }
1988   }
1989 }
1990 #endif // PRODUCT
1991 
1992 void G1ConcurrentMark::rebuild_rem_set_concurrently() {
1993   _g1h->rem_set()->rebuild_rem_set(this, _concurrent_workers, _worker_id_offset);
1994 }
1995 
1996 void G1ConcurrentMark::print_stats() {
1997   if (!log_is_enabled(Debug, gc, stats)) {
1998     return;
1999   }
2000   log_debug(gc, stats)("---------------------------------------------------------------------");
2001   for (size_t i = 0; i < _num_active_tasks; ++i) {
2002     _tasks[i]->print_stats();
2003     log_debug(gc, stats)("---------------------------------------------------------------------");
2004   }
2005 }
2006 
2007 void G1ConcurrentMark::concurrent_cycle_abort() {
2008   if (!cm_thread()->during_cycle() || _has_aborted) {
2009     // We haven't started a concurrent cycle or we have already aborted it. No need to do anything.
2010     return;
2011   }
2012 
2013   // Clear all marks in the next bitmap for the next marking cycle. This will allow us to skip the next
2014   // concurrent bitmap clearing.
2015   {
2016     GCTraceTime(Debug, gc) debug("Clear Next Bitmap");
2017     clear_bitmap(_next_mark_bitmap, _g1h->workers(), false);
2018   }
2019   // Note we cannot clear the previous marking bitmap here
2020   // since VerifyDuringGC verifies the objects marked during
2021   // a full GC against the previous bitmap.
2022 
2023   // Empty mark stack
2024   reset_marking_for_restart();
2025   for (uint i = 0; i < _max_num_tasks; ++i) {
2026     _tasks[i]->clear_region_fields();
2027   }
2028   _first_overflow_barrier_sync.abort();
2029   _second_overflow_barrier_sync.abort();
2030   _has_aborted = true;
2031 
2032   SATBMarkQueueSet& satb_mq_set = G1BarrierSet::satb_mark_queue_set();
2033   satb_mq_set.abandon_partial_marking();
2034   // This can be called either during or outside marking, we'll read
2035   // the expected_active value from the SATB queue set.
2036   satb_mq_set.set_active_all_threads(
2037                                  false, /* new active value */
2038                                  satb_mq_set.is_active() /* expected_active */);
2039 }
2040 
2041 static void print_ms_time_info(const char* prefix, const char* name,
2042                                NumberSeq& ns) {
2043   log_trace(gc, marking)("%s%5d %12s: total time = %8.2f s (avg = %8.2f ms).",
2044                          prefix, ns.num(), name, ns.sum()/1000.0, ns.avg());
2045   if (ns.num() > 0) {
2046     log_trace(gc, marking)("%s         [std. dev = %8.2f ms, max = %8.2f ms]",
2047                            prefix, ns.sd(), ns.maximum());
2048   }
2049 }
2050 
2051 void G1ConcurrentMark::print_summary_info() {
2052   Log(gc, marking) log;
2053   if (!log.is_trace()) {
2054     return;
2055   }
2056 
2057   log.trace(" Concurrent marking:");
2058   print_ms_time_info("  ", "init marks", _init_times);
2059   print_ms_time_info("  ", "remarks", _remark_times);
2060   {
2061     print_ms_time_info("     ", "final marks", _remark_mark_times);
2062     print_ms_time_info("     ", "weak refs", _remark_weak_ref_times);
2063 
2064   }
2065   print_ms_time_info("  ", "cleanups", _cleanup_times);
2066   log.trace("    Finalize live data total time = %8.2f s (avg = %8.2f ms).",
2067             _total_cleanup_time, (_cleanup_times.num() > 0 ? _total_cleanup_time * 1000.0 / (double)_cleanup_times.num() : 0.0));
2068   log.trace("  Total stop_world time = %8.2f s.",
2069             (_init_times.sum() + _remark_times.sum() + _cleanup_times.sum())/1000.0);
2070   log.trace("  Total concurrent time = %8.2f s (%8.2f s marking).",
2071             cm_thread()->vtime_accum(), cm_thread()->vtime_mark_accum());
2072 }
2073 
2074 void G1ConcurrentMark::print_worker_threads_on(outputStream* st) const {
2075   _concurrent_workers->print_worker_threads_on(st);
2076 }
2077 
2078 void G1ConcurrentMark::threads_do(ThreadClosure* tc) const {
2079   _concurrent_workers->threads_do(tc);
2080 }
2081 
2082 void G1ConcurrentMark::print_on_error(outputStream* st) const {
2083   st->print_cr("Marking Bits (Prev, Next): (CMBitMap*) " PTR_FORMAT ", (CMBitMap*) " PTR_FORMAT,
2084                p2i(_prev_mark_bitmap), p2i(_next_mark_bitmap));
2085   _prev_mark_bitmap->print_on_error(st, " Prev Bits: ");
2086   _next_mark_bitmap->print_on_error(st, " Next Bits: ");
2087 }
2088 
2089 static ReferenceProcessor* get_cm_oop_closure_ref_processor(G1CollectedHeap* g1h) {
2090   ReferenceProcessor* result = g1h->ref_processor_cm();
2091   assert(result != NULL, "CM reference processor should not be NULL");
2092   return result;
2093 }
2094 
2095 G1CMOopClosure::G1CMOopClosure(G1CollectedHeap* g1h,
2096                                G1CMTask* task)
2097   : MetadataVisitingOopIterateClosure(get_cm_oop_closure_ref_processor(g1h)),
2098     _g1h(g1h), _task(task)
2099 { }
2100 
2101 void G1CMTask::setup_for_region(HeapRegion* hr) {
2102   assert(hr != NULL,
2103         "claim_region() should have filtered out NULL regions");
2104   _curr_region  = hr;
2105   _finger       = hr->bottom();
2106   update_region_limit();
2107 }
2108 
2109 void G1CMTask::update_region_limit() {
2110   HeapRegion* hr            = _curr_region;
2111   HeapWord* bottom          = hr->bottom();
2112   HeapWord* limit           = hr->next_top_at_mark_start();
2113 
2114   if (limit == bottom) {
2115     // The region was collected underneath our feet.
2116     // We set the finger to bottom to ensure that the bitmap
2117     // iteration that will follow this will not do anything.
2118     // (this is not a condition that holds when we set the region up,
2119     // as the region is not supposed to be empty in the first place)
2120     _finger = bottom;
2121   } else if (limit >= _region_limit) {
2122     assert(limit >= _finger, "peace of mind");
2123   } else {
2124     assert(limit < _region_limit, "only way to get here");
2125     // This can happen under some pretty unusual circumstances.  An
2126     // evacuation pause empties the region underneath our feet (NTAMS
2127     // at bottom). We then do some allocation in the region (NTAMS
2128     // stays at bottom), followed by the region being used as a GC
2129     // alloc region (NTAMS will move to top() and the objects
2130     // originally below it will be grayed). All objects now marked in
2131     // the region are explicitly grayed, if below the global finger,
2132     // and we do not need in fact to scan anything else. So, we simply
2133     // set _finger to be limit to ensure that the bitmap iteration
2134     // doesn't do anything.
2135     _finger = limit;
2136   }
2137 
2138   _region_limit = limit;
2139 }
2140 
2141 void G1CMTask::giveup_current_region() {
2142   assert(_curr_region != NULL, "invariant");
2143   clear_region_fields();
2144 }
2145 
2146 void G1CMTask::clear_region_fields() {
2147   // Values for these three fields that indicate that we're not
2148   // holding on to a region.
2149   _curr_region   = NULL;
2150   _finger        = NULL;
2151   _region_limit  = NULL;
2152 }
2153 
2154 void G1CMTask::set_cm_oop_closure(G1CMOopClosure* cm_oop_closure) {
2155   if (cm_oop_closure == NULL) {
2156     assert(_cm_oop_closure != NULL, "invariant");
2157   } else {
2158     assert(_cm_oop_closure == NULL, "invariant");
2159   }
2160   _cm_oop_closure = cm_oop_closure;
2161 }
2162 
2163 void G1CMTask::reset(G1CMBitMap* next_mark_bitmap) {
2164   guarantee(next_mark_bitmap != NULL, "invariant");
2165   _next_mark_bitmap              = next_mark_bitmap;
2166   clear_region_fields();
2167 
2168   _calls                         = 0;
2169   _elapsed_time_ms               = 0.0;
2170   _termination_time_ms           = 0.0;
2171   _termination_start_time_ms     = 0.0;
2172 
2173   _mark_stats_cache.reset();
2174 }
2175 
2176 bool G1CMTask::should_exit_termination() {
2177   if (!regular_clock_call()) {
2178     return true;
2179   }
2180 
2181   // This is called when we are in the termination protocol. We should
2182   // quit if, for some reason, this task wants to abort or the global
2183   // stack is not empty (this means that we can get work from it).
2184   return !_cm->mark_stack_empty() || has_aborted();
2185 }
2186 
2187 void G1CMTask::reached_limit() {
2188   assert(_words_scanned >= _words_scanned_limit ||
2189          _refs_reached >= _refs_reached_limit ,
2190          "shouldn't have been called otherwise");
2191   abort_marking_if_regular_check_fail();
2192 }
2193 
2194 bool G1CMTask::regular_clock_call() {
2195   if (has_aborted()) {
2196     return false;
2197   }
2198 
2199   // First, we need to recalculate the words scanned and refs reached
2200   // limits for the next clock call.
2201   recalculate_limits();
2202 
2203   // During the regular clock call we do the following
2204 
2205   // (1) If an overflow has been flagged, then we abort.
2206   if (_cm->has_overflown()) {
2207     return false;
2208   }
2209 
2210   // If we are not concurrent (i.e. we're doing remark) we don't need
2211   // to check anything else. The other steps are only needed during
2212   // the concurrent marking phase.
2213   if (!_cm->concurrent()) {
2214     return true;
2215   }
2216 
2217   // (2) If marking has been aborted for Full GC, then we also abort.
2218   if (_cm->has_aborted()) {
2219     return false;
2220   }
2221 
2222   double curr_time_ms = os::elapsedVTime() * 1000.0;
2223 
2224   // (4) We check whether we should yield. If we have to, then we abort.
2225   if (SuspendibleThreadSet::should_yield()) {
2226     // We should yield. To do this we abort the task. The caller is
2227     // responsible for yielding.
2228     return false;
2229   }
2230 
2231   // (5) We check whether we've reached our time quota. If we have,
2232   // then we abort.
2233   double elapsed_time_ms = curr_time_ms - _start_time_ms;
2234   if (elapsed_time_ms > _time_target_ms) {
2235     _has_timed_out = true;
2236     return false;
2237   }
2238 
2239   // (6) Finally, we check whether there are enough completed STAB
2240   // buffers available for processing. If there are, we abort.
2241   SATBMarkQueueSet& satb_mq_set = G1BarrierSet::satb_mark_queue_set();
2242   if (!_draining_satb_buffers && satb_mq_set.process_completed_buffers()) {
2243     // we do need to process SATB buffers, we'll abort and restart
2244     // the marking task to do so
2245     return false;
2246   }
2247   return true;
2248 }
2249 
2250 void G1CMTask::recalculate_limits() {
2251   _real_words_scanned_limit = _words_scanned + words_scanned_period;
2252   _words_scanned_limit      = _real_words_scanned_limit;
2253 
2254   _real_refs_reached_limit  = _refs_reached  + refs_reached_period;
2255   _refs_reached_limit       = _real_refs_reached_limit;
2256 }
2257 
2258 void G1CMTask::decrease_limits() {
2259   // This is called when we believe that we're going to do an infrequent
2260   // operation which will increase the per byte scanned cost (i.e. move
2261   // entries to/from the global stack). It basically tries to decrease the
2262   // scanning limit so that the clock is called earlier.
2263 
2264   _words_scanned_limit = _real_words_scanned_limit - 3 * words_scanned_period / 4;
2265   _refs_reached_limit  = _real_refs_reached_limit - 3 * refs_reached_period / 4;
2266 }
2267 
2268 void G1CMTask::move_entries_to_global_stack() {
2269   // Local array where we'll store the entries that will be popped
2270   // from the local queue.
2271   G1TaskQueueEntry buffer[G1CMMarkStack::EntriesPerChunk];
2272 
2273   size_t n = 0;
2274   G1TaskQueueEntry task_entry;
2275   while (n < G1CMMarkStack::EntriesPerChunk && _task_queue->pop_local(task_entry)) {
2276     buffer[n] = task_entry;
2277     ++n;
2278   }
2279   if (n < G1CMMarkStack::EntriesPerChunk) {
2280     buffer[n] = G1TaskQueueEntry();
2281   }
2282 
2283   if (n > 0) {
2284     if (!_cm->mark_stack_push(buffer)) {
2285       set_has_aborted();
2286     }
2287   }
2288 
2289   // This operation was quite expensive, so decrease the limits.
2290   decrease_limits();
2291 }
2292 
2293 bool G1CMTask::get_entries_from_global_stack() {
2294   // Local array where we'll store the entries that will be popped
2295   // from the global stack.
2296   G1TaskQueueEntry buffer[G1CMMarkStack::EntriesPerChunk];
2297 
2298   if (!_cm->mark_stack_pop(buffer)) {
2299     return false;
2300   }
2301 
2302   // We did actually pop at least one entry.
2303   for (size_t i = 0; i < G1CMMarkStack::EntriesPerChunk; ++i) {
2304     G1TaskQueueEntry task_entry = buffer[i];
2305     if (task_entry.is_null()) {
2306       break;
2307     }
2308     assert(task_entry.is_array_slice() || oopDesc::is_oop(task_entry.obj()), "Element " PTR_FORMAT " must be an array slice or oop", p2i(task_entry.obj()));
2309     bool success = _task_queue->push(task_entry);
2310     // We only call this when the local queue is empty or under a
2311     // given target limit. So, we do not expect this push to fail.
2312     assert(success, "invariant");
2313   }
2314 
2315   // This operation was quite expensive, so decrease the limits
2316   decrease_limits();
2317   return true;
2318 }
2319 
2320 void G1CMTask::drain_local_queue(bool partially) {
2321   if (has_aborted()) {
2322     return;
2323   }
2324 
2325   // Decide what the target size is, depending whether we're going to
2326   // drain it partially (so that other tasks can steal if they run out
2327   // of things to do) or totally (at the very end).
2328   size_t target_size;
2329   if (partially) {
2330     target_size = MIN2((size_t)_task_queue->max_elems()/3, (size_t)GCDrainStackTargetSize);
2331   } else {
2332     target_size = 0;
2333   }
2334 
2335   if (_task_queue->size() > target_size) {
2336     G1TaskQueueEntry entry;
2337     bool ret = _task_queue->pop_local(entry);
2338     while (ret) {
2339       scan_task_entry(entry);
2340       if (_task_queue->size() <= target_size || has_aborted()) {
2341         ret = false;
2342       } else {
2343         ret = _task_queue->pop_local(entry);
2344       }
2345     }
2346   }
2347 }
2348 
2349 void G1CMTask::drain_global_stack(bool partially) {
2350   if (has_aborted()) {
2351     return;
2352   }
2353 
2354   // We have a policy to drain the local queue before we attempt to
2355   // drain the global stack.
2356   assert(partially || _task_queue->size() == 0, "invariant");
2357 
2358   // Decide what the target size is, depending whether we're going to
2359   // drain it partially (so that other tasks can steal if they run out
2360   // of things to do) or totally (at the very end).
2361   // Notice that when draining the global mark stack partially, due to the racyness
2362   // of the mark stack size update we might in fact drop below the target. But,
2363   // this is not a problem.
2364   // In case of total draining, we simply process until the global mark stack is
2365   // totally empty, disregarding the size counter.
2366   if (partially) {
2367     size_t const target_size = _cm->partial_mark_stack_size_target();
2368     while (!has_aborted() && _cm->mark_stack_size() > target_size) {
2369       if (get_entries_from_global_stack()) {
2370         drain_local_queue(partially);
2371       }
2372     }
2373   } else {
2374     while (!has_aborted() && get_entries_from_global_stack()) {
2375       drain_local_queue(partially);
2376     }
2377   }
2378 }
2379 
2380 // SATB Queue has several assumptions on whether to call the par or
2381 // non-par versions of the methods. this is why some of the code is
2382 // replicated. We should really get rid of the single-threaded version
2383 // of the code to simplify things.
2384 void G1CMTask::drain_satb_buffers() {
2385   if (has_aborted()) {
2386     return;
2387   }
2388 
2389   // We set this so that the regular clock knows that we're in the
2390   // middle of draining buffers and doesn't set the abort flag when it
2391   // notices that SATB buffers are available for draining. It'd be
2392   // very counter productive if it did that. :-)
2393   _draining_satb_buffers = true;
2394 
2395   G1CMSATBBufferClosure satb_cl(this, _g1h);
2396   SATBMarkQueueSet& satb_mq_set = G1BarrierSet::satb_mark_queue_set();
2397 
2398   // This keeps claiming and applying the closure to completed buffers
2399   // until we run out of buffers or we need to abort.
2400   while (!has_aborted() &&
2401          satb_mq_set.apply_closure_to_completed_buffer(&satb_cl)) {
2402     abort_marking_if_regular_check_fail();
2403   }
2404 
2405   _draining_satb_buffers = false;
2406 
2407   assert(has_aborted() ||
2408          _cm->concurrent() ||
2409          satb_mq_set.completed_buffers_num() == 0, "invariant");
2410 
2411   // again, this was a potentially expensive operation, decrease the
2412   // limits to get the regular clock call early
2413   decrease_limits();
2414 }
2415 
2416 void G1CMTask::clear_mark_stats_cache(uint region_idx) {
2417   _mark_stats_cache.reset(region_idx);
2418 }
2419 
2420 Pair<size_t, size_t> G1CMTask::flush_mark_stats_cache() {
2421   return _mark_stats_cache.evict_all();
2422 }
2423 
2424 void G1CMTask::print_stats() {
2425   log_debug(gc, stats)("Marking Stats, task = %u, calls = %u", _worker_id, _calls);
2426   log_debug(gc, stats)("  Elapsed time = %1.2lfms, Termination time = %1.2lfms",
2427                        _elapsed_time_ms, _termination_time_ms);
2428   log_debug(gc, stats)("  Step Times (cum): num = %d, avg = %1.2lfms, sd = %1.2lfms max = %1.2lfms, total = %1.2lfms",
2429                        _step_times_ms.num(),
2430                        _step_times_ms.avg(),
2431                        _step_times_ms.sd(),
2432                        _step_times_ms.maximum(),
2433                        _step_times_ms.sum());
2434   size_t const hits = _mark_stats_cache.hits();
2435   size_t const misses = _mark_stats_cache.misses();
2436   log_debug(gc, stats)("  Mark Stats Cache: hits " SIZE_FORMAT " misses " SIZE_FORMAT " ratio %.3f",
2437                        hits, misses, percent_of(hits, hits + misses));
2438 }
2439 
2440 bool G1ConcurrentMark::try_stealing(uint worker_id, G1TaskQueueEntry& task_entry) {
2441   return _task_queues->steal(worker_id, task_entry);
2442 }
2443 
2444 /*****************************************************************************
2445 
2446     The do_marking_step(time_target_ms, ...) method is the building
2447     block of the parallel marking framework. It can be called in parallel
2448     with other invocations of do_marking_step() on different tasks
2449     (but only one per task, obviously) and concurrently with the
2450     mutator threads, or during remark, hence it eliminates the need
2451     for two versions of the code. When called during remark, it will
2452     pick up from where the task left off during the concurrent marking
2453     phase. Interestingly, tasks are also claimable during evacuation
2454     pauses too, since do_marking_step() ensures that it aborts before
2455     it needs to yield.
2456 
2457     The data structures that it uses to do marking work are the
2458     following:
2459 
2460       (1) Marking Bitmap. If there are gray objects that appear only
2461       on the bitmap (this happens either when dealing with an overflow
2462       or when the initial marking phase has simply marked the roots
2463       and didn't push them on the stack), then tasks claim heap
2464       regions whose bitmap they then scan to find gray objects. A
2465       global finger indicates where the end of the last claimed region
2466       is. A local finger indicates how far into the region a task has
2467       scanned. The two fingers are used to determine how to gray an
2468       object (i.e. whether simply marking it is OK, as it will be
2469       visited by a task in the future, or whether it needs to be also
2470       pushed on a stack).
2471 
2472       (2) Local Queue. The local queue of the task which is accessed
2473       reasonably efficiently by the task. Other tasks can steal from
2474       it when they run out of work. Throughout the marking phase, a
2475       task attempts to keep its local queue short but not totally
2476       empty, so that entries are available for stealing by other
2477       tasks. Only when there is no more work, a task will totally
2478       drain its local queue.
2479 
2480       (3) Global Mark Stack. This handles local queue overflow. During
2481       marking only sets of entries are moved between it and the local
2482       queues, as access to it requires a mutex and more fine-grain
2483       interaction with it which might cause contention. If it
2484       overflows, then the marking phase should restart and iterate
2485       over the bitmap to identify gray objects. Throughout the marking
2486       phase, tasks attempt to keep the global mark stack at a small
2487       length but not totally empty, so that entries are available for
2488       popping by other tasks. Only when there is no more work, tasks
2489       will totally drain the global mark stack.
2490 
2491       (4) SATB Buffer Queue. This is where completed SATB buffers are
2492       made available. Buffers are regularly removed from this queue
2493       and scanned for roots, so that the queue doesn't get too
2494       long. During remark, all completed buffers are processed, as
2495       well as the filled in parts of any uncompleted buffers.
2496 
2497     The do_marking_step() method tries to abort when the time target
2498     has been reached. There are a few other cases when the
2499     do_marking_step() method also aborts:
2500 
2501       (1) When the marking phase has been aborted (after a Full GC).
2502 
2503       (2) When a global overflow (on the global stack) has been
2504       triggered. Before the task aborts, it will actually sync up with
2505       the other tasks to ensure that all the marking data structures
2506       (local queues, stacks, fingers etc.)  are re-initialized so that
2507       when do_marking_step() completes, the marking phase can
2508       immediately restart.
2509 
2510       (3) When enough completed SATB buffers are available. The
2511       do_marking_step() method only tries to drain SATB buffers right
2512       at the beginning. So, if enough buffers are available, the
2513       marking step aborts and the SATB buffers are processed at
2514       the beginning of the next invocation.
2515 
2516       (4) To yield. when we have to yield then we abort and yield
2517       right at the end of do_marking_step(). This saves us from a lot
2518       of hassle as, by yielding we might allow a Full GC. If this
2519       happens then objects will be compacted underneath our feet, the
2520       heap might shrink, etc. We save checking for this by just
2521       aborting and doing the yield right at the end.
2522 
2523     From the above it follows that the do_marking_step() method should
2524     be called in a loop (or, otherwise, regularly) until it completes.
2525 
2526     If a marking step completes without its has_aborted() flag being
2527     true, it means it has completed the current marking phase (and
2528     also all other marking tasks have done so and have all synced up).
2529 
2530     A method called regular_clock_call() is invoked "regularly" (in
2531     sub ms intervals) throughout marking. It is this clock method that
2532     checks all the abort conditions which were mentioned above and
2533     decides when the task should abort. A work-based scheme is used to
2534     trigger this clock method: when the number of object words the
2535     marking phase has scanned or the number of references the marking
2536     phase has visited reach a given limit. Additional invocations to
2537     the method clock have been planted in a few other strategic places
2538     too. The initial reason for the clock method was to avoid calling
2539     vtime too regularly, as it is quite expensive. So, once it was in
2540     place, it was natural to piggy-back all the other conditions on it
2541     too and not constantly check them throughout the code.
2542 
2543     If do_termination is true then do_marking_step will enter its
2544     termination protocol.
2545 
2546     The value of is_serial must be true when do_marking_step is being
2547     called serially (i.e. by the VMThread) and do_marking_step should
2548     skip any synchronization in the termination and overflow code.
2549     Examples include the serial remark code and the serial reference
2550     processing closures.
2551 
2552     The value of is_serial must be false when do_marking_step is
2553     being called by any of the worker threads in a work gang.
2554     Examples include the concurrent marking code (CMMarkingTask),
2555     the MT remark code, and the MT reference processing closures.
2556 
2557  *****************************************************************************/
2558 
2559 void G1CMTask::do_marking_step(double time_target_ms,
2560                                bool do_termination,
2561                                bool is_serial) {
2562   assert(time_target_ms >= 1.0, "minimum granularity is 1ms");
2563 
2564   _start_time_ms = os::elapsedVTime() * 1000.0;
2565 
2566   // If do_stealing is true then do_marking_step will attempt to
2567   // steal work from the other G1CMTasks. It only makes sense to
2568   // enable stealing when the termination protocol is enabled
2569   // and do_marking_step() is not being called serially.
2570   bool do_stealing = do_termination && !is_serial;
2571 
2572   double diff_prediction_ms = _g1h->policy()->predictor().get_new_prediction(&_marking_step_diffs_ms);
2573   _time_target_ms = time_target_ms - diff_prediction_ms;
2574 
2575   // set up the variables that are used in the work-based scheme to
2576   // call the regular clock method
2577   _words_scanned = 0;
2578   _refs_reached  = 0;
2579   recalculate_limits();
2580 
2581   // clear all flags
2582   clear_has_aborted();
2583   _has_timed_out = false;
2584   _draining_satb_buffers = false;
2585 
2586   ++_calls;
2587 
2588   // Set up the bitmap and oop closures. Anything that uses them is
2589   // eventually called from this method, so it is OK to allocate these
2590   // statically.
2591   G1CMBitMapClosure bitmap_closure(this, _cm);
2592   G1CMOopClosure cm_oop_closure(_g1h, this);
2593   set_cm_oop_closure(&cm_oop_closure);
2594 
2595   if (_cm->has_overflown()) {
2596     // This can happen if the mark stack overflows during a GC pause
2597     // and this task, after a yield point, restarts. We have to abort
2598     // as we need to get into the overflow protocol which happens
2599     // right at the end of this task.
2600     set_has_aborted();
2601   }
2602 
2603   // First drain any available SATB buffers. After this, we will not
2604   // look at SATB buffers before the next invocation of this method.
2605   // If enough completed SATB buffers are queued up, the regular clock
2606   // will abort this task so that it restarts.
2607   drain_satb_buffers();
2608   // ...then partially drain the local queue and the global stack
2609   drain_local_queue(true);
2610   drain_global_stack(true);
2611 
2612   do {
2613     if (!has_aborted() && _curr_region != NULL) {
2614       // This means that we're already holding on to a region.
2615       assert(_finger != NULL, "if region is not NULL, then the finger "
2616              "should not be NULL either");
2617 
2618       // We might have restarted this task after an evacuation pause
2619       // which might have evacuated the region we're holding on to
2620       // underneath our feet. Let's read its limit again to make sure
2621       // that we do not iterate over a region of the heap that
2622       // contains garbage (update_region_limit() will also move
2623       // _finger to the start of the region if it is found empty).
2624       update_region_limit();
2625       // We will start from _finger not from the start of the region,
2626       // as we might be restarting this task after aborting half-way
2627       // through scanning this region. In this case, _finger points to
2628       // the address where we last found a marked object. If this is a
2629       // fresh region, _finger points to start().
2630       MemRegion mr = MemRegion(_finger, _region_limit);
2631 
2632       assert(!_curr_region->is_humongous() || mr.start() == _curr_region->bottom(),
2633              "humongous regions should go around loop once only");
2634 
2635       // Some special cases:
2636       // If the memory region is empty, we can just give up the region.
2637       // If the current region is humongous then we only need to check
2638       // the bitmap for the bit associated with the start of the object,
2639       // scan the object if it's live, and give up the region.
2640       // Otherwise, let's iterate over the bitmap of the part of the region
2641       // that is left.
2642       // If the iteration is successful, give up the region.
2643       if (mr.is_empty()) {
2644         giveup_current_region();
2645         abort_marking_if_regular_check_fail();
2646       } else if (_curr_region->is_humongous() && mr.start() == _curr_region->bottom()) {
2647         if (_next_mark_bitmap->is_marked(mr.start())) {
2648           // The object is marked - apply the closure
2649           bitmap_closure.do_addr(mr.start());
2650         }
2651         // Even if this task aborted while scanning the humongous object
2652         // we can (and should) give up the current region.
2653         giveup_current_region();
2654         abort_marking_if_regular_check_fail();
2655       } else if (_next_mark_bitmap->iterate(&bitmap_closure, mr)) {
2656         giveup_current_region();
2657         abort_marking_if_regular_check_fail();
2658       } else {
2659         assert(has_aborted(), "currently the only way to do so");
2660         // The only way to abort the bitmap iteration is to return
2661         // false from the do_bit() method. However, inside the
2662         // do_bit() method we move the _finger to point to the
2663         // object currently being looked at. So, if we bail out, we
2664         // have definitely set _finger to something non-null.
2665         assert(_finger != NULL, "invariant");
2666 
2667         // Region iteration was actually aborted. So now _finger
2668         // points to the address of the object we last scanned. If we
2669         // leave it there, when we restart this task, we will rescan
2670         // the object. It is easy to avoid this. We move the finger by
2671         // enough to point to the next possible object header.
2672         assert(_finger < _region_limit, "invariant");
2673         HeapWord* const new_finger = _finger + ((oop)_finger)->size();
2674         // Check if bitmap iteration was aborted while scanning the last object
2675         if (new_finger >= _region_limit) {
2676           giveup_current_region();
2677         } else {
2678           move_finger_to(new_finger);
2679         }
2680       }
2681     }
2682     // At this point we have either completed iterating over the
2683     // region we were holding on to, or we have aborted.
2684 
2685     // We then partially drain the local queue and the global stack.
2686     // (Do we really need this?)
2687     drain_local_queue(true);
2688     drain_global_stack(true);
2689 
2690     // Read the note on the claim_region() method on why it might
2691     // return NULL with potentially more regions available for
2692     // claiming and why we have to check out_of_regions() to determine
2693     // whether we're done or not.
2694     while (!has_aborted() && _curr_region == NULL && !_cm->out_of_regions()) {
2695       // We are going to try to claim a new region. We should have
2696       // given up on the previous one.
2697       // Separated the asserts so that we know which one fires.
2698       assert(_curr_region  == NULL, "invariant");
2699       assert(_finger       == NULL, "invariant");
2700       assert(_region_limit == NULL, "invariant");
2701       HeapRegion* claimed_region = _cm->claim_region(_worker_id);
2702       if (claimed_region != NULL) {
2703         // Yes, we managed to claim one
2704         setup_for_region(claimed_region);
2705         assert(_curr_region == claimed_region, "invariant");
2706       }
2707       // It is important to call the regular clock here. It might take
2708       // a while to claim a region if, for example, we hit a large
2709       // block of empty regions. So we need to call the regular clock
2710       // method once round the loop to make sure it's called
2711       // frequently enough.
2712       abort_marking_if_regular_check_fail();
2713     }
2714 
2715     if (!has_aborted() && _curr_region == NULL) {
2716       assert(_cm->out_of_regions(),
2717              "at this point we should be out of regions");
2718     }
2719   } while ( _curr_region != NULL && !has_aborted());
2720 
2721   if (!has_aborted()) {
2722     // We cannot check whether the global stack is empty, since other
2723     // tasks might be pushing objects to it concurrently.
2724     assert(_cm->out_of_regions(),
2725            "at this point we should be out of regions");
2726     // Try to reduce the number of available SATB buffers so that
2727     // remark has less work to do.
2728     drain_satb_buffers();
2729   }
2730 
2731   // Since we've done everything else, we can now totally drain the
2732   // local queue and global stack.
2733   drain_local_queue(false);
2734   drain_global_stack(false);
2735 
2736   // Attempt at work stealing from other task's queues.
2737   if (do_stealing && !has_aborted()) {
2738     // We have not aborted. This means that we have finished all that
2739     // we could. Let's try to do some stealing...
2740 
2741     // We cannot check whether the global stack is empty, since other
2742     // tasks might be pushing objects to it concurrently.
2743     assert(_cm->out_of_regions() && _task_queue->size() == 0,
2744            "only way to reach here");
2745     while (!has_aborted()) {
2746       G1TaskQueueEntry entry;
2747       if (_cm->try_stealing(_worker_id, entry)) {
2748         scan_task_entry(entry);
2749 
2750         // And since we're towards the end, let's totally drain the
2751         // local queue and global stack.
2752         drain_local_queue(false);
2753         drain_global_stack(false);
2754       } else {
2755         break;
2756       }
2757     }
2758   }
2759 
2760   // We still haven't aborted. Now, let's try to get into the
2761   // termination protocol.
2762   if (do_termination && !has_aborted()) {
2763     // We cannot check whether the global stack is empty, since other
2764     // tasks might be concurrently pushing objects on it.
2765     // Separated the asserts so that we know which one fires.
2766     assert(_cm->out_of_regions(), "only way to reach here");
2767     assert(_task_queue->size() == 0, "only way to reach here");
2768     _termination_start_time_ms = os::elapsedVTime() * 1000.0;
2769 
2770     // The G1CMTask class also extends the TerminatorTerminator class,
2771     // hence its should_exit_termination() method will also decide
2772     // whether to exit the termination protocol or not.
2773     bool finished = (is_serial ||
2774                      _cm->terminator()->offer_termination(this));
2775     double termination_end_time_ms = os::elapsedVTime() * 1000.0;
2776     _termination_time_ms +=
2777       termination_end_time_ms - _termination_start_time_ms;
2778 
2779     if (finished) {
2780       // We're all done.
2781 
2782       // We can now guarantee that the global stack is empty, since
2783       // all other tasks have finished. We separated the guarantees so
2784       // that, if a condition is false, we can immediately find out
2785       // which one.
2786       guarantee(_cm->out_of_regions(), "only way to reach here");
2787       guarantee(_cm->mark_stack_empty(), "only way to reach here");
2788       guarantee(_task_queue->size() == 0, "only way to reach here");
2789       guarantee(!_cm->has_overflown(), "only way to reach here");
2790       guarantee(!has_aborted(), "should never happen if termination has completed");
2791     } else {
2792       // Apparently there's more work to do. Let's abort this task. It
2793       // will restart it and we can hopefully find more things to do.
2794       set_has_aborted();
2795     }
2796   }
2797 
2798   // Mainly for debugging purposes to make sure that a pointer to the
2799   // closure which was statically allocated in this frame doesn't
2800   // escape it by accident.
2801   set_cm_oop_closure(NULL);
2802   double end_time_ms = os::elapsedVTime() * 1000.0;
2803   double elapsed_time_ms = end_time_ms - _start_time_ms;
2804   // Update the step history.
2805   _step_times_ms.add(elapsed_time_ms);
2806 
2807   if (has_aborted()) {
2808     // The task was aborted for some reason.
2809     if (_has_timed_out) {
2810       double diff_ms = elapsed_time_ms - _time_target_ms;
2811       // Keep statistics of how well we did with respect to hitting
2812       // our target only if we actually timed out (if we aborted for
2813       // other reasons, then the results might get skewed).
2814       _marking_step_diffs_ms.add(diff_ms);
2815     }
2816 
2817     if (_cm->has_overflown()) {
2818       // This is the interesting one. We aborted because a global
2819       // overflow was raised. This means we have to restart the
2820       // marking phase and start iterating over regions. However, in
2821       // order to do this we have to make sure that all tasks stop
2822       // what they are doing and re-initialize in a safe manner. We
2823       // will achieve this with the use of two barrier sync points.
2824 
2825       if (!is_serial) {
2826         // We only need to enter the sync barrier if being called
2827         // from a parallel context
2828         _cm->enter_first_sync_barrier(_worker_id);
2829 
2830         // When we exit this sync barrier we know that all tasks have
2831         // stopped doing marking work. So, it's now safe to
2832         // re-initialize our data structures.
2833       }
2834 
2835       clear_region_fields();
2836       flush_mark_stats_cache();
2837 
2838       if (!is_serial) {
2839         // If we're executing the concurrent phase of marking, reset the marking
2840         // state; otherwise the marking state is reset after reference processing,
2841         // during the remark pause.
2842         // If we reset here as a result of an overflow during the remark we will
2843         // see assertion failures from any subsequent set_concurrency_and_phase()
2844         // calls.
2845         if (_cm->concurrent() && _worker_id == 0) {
2846           // Worker 0 is responsible for clearing the global data structures because
2847           // of an overflow. During STW we should not clear the overflow flag (in
2848           // G1ConcurrentMark::reset_marking_state()) since we rely on it being true when we exit
2849           // method to abort the pause and restart concurrent marking.
2850           _cm->reset_marking_for_restart();
2851 
2852           log_info(gc, marking)("Concurrent Mark reset for overflow");
2853         }
2854 
2855         // ...and enter the second barrier.
2856         _cm->enter_second_sync_barrier(_worker_id);
2857       }
2858       // At this point, if we're during the concurrent phase of
2859       // marking, everything has been re-initialized and we're
2860       // ready to restart.
2861     }
2862   }
2863 }
2864 
2865 G1CMTask::G1CMTask(uint worker_id,
2866                    G1ConcurrentMark* cm,
2867                    G1CMTaskQueue* task_queue,
2868                    G1RegionMarkStats* mark_stats,
2869                    uint max_regions) :
2870   _objArray_processor(this),
2871   _worker_id(worker_id),
2872   _g1h(G1CollectedHeap::heap()),
2873   _cm(cm),
2874   _next_mark_bitmap(NULL),
2875   _task_queue(task_queue),
2876   _mark_stats_cache(mark_stats, max_regions, RegionMarkStatsCacheSize),
2877   _calls(0),
2878   _time_target_ms(0.0),
2879   _start_time_ms(0.0),
2880   _cm_oop_closure(NULL),
2881   _curr_region(NULL),
2882   _finger(NULL),
2883   _region_limit(NULL),
2884   _words_scanned(0),
2885   _words_scanned_limit(0),
2886   _real_words_scanned_limit(0),
2887   _refs_reached(0),
2888   _refs_reached_limit(0),
2889   _real_refs_reached_limit(0),
2890   _has_aborted(false),
2891   _has_timed_out(false),
2892   _draining_satb_buffers(false),
2893   _step_times_ms(),
2894   _elapsed_time_ms(0.0),
2895   _termination_time_ms(0.0),
2896   _termination_start_time_ms(0.0),
2897   _marking_step_diffs_ms()
2898 {
2899   guarantee(task_queue != NULL, "invariant");
2900 
2901   _marking_step_diffs_ms.add(0.5);
2902 }
2903 
2904 // These are formatting macros that are used below to ensure
2905 // consistent formatting. The *_H_* versions are used to format the
2906 // header for a particular value and they should be kept consistent
2907 // with the corresponding macro. Also note that most of the macros add
2908 // the necessary white space (as a prefix) which makes them a bit
2909 // easier to compose.
2910 
2911 // All the output lines are prefixed with this string to be able to
2912 // identify them easily in a large log file.
2913 #define G1PPRL_LINE_PREFIX            "###"
2914 
2915 #define G1PPRL_ADDR_BASE_FORMAT    " " PTR_FORMAT "-" PTR_FORMAT
2916 #ifdef _LP64
2917 #define G1PPRL_ADDR_BASE_H_FORMAT  " %37s"
2918 #else // _LP64
2919 #define G1PPRL_ADDR_BASE_H_FORMAT  " %21s"
2920 #endif // _LP64
2921 
2922 // For per-region info
2923 #define G1PPRL_TYPE_FORMAT            "   %-4s"
2924 #define G1PPRL_TYPE_H_FORMAT          "   %4s"
2925 #define G1PPRL_STATE_FORMAT           "   %-5s"
2926 #define G1PPRL_STATE_H_FORMAT         "   %5s"
2927 #define G1PPRL_BYTE_FORMAT            "  " SIZE_FORMAT_W(9)
2928 #define G1PPRL_BYTE_H_FORMAT          "  %9s"
2929 #define G1PPRL_DOUBLE_FORMAT          "  %14.1f"
2930 #define G1PPRL_DOUBLE_H_FORMAT        "  %14s"
2931 
2932 // For summary info
2933 #define G1PPRL_SUM_ADDR_FORMAT(tag)    "  " tag ":" G1PPRL_ADDR_BASE_FORMAT
2934 #define G1PPRL_SUM_BYTE_FORMAT(tag)    "  " tag ": " SIZE_FORMAT
2935 #define G1PPRL_SUM_MB_FORMAT(tag)      "  " tag ": %1.2f MB"
2936 #define G1PPRL_SUM_MB_PERC_FORMAT(tag) G1PPRL_SUM_MB_FORMAT(tag) " / %1.2f %%"
2937 
2938 G1PrintRegionLivenessInfoClosure::G1PrintRegionLivenessInfoClosure(const char* phase_name) :
2939   _total_used_bytes(0), _total_capacity_bytes(0),
2940   _total_prev_live_bytes(0), _total_next_live_bytes(0),
2941   _total_remset_bytes(0), _total_strong_code_roots_bytes(0)
2942 {
2943   if (!log_is_enabled(Trace, gc, liveness)) {
2944     return;
2945   }
2946 
2947   G1CollectedHeap* g1h = G1CollectedHeap::heap();
2948   MemRegion g1_reserved = g1h->g1_reserved();
2949   double now = os::elapsedTime();
2950 
2951   // Print the header of the output.
2952   log_trace(gc, liveness)(G1PPRL_LINE_PREFIX" PHASE %s @ %1.3f", phase_name, now);
2953   log_trace(gc, liveness)(G1PPRL_LINE_PREFIX" HEAP"
2954                           G1PPRL_SUM_ADDR_FORMAT("reserved")
2955                           G1PPRL_SUM_BYTE_FORMAT("region-size"),
2956                           p2i(g1_reserved.start()), p2i(g1_reserved.end()),
2957                           HeapRegion::GrainBytes);
2958   log_trace(gc, liveness)(G1PPRL_LINE_PREFIX);
2959   log_trace(gc, liveness)(G1PPRL_LINE_PREFIX
2960                           G1PPRL_TYPE_H_FORMAT
2961                           G1PPRL_ADDR_BASE_H_FORMAT
2962                           G1PPRL_BYTE_H_FORMAT
2963                           G1PPRL_BYTE_H_FORMAT
2964                           G1PPRL_BYTE_H_FORMAT
2965                           G1PPRL_DOUBLE_H_FORMAT
2966                           G1PPRL_BYTE_H_FORMAT
2967                           G1PPRL_STATE_H_FORMAT
2968                           G1PPRL_BYTE_H_FORMAT,
2969                           "type", "address-range",
2970                           "used", "prev-live", "next-live", "gc-eff",
2971                           "remset", "state", "code-roots");
2972   log_trace(gc, liveness)(G1PPRL_LINE_PREFIX
2973                           G1PPRL_TYPE_H_FORMAT
2974                           G1PPRL_ADDR_BASE_H_FORMAT
2975                           G1PPRL_BYTE_H_FORMAT
2976                           G1PPRL_BYTE_H_FORMAT
2977                           G1PPRL_BYTE_H_FORMAT
2978                           G1PPRL_DOUBLE_H_FORMAT
2979                           G1PPRL_BYTE_H_FORMAT
2980                           G1PPRL_STATE_H_FORMAT
2981                           G1PPRL_BYTE_H_FORMAT,
2982                           "", "",
2983                           "(bytes)", "(bytes)", "(bytes)", "(bytes/ms)",
2984                           "(bytes)", "", "(bytes)");
2985 }
2986 
2987 bool G1PrintRegionLivenessInfoClosure::do_heap_region(HeapRegion* r) {
2988   if (!log_is_enabled(Trace, gc, liveness)) {
2989     return false;
2990   }
2991 
2992   const char* type       = r->get_type_str();
2993   HeapWord* bottom       = r->bottom();
2994   HeapWord* end          = r->end();
2995   size_t capacity_bytes  = r->capacity();
2996   size_t used_bytes      = r->used();
2997   size_t prev_live_bytes = r->live_bytes();
2998   size_t next_live_bytes = r->next_live_bytes();
2999   double gc_eff          = r->gc_efficiency();
3000   size_t remset_bytes    = r->rem_set()->mem_size();
3001   size_t strong_code_roots_bytes = r->rem_set()->strong_code_roots_mem_size();
3002   const char* remset_type = r->rem_set()->get_short_state_str();
3003 
3004   _total_used_bytes      += used_bytes;
3005   _total_capacity_bytes  += capacity_bytes;
3006   _total_prev_live_bytes += prev_live_bytes;
3007   _total_next_live_bytes += next_live_bytes;
3008   _total_remset_bytes    += remset_bytes;
3009   _total_strong_code_roots_bytes += strong_code_roots_bytes;
3010 
3011   // Print a line for this particular region.
3012   log_trace(gc, liveness)(G1PPRL_LINE_PREFIX
3013                           G1PPRL_TYPE_FORMAT
3014                           G1PPRL_ADDR_BASE_FORMAT
3015                           G1PPRL_BYTE_FORMAT
3016                           G1PPRL_BYTE_FORMAT
3017                           G1PPRL_BYTE_FORMAT
3018                           G1PPRL_DOUBLE_FORMAT
3019                           G1PPRL_BYTE_FORMAT
3020                           G1PPRL_STATE_FORMAT
3021                           G1PPRL_BYTE_FORMAT,
3022                           type, p2i(bottom), p2i(end),
3023                           used_bytes, prev_live_bytes, next_live_bytes, gc_eff,
3024                           remset_bytes, remset_type, strong_code_roots_bytes);
3025 
3026   return false;
3027 }
3028 
3029 G1PrintRegionLivenessInfoClosure::~G1PrintRegionLivenessInfoClosure() {
3030   if (!log_is_enabled(Trace, gc, liveness)) {
3031     return;
3032   }
3033 
3034   // add static memory usages to remembered set sizes
3035   _total_remset_bytes += HeapRegionRemSet::fl_mem_size() + HeapRegionRemSet::static_mem_size();
3036   // Print the footer of the output.
3037   log_trace(gc, liveness)(G1PPRL_LINE_PREFIX);
3038   log_trace(gc, liveness)(G1PPRL_LINE_PREFIX
3039                          " SUMMARY"
3040                          G1PPRL_SUM_MB_FORMAT("capacity")
3041                          G1PPRL_SUM_MB_PERC_FORMAT("used")
3042                          G1PPRL_SUM_MB_PERC_FORMAT("prev-live")
3043                          G1PPRL_SUM_MB_PERC_FORMAT("next-live")
3044                          G1PPRL_SUM_MB_FORMAT("remset")
3045                          G1PPRL_SUM_MB_FORMAT("code-roots"),
3046                          bytes_to_mb(_total_capacity_bytes),
3047                          bytes_to_mb(_total_used_bytes),
3048                          percent_of(_total_used_bytes, _total_capacity_bytes),
3049                          bytes_to_mb(_total_prev_live_bytes),
3050                          percent_of(_total_prev_live_bytes, _total_capacity_bytes),
3051                          bytes_to_mb(_total_next_live_bytes),
3052                          percent_of(_total_next_live_bytes, _total_capacity_bytes),
3053                          bytes_to_mb(_total_remset_bytes),
3054                          bytes_to_mb(_total_strong_code_roots_bytes));
3055 }