1 /*
   2  * Copyright (c) 2001, 2013, 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/symbolTable.hpp"
  27 #include "gc_implementation/g1/concurrentMark.inline.hpp"
  28 #include "gc_implementation/g1/concurrentMarkThread.inline.hpp"
  29 #include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
  30 #include "gc_implementation/g1/g1CollectorPolicy.hpp"
  31 #include "gc_implementation/g1/g1ErgoVerbose.hpp"
  32 #include "gc_implementation/g1/g1Log.hpp"
  33 #include "gc_implementation/g1/g1OopClosures.inline.hpp"
  34 #include "gc_implementation/g1/g1RemSet.hpp"
  35 #include "gc_implementation/g1/heapRegion.inline.hpp"
  36 #include "gc_implementation/g1/heapRegionRemSet.hpp"
  37 #include "gc_implementation/g1/heapRegionSeq.inline.hpp"
  38 #include "gc_implementation/shared/vmGCOperations.hpp"
  39 #include "memory/genOopClosures.inline.hpp"
  40 #include "memory/referencePolicy.hpp"
  41 #include "memory/resourceArea.hpp"
  42 #include "oops/oop.inline.hpp"
  43 #include "runtime/handles.inline.hpp"
  44 #include "runtime/java.hpp"
  45 #include "services/memTracker.hpp"
  46 
  47 // Concurrent marking bit map wrapper
  48 
  49 CMBitMapRO::CMBitMapRO(int shifter) :
  50   _bm(),
  51   _shifter(shifter) {
  52   _bmStartWord = 0;
  53   _bmWordSize = 0;
  54 }
  55 
  56 HeapWord* CMBitMapRO::getNextMarkedWordAddress(HeapWord* addr,
  57                                                HeapWord* limit) const {
  58   // First we must round addr *up* to a possible object boundary.
  59   addr = (HeapWord*)align_size_up((intptr_t)addr,
  60                                   HeapWordSize << _shifter);
  61   size_t addrOffset = heapWordToOffset(addr);
  62   if (limit == NULL) {
  63     limit = _bmStartWord + _bmWordSize;
  64   }
  65   size_t limitOffset = heapWordToOffset(limit);
  66   size_t nextOffset = _bm.get_next_one_offset(addrOffset, limitOffset);
  67   HeapWord* nextAddr = offsetToHeapWord(nextOffset);
  68   assert(nextAddr >= addr, "get_next_one postcondition");
  69   assert(nextAddr == limit || isMarked(nextAddr),
  70          "get_next_one postcondition");
  71   return nextAddr;
  72 }
  73 
  74 HeapWord* CMBitMapRO::getNextUnmarkedWordAddress(HeapWord* addr,
  75                                                  HeapWord* limit) const {
  76   size_t addrOffset = heapWordToOffset(addr);
  77   if (limit == NULL) {
  78     limit = _bmStartWord + _bmWordSize;
  79   }
  80   size_t limitOffset = heapWordToOffset(limit);
  81   size_t nextOffset = _bm.get_next_zero_offset(addrOffset, limitOffset);
  82   HeapWord* nextAddr = offsetToHeapWord(nextOffset);
  83   assert(nextAddr >= addr, "get_next_one postcondition");
  84   assert(nextAddr == limit || !isMarked(nextAddr),
  85          "get_next_one postcondition");
  86   return nextAddr;
  87 }
  88 
  89 int CMBitMapRO::heapWordDiffToOffsetDiff(size_t diff) const {
  90   assert((diff & ((1 << _shifter) - 1)) == 0, "argument check");
  91   return (int) (diff >> _shifter);
  92 }
  93 
  94 #ifndef PRODUCT
  95 bool CMBitMapRO::covers(ReservedSpace heap_rs) const {
  96   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
  97   assert(((size_t)_bm.size() * ((size_t)1 << _shifter)) == _bmWordSize,
  98          "size inconsistency");
  99   return _bmStartWord == (HeapWord*)(heap_rs.base()) &&
 100          _bmWordSize  == heap_rs.size()>>LogHeapWordSize;
 101 }
 102 #endif
 103 
 104 bool CMBitMap::allocate(ReservedSpace heap_rs) {
 105   _bmStartWord = (HeapWord*)(heap_rs.base());
 106   _bmWordSize  = heap_rs.size()/HeapWordSize;    // heap_rs.size() is in bytes
 107   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
 108                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
 109   if (!brs.is_reserved()) {
 110     warning("ConcurrentMark marking bit map allocation failure");
 111     return false;
 112   }
 113   MemTracker::record_virtual_memory_type((address)brs.base(), mtGC);
 114   // For now we'll just commit all of the bit map up front.
 115   // Later on we'll try to be more parsimonious with swap.
 116   if (!_virtual_space.initialize(brs, brs.size())) {
 117     warning("ConcurrentMark marking bit map backing store failure");
 118     return false;
 119   }
 120   assert(_virtual_space.committed_size() == brs.size(),
 121          "didn't reserve backing store for all of concurrent marking bit map?");
 122   _bm.set_map((uintptr_t*)_virtual_space.low());
 123   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
 124          _bmWordSize, "inconsistency in bit map sizing");
 125   _bm.set_size(_bmWordSize >> _shifter);
 126   return true;
 127 }
 128 
 129 void CMBitMap::clearAll() {
 130   _bm.clear();
 131   return;
 132 }
 133 
 134 void CMBitMap::markRange(MemRegion mr) {
 135   mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
 136   assert(!mr.is_empty(), "unexpected empty region");
 137   assert((offsetToHeapWord(heapWordToOffset(mr.end())) ==
 138           ((HeapWord *) mr.end())),
 139          "markRange memory region end is not card aligned");
 140   // convert address range into offset range
 141   _bm.at_put_range(heapWordToOffset(mr.start()),
 142                    heapWordToOffset(mr.end()), true);
 143 }
 144 
 145 void CMBitMap::clearRange(MemRegion mr) {
 146   mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
 147   assert(!mr.is_empty(), "unexpected empty region");
 148   // convert address range into offset range
 149   _bm.at_put_range(heapWordToOffset(mr.start()),
 150                    heapWordToOffset(mr.end()), false);
 151 }
 152 
 153 MemRegion CMBitMap::getAndClearMarkedRegion(HeapWord* addr,
 154                                             HeapWord* end_addr) {
 155   HeapWord* start = getNextMarkedWordAddress(addr);
 156   start = MIN2(start, end_addr);
 157   HeapWord* end   = getNextUnmarkedWordAddress(start);
 158   end = MIN2(end, end_addr);
 159   assert(start <= end, "Consistency check");
 160   MemRegion mr(start, end);
 161   if (!mr.is_empty()) {
 162     clearRange(mr);
 163   }
 164   return mr;
 165 }
 166 
 167 CMMarkStack::CMMarkStack(ConcurrentMark* cm) :
 168   _base(NULL), _cm(cm)
 169 #ifdef ASSERT
 170   , _drain_in_progress(false)
 171   , _drain_in_progress_yields(false)
 172 #endif
 173 {}
 174 
 175 bool CMMarkStack::allocate(size_t capacity) {
 176   // allocate a stack of the requisite depth
 177   ReservedSpace rs(ReservedSpace::allocation_align_size_up(capacity * sizeof(oop)));
 178   if (!rs.is_reserved()) {
 179     warning("ConcurrentMark MarkStack allocation failure");
 180     return false;
 181   }
 182   MemTracker::record_virtual_memory_type((address)rs.base(), mtGC);
 183   if (!_virtual_space.initialize(rs, rs.size())) {
 184     warning("ConcurrentMark MarkStack backing store failure");
 185     // Release the virtual memory reserved for the marking stack
 186     rs.release();
 187     return false;
 188   }
 189   assert(_virtual_space.committed_size() == rs.size(),
 190          "Didn't reserve backing store for all of ConcurrentMark stack?");
 191   _base = (oop*) _virtual_space.low();
 192   setEmpty();
 193   _capacity = (jint) capacity;
 194   _saved_index = -1;
 195   _should_expand = false;
 196   NOT_PRODUCT(_max_depth = 0);
 197   return true;
 198 }
 199 
 200 void CMMarkStack::expand() {
 201   // Called, during remark, if we've overflown the marking stack during marking.
 202   assert(isEmpty(), "stack should been emptied while handling overflow");
 203   assert(_capacity <= (jint) MarkStackSizeMax, "stack bigger than permitted");
 204   // Clear expansion flag
 205   _should_expand = false;
 206   if (_capacity == (jint) MarkStackSizeMax) {
 207     if (PrintGCDetails && Verbose) {
 208       gclog_or_tty->print_cr(" (benign) Can't expand marking stack capacity, at max size limit");
 209     }
 210     return;
 211   }
 212   // Double capacity if possible
 213   jint new_capacity = MIN2(_capacity*2, (jint) MarkStackSizeMax);
 214   // Do not give up existing stack until we have managed to
 215   // get the double capacity that we desired.
 216   ReservedSpace rs(ReservedSpace::allocation_align_size_up(new_capacity *
 217                                                            sizeof(oop)));
 218   if (rs.is_reserved()) {
 219     // Release the backing store associated with old stack
 220     _virtual_space.release();
 221     // Reinitialize virtual space for new stack
 222     if (!_virtual_space.initialize(rs, rs.size())) {
 223       fatal("Not enough swap for expanded marking stack capacity");
 224     }
 225     _base = (oop*)(_virtual_space.low());
 226     _index = 0;
 227     _capacity = new_capacity;
 228   } else {
 229     if (PrintGCDetails && Verbose) {
 230       // Failed to double capacity, continue;
 231       gclog_or_tty->print(" (benign) Failed to expand marking stack capacity from "
 232                           SIZE_FORMAT"K to " SIZE_FORMAT"K",
 233                           _capacity / K, new_capacity / K);
 234     }
 235   }
 236 }
 237 
 238 void CMMarkStack::set_should_expand() {
 239   // If we're resetting the marking state because of an
 240   // marking stack overflow, record that we should, if
 241   // possible, expand the stack.
 242   _should_expand = _cm->has_overflown();
 243 }
 244 
 245 CMMarkStack::~CMMarkStack() {
 246   if (_base != NULL) {
 247     _base = NULL;
 248     _virtual_space.release();
 249   }
 250 }
 251 
 252 void CMMarkStack::par_push(oop ptr) {
 253   while (true) {
 254     if (isFull()) {
 255       _overflow = true;
 256       return;
 257     }
 258     // Otherwise...
 259     jint index = _index;
 260     jint next_index = index+1;
 261     jint res = Atomic::cmpxchg(next_index, &_index, index);
 262     if (res == index) {
 263       _base[index] = ptr;
 264       // Note that we don't maintain this atomically.  We could, but it
 265       // doesn't seem necessary.
 266       NOT_PRODUCT(_max_depth = MAX2(_max_depth, next_index));
 267       return;
 268     }
 269     // Otherwise, we need to try again.
 270   }
 271 }
 272 
 273 void CMMarkStack::par_adjoin_arr(oop* ptr_arr, int n) {
 274   while (true) {
 275     if (isFull()) {
 276       _overflow = true;
 277       return;
 278     }
 279     // Otherwise...
 280     jint index = _index;
 281     jint next_index = index + n;
 282     if (next_index > _capacity) {
 283       _overflow = true;
 284       return;
 285     }
 286     jint res = Atomic::cmpxchg(next_index, &_index, index);
 287     if (res == index) {
 288       for (int i = 0; i < n; i++) {
 289         int  ind = index + i;
 290         assert(ind < _capacity, "By overflow test above.");
 291         _base[ind] = ptr_arr[i];
 292       }
 293       NOT_PRODUCT(_max_depth = MAX2(_max_depth, next_index));
 294       return;
 295     }
 296     // Otherwise, we need to try again.
 297   }
 298 }
 299 
 300 void CMMarkStack::par_push_arr(oop* ptr_arr, int n) {
 301   MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
 302   jint start = _index;
 303   jint next_index = start + n;
 304   if (next_index > _capacity) {
 305     _overflow = true;
 306     return;
 307   }
 308   // Otherwise.
 309   _index = next_index;
 310   for (int i = 0; i < n; i++) {
 311     int ind = start + i;
 312     assert(ind < _capacity, "By overflow test above.");
 313     _base[ind] = ptr_arr[i];
 314   }
 315   NOT_PRODUCT(_max_depth = MAX2(_max_depth, next_index));
 316 }
 317 
 318 bool CMMarkStack::par_pop_arr(oop* ptr_arr, int max, int* n) {
 319   MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
 320   jint index = _index;
 321   if (index == 0) {
 322     *n = 0;
 323     return false;
 324   } else {
 325     int k = MIN2(max, index);
 326     jint  new_ind = index - k;
 327     for (int j = 0; j < k; j++) {
 328       ptr_arr[j] = _base[new_ind + j];
 329     }
 330     _index = new_ind;
 331     *n = k;
 332     return true;
 333   }
 334 }
 335 
 336 template<class OopClosureClass>
 337 bool CMMarkStack::drain(OopClosureClass* cl, CMBitMap* bm, bool yield_after) {
 338   assert(!_drain_in_progress || !_drain_in_progress_yields || yield_after
 339          || SafepointSynchronize::is_at_safepoint(),
 340          "Drain recursion must be yield-safe.");
 341   bool res = true;
 342   debug_only(_drain_in_progress = true);
 343   debug_only(_drain_in_progress_yields = yield_after);
 344   while (!isEmpty()) {
 345     oop newOop = pop();
 346     assert(G1CollectedHeap::heap()->is_in_reserved(newOop), "Bad pop");
 347     assert(newOop->is_oop(), "Expected an oop");
 348     assert(bm == NULL || bm->isMarked((HeapWord*)newOop),
 349            "only grey objects on this stack");
 350     newOop->oop_iterate(cl);
 351     if (yield_after && _cm->do_yield_check()) {
 352       res = false;
 353       break;
 354     }
 355   }
 356   debug_only(_drain_in_progress = false);
 357   return res;
 358 }
 359 
 360 void CMMarkStack::note_start_of_gc() {
 361   assert(_saved_index == -1,
 362          "note_start_of_gc()/end_of_gc() bracketed incorrectly");
 363   _saved_index = _index;
 364 }
 365 
 366 void CMMarkStack::note_end_of_gc() {
 367   // This is intentionally a guarantee, instead of an assert. If we
 368   // accidentally add something to the mark stack during GC, it
 369   // will be a correctness issue so it's better if we crash. we'll
 370   // only check this once per GC anyway, so it won't be a performance
 371   // issue in any way.
 372   guarantee(_saved_index == _index,
 373             err_msg("saved index: %d index: %d", _saved_index, _index));
 374   _saved_index = -1;
 375 }
 376 
 377 void CMMarkStack::oops_do(OopClosure* f) {
 378   assert(_saved_index == _index,
 379          err_msg("saved index: %d index: %d", _saved_index, _index));
 380   for (int i = 0; i < _index; i += 1) {
 381     f->do_oop(&_base[i]);
 382   }
 383 }
 384 
 385 bool ConcurrentMark::not_yet_marked(oop obj) const {
 386   return _g1h->is_obj_ill(obj);
 387 }
 388 
 389 CMRootRegions::CMRootRegions() :
 390   _young_list(NULL), _cm(NULL), _scan_in_progress(false),
 391   _should_abort(false),  _next_survivor(NULL) { }
 392 
 393 void CMRootRegions::init(G1CollectedHeap* g1h, ConcurrentMark* cm) {
 394   _young_list = g1h->young_list();
 395   _cm = cm;
 396 }
 397 
 398 void CMRootRegions::prepare_for_scan() {
 399   assert(!scan_in_progress(), "pre-condition");
 400 
 401   // Currently, only survivors can be root regions.
 402   assert(_next_survivor == NULL, "pre-condition");
 403   _next_survivor = _young_list->first_survivor_region();
 404   _scan_in_progress = (_next_survivor != NULL);
 405   _should_abort = false;
 406 }
 407 
 408 HeapRegion* CMRootRegions::claim_next() {
 409   if (_should_abort) {
 410     // If someone has set the should_abort flag, we return NULL to
 411     // force the caller to bail out of their loop.
 412     return NULL;
 413   }
 414 
 415   // Currently, only survivors can be root regions.
 416   HeapRegion* res = _next_survivor;
 417   if (res != NULL) {
 418     MutexLockerEx x(RootRegionScan_lock, Mutex::_no_safepoint_check_flag);
 419     // Read it again in case it changed while we were waiting for the lock.
 420     res = _next_survivor;
 421     if (res != NULL) {
 422       if (res == _young_list->last_survivor_region()) {
 423         // We just claimed the last survivor so store NULL to indicate
 424         // that we're done.
 425         _next_survivor = NULL;
 426       } else {
 427         _next_survivor = res->get_next_young_region();
 428       }
 429     } else {
 430       // Someone else claimed the last survivor while we were trying
 431       // to take the lock so nothing else to do.
 432     }
 433   }
 434   assert(res == NULL || res->is_survivor(), "post-condition");
 435 
 436   return res;
 437 }
 438 
 439 void CMRootRegions::scan_finished() {
 440   assert(scan_in_progress(), "pre-condition");
 441 
 442   // Currently, only survivors can be root regions.
 443   if (!_should_abort) {
 444     assert(_next_survivor == NULL, "we should have claimed all survivors");
 445   }
 446   _next_survivor = NULL;
 447 
 448   {
 449     MutexLockerEx x(RootRegionScan_lock, Mutex::_no_safepoint_check_flag);
 450     _scan_in_progress = false;
 451     RootRegionScan_lock->notify_all();
 452   }
 453 }
 454 
 455 bool CMRootRegions::wait_until_scan_finished() {
 456   if (!scan_in_progress()) return false;
 457 
 458   {
 459     MutexLockerEx x(RootRegionScan_lock, Mutex::_no_safepoint_check_flag);
 460     while (scan_in_progress()) {
 461       RootRegionScan_lock->wait(Mutex::_no_safepoint_check_flag);
 462     }
 463   }
 464   return true;
 465 }
 466 
 467 #ifdef _MSC_VER // the use of 'this' below gets a warning, make it go away
 468 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list
 469 #endif // _MSC_VER
 470 
 471 uint ConcurrentMark::scale_parallel_threads(uint n_par_threads) {
 472   return MAX2((n_par_threads + 2) / 4, 1U);
 473 }
 474 
 475 ConcurrentMark::ConcurrentMark(G1CollectedHeap* g1h, ReservedSpace heap_rs) :
 476   _g1h(g1h),
 477   _markBitMap1(MinObjAlignment - 1),
 478   _markBitMap2(MinObjAlignment - 1),
 479 
 480   _parallel_marking_threads(0),
 481   _max_parallel_marking_threads(0),
 482   _sleep_factor(0.0),
 483   _marking_task_overhead(1.0),
 484   _cleanup_sleep_factor(0.0),
 485   _cleanup_task_overhead(1.0),
 486   _cleanup_list("Cleanup List"),
 487   _region_bm((BitMap::idx_t)(g1h->max_regions()), false /* in_resource_area*/),
 488   _card_bm((heap_rs.size() + CardTableModRefBS::card_size - 1) >>
 489             CardTableModRefBS::card_shift,
 490             false /* in_resource_area*/),
 491 
 492   _prevMarkBitMap(&_markBitMap1),
 493   _nextMarkBitMap(&_markBitMap2),
 494 
 495   _markStack(this),
 496   // _finger set in set_non_marking_state
 497 
 498   _max_worker_id(MAX2((uint)ParallelGCThreads, 1U)),
 499   // _active_tasks set in set_non_marking_state
 500   // _tasks set inside the constructor
 501   _task_queues(new CMTaskQueueSet((int) _max_worker_id)),
 502   _terminator(ParallelTaskTerminator((int) _max_worker_id, _task_queues)),
 503 
 504   _has_overflown(false),
 505   _concurrent(false),
 506   _has_aborted(false),
 507   _restart_for_overflow(false),
 508   _concurrent_marking_in_progress(false),
 509 
 510   // _verbose_level set below
 511 
 512   _init_times(),
 513   _remark_times(), _remark_mark_times(), _remark_weak_ref_times(),
 514   _cleanup_times(),
 515   _total_counting_time(0.0),
 516   _total_rs_scrub_time(0.0),
 517 
 518   _parallel_workers(NULL),
 519 
 520   _count_card_bitmaps(NULL),
 521   _count_marked_bytes(NULL),
 522   _completed_initialization(false) {
 523   CMVerboseLevel verbose_level = (CMVerboseLevel) G1MarkingVerboseLevel;
 524   if (verbose_level < no_verbose) {
 525     verbose_level = no_verbose;
 526   }
 527   if (verbose_level > high_verbose) {
 528     verbose_level = high_verbose;
 529   }
 530   _verbose_level = verbose_level;
 531 
 532   if (verbose_low()) {
 533     gclog_or_tty->print_cr("[global] init, heap start = "PTR_FORMAT", "
 534                            "heap end = "PTR_FORMAT, _heap_start, _heap_end);
 535   }
 536 
 537   if (!_markBitMap1.allocate(heap_rs)) {
 538     warning("Failed to allocate first CM bit map");
 539     return;
 540   }
 541   if (!_markBitMap2.allocate(heap_rs)) {
 542     warning("Failed to allocate second CM bit map");
 543     return;
 544   }
 545 
 546   // Create & start a ConcurrentMark thread.
 547   _cmThread = new ConcurrentMarkThread(this);
 548   assert(cmThread() != NULL, "CM Thread should have been created");
 549   assert(cmThread()->cm() != NULL, "CM Thread should refer to this cm");
 550 
 551   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 552   assert(_markBitMap1.covers(heap_rs), "_markBitMap1 inconsistency");
 553   assert(_markBitMap2.covers(heap_rs), "_markBitMap2 inconsistency");
 554 
 555   SATBMarkQueueSet& satb_qs = JavaThread::satb_mark_queue_set();
 556   satb_qs.set_buffer_size(G1SATBBufferSize);
 557 
 558   _root_regions.init(_g1h, this);
 559 
 560   if (ConcGCThreads > ParallelGCThreads) {
 561     warning("Can't have more ConcGCThreads (" UINT32_FORMAT ") "
 562             "than ParallelGCThreads (" UINT32_FORMAT ").",
 563             ConcGCThreads, ParallelGCThreads);
 564     return;
 565   }
 566   if (ParallelGCThreads == 0) {
 567     // if we are not running with any parallel GC threads we will not
 568     // spawn any marking threads either
 569     _parallel_marking_threads =       0;
 570     _max_parallel_marking_threads =   0;
 571     _sleep_factor             =     0.0;
 572     _marking_task_overhead    =     1.0;
 573   } else {
 574     if (!FLAG_IS_DEFAULT(ConcGCThreads) && ConcGCThreads > 0) {
 575       // Note: ConcGCThreads has precedence over G1MarkingOverheadPercent
 576       // if both are set
 577       _sleep_factor             = 0.0;
 578       _marking_task_overhead    = 1.0;
 579     } else if (G1MarkingOverheadPercent > 0) {
 580       // We will calculate the number of parallel marking threads based
 581       // on a target overhead with respect to the soft real-time goal
 582       double marking_overhead = (double) G1MarkingOverheadPercent / 100.0;
 583       double overall_cm_overhead =
 584         (double) MaxGCPauseMillis * marking_overhead /
 585         (double) GCPauseIntervalMillis;
 586       double cpu_ratio = 1.0 / (double) os::processor_count();
 587       double marking_thread_num = ceil(overall_cm_overhead / cpu_ratio);
 588       double marking_task_overhead =
 589         overall_cm_overhead / marking_thread_num *
 590                                                 (double) os::processor_count();
 591       double sleep_factor =
 592                          (1.0 - marking_task_overhead) / marking_task_overhead;
 593 
 594       FLAG_SET_ERGO(uintx, ConcGCThreads, (uint) marking_thread_num);
 595       _sleep_factor             = sleep_factor;
 596       _marking_task_overhead    = marking_task_overhead;
 597     } else {
 598       // Calculate the number of parallel marking threads by scaling
 599       // the number of parallel GC threads.
 600       uint marking_thread_num = scale_parallel_threads((uint) ParallelGCThreads);
 601       FLAG_SET_ERGO(uintx, ConcGCThreads, marking_thread_num);
 602       _sleep_factor             = 0.0;
 603       _marking_task_overhead    = 1.0;
 604     }
 605 
 606     assert(ConcGCThreads > 0, "Should have been set");
 607     _parallel_marking_threads = (uint) ConcGCThreads;
 608     _max_parallel_marking_threads = _parallel_marking_threads;
 609 
 610     if (parallel_marking_threads() > 1) {
 611       _cleanup_task_overhead = 1.0;
 612     } else {
 613       _cleanup_task_overhead = marking_task_overhead();
 614     }
 615     _cleanup_sleep_factor =
 616                      (1.0 - cleanup_task_overhead()) / cleanup_task_overhead();
 617 
 618 #if 0
 619     gclog_or_tty->print_cr("Marking Threads          %d", parallel_marking_threads());
 620     gclog_or_tty->print_cr("CM Marking Task Overhead %1.4lf", marking_task_overhead());
 621     gclog_or_tty->print_cr("CM Sleep Factor          %1.4lf", sleep_factor());
 622     gclog_or_tty->print_cr("CL Marking Task Overhead %1.4lf", cleanup_task_overhead());
 623     gclog_or_tty->print_cr("CL Sleep Factor          %1.4lf", cleanup_sleep_factor());
 624 #endif
 625 
 626     guarantee(parallel_marking_threads() > 0, "peace of mind");
 627     _parallel_workers = new FlexibleWorkGang("G1 Parallel Marking Threads",
 628          _max_parallel_marking_threads, false, true);
 629     if (_parallel_workers == NULL) {
 630       vm_exit_during_initialization("Failed necessary allocation.");
 631     } else {
 632       _parallel_workers->initialize_workers();
 633     }
 634   }
 635 
 636   if (FLAG_IS_DEFAULT(MarkStackSize)) {
 637     uintx mark_stack_size =
 638       MIN2(MarkStackSizeMax,
 639           MAX2(MarkStackSize, (uintx) (parallel_marking_threads() * TASKQUEUE_SIZE)));
 640     // Verify that the calculated value for MarkStackSize is in range.
 641     // It would be nice to use the private utility routine from Arguments.
 642     if (!(mark_stack_size >= 1 && mark_stack_size <= MarkStackSizeMax)) {
 643       warning("Invalid value calculated for MarkStackSize (" UINTX_FORMAT "): "
 644               "must be between " UINTX_FORMAT " and " UINTX_FORMAT,
 645               mark_stack_size, 1, MarkStackSizeMax);
 646       return;
 647     }
 648     FLAG_SET_ERGO(uintx, MarkStackSize, mark_stack_size);
 649   } else {
 650     // Verify MarkStackSize is in range.
 651     if (FLAG_IS_CMDLINE(MarkStackSize)) {
 652       if (FLAG_IS_DEFAULT(MarkStackSizeMax)) {
 653         if (!(MarkStackSize >= 1 && MarkStackSize <= MarkStackSizeMax)) {
 654           warning("Invalid value specified for MarkStackSize (" UINTX_FORMAT "): "
 655                   "must be between " UINTX_FORMAT " and " UINTX_FORMAT,
 656                   MarkStackSize, 1, MarkStackSizeMax);
 657           return;
 658         }
 659       } else if (FLAG_IS_CMDLINE(MarkStackSizeMax)) {
 660         if (!(MarkStackSize >= 1 && MarkStackSize <= MarkStackSizeMax)) {
 661           warning("Invalid value specified for MarkStackSize (" UINTX_FORMAT ")"
 662                   " or for MarkStackSizeMax (" UINTX_FORMAT ")",
 663                   MarkStackSize, MarkStackSizeMax);
 664           return;
 665         }
 666       }
 667     }
 668   }
 669 
 670   if (!_markStack.allocate(MarkStackSize)) {
 671     warning("Failed to allocate CM marking stack");
 672     return;
 673   }
 674 
 675   _tasks = NEW_C_HEAP_ARRAY(CMTask*, _max_worker_id, mtGC);
 676   _accum_task_vtime = NEW_C_HEAP_ARRAY(double, _max_worker_id, mtGC);
 677 
 678   _count_card_bitmaps = NEW_C_HEAP_ARRAY(BitMap,  _max_worker_id, mtGC);
 679   _count_marked_bytes = NEW_C_HEAP_ARRAY(size_t*, _max_worker_id, mtGC);
 680 
 681   BitMap::idx_t card_bm_size = _card_bm.size();
 682 
 683   // so that the assertion in MarkingTaskQueue::task_queue doesn't fail
 684   _active_tasks = _max_worker_id;
 685 
 686   size_t max_regions = (size_t) _g1h->max_regions();
 687   for (uint i = 0; i < _max_worker_id; ++i) {
 688     CMTaskQueue* task_queue = new CMTaskQueue();
 689     task_queue->initialize();
 690     _task_queues->register_queue(i, task_queue);
 691 
 692     _count_card_bitmaps[i] = BitMap(card_bm_size, false);
 693     _count_marked_bytes[i] = NEW_C_HEAP_ARRAY(size_t, max_regions, mtGC);
 694 
 695     _tasks[i] = new CMTask(i, this,
 696                            _count_marked_bytes[i],
 697                            &_count_card_bitmaps[i],
 698                            task_queue, _task_queues);
 699 
 700     _accum_task_vtime[i] = 0.0;
 701   }
 702 
 703   // Calculate the card number for the bottom of the heap. Used
 704   // in biasing indexes into the accounting card bitmaps.
 705   _heap_bottom_card_num =
 706     intptr_t(uintptr_t(_g1h->reserved_region().start()) >>
 707                                 CardTableModRefBS::card_shift);
 708 
 709   // Clear all the liveness counting data
 710   clear_all_count_data();
 711 
 712   // so that the call below can read a sensible value
 713   _heap_start = (HeapWord*) heap_rs.base();
 714   set_non_marking_state();
 715   _completed_initialization = true;
 716 }
 717 
 718 void ConcurrentMark::update_g1_committed(bool force) {
 719   // If concurrent marking is not in progress, then we do not need to
 720   // update _heap_end.
 721   if (!concurrent_marking_in_progress() && !force) return;
 722 
 723   MemRegion committed = _g1h->g1_committed();
 724   assert(committed.start() == _heap_start, "start shouldn't change");
 725   HeapWord* new_end = committed.end();
 726   if (new_end > _heap_end) {
 727     // The heap has been expanded.
 728 
 729     _heap_end = new_end;
 730   }
 731   // Notice that the heap can also shrink. However, this only happens
 732   // during a Full GC (at least currently) and the entire marking
 733   // phase will bail out and the task will not be restarted. So, let's
 734   // do nothing.
 735 }
 736 
 737 void ConcurrentMark::reset() {
 738   // Starting values for these two. This should be called in a STW
 739   // phase. CM will be notified of any future g1_committed expansions
 740   // will be at the end of evacuation pauses, when tasks are
 741   // inactive.
 742   MemRegion committed = _g1h->g1_committed();
 743   _heap_start = committed.start();
 744   _heap_end   = committed.end();
 745 
 746   // Separated the asserts so that we know which one fires.
 747   assert(_heap_start != NULL, "heap bounds should look ok");
 748   assert(_heap_end != NULL, "heap bounds should look ok");
 749   assert(_heap_start < _heap_end, "heap bounds should look ok");
 750 
 751   // Reset all the marking data structures and any necessary flags
 752   reset_marking_state();
 753 
 754   if (verbose_low()) {
 755     gclog_or_tty->print_cr("[global] resetting");
 756   }
 757 
 758   // We do reset all of them, since different phases will use
 759   // different number of active threads. So, it's easiest to have all
 760   // of them ready.
 761   for (uint i = 0; i < _max_worker_id; ++i) {
 762     _tasks[i]->reset(_nextMarkBitMap);
 763   }
 764 
 765   // we need this to make sure that the flag is on during the evac
 766   // pause with initial mark piggy-backed
 767   set_concurrent_marking_in_progress();
 768 }
 769 
 770 
 771 void ConcurrentMark::reset_marking_state(bool clear_overflow) {
 772   _markStack.set_should_expand();
 773   _markStack.setEmpty();        // Also clears the _markStack overflow flag
 774   if (clear_overflow) {
 775     clear_has_overflown();
 776   } else {
 777     assert(has_overflown(), "pre-condition");
 778   }
 779   _finger = _heap_start;
 780 
 781   for (uint i = 0; i < _max_worker_id; ++i) {
 782     CMTaskQueue* queue = _task_queues->queue(i);
 783     queue->set_empty();
 784   }
 785 }
 786 
 787 void ConcurrentMark::set_phase(uint active_tasks, bool concurrent) {
 788   assert(active_tasks <= _max_worker_id, "we should not have more");
 789 
 790   _active_tasks = active_tasks;
 791   // Need to update the three data structures below according to the
 792   // number of active threads for this phase.
 793   _terminator   = ParallelTaskTerminator((int) active_tasks, _task_queues);
 794   _first_overflow_barrier_sync.set_n_workers((int) active_tasks);
 795   _second_overflow_barrier_sync.set_n_workers((int) active_tasks);
 796 
 797   _concurrent = concurrent;
 798   // We propagate this to all tasks, not just the active ones.
 799   for (uint i = 0; i < _max_worker_id; ++i)
 800     _tasks[i]->set_concurrent(concurrent);
 801 
 802   if (concurrent) {
 803     set_concurrent_marking_in_progress();
 804   } else {
 805     // We currently assume that the concurrent flag has been set to
 806     // false before we start remark. At this point we should also be
 807     // in a STW phase.
 808     assert(!concurrent_marking_in_progress(), "invariant");
 809     assert(_finger == _heap_end, "only way to get here");
 810     update_g1_committed(true);
 811   }
 812 }
 813 
 814 void ConcurrentMark::set_non_marking_state() {
 815   // We set the global marking state to some default values when we're
 816   // not doing marking.
 817   reset_marking_state();
 818   _active_tasks = 0;
 819   clear_concurrent_marking_in_progress();
 820 }
 821 
 822 ConcurrentMark::~ConcurrentMark() {
 823   // The ConcurrentMark instance is never freed.
 824   ShouldNotReachHere();
 825 }
 826 
 827 void ConcurrentMark::clearNextBitmap() {
 828   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 829   G1CollectorPolicy* g1p = g1h->g1_policy();
 830 
 831   // Make sure that the concurrent mark thread looks to still be in
 832   // the current cycle.
 833   guarantee(cmThread()->during_cycle(), "invariant");
 834 
 835   // We are finishing up the current cycle by clearing the next
 836   // marking bitmap and getting it ready for the next cycle. During
 837   // this time no other cycle can start. So, let's make sure that this
 838   // is the case.
 839   guarantee(!g1h->mark_in_progress(), "invariant");
 840 
 841   // clear the mark bitmap (no grey objects to start with).
 842   // We need to do this in chunks and offer to yield in between
 843   // each chunk.
 844   HeapWord* start  = _nextMarkBitMap->startWord();
 845   HeapWord* end    = _nextMarkBitMap->endWord();
 846   HeapWord* cur    = start;
 847   size_t chunkSize = M;
 848   while (cur < end) {
 849     HeapWord* next = cur + chunkSize;
 850     if (next > end) {
 851       next = end;
 852     }
 853     MemRegion mr(cur,next);
 854     _nextMarkBitMap->clearRange(mr);
 855     cur = next;
 856     do_yield_check();
 857 
 858     // Repeat the asserts from above. We'll do them as asserts here to
 859     // minimize their overhead on the product. However, we'll have
 860     // them as guarantees at the beginning / end of the bitmap
 861     // clearing to get some checking in the product.
 862     assert(cmThread()->during_cycle(), "invariant");
 863     assert(!g1h->mark_in_progress(), "invariant");
 864   }
 865 
 866   // Clear the liveness counting data
 867   clear_all_count_data();
 868 
 869   // Repeat the asserts from above.
 870   guarantee(cmThread()->during_cycle(), "invariant");
 871   guarantee(!g1h->mark_in_progress(), "invariant");
 872 }
 873 
 874 class NoteStartOfMarkHRClosure: public HeapRegionClosure {
 875 public:
 876   bool doHeapRegion(HeapRegion* r) {
 877     if (!r->continuesHumongous()) {
 878       r->note_start_of_marking();
 879     }
 880     return false;
 881   }
 882 };
 883 
 884 void ConcurrentMark::checkpointRootsInitialPre() {
 885   G1CollectedHeap*   g1h = G1CollectedHeap::heap();
 886   G1CollectorPolicy* g1p = g1h->g1_policy();
 887 
 888   _has_aborted = false;
 889 
 890 #ifndef PRODUCT
 891   if (G1PrintReachableAtInitialMark) {
 892     print_reachable("at-cycle-start",
 893                     VerifyOption_G1UsePrevMarking, true /* all */);
 894   }
 895 #endif
 896 
 897   // Initialise marking structures. This has to be done in a STW phase.
 898   reset();
 899 
 900   // For each region note start of marking.
 901   NoteStartOfMarkHRClosure startcl;
 902   g1h->heap_region_iterate(&startcl);
 903 }
 904 
 905 
 906 void ConcurrentMark::checkpointRootsInitialPost() {
 907   G1CollectedHeap*   g1h = G1CollectedHeap::heap();
 908 
 909   // If we force an overflow during remark, the remark operation will
 910   // actually abort and we'll restart concurrent marking. If we always
 911   // force an oveflow during remark we'll never actually complete the
 912   // marking phase. So, we initilize this here, at the start of the
 913   // cycle, so that at the remaining overflow number will decrease at
 914   // every remark and we'll eventually not need to cause one.
 915   force_overflow_stw()->init();
 916 
 917   // Start Concurrent Marking weak-reference discovery.
 918   ReferenceProcessor* rp = g1h->ref_processor_cm();
 919   // enable ("weak") refs discovery
 920   rp->enable_discovery(true /*verify_disabled*/, true /*verify_no_refs*/);
 921   rp->setup_policy(false); // snapshot the soft ref policy to be used in this cycle
 922 
 923   SATBMarkQueueSet& satb_mq_set = JavaThread::satb_mark_queue_set();
 924   // This is the start of  the marking cycle, we're expected all
 925   // threads to have SATB queues with active set to false.
 926   satb_mq_set.set_active_all_threads(true, /* new active value */
 927                                      false /* expected_active */);
 928 
 929   _root_regions.prepare_for_scan();
 930 
 931   // update_g1_committed() will be called at the end of an evac pause
 932   // when marking is on. So, it's also called at the end of the
 933   // initial-mark pause to update the heap end, if the heap expands
 934   // during it. No need to call it here.
 935 }
 936 
 937 /*
 938  * Notice that in the next two methods, we actually leave the STS
 939  * during the barrier sync and join it immediately afterwards. If we
 940  * do not do this, the following deadlock can occur: one thread could
 941  * be in the barrier sync code, waiting for the other thread to also
 942  * sync up, whereas another one could be trying to yield, while also
 943  * waiting for the other threads to sync up too.
 944  *
 945  * Note, however, that this code is also used during remark and in
 946  * this case we should not attempt to leave / enter the STS, otherwise
 947  * we'll either hit an asseert (debug / fastdebug) or deadlock
 948  * (product). So we should only leave / enter the STS if we are
 949  * operating concurrently.
 950  *
 951  * Because the thread that does the sync barrier has left the STS, it
 952  * is possible to be suspended for a Full GC or an evacuation pause
 953  * could occur. This is actually safe, since the entering the sync
 954  * barrier is one of the last things do_marking_step() does, and it
 955  * doesn't manipulate any data structures afterwards.
 956  */
 957 
 958 void ConcurrentMark::enter_first_sync_barrier(uint worker_id) {
 959   if (verbose_low()) {
 960     gclog_or_tty->print_cr("[%u] entering first barrier", worker_id);
 961   }
 962 
 963   if (concurrent()) {
 964     ConcurrentGCThread::stsLeave();
 965   }
 966   _first_overflow_barrier_sync.enter();
 967   if (concurrent()) {
 968     ConcurrentGCThread::stsJoin();
 969   }
 970   // at this point everyone should have synced up and not be doing any
 971   // more work
 972 
 973   if (verbose_low()) {
 974     gclog_or_tty->print_cr("[%u] leaving first barrier", worker_id);
 975   }
 976 
 977   // let the task associated with with worker 0 do this
 978   if (worker_id == 0) {
 979     // task 0 is responsible for clearing the global data structures
 980     // We should be here because of an overflow. During STW we should
 981     // not clear the overflow flag since we rely on it being true when
 982     // we exit this method to abort the pause and restart concurent
 983     // marking.
 984     reset_marking_state(concurrent() /* clear_overflow */);
 985     force_overflow()->update();
 986 
 987     if (G1Log::fine()) {
 988       gclog_or_tty->date_stamp(PrintGCDateStamps);
 989       gclog_or_tty->stamp(PrintGCTimeStamps);
 990       gclog_or_tty->print_cr("[GC concurrent-mark-reset-for-overflow]");
 991     }
 992   }
 993 
 994   // after this, each task should reset its own data structures then
 995   // then go into the second barrier
 996 }
 997 
 998 void ConcurrentMark::enter_second_sync_barrier(uint worker_id) {
 999   if (verbose_low()) {
1000     gclog_or_tty->print_cr("[%u] entering second barrier", worker_id);
1001   }
1002 
1003   if (concurrent()) {
1004     ConcurrentGCThread::stsLeave();
1005   }
1006   _second_overflow_barrier_sync.enter();
1007   if (concurrent()) {
1008     ConcurrentGCThread::stsJoin();
1009   }
1010   // at this point everything should be re-initialised and ready to go
1011 
1012   if (verbose_low()) {
1013     gclog_or_tty->print_cr("[%u] leaving second barrier", worker_id);
1014   }
1015 }
1016 
1017 #ifndef PRODUCT
1018 void ForceOverflowSettings::init() {
1019   _num_remaining = G1ConcMarkForceOverflow;
1020   _force = false;
1021   update();
1022 }
1023 
1024 void ForceOverflowSettings::update() {
1025   if (_num_remaining > 0) {
1026     _num_remaining -= 1;
1027     _force = true;
1028   } else {
1029     _force = false;
1030   }
1031 }
1032 
1033 bool ForceOverflowSettings::should_force() {
1034   if (_force) {
1035     _force = false;
1036     return true;
1037   } else {
1038     return false;
1039   }
1040 }
1041 #endif // !PRODUCT
1042 
1043 class CMConcurrentMarkingTask: public AbstractGangTask {
1044 private:
1045   ConcurrentMark*       _cm;
1046   ConcurrentMarkThread* _cmt;
1047 
1048 public:
1049   void work(uint worker_id) {
1050     assert(Thread::current()->is_ConcurrentGC_thread(),
1051            "this should only be done by a conc GC thread");
1052     ResourceMark rm;
1053 
1054     double start_vtime = os::elapsedVTime();
1055 
1056     ConcurrentGCThread::stsJoin();
1057 
1058     assert(worker_id < _cm->active_tasks(), "invariant");
1059     CMTask* the_task = _cm->task(worker_id);
1060     the_task->record_start_time();
1061     if (!_cm->has_aborted()) {
1062       do {
1063         double start_vtime_sec = os::elapsedVTime();
1064         double start_time_sec = os::elapsedTime();
1065         double mark_step_duration_ms = G1ConcMarkStepDurationMillis;
1066 
1067         the_task->do_marking_step(mark_step_duration_ms,
1068                                   true  /* do_termination */,
1069                                   false /* is_serial*/);
1070 
1071         double end_time_sec = os::elapsedTime();
1072         double end_vtime_sec = os::elapsedVTime();
1073         double elapsed_vtime_sec = end_vtime_sec - start_vtime_sec;
1074         double elapsed_time_sec = end_time_sec - start_time_sec;
1075         _cm->clear_has_overflown();
1076 
1077         bool ret = _cm->do_yield_check(worker_id);
1078 
1079         jlong sleep_time_ms;
1080         if (!_cm->has_aborted() && the_task->has_aborted()) {
1081           sleep_time_ms =
1082             (jlong) (elapsed_vtime_sec * _cm->sleep_factor() * 1000.0);
1083           ConcurrentGCThread::stsLeave();
1084           os::sleep(Thread::current(), sleep_time_ms, false);
1085           ConcurrentGCThread::stsJoin();
1086         }
1087         double end_time2_sec = os::elapsedTime();
1088         double elapsed_time2_sec = end_time2_sec - start_time_sec;
1089 
1090 #if 0
1091           gclog_or_tty->print_cr("CM: elapsed %1.4lf ms, sleep %1.4lf ms, "
1092                                  "overhead %1.4lf",
1093                                  elapsed_vtime_sec * 1000.0, (double) sleep_time_ms,
1094                                  the_task->conc_overhead(os::elapsedTime()) * 8.0);
1095           gclog_or_tty->print_cr("elapsed time %1.4lf ms, time 2: %1.4lf ms",
1096                                  elapsed_time_sec * 1000.0, elapsed_time2_sec * 1000.0);
1097 #endif
1098       } while (!_cm->has_aborted() && the_task->has_aborted());
1099     }
1100     the_task->record_end_time();
1101     guarantee(!the_task->has_aborted() || _cm->has_aborted(), "invariant");
1102 
1103     ConcurrentGCThread::stsLeave();
1104 
1105     double end_vtime = os::elapsedVTime();
1106     _cm->update_accum_task_vtime(worker_id, end_vtime - start_vtime);
1107   }
1108 
1109   CMConcurrentMarkingTask(ConcurrentMark* cm,
1110                           ConcurrentMarkThread* cmt) :
1111       AbstractGangTask("Concurrent Mark"), _cm(cm), _cmt(cmt) { }
1112 
1113   ~CMConcurrentMarkingTask() { }
1114 };
1115 
1116 // Calculates the number of active workers for a concurrent
1117 // phase.
1118 uint ConcurrentMark::calc_parallel_marking_threads() {
1119   if (G1CollectedHeap::use_parallel_gc_threads()) {
1120     uint n_conc_workers = 0;
1121     if (!UseDynamicNumberOfGCThreads ||
1122         (!FLAG_IS_DEFAULT(ConcGCThreads) &&
1123          !ForceDynamicNumberOfGCThreads)) {
1124       n_conc_workers = max_parallel_marking_threads();
1125     } else {
1126       n_conc_workers =
1127         AdaptiveSizePolicy::calc_default_active_workers(
1128                                      max_parallel_marking_threads(),
1129                                      1, /* Minimum workers */
1130                                      parallel_marking_threads(),
1131                                      Threads::number_of_non_daemon_threads());
1132       // Don't scale down "n_conc_workers" by scale_parallel_threads() because
1133       // that scaling has already gone into "_max_parallel_marking_threads".
1134     }
1135     assert(n_conc_workers > 0, "Always need at least 1");
1136     return n_conc_workers;
1137   }
1138   // If we are not running with any parallel GC threads we will not
1139   // have spawned any marking threads either. Hence the number of
1140   // concurrent workers should be 0.
1141   return 0;
1142 }
1143 
1144 void ConcurrentMark::scanRootRegion(HeapRegion* hr, uint worker_id) {
1145   // Currently, only survivors can be root regions.
1146   assert(hr->next_top_at_mark_start() == hr->bottom(), "invariant");
1147   G1RootRegionScanClosure cl(_g1h, this, worker_id);
1148 
1149   const uintx interval = PrefetchScanIntervalInBytes;
1150   HeapWord* curr = hr->bottom();
1151   const HeapWord* end = hr->top();
1152   while (curr < end) {
1153     Prefetch::read(curr, interval);
1154     oop obj = oop(curr);
1155     int size = obj->oop_iterate(&cl);
1156     assert(size == obj->size(), "sanity");
1157     curr += size;
1158   }
1159 }
1160 
1161 class CMRootRegionScanTask : public AbstractGangTask {
1162 private:
1163   ConcurrentMark* _cm;
1164 
1165 public:
1166   CMRootRegionScanTask(ConcurrentMark* cm) :
1167     AbstractGangTask("Root Region Scan"), _cm(cm) { }
1168 
1169   void work(uint worker_id) {
1170     assert(Thread::current()->is_ConcurrentGC_thread(),
1171            "this should only be done by a conc GC thread");
1172 
1173     CMRootRegions* root_regions = _cm->root_regions();
1174     HeapRegion* hr = root_regions->claim_next();
1175     while (hr != NULL) {
1176       _cm->scanRootRegion(hr, worker_id);
1177       hr = root_regions->claim_next();
1178     }
1179   }
1180 };
1181 
1182 void ConcurrentMark::scanRootRegions() {
1183   // scan_in_progress() will have been set to true only if there was
1184   // at least one root region to scan. So, if it's false, we
1185   // should not attempt to do any further work.
1186   if (root_regions()->scan_in_progress()) {
1187     _parallel_marking_threads = calc_parallel_marking_threads();
1188     assert(parallel_marking_threads() <= max_parallel_marking_threads(),
1189            "Maximum number of marking threads exceeded");
1190     uint active_workers = MAX2(1U, parallel_marking_threads());
1191 
1192     CMRootRegionScanTask task(this);
1193     if (use_parallel_marking_threads()) {
1194       _parallel_workers->set_active_workers((int) active_workers);
1195       _parallel_workers->run_task(&task);
1196     } else {
1197       task.work(0);
1198     }
1199 
1200     // It's possible that has_aborted() is true here without actually
1201     // aborting the survivor scan earlier. This is OK as it's
1202     // mainly used for sanity checking.
1203     root_regions()->scan_finished();
1204   }
1205 }
1206 
1207 void ConcurrentMark::markFromRoots() {
1208   // we might be tempted to assert that:
1209   // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
1210   //        "inconsistent argument?");
1211   // However that wouldn't be right, because it's possible that
1212   // a safepoint is indeed in progress as a younger generation
1213   // stop-the-world GC happens even as we mark in this generation.
1214 
1215   _restart_for_overflow = false;
1216   force_overflow_conc()->init();
1217 
1218   // _g1h has _n_par_threads
1219   _parallel_marking_threads = calc_parallel_marking_threads();
1220   assert(parallel_marking_threads() <= max_parallel_marking_threads(),
1221     "Maximum number of marking threads exceeded");
1222 
1223   uint active_workers = MAX2(1U, parallel_marking_threads());
1224 
1225   // Parallel task terminator is set in "set_phase()"
1226   set_phase(active_workers, true /* concurrent */);
1227 
1228   CMConcurrentMarkingTask markingTask(this, cmThread());
1229   if (use_parallel_marking_threads()) {
1230     _parallel_workers->set_active_workers((int)active_workers);
1231     // Don't set _n_par_threads because it affects MT in proceess_strong_roots()
1232     // and the decisions on that MT processing is made elsewhere.
1233     assert(_parallel_workers->active_workers() > 0, "Should have been set");
1234     _parallel_workers->run_task(&markingTask);
1235   } else {
1236     markingTask.work(0);
1237   }
1238   print_stats();
1239 }
1240 
1241 void ConcurrentMark::checkpointRootsFinal(bool clear_all_soft_refs) {
1242   // world is stopped at this checkpoint
1243   assert(SafepointSynchronize::is_at_safepoint(),
1244          "world should be stopped");
1245 
1246   G1CollectedHeap* g1h = G1CollectedHeap::heap();
1247 
1248   // If a full collection has happened, we shouldn't do this.
1249   if (has_aborted()) {
1250     g1h->set_marking_complete(); // So bitmap clearing isn't confused
1251     return;
1252   }
1253 
1254   SvcGCMarker sgcm(SvcGCMarker::OTHER);
1255 
1256   if (VerifyDuringGC) {
1257     HandleMark hm;  // handle scope
1258     gclog_or_tty->print(" VerifyDuringGC:(before)");
1259     Universe::heap()->prepare_for_verify();
1260     Universe::verify(/* silent */ false,
1261                      /* option */ VerifyOption_G1UsePrevMarking);
1262   }
1263 
1264   G1CollectorPolicy* g1p = g1h->g1_policy();
1265   g1p->record_concurrent_mark_remark_start();
1266 
1267   double start = os::elapsedTime();
1268 
1269   checkpointRootsFinalWork();
1270 
1271   double mark_work_end = os::elapsedTime();
1272 
1273   weakRefsWork(clear_all_soft_refs);
1274 
1275   if (has_overflown()) {
1276     // Oops.  We overflowed.  Restart concurrent marking.
1277     _restart_for_overflow = true;
1278     // Clear the marking state because we will be restarting
1279     // marking due to overflowing the global mark stack.
1280     reset_marking_state();
1281     if (G1TraceMarkStackOverflow) {
1282       gclog_or_tty->print_cr("\nRemark led to restart for overflow.");
1283     }
1284   } else {
1285     // Aggregate the per-task counting data that we have accumulated
1286     // while marking.
1287     aggregate_count_data();
1288 
1289     SATBMarkQueueSet& satb_mq_set = JavaThread::satb_mark_queue_set();
1290     // We're done with marking.
1291     // This is the end of  the marking cycle, we're expected all
1292     // threads to have SATB queues with active set to true.
1293     satb_mq_set.set_active_all_threads(false, /* new active value */
1294                                        true /* expected_active */);
1295 
1296     if (VerifyDuringGC) {
1297       HandleMark hm;  // handle scope
1298       gclog_or_tty->print(" VerifyDuringGC:(after)");
1299       Universe::heap()->prepare_for_verify();
1300       Universe::verify(/* silent */ false,
1301                        /* option */ VerifyOption_G1UseNextMarking);
1302     }
1303     assert(!restart_for_overflow(), "sanity");
1304     // Completely reset the marking state since marking completed
1305     set_non_marking_state();
1306   }
1307 
1308   // Expand the marking stack, if we have to and if we can.
1309   if (_markStack.should_expand()) {
1310     _markStack.expand();
1311   }
1312 
1313 #if VERIFY_OBJS_PROCESSED
1314   _scan_obj_cl.objs_processed = 0;
1315   ThreadLocalObjQueue::objs_enqueued = 0;
1316 #endif
1317 
1318   // Statistics
1319   double now = os::elapsedTime();
1320   _remark_mark_times.add((mark_work_end - start) * 1000.0);
1321   _remark_weak_ref_times.add((now - mark_work_end) * 1000.0);
1322   _remark_times.add((now - start) * 1000.0);
1323 
1324   g1p->record_concurrent_mark_remark_end();
1325 }
1326 
1327 // Base class of the closures that finalize and verify the
1328 // liveness counting data.
1329 class CMCountDataClosureBase: public HeapRegionClosure {
1330 protected:
1331   G1CollectedHeap* _g1h;
1332   ConcurrentMark* _cm;
1333   CardTableModRefBS* _ct_bs;
1334 
1335   BitMap* _region_bm;
1336   BitMap* _card_bm;
1337 
1338   // Takes a region that's not empty (i.e., it has at least one
1339   // live object in it and sets its corresponding bit on the region
1340   // bitmap to 1. If the region is "starts humongous" it will also set
1341   // to 1 the bits on the region bitmap that correspond to its
1342   // associated "continues humongous" regions.
1343   void set_bit_for_region(HeapRegion* hr) {
1344     assert(!hr->continuesHumongous(), "should have filtered those out");
1345 
1346     BitMap::idx_t index = (BitMap::idx_t) hr->hrs_index();
1347     if (!hr->startsHumongous()) {
1348       // Normal (non-humongous) case: just set the bit.
1349       _region_bm->par_at_put(index, true);
1350     } else {
1351       // Starts humongous case: calculate how many regions are part of
1352       // this humongous region and then set the bit range.
1353       BitMap::idx_t end_index = (BitMap::idx_t) hr->last_hc_index();
1354       _region_bm->par_at_put_range(index, end_index, true);
1355     }
1356   }
1357 
1358 public:
1359   CMCountDataClosureBase(G1CollectedHeap* g1h,
1360                          BitMap* region_bm, BitMap* card_bm):
1361     _g1h(g1h), _cm(g1h->concurrent_mark()),
1362     _ct_bs((CardTableModRefBS*) (g1h->barrier_set())),
1363     _region_bm(region_bm), _card_bm(card_bm) { }
1364 };
1365 
1366 // Closure that calculates the # live objects per region. Used
1367 // for verification purposes during the cleanup pause.
1368 class CalcLiveObjectsClosure: public CMCountDataClosureBase {
1369   CMBitMapRO* _bm;
1370   size_t _region_marked_bytes;
1371 
1372 public:
1373   CalcLiveObjectsClosure(CMBitMapRO *bm, G1CollectedHeap* g1h,
1374                          BitMap* region_bm, BitMap* card_bm) :
1375     CMCountDataClosureBase(g1h, region_bm, card_bm),
1376     _bm(bm), _region_marked_bytes(0) { }
1377 
1378   bool doHeapRegion(HeapRegion* hr) {
1379 
1380     if (hr->continuesHumongous()) {
1381       // We will ignore these here and process them when their
1382       // associated "starts humongous" region is processed (see
1383       // set_bit_for_heap_region()). Note that we cannot rely on their
1384       // associated "starts humongous" region to have their bit set to
1385       // 1 since, due to the region chunking in the parallel region
1386       // iteration, a "continues humongous" region might be visited
1387       // before its associated "starts humongous".
1388       return false;
1389     }
1390 
1391     HeapWord* ntams = hr->next_top_at_mark_start();
1392     HeapWord* start = hr->bottom();
1393 
1394     assert(start <= hr->end() && start <= ntams && ntams <= hr->end(),
1395            err_msg("Preconditions not met - "
1396                    "start: "PTR_FORMAT", ntams: "PTR_FORMAT", end: "PTR_FORMAT,
1397                    start, ntams, hr->end()));
1398 
1399     // Find the first marked object at or after "start".
1400     start = _bm->getNextMarkedWordAddress(start, ntams);
1401 
1402     size_t marked_bytes = 0;
1403 
1404     while (start < ntams) {
1405       oop obj = oop(start);
1406       int obj_sz = obj->size();
1407       HeapWord* obj_end = start + obj_sz;
1408 
1409       BitMap::idx_t start_idx = _cm->card_bitmap_index_for(start);
1410       BitMap::idx_t end_idx = _cm->card_bitmap_index_for(obj_end);
1411 
1412       // Note: if we're looking at the last region in heap - obj_end
1413       // could be actually just beyond the end of the heap; end_idx
1414       // will then correspond to a (non-existent) card that is also
1415       // just beyond the heap.
1416       if (_g1h->is_in_g1_reserved(obj_end) && !_ct_bs->is_card_aligned(obj_end)) {
1417         // end of object is not card aligned - increment to cover
1418         // all the cards spanned by the object
1419         end_idx += 1;
1420       }
1421 
1422       // Set the bits in the card BM for the cards spanned by this object.
1423       _cm->set_card_bitmap_range(_card_bm, start_idx, end_idx, true /* is_par */);
1424 
1425       // Add the size of this object to the number of marked bytes.
1426       marked_bytes += (size_t)obj_sz * HeapWordSize;
1427 
1428       // Find the next marked object after this one.
1429       start = _bm->getNextMarkedWordAddress(obj_end, ntams);
1430     }
1431 
1432     // Mark the allocated-since-marking portion...
1433     HeapWord* top = hr->top();
1434     if (ntams < top) {
1435       BitMap::idx_t start_idx = _cm->card_bitmap_index_for(ntams);
1436       BitMap::idx_t end_idx = _cm->card_bitmap_index_for(top);
1437 
1438       // Note: if we're looking at the last region in heap - top
1439       // could be actually just beyond the end of the heap; end_idx
1440       // will then correspond to a (non-existent) card that is also
1441       // just beyond the heap.
1442       if (_g1h->is_in_g1_reserved(top) && !_ct_bs->is_card_aligned(top)) {
1443         // end of object is not card aligned - increment to cover
1444         // all the cards spanned by the object
1445         end_idx += 1;
1446       }
1447       _cm->set_card_bitmap_range(_card_bm, start_idx, end_idx, true /* is_par */);
1448 
1449       // This definitely means the region has live objects.
1450       set_bit_for_region(hr);
1451     }
1452 
1453     // Update the live region bitmap.
1454     if (marked_bytes > 0) {
1455       set_bit_for_region(hr);
1456     }
1457 
1458     // Set the marked bytes for the current region so that
1459     // it can be queried by a calling verificiation routine
1460     _region_marked_bytes = marked_bytes;
1461 
1462     return false;
1463   }
1464 
1465   size_t region_marked_bytes() const { return _region_marked_bytes; }
1466 };
1467 
1468 // Heap region closure used for verifying the counting data
1469 // that was accumulated concurrently and aggregated during
1470 // the remark pause. This closure is applied to the heap
1471 // regions during the STW cleanup pause.
1472 
1473 class VerifyLiveObjectDataHRClosure: public HeapRegionClosure {
1474   G1CollectedHeap* _g1h;
1475   ConcurrentMark* _cm;
1476   CalcLiveObjectsClosure _calc_cl;
1477   BitMap* _region_bm;   // Region BM to be verified
1478   BitMap* _card_bm;     // Card BM to be verified
1479   bool _verbose;        // verbose output?
1480 
1481   BitMap* _exp_region_bm; // Expected Region BM values
1482   BitMap* _exp_card_bm;   // Expected card BM values
1483 
1484   int _failures;
1485 
1486 public:
1487   VerifyLiveObjectDataHRClosure(G1CollectedHeap* g1h,
1488                                 BitMap* region_bm,
1489                                 BitMap* card_bm,
1490                                 BitMap* exp_region_bm,
1491                                 BitMap* exp_card_bm,
1492                                 bool verbose) :
1493     _g1h(g1h), _cm(g1h->concurrent_mark()),
1494     _calc_cl(_cm->nextMarkBitMap(), g1h, exp_region_bm, exp_card_bm),
1495     _region_bm(region_bm), _card_bm(card_bm), _verbose(verbose),
1496     _exp_region_bm(exp_region_bm), _exp_card_bm(exp_card_bm),
1497     _failures(0) { }
1498 
1499   int failures() const { return _failures; }
1500 
1501   bool doHeapRegion(HeapRegion* hr) {
1502     if (hr->continuesHumongous()) {
1503       // We will ignore these here and process them when their
1504       // associated "starts humongous" region is processed (see
1505       // set_bit_for_heap_region()). Note that we cannot rely on their
1506       // associated "starts humongous" region to have their bit set to
1507       // 1 since, due to the region chunking in the parallel region
1508       // iteration, a "continues humongous" region might be visited
1509       // before its associated "starts humongous".
1510       return false;
1511     }
1512 
1513     int failures = 0;
1514 
1515     // Call the CalcLiveObjectsClosure to walk the marking bitmap for
1516     // this region and set the corresponding bits in the expected region
1517     // and card bitmaps.
1518     bool res = _calc_cl.doHeapRegion(hr);
1519     assert(res == false, "should be continuing");
1520 
1521     MutexLockerEx x((_verbose ? ParGCRareEvent_lock : NULL),
1522                     Mutex::_no_safepoint_check_flag);
1523 
1524     // Verify the marked bytes for this region.
1525     size_t exp_marked_bytes = _calc_cl.region_marked_bytes();
1526     size_t act_marked_bytes = hr->next_marked_bytes();
1527 
1528     // We're not OK if expected marked bytes > actual marked bytes. It means
1529     // we have missed accounting some objects during the actual marking.
1530     if (exp_marked_bytes > act_marked_bytes) {
1531       if (_verbose) {
1532         gclog_or_tty->print_cr("Region %u: marked bytes mismatch: "
1533                                "expected: " SIZE_FORMAT ", actual: " SIZE_FORMAT,
1534                                hr->hrs_index(), exp_marked_bytes, act_marked_bytes);
1535       }
1536       failures += 1;
1537     }
1538 
1539     // Verify the bit, for this region, in the actual and expected
1540     // (which was just calculated) region bit maps.
1541     // We're not OK if the bit in the calculated expected region
1542     // bitmap is set and the bit in the actual region bitmap is not.
1543     BitMap::idx_t index = (BitMap::idx_t) hr->hrs_index();
1544 
1545     bool expected = _exp_region_bm->at(index);
1546     bool actual = _region_bm->at(index);
1547     if (expected && !actual) {
1548       if (_verbose) {
1549         gclog_or_tty->print_cr("Region %u: region bitmap mismatch: "
1550                                "expected: %s, actual: %s",
1551                                hr->hrs_index(),
1552                                BOOL_TO_STR(expected), BOOL_TO_STR(actual));
1553       }
1554       failures += 1;
1555     }
1556 
1557     // Verify that the card bit maps for the cards spanned by the current
1558     // region match. We have an error if we have a set bit in the expected
1559     // bit map and the corresponding bit in the actual bitmap is not set.
1560 
1561     BitMap::idx_t start_idx = _cm->card_bitmap_index_for(hr->bottom());
1562     BitMap::idx_t end_idx = _cm->card_bitmap_index_for(hr->top());
1563 
1564     for (BitMap::idx_t i = start_idx; i < end_idx; i+=1) {
1565       expected = _exp_card_bm->at(i);
1566       actual = _card_bm->at(i);
1567 
1568       if (expected && !actual) {
1569         if (_verbose) {
1570           gclog_or_tty->print_cr("Region %u: card bitmap mismatch at " SIZE_FORMAT ": "
1571                                  "expected: %s, actual: %s",
1572                                  hr->hrs_index(), i,
1573                                  BOOL_TO_STR(expected), BOOL_TO_STR(actual));
1574         }
1575         failures += 1;
1576       }
1577     }
1578 
1579     if (failures > 0 && _verbose)  {
1580       gclog_or_tty->print_cr("Region " HR_FORMAT ", ntams: " PTR_FORMAT ", "
1581                              "marked_bytes: calc/actual " SIZE_FORMAT "/" SIZE_FORMAT,
1582                              HR_FORMAT_PARAMS(hr), hr->next_top_at_mark_start(),
1583                              _calc_cl.region_marked_bytes(), hr->next_marked_bytes());
1584     }
1585 
1586     _failures += failures;
1587 
1588     // We could stop iteration over the heap when we
1589     // find the first violating region by returning true.
1590     return false;
1591   }
1592 };
1593 
1594 
1595 class G1ParVerifyFinalCountTask: public AbstractGangTask {
1596 protected:
1597   G1CollectedHeap* _g1h;
1598   ConcurrentMark* _cm;
1599   BitMap* _actual_region_bm;
1600   BitMap* _actual_card_bm;
1601 
1602   uint    _n_workers;
1603 
1604   BitMap* _expected_region_bm;
1605   BitMap* _expected_card_bm;
1606 
1607   int  _failures;
1608   bool _verbose;
1609 
1610 public:
1611   G1ParVerifyFinalCountTask(G1CollectedHeap* g1h,
1612                             BitMap* region_bm, BitMap* card_bm,
1613                             BitMap* expected_region_bm, BitMap* expected_card_bm)
1614     : AbstractGangTask("G1 verify final counting"),
1615       _g1h(g1h), _cm(_g1h->concurrent_mark()),
1616       _actual_region_bm(region_bm), _actual_card_bm(card_bm),
1617       _expected_region_bm(expected_region_bm), _expected_card_bm(expected_card_bm),
1618       _failures(0), _verbose(false),
1619       _n_workers(0) {
1620     assert(VerifyDuringGC, "don't call this otherwise");
1621 
1622     // Use the value already set as the number of active threads
1623     // in the call to run_task().
1624     if (G1CollectedHeap::use_parallel_gc_threads()) {
1625       assert( _g1h->workers()->active_workers() > 0,
1626         "Should have been previously set");
1627       _n_workers = _g1h->workers()->active_workers();
1628     } else {
1629       _n_workers = 1;
1630     }
1631 
1632     assert(_expected_card_bm->size() == _actual_card_bm->size(), "sanity");
1633     assert(_expected_region_bm->size() == _actual_region_bm->size(), "sanity");
1634 
1635     _verbose = _cm->verbose_medium();
1636   }
1637 
1638   void work(uint worker_id) {
1639     assert(worker_id < _n_workers, "invariant");
1640 
1641     VerifyLiveObjectDataHRClosure verify_cl(_g1h,
1642                                             _actual_region_bm, _actual_card_bm,
1643                                             _expected_region_bm,
1644                                             _expected_card_bm,
1645                                             _verbose);
1646 
1647     if (G1CollectedHeap::use_parallel_gc_threads()) {
1648       _g1h->heap_region_par_iterate_chunked(&verify_cl,
1649                                             worker_id,
1650                                             _n_workers,
1651                                             HeapRegion::VerifyCountClaimValue);
1652     } else {
1653       _g1h->heap_region_iterate(&verify_cl);
1654     }
1655 
1656     Atomic::add(verify_cl.failures(), &_failures);
1657   }
1658 
1659   int failures() const { return _failures; }
1660 };
1661 
1662 // Closure that finalizes the liveness counting data.
1663 // Used during the cleanup pause.
1664 // Sets the bits corresponding to the interval [NTAMS, top]
1665 // (which contains the implicitly live objects) in the
1666 // card liveness bitmap. Also sets the bit for each region,
1667 // containing live data, in the region liveness bitmap.
1668 
1669 class FinalCountDataUpdateClosure: public CMCountDataClosureBase {
1670  public:
1671   FinalCountDataUpdateClosure(G1CollectedHeap* g1h,
1672                               BitMap* region_bm,
1673                               BitMap* card_bm) :
1674     CMCountDataClosureBase(g1h, region_bm, card_bm) { }
1675 
1676   bool doHeapRegion(HeapRegion* hr) {
1677 
1678     if (hr->continuesHumongous()) {
1679       // We will ignore these here and process them when their
1680       // associated "starts humongous" region is processed (see
1681       // set_bit_for_heap_region()). Note that we cannot rely on their
1682       // associated "starts humongous" region to have their bit set to
1683       // 1 since, due to the region chunking in the parallel region
1684       // iteration, a "continues humongous" region might be visited
1685       // before its associated "starts humongous".
1686       return false;
1687     }
1688 
1689     HeapWord* ntams = hr->next_top_at_mark_start();
1690     HeapWord* top   = hr->top();
1691 
1692     assert(hr->bottom() <= ntams && ntams <= hr->end(), "Preconditions.");
1693 
1694     // Mark the allocated-since-marking portion...
1695     if (ntams < top) {
1696       // This definitely means the region has live objects.
1697       set_bit_for_region(hr);
1698 
1699       // Now set the bits in the card bitmap for [ntams, top)
1700       BitMap::idx_t start_idx = _cm->card_bitmap_index_for(ntams);
1701       BitMap::idx_t end_idx = _cm->card_bitmap_index_for(top);
1702 
1703       // Note: if we're looking at the last region in heap - top
1704       // could be actually just beyond the end of the heap; end_idx
1705       // will then correspond to a (non-existent) card that is also
1706       // just beyond the heap.
1707       if (_g1h->is_in_g1_reserved(top) && !_ct_bs->is_card_aligned(top)) {
1708         // end of object is not card aligned - increment to cover
1709         // all the cards spanned by the object
1710         end_idx += 1;
1711       }
1712 
1713       assert(end_idx <= _card_bm->size(),
1714              err_msg("oob: end_idx=  "SIZE_FORMAT", bitmap size= "SIZE_FORMAT,
1715                      end_idx, _card_bm->size()));
1716       assert(start_idx < _card_bm->size(),
1717              err_msg("oob: start_idx=  "SIZE_FORMAT", bitmap size= "SIZE_FORMAT,
1718                      start_idx, _card_bm->size()));
1719 
1720       _cm->set_card_bitmap_range(_card_bm, start_idx, end_idx, true /* is_par */);
1721     }
1722 
1723     // Set the bit for the region if it contains live data
1724     if (hr->next_marked_bytes() > 0) {
1725       set_bit_for_region(hr);
1726     }
1727 
1728     return false;
1729   }
1730 };
1731 
1732 class G1ParFinalCountTask: public AbstractGangTask {
1733 protected:
1734   G1CollectedHeap* _g1h;
1735   ConcurrentMark* _cm;
1736   BitMap* _actual_region_bm;
1737   BitMap* _actual_card_bm;
1738 
1739   uint    _n_workers;
1740 
1741 public:
1742   G1ParFinalCountTask(G1CollectedHeap* g1h, BitMap* region_bm, BitMap* card_bm)
1743     : AbstractGangTask("G1 final counting"),
1744       _g1h(g1h), _cm(_g1h->concurrent_mark()),
1745       _actual_region_bm(region_bm), _actual_card_bm(card_bm),
1746       _n_workers(0) {
1747     // Use the value already set as the number of active threads
1748     // in the call to run_task().
1749     if (G1CollectedHeap::use_parallel_gc_threads()) {
1750       assert( _g1h->workers()->active_workers() > 0,
1751         "Should have been previously set");
1752       _n_workers = _g1h->workers()->active_workers();
1753     } else {
1754       _n_workers = 1;
1755     }
1756   }
1757 
1758   void work(uint worker_id) {
1759     assert(worker_id < _n_workers, "invariant");
1760 
1761     FinalCountDataUpdateClosure final_update_cl(_g1h,
1762                                                 _actual_region_bm,
1763                                                 _actual_card_bm);
1764 
1765     if (G1CollectedHeap::use_parallel_gc_threads()) {
1766       _g1h->heap_region_par_iterate_chunked(&final_update_cl,
1767                                             worker_id,
1768                                             _n_workers,
1769                                             HeapRegion::FinalCountClaimValue);
1770     } else {
1771       _g1h->heap_region_iterate(&final_update_cl);
1772     }
1773   }
1774 };
1775 
1776 class G1ParNoteEndTask;
1777 
1778 class G1NoteEndOfConcMarkClosure : public HeapRegionClosure {
1779   G1CollectedHeap* _g1;
1780   int _worker_num;
1781   size_t _max_live_bytes;
1782   uint _regions_claimed;
1783   size_t _freed_bytes;
1784   FreeRegionList* _local_cleanup_list;
1785   OldRegionSet* _old_proxy_set;
1786   HumongousRegionSet* _humongous_proxy_set;
1787   HRRSCleanupTask* _hrrs_cleanup_task;
1788   double _claimed_region_time;
1789   double _max_region_time;
1790 
1791 public:
1792   G1NoteEndOfConcMarkClosure(G1CollectedHeap* g1,
1793                              int worker_num,
1794                              FreeRegionList* local_cleanup_list,
1795                              OldRegionSet* old_proxy_set,
1796                              HumongousRegionSet* humongous_proxy_set,
1797                              HRRSCleanupTask* hrrs_cleanup_task) :
1798     _g1(g1), _worker_num(worker_num),
1799     _max_live_bytes(0), _regions_claimed(0),
1800     _freed_bytes(0),
1801     _claimed_region_time(0.0), _max_region_time(0.0),
1802     _local_cleanup_list(local_cleanup_list),
1803     _old_proxy_set(old_proxy_set),
1804     _humongous_proxy_set(humongous_proxy_set),
1805     _hrrs_cleanup_task(hrrs_cleanup_task) { }
1806 
1807   size_t freed_bytes() { return _freed_bytes; }
1808 
1809   bool doHeapRegion(HeapRegion *hr) {
1810     if (hr->continuesHumongous()) {
1811       return false;
1812     }
1813     // We use a claim value of zero here because all regions
1814     // were claimed with value 1 in the FinalCount task.
1815     _g1->reset_gc_time_stamps(hr);
1816     double start = os::elapsedTime();
1817     _regions_claimed++;
1818     hr->note_end_of_marking();
1819     _max_live_bytes += hr->max_live_bytes();
1820     _g1->free_region_if_empty(hr,
1821                               &_freed_bytes,
1822                               _local_cleanup_list,
1823                               _old_proxy_set,
1824                               _humongous_proxy_set,
1825                               _hrrs_cleanup_task,
1826                               true /* par */);
1827     double region_time = (os::elapsedTime() - start);
1828     _claimed_region_time += region_time;
1829     if (region_time > _max_region_time) {
1830       _max_region_time = region_time;
1831     }
1832     return false;
1833   }
1834 
1835   size_t max_live_bytes() { return _max_live_bytes; }
1836   uint regions_claimed() { return _regions_claimed; }
1837   double claimed_region_time_sec() { return _claimed_region_time; }
1838   double max_region_time_sec() { return _max_region_time; }
1839 };
1840 
1841 class G1ParNoteEndTask: public AbstractGangTask {
1842   friend class G1NoteEndOfConcMarkClosure;
1843 
1844 protected:
1845   G1CollectedHeap* _g1h;
1846   size_t _max_live_bytes;
1847   size_t _freed_bytes;
1848   FreeRegionList* _cleanup_list;
1849 
1850 public:
1851   G1ParNoteEndTask(G1CollectedHeap* g1h,
1852                    FreeRegionList* cleanup_list) :
1853     AbstractGangTask("G1 note end"), _g1h(g1h),
1854     _max_live_bytes(0), _freed_bytes(0), _cleanup_list(cleanup_list) { }
1855 
1856   void work(uint worker_id) {
1857     double start = os::elapsedTime();
1858     FreeRegionList local_cleanup_list("Local Cleanup List");
1859     OldRegionSet old_proxy_set("Local Cleanup Old Proxy Set");
1860     HumongousRegionSet humongous_proxy_set("Local Cleanup Humongous Proxy Set");
1861     HRRSCleanupTask hrrs_cleanup_task;
1862     G1NoteEndOfConcMarkClosure g1_note_end(_g1h, worker_id, &local_cleanup_list,
1863                                            &old_proxy_set,
1864                                            &humongous_proxy_set,
1865                                            &hrrs_cleanup_task);
1866     if (G1CollectedHeap::use_parallel_gc_threads()) {
1867       _g1h->heap_region_par_iterate_chunked(&g1_note_end, worker_id,
1868                                             _g1h->workers()->active_workers(),
1869                                             HeapRegion::NoteEndClaimValue);
1870     } else {
1871       _g1h->heap_region_iterate(&g1_note_end);
1872     }
1873     assert(g1_note_end.complete(), "Shouldn't have yielded!");
1874 
1875     // Now update the lists
1876     _g1h->update_sets_after_freeing_regions(g1_note_end.freed_bytes(),
1877                                             NULL /* free_list */,
1878                                             &old_proxy_set,
1879                                             &humongous_proxy_set,
1880                                             true /* par */);
1881     {
1882       MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
1883       _max_live_bytes += g1_note_end.max_live_bytes();
1884       _freed_bytes += g1_note_end.freed_bytes();
1885 
1886       // If we iterate over the global cleanup list at the end of
1887       // cleanup to do this printing we will not guarantee to only
1888       // generate output for the newly-reclaimed regions (the list
1889       // might not be empty at the beginning of cleanup; we might
1890       // still be working on its previous contents). So we do the
1891       // printing here, before we append the new regions to the global
1892       // cleanup list.
1893 
1894       G1HRPrinter* hr_printer = _g1h->hr_printer();
1895       if (hr_printer->is_active()) {
1896         HeapRegionLinkedListIterator iter(&local_cleanup_list);
1897         while (iter.more_available()) {
1898           HeapRegion* hr = iter.get_next();
1899           hr_printer->cleanup(hr);
1900         }
1901       }
1902 
1903       _cleanup_list->add_as_tail(&local_cleanup_list);
1904       assert(local_cleanup_list.is_empty(), "post-condition");
1905 
1906       HeapRegionRemSet::finish_cleanup_task(&hrrs_cleanup_task);
1907     }
1908   }
1909   size_t max_live_bytes() { return _max_live_bytes; }
1910   size_t freed_bytes() { return _freed_bytes; }
1911 };
1912 
1913 class G1ParScrubRemSetTask: public AbstractGangTask {
1914 protected:
1915   G1RemSet* _g1rs;
1916   BitMap* _region_bm;
1917   BitMap* _card_bm;
1918 public:
1919   G1ParScrubRemSetTask(G1CollectedHeap* g1h,
1920                        BitMap* region_bm, BitMap* card_bm) :
1921     AbstractGangTask("G1 ScrubRS"), _g1rs(g1h->g1_rem_set()),
1922     _region_bm(region_bm), _card_bm(card_bm) { }
1923 
1924   void work(uint worker_id) {
1925     if (G1CollectedHeap::use_parallel_gc_threads()) {
1926       _g1rs->scrub_par(_region_bm, _card_bm, worker_id,
1927                        HeapRegion::ScrubRemSetClaimValue);
1928     } else {
1929       _g1rs->scrub(_region_bm, _card_bm);
1930     }
1931   }
1932 
1933 };
1934 
1935 void ConcurrentMark::cleanup() {
1936   // world is stopped at this checkpoint
1937   assert(SafepointSynchronize::is_at_safepoint(),
1938          "world should be stopped");
1939   G1CollectedHeap* g1h = G1CollectedHeap::heap();
1940 
1941   // If a full collection has happened, we shouldn't do this.
1942   if (has_aborted()) {
1943     g1h->set_marking_complete(); // So bitmap clearing isn't confused
1944     return;
1945   }
1946 
1947   HRSPhaseSetter x(HRSPhaseCleanup);
1948   g1h->verify_region_sets_optional();
1949 
1950   if (VerifyDuringGC) {
1951     HandleMark hm;  // handle scope
1952     gclog_or_tty->print(" VerifyDuringGC:(before)");
1953     Universe::heap()->prepare_for_verify();
1954     Universe::verify(/* silent */ false,
1955                      /* option */ VerifyOption_G1UsePrevMarking);
1956   }
1957 
1958   G1CollectorPolicy* g1p = G1CollectedHeap::heap()->g1_policy();
1959   g1p->record_concurrent_mark_cleanup_start();
1960 
1961   double start = os::elapsedTime();
1962 
1963   HeapRegionRemSet::reset_for_cleanup_tasks();
1964 
1965   uint n_workers;
1966 
1967   // Do counting once more with the world stopped for good measure.
1968   G1ParFinalCountTask g1_par_count_task(g1h, &_region_bm, &_card_bm);
1969 
1970   if (G1CollectedHeap::use_parallel_gc_threads()) {
1971    assert(g1h->check_heap_region_claim_values(HeapRegion::InitialClaimValue),
1972            "sanity check");
1973 
1974     g1h->set_par_threads();
1975     n_workers = g1h->n_par_threads();
1976     assert(g1h->n_par_threads() == n_workers,
1977            "Should not have been reset");
1978     g1h->workers()->run_task(&g1_par_count_task);
1979     // Done with the parallel phase so reset to 0.
1980     g1h->set_par_threads(0);
1981 
1982     assert(g1h->check_heap_region_claim_values(HeapRegion::FinalCountClaimValue),
1983            "sanity check");
1984   } else {
1985     n_workers = 1;
1986     g1_par_count_task.work(0);
1987   }
1988 
1989   if (VerifyDuringGC) {
1990     // Verify that the counting data accumulated during marking matches
1991     // that calculated by walking the marking bitmap.
1992 
1993     // Bitmaps to hold expected values
1994     BitMap expected_region_bm(_region_bm.size(), false);
1995     BitMap expected_card_bm(_card_bm.size(), false);
1996 
1997     G1ParVerifyFinalCountTask g1_par_verify_task(g1h,
1998                                                  &_region_bm,
1999                                                  &_card_bm,
2000                                                  &expected_region_bm,
2001                                                  &expected_card_bm);
2002 
2003     if (G1CollectedHeap::use_parallel_gc_threads()) {
2004       g1h->set_par_threads((int)n_workers);
2005       g1h->workers()->run_task(&g1_par_verify_task);
2006       // Done with the parallel phase so reset to 0.
2007       g1h->set_par_threads(0);
2008 
2009       assert(g1h->check_heap_region_claim_values(HeapRegion::VerifyCountClaimValue),
2010              "sanity check");
2011     } else {
2012       g1_par_verify_task.work(0);
2013     }
2014 
2015     guarantee(g1_par_verify_task.failures() == 0, "Unexpected accounting failures");
2016   }
2017 
2018   size_t start_used_bytes = g1h->used();
2019   g1h->set_marking_complete();
2020 
2021   double count_end = os::elapsedTime();
2022   double this_final_counting_time = (count_end - start);
2023   _total_counting_time += this_final_counting_time;
2024 
2025   if (G1PrintRegionLivenessInfo) {
2026     G1PrintRegionLivenessInfoClosure cl(gclog_or_tty, "Post-Marking");
2027     _g1h->heap_region_iterate(&cl);
2028   }
2029 
2030   // Install newly created mark bitMap as "prev".
2031   swapMarkBitMaps();
2032 
2033   g1h->reset_gc_time_stamp();
2034 
2035   // Note end of marking in all heap regions.
2036   G1ParNoteEndTask g1_par_note_end_task(g1h, &_cleanup_list);
2037   if (G1CollectedHeap::use_parallel_gc_threads()) {
2038     g1h->set_par_threads((int)n_workers);
2039     g1h->workers()->run_task(&g1_par_note_end_task);
2040     g1h->set_par_threads(0);
2041 
2042     assert(g1h->check_heap_region_claim_values(HeapRegion::NoteEndClaimValue),
2043            "sanity check");
2044   } else {
2045     g1_par_note_end_task.work(0);
2046   }
2047   g1h->check_gc_time_stamps();
2048 
2049   if (!cleanup_list_is_empty()) {
2050     // The cleanup list is not empty, so we'll have to process it
2051     // concurrently. Notify anyone else that might be wanting free
2052     // regions that there will be more free regions coming soon.
2053     g1h->set_free_regions_coming();
2054   }
2055 
2056   // call below, since it affects the metric by which we sort the heap
2057   // regions.
2058   if (G1ScrubRemSets) {
2059     double rs_scrub_start = os::elapsedTime();
2060     G1ParScrubRemSetTask g1_par_scrub_rs_task(g1h, &_region_bm, &_card_bm);
2061     if (G1CollectedHeap::use_parallel_gc_threads()) {
2062       g1h->set_par_threads((int)n_workers);
2063       g1h->workers()->run_task(&g1_par_scrub_rs_task);
2064       g1h->set_par_threads(0);
2065 
2066       assert(g1h->check_heap_region_claim_values(
2067                                             HeapRegion::ScrubRemSetClaimValue),
2068              "sanity check");
2069     } else {
2070       g1_par_scrub_rs_task.work(0);
2071     }
2072 
2073     double rs_scrub_end = os::elapsedTime();
2074     double this_rs_scrub_time = (rs_scrub_end - rs_scrub_start);
2075     _total_rs_scrub_time += this_rs_scrub_time;
2076   }
2077 
2078   // this will also free any regions totally full of garbage objects,
2079   // and sort the regions.
2080   g1h->g1_policy()->record_concurrent_mark_cleanup_end((int)n_workers);
2081 
2082   // Statistics.
2083   double end = os::elapsedTime();
2084   _cleanup_times.add((end - start) * 1000.0);
2085 
2086   if (G1Log::fine()) {
2087     g1h->print_size_transition(gclog_or_tty,
2088                                start_used_bytes,
2089                                g1h->used(),
2090                                g1h->capacity());
2091   }
2092 
2093   // Clean up will have freed any regions completely full of garbage.
2094   // Update the soft reference policy with the new heap occupancy.
2095   Universe::update_heap_info_at_gc();
2096 
2097   // We need to make this be a "collection" so any collection pause that
2098   // races with it goes around and waits for completeCleanup to finish.
2099   g1h->increment_total_collections();
2100 
2101   // We reclaimed old regions so we should calculate the sizes to make
2102   // sure we update the old gen/space data.
2103   g1h->g1mm()->update_sizes();
2104 
2105   if (VerifyDuringGC) {
2106     HandleMark hm;  // handle scope
2107     gclog_or_tty->print(" VerifyDuringGC:(after)");
2108     Universe::heap()->prepare_for_verify();
2109     Universe::verify(/* silent */ false,
2110                      /* option */ VerifyOption_G1UsePrevMarking);
2111   }
2112 
2113   g1h->verify_region_sets_optional();
2114 }
2115 
2116 void ConcurrentMark::completeCleanup() {
2117   if (has_aborted()) return;
2118 
2119   G1CollectedHeap* g1h = G1CollectedHeap::heap();
2120 
2121   _cleanup_list.verify_optional();
2122   FreeRegionList tmp_free_list("Tmp Free List");
2123 
2124   if (G1ConcRegionFreeingVerbose) {
2125     gclog_or_tty->print_cr("G1ConcRegionFreeing [complete cleanup] : "
2126                            "cleanup list has %u entries",
2127                            _cleanup_list.length());
2128   }
2129 
2130   // Noone else should be accessing the _cleanup_list at this point,
2131   // so it's not necessary to take any locks
2132   while (!_cleanup_list.is_empty()) {
2133     HeapRegion* hr = _cleanup_list.remove_head();
2134     assert(hr != NULL, "the list was not empty");
2135     hr->par_clear();
2136     tmp_free_list.add_as_tail(hr);
2137 
2138     // Instead of adding one region at a time to the secondary_free_list,
2139     // we accumulate them in the local list and move them a few at a
2140     // time. This also cuts down on the number of notify_all() calls
2141     // we do during this process. We'll also append the local list when
2142     // _cleanup_list is empty (which means we just removed the last
2143     // region from the _cleanup_list).
2144     if ((tmp_free_list.length() % G1SecondaryFreeListAppendLength == 0) ||
2145         _cleanup_list.is_empty()) {
2146       if (G1ConcRegionFreeingVerbose) {
2147         gclog_or_tty->print_cr("G1ConcRegionFreeing [complete cleanup] : "
2148                                "appending %u entries to the secondary_free_list, "
2149                                "cleanup list still has %u entries",
2150                                tmp_free_list.length(),
2151                                _cleanup_list.length());
2152       }
2153 
2154       {
2155         MutexLockerEx x(SecondaryFreeList_lock, Mutex::_no_safepoint_check_flag);
2156         g1h->secondary_free_list_add_as_tail(&tmp_free_list);
2157         SecondaryFreeList_lock->notify_all();
2158       }
2159 
2160       if (G1StressConcRegionFreeing) {
2161         for (uintx i = 0; i < G1StressConcRegionFreeingDelayMillis; ++i) {
2162           os::sleep(Thread::current(), (jlong) 1, false);
2163         }
2164       }
2165     }
2166   }
2167   assert(tmp_free_list.is_empty(), "post-condition");
2168 }
2169 
2170 // Supporting Object and Oop closures for reference discovery
2171 // and processing in during marking
2172 
2173 bool G1CMIsAliveClosure::do_object_b(oop obj) {
2174   HeapWord* addr = (HeapWord*)obj;
2175   return addr != NULL &&
2176          (!_g1->is_in_g1_reserved(addr) || !_g1->is_obj_ill(obj));
2177 }
2178 
2179 // 'Keep Alive' oop closure used by both serial parallel reference processing.
2180 // Uses the CMTask associated with a worker thread (for serial reference
2181 // processing the CMTask for worker 0 is used) to preserve (mark) and
2182 // trace referent objects.
2183 //
2184 // Using the CMTask and embedded local queues avoids having the worker
2185 // threads operating on the global mark stack. This reduces the risk
2186 // of overflowing the stack - which we would rather avoid at this late
2187 // state. Also using the tasks' local queues removes the potential
2188 // of the workers interfering with each other that could occur if
2189 // operating on the global stack.
2190 
2191 class G1CMKeepAliveAndDrainClosure: public OopClosure {
2192   ConcurrentMark* _cm;
2193   CMTask*         _task;
2194   int             _ref_counter_limit;
2195   int             _ref_counter;
2196   bool            _is_serial;
2197  public:
2198   G1CMKeepAliveAndDrainClosure(ConcurrentMark* cm, CMTask* task, bool is_serial) :
2199     _cm(cm), _task(task), _is_serial(is_serial),
2200     _ref_counter_limit(G1RefProcDrainInterval) {
2201     assert(_ref_counter_limit > 0, "sanity");
2202     assert(!_is_serial || _task->worker_id() == 0, "only task 0 for serial code");
2203     _ref_counter = _ref_counter_limit;
2204   }
2205 
2206   virtual void do_oop(narrowOop* p) { do_oop_work(p); }
2207   virtual void do_oop(      oop* p) { do_oop_work(p); }
2208 
2209   template <class T> void do_oop_work(T* p) {
2210     if (!_cm->has_overflown()) {
2211       oop obj = oopDesc::load_decode_heap_oop(p);
2212       if (_cm->verbose_high()) {
2213         gclog_or_tty->print_cr("\t[%u] we're looking at location "
2214                                "*"PTR_FORMAT" = "PTR_FORMAT,
2215                                _task->worker_id(), p, (void*) obj);
2216       }
2217 
2218       _task->deal_with_reference(obj);
2219       _ref_counter--;
2220 
2221       if (_ref_counter == 0) {
2222         // We have dealt with _ref_counter_limit references, pushing them
2223         // and objects reachable from them on to the local stack (and
2224         // possibly the global stack). Call CMTask::do_marking_step() to
2225         // process these entries.
2226         //
2227         // We call CMTask::do_marking_step() in a loop, which we'll exit if
2228         // there's nothing more to do (i.e. we're done with the entries that
2229         // were pushed as a result of the CMTask::deal_with_reference() calls
2230         // above) or we overflow.
2231         //
2232         // Note: CMTask::do_marking_step() can set the CMTask::has_aborted()
2233         // flag while there may still be some work to do. (See the comment at
2234         // the beginning of CMTask::do_marking_step() for those conditions -
2235         // one of which is reaching the specified time target.) It is only
2236         // when CMTask::do_marking_step() returns without setting the
2237         // has_aborted() flag that the marking step has completed.
2238         do {
2239           double mark_step_duration_ms = G1ConcMarkStepDurationMillis;
2240           _task->do_marking_step(mark_step_duration_ms,
2241                                  false      /* do_termination */,
2242                                  _is_serial /* is_serial      */);
2243         } while (_task->has_aborted() && !_cm->has_overflown());
2244         _ref_counter = _ref_counter_limit;
2245       }
2246     } else {
2247       if (_cm->verbose_high()) {
2248          gclog_or_tty->print_cr("\t[%u] CM Overflow", _task->worker_id());
2249       }
2250     }
2251   }
2252 };
2253 
2254 // 'Drain' oop closure used by both serial and parallel reference processing.
2255 // Uses the CMTask associated with a given worker thread (for serial
2256 // reference processing the CMtask for worker 0 is used). Calls the
2257 // do_marking_step routine, with an unbelievably large timeout value,
2258 // to drain the marking data structures of the remaining entries
2259 // added by the 'keep alive' oop closure above.
2260 
2261 class G1CMDrainMarkingStackClosure: public VoidClosure {
2262   ConcurrentMark* _cm;
2263   CMTask*         _task;
2264   bool            _is_serial;
2265  public:
2266   G1CMDrainMarkingStackClosure(ConcurrentMark* cm, CMTask* task, bool is_serial) :
2267     _cm(cm), _task(task) {
2268     assert(!_is_serial || _task->worker_id() == 0, "only task 0 for serial code");
2269   }
2270 
2271   void do_void() {
2272     do {
2273       if (_cm->verbose_high()) {
2274         gclog_or_tty->print_cr("\t[%u] Drain: Calling do_marking_step - serial: %s",
2275                                _task->worker_id(), BOOL_TO_STR(_is_serial));
2276       }
2277 
2278       // We call CMTask::do_marking_step() to completely drain the local
2279       // and global marking stacks of entries pushed by the 'keep alive'
2280       // oop closure (an instance of G1CMKeepAliveAndDrainClosure above).
2281       //
2282       // CMTask::do_marking_step() is called in a loop, which we'll exit
2283       // if there's nothing more to do (i.e. we'completely drained the
2284       // entries that were pushed as a a result of applying the 'keep alive'
2285       // closure to the entries on the discovered ref lists) or we overflow
2286       // the global marking stack.
2287       //
2288       // Note: CMTask::do_marking_step() can set the CMTask::has_aborted()
2289       // flag while there may still be some work to do. (See the comment at
2290       // the beginning of CMTask::do_marking_step() for those conditions -
2291       // one of which is reaching the specified time target.) It is only
2292       // when CMTask::do_marking_step() returns without setting the
2293       // has_aborted() flag that the marking step has completed.
2294 
2295       _task->do_marking_step(1000000000.0 /* something very large */,
2296                              true        /* do_termination */,
2297                              _is_serial  /* is_serial      */);
2298     } while (_task->has_aborted() && !_cm->has_overflown());
2299   }
2300 };
2301 
2302 // Implementation of AbstractRefProcTaskExecutor for parallel
2303 // reference processing at the end of G1 concurrent marking
2304 
2305 class G1CMRefProcTaskExecutor: public AbstractRefProcTaskExecutor {
2306 private:
2307   G1CollectedHeap* _g1h;
2308   ConcurrentMark*  _cm;
2309   WorkGang*        _workers;
2310   int              _active_workers;
2311 
2312 public:
2313   G1CMRefProcTaskExecutor(G1CollectedHeap* g1h,
2314                         ConcurrentMark* cm,
2315                         WorkGang* workers,
2316                         int n_workers) :
2317     _g1h(g1h), _cm(cm),
2318     _workers(workers), _active_workers(n_workers) { }
2319 
2320   // Executes the given task using concurrent marking worker threads.
2321   virtual void execute(ProcessTask& task);
2322   virtual void execute(EnqueueTask& task);
2323 };
2324 
2325 class G1CMRefProcTaskProxy: public AbstractGangTask {
2326   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
2327   ProcessTask&     _proc_task;
2328   G1CollectedHeap* _g1h;
2329   ConcurrentMark*  _cm;
2330 
2331 public:
2332   G1CMRefProcTaskProxy(ProcessTask& proc_task,
2333                      G1CollectedHeap* g1h,
2334                      ConcurrentMark* cm) :
2335     AbstractGangTask("Process reference objects in parallel"),
2336     _proc_task(proc_task), _g1h(g1h), _cm(cm) {
2337     ReferenceProcessor* rp = _g1h->ref_processor_cm();
2338     assert(rp->processing_is_mt(), "shouldn't be here otherwise");
2339   }
2340 
2341   virtual void work(uint worker_id) {
2342     CMTask* task = _cm->task(worker_id);
2343     G1CMIsAliveClosure g1_is_alive(_g1h);
2344     G1CMKeepAliveAndDrainClosure g1_par_keep_alive(_cm, task, false /* is_serial */);
2345     G1CMDrainMarkingStackClosure g1_par_drain(_cm, task, false /* is_serial */);
2346 
2347     _proc_task.work(worker_id, g1_is_alive, g1_par_keep_alive, g1_par_drain);
2348   }
2349 };
2350 
2351 void G1CMRefProcTaskExecutor::execute(ProcessTask& proc_task) {
2352   assert(_workers != NULL, "Need parallel worker threads.");
2353   assert(_g1h->ref_processor_cm()->processing_is_mt(), "processing is not MT");
2354 
2355   G1CMRefProcTaskProxy proc_task_proxy(proc_task, _g1h, _cm);
2356 
2357   // We need to reset the phase for each task execution so that
2358   // the termination protocol of CMTask::do_marking_step works.
2359   _cm->set_phase(_active_workers, false /* concurrent */);
2360   _g1h->set_par_threads(_active_workers);
2361   _workers->run_task(&proc_task_proxy);
2362   _g1h->set_par_threads(0);
2363 }
2364 
2365 class G1CMRefEnqueueTaskProxy: public AbstractGangTask {
2366   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
2367   EnqueueTask& _enq_task;
2368 
2369 public:
2370   G1CMRefEnqueueTaskProxy(EnqueueTask& enq_task) :
2371     AbstractGangTask("Enqueue reference objects in parallel"),
2372     _enq_task(enq_task) { }
2373 
2374   virtual void work(uint worker_id) {
2375     _enq_task.work(worker_id);
2376   }
2377 };
2378 
2379 void G1CMRefProcTaskExecutor::execute(EnqueueTask& enq_task) {
2380   assert(_workers != NULL, "Need parallel worker threads.");
2381   assert(_g1h->ref_processor_cm()->processing_is_mt(), "processing is not MT");
2382 
2383   G1CMRefEnqueueTaskProxy enq_task_proxy(enq_task);
2384 
2385   _g1h->set_par_threads(_active_workers);
2386   _workers->run_task(&enq_task_proxy);
2387   _g1h->set_par_threads(0);
2388 }
2389 
2390 void ConcurrentMark::weakRefsWork(bool clear_all_soft_refs) {
2391   ResourceMark rm;
2392   HandleMark   hm;
2393 
2394   G1CollectedHeap* g1h = G1CollectedHeap::heap();
2395 
2396   // Is alive closure.
2397   G1CMIsAliveClosure g1_is_alive(g1h);
2398 
2399   // Inner scope to exclude the cleaning of the string and symbol
2400   // tables from the displayed time.
2401   {
2402     if (G1Log::finer()) {
2403       gclog_or_tty->put(' ');
2404     }
2405     TraceTime t("GC ref-proc", G1Log::finer(), false, gclog_or_tty);
2406 
2407     ReferenceProcessor* rp = g1h->ref_processor_cm();
2408 
2409     // See the comment in G1CollectedHeap::ref_processing_init()
2410     // about how reference processing currently works in G1.
2411 
2412     // Set the soft reference policy
2413     rp->setup_policy(clear_all_soft_refs);
2414     assert(_markStack.isEmpty(), "mark stack should be empty");
2415 
2416     // Instances of the 'Keep Alive' and 'Complete GC' closures used
2417     // in serial reference processing. Note these closures are also
2418     // used for serially processing (by the the current thread) the
2419     // JNI references during parallel reference processing.
2420     //
2421     // These closures do not need to synchronize with the worker
2422     // threads involved in parallel reference processing as these
2423     // instances are executed serially by the current thread (e.g.
2424     // reference processing is not multi-threaded and is thus
2425     // performed by the current thread instead of a gang worker).
2426     //
2427     // The gang tasks involved in parallel reference procssing create
2428     // their own instances of these closures, which do their own
2429     // synchronization among themselves.
2430     G1CMKeepAliveAndDrainClosure g1_keep_alive(this, task(0), true /* is_serial */);
2431     G1CMDrainMarkingStackClosure g1_drain_mark_stack(this, task(0), true /* is_serial */);
2432 
2433     // We need at least one active thread. If reference processing
2434     // is not multi-threaded we use the current (VMThread) thread,
2435     // otherwise we use the work gang from the G1CollectedHeap and
2436     // we utilize all the worker threads we can.
2437     bool processing_is_mt = rp->processing_is_mt() && g1h->workers() != NULL;
2438     uint active_workers = (processing_is_mt ? g1h->workers()->active_workers() : 1U);
2439     active_workers = MAX2(MIN2(active_workers, _max_worker_id), 1U);
2440 
2441     // Parallel processing task executor.
2442     G1CMRefProcTaskExecutor par_task_executor(g1h, this,
2443                                               g1h->workers(), active_workers);
2444     AbstractRefProcTaskExecutor* executor = (processing_is_mt ? &par_task_executor : NULL);
2445 
2446     // Set the degree of MT processing here.  If the discovery was done MT,
2447     // the number of threads involved during discovery could differ from
2448     // the number of active workers.  This is OK as long as the discovered
2449     // Reference lists are balanced (see balance_all_queues() and balance_queues()).
2450     rp->set_active_mt_degree(active_workers);
2451 
2452     // Process the weak references.
2453     rp->process_discovered_references(&g1_is_alive,
2454                                       &g1_keep_alive,
2455                                       &g1_drain_mark_stack,
2456                                       executor);
2457 
2458     // The do_oop work routines of the keep_alive and drain_marking_stack
2459     // oop closures will set the has_overflown flag if we overflow the
2460     // global marking stack.
2461 
2462     assert(_markStack.overflow() || _markStack.isEmpty(),
2463             "mark stack should be empty (unless it overflowed)");
2464 
2465     if (_markStack.overflow()) {
2466       // This should have been done already when we tried to push an
2467       // entry on to the global mark stack. But let's do it again.
2468       set_has_overflown();
2469     }
2470 
2471     assert(rp->num_q() == active_workers, "why not");
2472 
2473     rp->enqueue_discovered_references(executor);
2474 
2475     rp->verify_no_references_recorded();
2476     assert(!rp->discovery_enabled(), "Post condition");
2477   }
2478 
2479   // Now clean up stale oops in StringTable
2480   StringTable::unlink(&g1_is_alive);
2481   // Clean up unreferenced symbols in symbol table.
2482   SymbolTable::unlink();
2483 }
2484 
2485 void ConcurrentMark::swapMarkBitMaps() {
2486   CMBitMapRO* temp = _prevMarkBitMap;
2487   _prevMarkBitMap  = (CMBitMapRO*)_nextMarkBitMap;
2488   _nextMarkBitMap  = (CMBitMap*)  temp;
2489 }
2490 
2491 class CMRemarkTask: public AbstractGangTask {
2492 private:
2493   ConcurrentMark* _cm;
2494   bool            _is_serial;
2495 public:
2496   void work(uint worker_id) {
2497     // Since all available tasks are actually started, we should
2498     // only proceed if we're supposed to be actived.
2499     if (worker_id < _cm->active_tasks()) {
2500       CMTask* task = _cm->task(worker_id);
2501       task->record_start_time();
2502       do {
2503         task->do_marking_step(1000000000.0 /* something very large */,
2504                               true         /* do_termination       */,
2505                               _is_serial);
2506       } while (task->has_aborted() && !_cm->has_overflown());
2507       // If we overflow, then we do not want to restart. We instead
2508       // want to abort remark and do concurrent marking again.
2509       task->record_end_time();
2510     }
2511   }
2512 
2513   CMRemarkTask(ConcurrentMark* cm, int active_workers, bool is_serial) :
2514     AbstractGangTask("Par Remark"), _cm(cm), _is_serial(is_serial) {
2515     _cm->terminator()->reset_for_reuse(active_workers);
2516   }
2517 };
2518 
2519 void ConcurrentMark::checkpointRootsFinalWork() {
2520   ResourceMark rm;
2521   HandleMark   hm;
2522   G1CollectedHeap* g1h = G1CollectedHeap::heap();
2523 
2524   g1h->ensure_parsability(false);
2525 
2526   if (G1CollectedHeap::use_parallel_gc_threads()) {
2527     G1CollectedHeap::StrongRootsScope srs(g1h);
2528     // this is remark, so we'll use up all active threads
2529     uint active_workers = g1h->workers()->active_workers();
2530     if (active_workers == 0) {
2531       assert(active_workers > 0, "Should have been set earlier");
2532       active_workers = (uint) ParallelGCThreads;
2533       g1h->workers()->set_active_workers(active_workers);
2534     }
2535     set_phase(active_workers, false /* concurrent */);
2536     // Leave _parallel_marking_threads at it's
2537     // value originally calculated in the ConcurrentMark
2538     // constructor and pass values of the active workers
2539     // through the gang in the task.
2540 
2541     CMRemarkTask remarkTask(this, active_workers, false /* is_serial */);
2542     // We will start all available threads, even if we decide that the
2543     // active_workers will be fewer. The extra ones will just bail out
2544     // immediately.
2545     g1h->set_par_threads(active_workers);
2546     g1h->workers()->run_task(&remarkTask);
2547     g1h->set_par_threads(0);
2548   } else {
2549     G1CollectedHeap::StrongRootsScope srs(g1h);
2550     uint active_workers = 1;
2551     set_phase(active_workers, false /* concurrent */);
2552 
2553     // Note - if there's no work gang then the VMThread will be
2554     // the thread to execute the remark - serially. We have
2555     // to pass true for the is_serial parameter so that
2556     // CMTask::do_marking_step() doesn't enter the sync
2557     // barriers in the event of an overflow. Doing so will
2558     // cause an assert that the current thread is not a
2559     // concurrent GC thread.
2560     CMRemarkTask remarkTask(this, active_workers, true /* is_serial*/);
2561     remarkTask.work(0);
2562   }
2563   SATBMarkQueueSet& satb_mq_set = JavaThread::satb_mark_queue_set();
2564   guarantee(satb_mq_set.completed_buffers_num() == 0, "invariant");
2565 
2566   print_stats();
2567 
2568 #if VERIFY_OBJS_PROCESSED
2569   if (_scan_obj_cl.objs_processed != ThreadLocalObjQueue::objs_enqueued) {
2570     gclog_or_tty->print_cr("Processed = %d, enqueued = %d.",
2571                            _scan_obj_cl.objs_processed,
2572                            ThreadLocalObjQueue::objs_enqueued);
2573     guarantee(_scan_obj_cl.objs_processed ==
2574               ThreadLocalObjQueue::objs_enqueued,
2575               "Different number of objs processed and enqueued.");
2576   }
2577 #endif
2578 }
2579 
2580 #ifndef PRODUCT
2581 
2582 class PrintReachableOopClosure: public OopClosure {
2583 private:
2584   G1CollectedHeap* _g1h;
2585   outputStream*    _out;
2586   VerifyOption     _vo;
2587   bool             _all;
2588 
2589 public:
2590   PrintReachableOopClosure(outputStream* out,
2591                            VerifyOption  vo,
2592                            bool          all) :
2593     _g1h(G1CollectedHeap::heap()),
2594     _out(out), _vo(vo), _all(all) { }
2595 
2596   void do_oop(narrowOop* p) { do_oop_work(p); }
2597   void do_oop(      oop* p) { do_oop_work(p); }
2598 
2599   template <class T> void do_oop_work(T* p) {
2600     oop         obj = oopDesc::load_decode_heap_oop(p);
2601     const char* str = NULL;
2602     const char* str2 = "";
2603 
2604     if (obj == NULL) {
2605       str = "";
2606     } else if (!_g1h->is_in_g1_reserved(obj)) {
2607       str = " O";
2608     } else {
2609       HeapRegion* hr  = _g1h->heap_region_containing(obj);
2610       guarantee(hr != NULL, "invariant");
2611       bool over_tams = _g1h->allocated_since_marking(obj, hr, _vo);
2612       bool marked = _g1h->is_marked(obj, _vo);
2613 
2614       if (over_tams) {
2615         str = " >";
2616         if (marked) {
2617           str2 = " AND MARKED";
2618         }
2619       } else if (marked) {
2620         str = " M";
2621       } else {
2622         str = " NOT";
2623       }
2624     }
2625 
2626     _out->print_cr("  "PTR_FORMAT": "PTR_FORMAT"%s%s",
2627                    p, (void*) obj, str, str2);
2628   }
2629 };
2630 
2631 class PrintReachableObjectClosure : public ObjectClosure {
2632 private:
2633   G1CollectedHeap* _g1h;
2634   outputStream*    _out;
2635   VerifyOption     _vo;
2636   bool             _all;
2637   HeapRegion*      _hr;
2638 
2639 public:
2640   PrintReachableObjectClosure(outputStream* out,
2641                               VerifyOption  vo,
2642                               bool          all,
2643                               HeapRegion*   hr) :
2644     _g1h(G1CollectedHeap::heap()),
2645     _out(out), _vo(vo), _all(all), _hr(hr) { }
2646 
2647   void do_object(oop o) {
2648     bool over_tams = _g1h->allocated_since_marking(o, _hr, _vo);
2649     bool marked = _g1h->is_marked(o, _vo);
2650     bool print_it = _all || over_tams || marked;
2651 
2652     if (print_it) {
2653       _out->print_cr(" "PTR_FORMAT"%s",
2654                      o, (over_tams) ? " >" : (marked) ? " M" : "");
2655       PrintReachableOopClosure oopCl(_out, _vo, _all);
2656       o->oop_iterate_no_header(&oopCl);
2657     }
2658   }
2659 };
2660 
2661 class PrintReachableRegionClosure : public HeapRegionClosure {
2662 private:
2663   G1CollectedHeap* _g1h;
2664   outputStream*    _out;
2665   VerifyOption     _vo;
2666   bool             _all;
2667 
2668 public:
2669   bool doHeapRegion(HeapRegion* hr) {
2670     HeapWord* b = hr->bottom();
2671     HeapWord* e = hr->end();
2672     HeapWord* t = hr->top();
2673     HeapWord* p = _g1h->top_at_mark_start(hr, _vo);
2674     _out->print_cr("** ["PTR_FORMAT", "PTR_FORMAT"] top: "PTR_FORMAT" "
2675                    "TAMS: "PTR_FORMAT, b, e, t, p);
2676     _out->cr();
2677 
2678     HeapWord* from = b;
2679     HeapWord* to   = t;
2680 
2681     if (to > from) {
2682       _out->print_cr("Objects in ["PTR_FORMAT", "PTR_FORMAT"]", from, to);
2683       _out->cr();
2684       PrintReachableObjectClosure ocl(_out, _vo, _all, hr);
2685       hr->object_iterate_mem_careful(MemRegion(from, to), &ocl);
2686       _out->cr();
2687     }
2688 
2689     return false;
2690   }
2691 
2692   PrintReachableRegionClosure(outputStream* out,
2693                               VerifyOption  vo,
2694                               bool          all) :
2695     _g1h(G1CollectedHeap::heap()), _out(out), _vo(vo), _all(all) { }
2696 };
2697 
2698 void ConcurrentMark::print_reachable(const char* str,
2699                                      VerifyOption vo,
2700                                      bool all) {
2701   gclog_or_tty->cr();
2702   gclog_or_tty->print_cr("== Doing heap dump... ");
2703 
2704   if (G1PrintReachableBaseFile == NULL) {
2705     gclog_or_tty->print_cr("  #### error: no base file defined");
2706     return;
2707   }
2708 
2709   if (strlen(G1PrintReachableBaseFile) + 1 + strlen(str) >
2710       (JVM_MAXPATHLEN - 1)) {
2711     gclog_or_tty->print_cr("  #### error: file name too long");
2712     return;
2713   }
2714 
2715   char file_name[JVM_MAXPATHLEN];
2716   sprintf(file_name, "%s.%s", G1PrintReachableBaseFile, str);
2717   gclog_or_tty->print_cr("  dumping to file %s", file_name);
2718 
2719   fileStream fout(file_name);
2720   if (!fout.is_open()) {
2721     gclog_or_tty->print_cr("  #### error: could not open file");
2722     return;
2723   }
2724 
2725   outputStream* out = &fout;
2726   out->print_cr("-- USING %s", _g1h->top_at_mark_start_str(vo));
2727   out->cr();
2728 
2729   out->print_cr("--- ITERATING OVER REGIONS");
2730   out->cr();
2731   PrintReachableRegionClosure rcl(out, vo, all);
2732   _g1h->heap_region_iterate(&rcl);
2733   out->cr();
2734 
2735   gclog_or_tty->print_cr("  done");
2736   gclog_or_tty->flush();
2737 }
2738 
2739 #endif // PRODUCT
2740 
2741 void ConcurrentMark::clearRangePrevBitmap(MemRegion mr) {
2742   // Note we are overriding the read-only view of the prev map here, via
2743   // the cast.
2744   ((CMBitMap*)_prevMarkBitMap)->clearRange(mr);
2745 }
2746 
2747 void ConcurrentMark::clearRangeNextBitmap(MemRegion mr) {
2748   _nextMarkBitMap->clearRange(mr);
2749 }
2750 
2751 void ConcurrentMark::clearRangeBothBitmaps(MemRegion mr) {
2752   clearRangePrevBitmap(mr);
2753   clearRangeNextBitmap(mr);
2754 }
2755 
2756 HeapRegion*
2757 ConcurrentMark::claim_region(uint worker_id) {
2758   // "checkpoint" the finger
2759   HeapWord* finger = _finger;
2760 
2761   // _heap_end will not change underneath our feet; it only changes at
2762   // yield points.
2763   while (finger < _heap_end) {
2764     assert(_g1h->is_in_g1_reserved(finger), "invariant");
2765 
2766     // Note on how this code handles humongous regions. In the
2767     // normal case the finger will reach the start of a "starts
2768     // humongous" (SH) region. Its end will either be the end of the
2769     // last "continues humongous" (CH) region in the sequence, or the
2770     // standard end of the SH region (if the SH is the only region in
2771     // the sequence). That way claim_region() will skip over the CH
2772     // regions. However, there is a subtle race between a CM thread
2773     // executing this method and a mutator thread doing a humongous
2774     // object allocation. The two are not mutually exclusive as the CM
2775     // thread does not need to hold the Heap_lock when it gets
2776     // here. So there is a chance that claim_region() will come across
2777     // a free region that's in the progress of becoming a SH or a CH
2778     // region. In the former case, it will either
2779     //   a) Miss the update to the region's end, in which case it will
2780     //      visit every subsequent CH region, will find their bitmaps
2781     //      empty, and do nothing, or
2782     //   b) Will observe the update of the region's end (in which case
2783     //      it will skip the subsequent CH regions).
2784     // If it comes across a region that suddenly becomes CH, the
2785     // scenario will be similar to b). So, the race between
2786     // claim_region() and a humongous object allocation might force us
2787     // to do a bit of unnecessary work (due to some unnecessary bitmap
2788     // iterations) but it should not introduce and correctness issues.
2789     HeapRegion* curr_region   = _g1h->heap_region_containing_raw(finger);
2790     HeapWord*   bottom        = curr_region->bottom();
2791     HeapWord*   end           = curr_region->end();
2792     HeapWord*   limit         = curr_region->next_top_at_mark_start();
2793 
2794     if (verbose_low()) {
2795       gclog_or_tty->print_cr("[%u] curr_region = "PTR_FORMAT" "
2796                              "["PTR_FORMAT", "PTR_FORMAT"), "
2797                              "limit = "PTR_FORMAT,
2798                              worker_id, curr_region, bottom, end, limit);
2799     }
2800 
2801     // Is the gap between reading the finger and doing the CAS too long?
2802     HeapWord* res = (HeapWord*) Atomic::cmpxchg_ptr(end, &_finger, finger);
2803     if (res == finger) {
2804       // we succeeded
2805 
2806       // notice that _finger == end cannot be guaranteed here since,
2807       // someone else might have moved the finger even further
2808       assert(_finger >= end, "the finger should have moved forward");
2809 
2810       if (verbose_low()) {
2811         gclog_or_tty->print_cr("[%u] we were successful with region = "
2812                                PTR_FORMAT, worker_id, curr_region);
2813       }
2814 
2815       if (limit > bottom) {
2816         if (verbose_low()) {
2817           gclog_or_tty->print_cr("[%u] region "PTR_FORMAT" is not empty, "
2818                                  "returning it ", worker_id, curr_region);
2819         }
2820         return curr_region;
2821       } else {
2822         assert(limit == bottom,
2823                "the region limit should be at bottom");
2824         if (verbose_low()) {
2825           gclog_or_tty->print_cr("[%u] region "PTR_FORMAT" is empty, "
2826                                  "returning NULL", worker_id, curr_region);
2827         }
2828         // we return NULL and the caller should try calling
2829         // claim_region() again.
2830         return NULL;
2831       }
2832     } else {
2833       assert(_finger > finger, "the finger should have moved forward");
2834       if (verbose_low()) {
2835         gclog_or_tty->print_cr("[%u] somebody else moved the finger, "
2836                                "global finger = "PTR_FORMAT", "
2837                                "our finger = "PTR_FORMAT,
2838                                worker_id, _finger, finger);
2839       }
2840 
2841       // read it again
2842       finger = _finger;
2843     }
2844   }
2845 
2846   return NULL;
2847 }
2848 
2849 #ifndef PRODUCT
2850 enum VerifyNoCSetOopsPhase {
2851   VerifyNoCSetOopsStack,
2852   VerifyNoCSetOopsQueues,
2853   VerifyNoCSetOopsSATBCompleted,
2854   VerifyNoCSetOopsSATBThread
2855 };
2856 
2857 class VerifyNoCSetOopsClosure : public OopClosure, public ObjectClosure  {
2858 private:
2859   G1CollectedHeap* _g1h;
2860   VerifyNoCSetOopsPhase _phase;
2861   int _info;
2862 
2863   const char* phase_str() {
2864     switch (_phase) {
2865     case VerifyNoCSetOopsStack:         return "Stack";
2866     case VerifyNoCSetOopsQueues:        return "Queue";
2867     case VerifyNoCSetOopsSATBCompleted: return "Completed SATB Buffers";
2868     case VerifyNoCSetOopsSATBThread:    return "Thread SATB Buffers";
2869     default:                            ShouldNotReachHere();
2870     }
2871     return NULL;
2872   }
2873 
2874   void do_object_work(oop obj) {
2875     guarantee(!_g1h->obj_in_cs(obj),
2876               err_msg("obj: "PTR_FORMAT" in CSet, phase: %s, info: %d",
2877                       (void*) obj, phase_str(), _info));
2878   }
2879 
2880 public:
2881   VerifyNoCSetOopsClosure() : _g1h(G1CollectedHeap::heap()) { }
2882 
2883   void set_phase(VerifyNoCSetOopsPhase phase, int info = -1) {
2884     _phase = phase;
2885     _info = info;
2886   }
2887 
2888   virtual void do_oop(oop* p) {
2889     oop obj = oopDesc::load_decode_heap_oop(p);
2890     do_object_work(obj);
2891   }
2892 
2893   virtual void do_oop(narrowOop* p) {
2894     // We should not come across narrow oops while scanning marking
2895     // stacks and SATB buffers.
2896     ShouldNotReachHere();
2897   }
2898 
2899   virtual void do_object(oop obj) {
2900     do_object_work(obj);
2901   }
2902 };
2903 
2904 void ConcurrentMark::verify_no_cset_oops(bool verify_stacks,
2905                                          bool verify_enqueued_buffers,
2906                                          bool verify_thread_buffers,
2907                                          bool verify_fingers) {
2908   assert(SafepointSynchronize::is_at_safepoint(), "should be at a safepoint");
2909   if (!G1CollectedHeap::heap()->mark_in_progress()) {
2910     return;
2911   }
2912 
2913   VerifyNoCSetOopsClosure cl;
2914 
2915   if (verify_stacks) {
2916     // Verify entries on the global mark stack
2917     cl.set_phase(VerifyNoCSetOopsStack);
2918     _markStack.oops_do(&cl);
2919 
2920     // Verify entries on the task queues
2921     for (uint i = 0; i < _max_worker_id; i += 1) {
2922       cl.set_phase(VerifyNoCSetOopsQueues, i);
2923       CMTaskQueue* queue = _task_queues->queue(i);
2924       queue->oops_do(&cl);
2925     }
2926   }
2927 
2928   SATBMarkQueueSet& satb_qs = JavaThread::satb_mark_queue_set();
2929 
2930   // Verify entries on the enqueued SATB buffers
2931   if (verify_enqueued_buffers) {
2932     cl.set_phase(VerifyNoCSetOopsSATBCompleted);
2933     satb_qs.iterate_completed_buffers_read_only(&cl);
2934   }
2935 
2936   // Verify entries on the per-thread SATB buffers
2937   if (verify_thread_buffers) {
2938     cl.set_phase(VerifyNoCSetOopsSATBThread);
2939     satb_qs.iterate_thread_buffers_read_only(&cl);
2940   }
2941 
2942   if (verify_fingers) {
2943     // Verify the global finger
2944     HeapWord* global_finger = finger();
2945     if (global_finger != NULL && global_finger < _heap_end) {
2946       // The global finger always points to a heap region boundary. We
2947       // use heap_region_containing_raw() to get the containing region
2948       // given that the global finger could be pointing to a free region
2949       // which subsequently becomes continues humongous. If that
2950       // happens, heap_region_containing() will return the bottom of the
2951       // corresponding starts humongous region and the check below will
2952       // not hold any more.
2953       HeapRegion* global_hr = _g1h->heap_region_containing_raw(global_finger);
2954       guarantee(global_finger == global_hr->bottom(),
2955                 err_msg("global finger: "PTR_FORMAT" region: "HR_FORMAT,
2956                         global_finger, HR_FORMAT_PARAMS(global_hr)));
2957     }
2958 
2959     // Verify the task fingers
2960     assert(parallel_marking_threads() <= _max_worker_id, "sanity");
2961     for (int i = 0; i < (int) parallel_marking_threads(); i += 1) {
2962       CMTask* task = _tasks[i];
2963       HeapWord* task_finger = task->finger();
2964       if (task_finger != NULL && task_finger < _heap_end) {
2965         // See above note on the global finger verification.
2966         HeapRegion* task_hr = _g1h->heap_region_containing_raw(task_finger);
2967         guarantee(task_finger == task_hr->bottom() ||
2968                   !task_hr->in_collection_set(),
2969                   err_msg("task finger: "PTR_FORMAT" region: "HR_FORMAT,
2970                           task_finger, HR_FORMAT_PARAMS(task_hr)));
2971       }
2972     }
2973   }
2974 }
2975 #endif // PRODUCT
2976 
2977 // Aggregate the counting data that was constructed concurrently
2978 // with marking.
2979 class AggregateCountDataHRClosure: public HeapRegionClosure {
2980   G1CollectedHeap* _g1h;
2981   ConcurrentMark* _cm;
2982   CardTableModRefBS* _ct_bs;
2983   BitMap* _cm_card_bm;
2984   uint _max_worker_id;
2985 
2986  public:
2987   AggregateCountDataHRClosure(G1CollectedHeap* g1h,
2988                               BitMap* cm_card_bm,
2989                               uint max_worker_id) :
2990     _g1h(g1h), _cm(g1h->concurrent_mark()),
2991     _ct_bs((CardTableModRefBS*) (g1h->barrier_set())),
2992     _cm_card_bm(cm_card_bm), _max_worker_id(max_worker_id) { }
2993 
2994   bool doHeapRegion(HeapRegion* hr) {
2995     if (hr->continuesHumongous()) {
2996       // We will ignore these here and process them when their
2997       // associated "starts humongous" region is processed.
2998       // Note that we cannot rely on their associated
2999       // "starts humongous" region to have their bit set to 1
3000       // since, due to the region chunking in the parallel region
3001       // iteration, a "continues humongous" region might be visited
3002       // before its associated "starts humongous".
3003       return false;
3004     }
3005 
3006     HeapWord* start = hr->bottom();
3007     HeapWord* limit = hr->next_top_at_mark_start();
3008     HeapWord* end = hr->end();
3009 
3010     assert(start <= limit && limit <= hr->top() && hr->top() <= hr->end(),
3011            err_msg("Preconditions not met - "
3012                    "start: "PTR_FORMAT", limit: "PTR_FORMAT", "
3013                    "top: "PTR_FORMAT", end: "PTR_FORMAT,
3014                    start, limit, hr->top(), hr->end()));
3015 
3016     assert(hr->next_marked_bytes() == 0, "Precondition");
3017 
3018     if (start == limit) {
3019       // NTAMS of this region has not been set so nothing to do.
3020       return false;
3021     }
3022 
3023     // 'start' should be in the heap.
3024     assert(_g1h->is_in_g1_reserved(start) && _ct_bs->is_card_aligned(start), "sanity");
3025     // 'end' *may* be just beyone the end of the heap (if hr is the last region)
3026     assert(!_g1h->is_in_g1_reserved(end) || _ct_bs->is_card_aligned(end), "sanity");
3027 
3028     BitMap::idx_t start_idx = _cm->card_bitmap_index_for(start);
3029     BitMap::idx_t limit_idx = _cm->card_bitmap_index_for(limit);
3030     BitMap::idx_t end_idx = _cm->card_bitmap_index_for(end);
3031 
3032     // If ntams is not card aligned then we bump card bitmap index
3033     // for limit so that we get the all the cards spanned by
3034     // the object ending at ntams.
3035     // Note: if this is the last region in the heap then ntams
3036     // could be actually just beyond the end of the the heap;
3037     // limit_idx will then  correspond to a (non-existent) card
3038     // that is also outside the heap.
3039     if (_g1h->is_in_g1_reserved(limit) && !_ct_bs->is_card_aligned(limit)) {
3040       limit_idx += 1;
3041     }
3042 
3043     assert(limit_idx <= end_idx, "or else use atomics");
3044 
3045     // Aggregate the "stripe" in the count data associated with hr.
3046     uint hrs_index = hr->hrs_index();
3047     size_t marked_bytes = 0;
3048 
3049     for (uint i = 0; i < _max_worker_id; i += 1) {
3050       size_t* marked_bytes_array = _cm->count_marked_bytes_array_for(i);
3051       BitMap* task_card_bm = _cm->count_card_bitmap_for(i);
3052 
3053       // Fetch the marked_bytes in this region for task i and
3054       // add it to the running total for this region.
3055       marked_bytes += marked_bytes_array[hrs_index];
3056 
3057       // Now union the bitmaps[0,max_worker_id)[start_idx..limit_idx)
3058       // into the global card bitmap.
3059       BitMap::idx_t scan_idx = task_card_bm->get_next_one_offset(start_idx, limit_idx);
3060 
3061       while (scan_idx < limit_idx) {
3062         assert(task_card_bm->at(scan_idx) == true, "should be");
3063         _cm_card_bm->set_bit(scan_idx);
3064         assert(_cm_card_bm->at(scan_idx) == true, "should be");
3065 
3066         // BitMap::get_next_one_offset() can handle the case when
3067         // its left_offset parameter is greater than its right_offset
3068         // parameter. It does, however, have an early exit if
3069         // left_offset == right_offset. So let's limit the value
3070         // passed in for left offset here.
3071         BitMap::idx_t next_idx = MIN2(scan_idx + 1, limit_idx);
3072         scan_idx = task_card_bm->get_next_one_offset(next_idx, limit_idx);
3073       }
3074     }
3075 
3076     // Update the marked bytes for this region.
3077     hr->add_to_marked_bytes(marked_bytes);
3078 
3079     // Next heap region
3080     return false;
3081   }
3082 };
3083 
3084 class G1AggregateCountDataTask: public AbstractGangTask {
3085 protected:
3086   G1CollectedHeap* _g1h;
3087   ConcurrentMark* _cm;
3088   BitMap* _cm_card_bm;
3089   uint _max_worker_id;
3090   int _active_workers;
3091 
3092 public:
3093   G1AggregateCountDataTask(G1CollectedHeap* g1h,
3094                            ConcurrentMark* cm,
3095                            BitMap* cm_card_bm,
3096                            uint max_worker_id,
3097                            int n_workers) :
3098     AbstractGangTask("Count Aggregation"),
3099     _g1h(g1h), _cm(cm), _cm_card_bm(cm_card_bm),
3100     _max_worker_id(max_worker_id),
3101     _active_workers(n_workers) { }
3102 
3103   void work(uint worker_id) {
3104     AggregateCountDataHRClosure cl(_g1h, _cm_card_bm, _max_worker_id);
3105 
3106     if (G1CollectedHeap::use_parallel_gc_threads()) {
3107       _g1h->heap_region_par_iterate_chunked(&cl, worker_id,
3108                                             _active_workers,
3109                                             HeapRegion::AggregateCountClaimValue);
3110     } else {
3111       _g1h->heap_region_iterate(&cl);
3112     }
3113   }
3114 };
3115 
3116 
3117 void ConcurrentMark::aggregate_count_data() {
3118   int n_workers = (G1CollectedHeap::use_parallel_gc_threads() ?
3119                         _g1h->workers()->active_workers() :
3120                         1);
3121 
3122   G1AggregateCountDataTask g1_par_agg_task(_g1h, this, &_card_bm,
3123                                            _max_worker_id, n_workers);
3124 
3125   if (G1CollectedHeap::use_parallel_gc_threads()) {
3126     assert(_g1h->check_heap_region_claim_values(HeapRegion::InitialClaimValue),
3127            "sanity check");
3128     _g1h->set_par_threads(n_workers);
3129     _g1h->workers()->run_task(&g1_par_agg_task);
3130     _g1h->set_par_threads(0);
3131 
3132     assert(_g1h->check_heap_region_claim_values(HeapRegion::AggregateCountClaimValue),
3133            "sanity check");
3134     _g1h->reset_heap_region_claim_values();
3135   } else {
3136     g1_par_agg_task.work(0);
3137   }
3138 }
3139 
3140 // Clear the per-worker arrays used to store the per-region counting data
3141 void ConcurrentMark::clear_all_count_data() {
3142   // Clear the global card bitmap - it will be filled during
3143   // liveness count aggregation (during remark) and the
3144   // final counting task.
3145   _card_bm.clear();
3146 
3147   // Clear the global region bitmap - it will be filled as part
3148   // of the final counting task.
3149   _region_bm.clear();
3150 
3151   uint max_regions = _g1h->max_regions();
3152   assert(_max_worker_id > 0, "uninitialized");
3153 
3154   for (uint i = 0; i < _max_worker_id; i += 1) {
3155     BitMap* task_card_bm = count_card_bitmap_for(i);
3156     size_t* marked_bytes_array = count_marked_bytes_array_for(i);
3157 
3158     assert(task_card_bm->size() == _card_bm.size(), "size mismatch");
3159     assert(marked_bytes_array != NULL, "uninitialized");
3160 
3161     memset(marked_bytes_array, 0, (size_t) max_regions * sizeof(size_t));
3162     task_card_bm->clear();
3163   }
3164 }
3165 
3166 void ConcurrentMark::print_stats() {
3167   if (verbose_stats()) {
3168     gclog_or_tty->print_cr("---------------------------------------------------------------------");
3169     for (size_t i = 0; i < _active_tasks; ++i) {
3170       _tasks[i]->print_stats();
3171       gclog_or_tty->print_cr("---------------------------------------------------------------------");
3172     }
3173   }
3174 }
3175 
3176 // abandon current marking iteration due to a Full GC
3177 void ConcurrentMark::abort() {
3178   // Clear all marks to force marking thread to do nothing
3179   _nextMarkBitMap->clearAll();
3180   // Clear the liveness counting data
3181   clear_all_count_data();
3182   // Empty mark stack
3183   reset_marking_state();
3184   for (uint i = 0; i < _max_worker_id; ++i) {
3185     _tasks[i]->clear_region_fields();
3186   }
3187   _has_aborted = true;
3188 
3189   SATBMarkQueueSet& satb_mq_set = JavaThread::satb_mark_queue_set();
3190   satb_mq_set.abandon_partial_marking();
3191   // This can be called either during or outside marking, we'll read
3192   // the expected_active value from the SATB queue set.
3193   satb_mq_set.set_active_all_threads(
3194                                  false, /* new active value */
3195                                  satb_mq_set.is_active() /* expected_active */);
3196 }
3197 
3198 static void print_ms_time_info(const char* prefix, const char* name,
3199                                NumberSeq& ns) {
3200   gclog_or_tty->print_cr("%s%5d %12s: total time = %8.2f s (avg = %8.2f ms).",
3201                          prefix, ns.num(), name, ns.sum()/1000.0, ns.avg());
3202   if (ns.num() > 0) {
3203     gclog_or_tty->print_cr("%s         [std. dev = %8.2f ms, max = %8.2f ms]",
3204                            prefix, ns.sd(), ns.maximum());
3205   }
3206 }
3207 
3208 void ConcurrentMark::print_summary_info() {
3209   gclog_or_tty->print_cr(" Concurrent marking:");
3210   print_ms_time_info("  ", "init marks", _init_times);
3211   print_ms_time_info("  ", "remarks", _remark_times);
3212   {
3213     print_ms_time_info("     ", "final marks", _remark_mark_times);
3214     print_ms_time_info("     ", "weak refs", _remark_weak_ref_times);
3215 
3216   }
3217   print_ms_time_info("  ", "cleanups", _cleanup_times);
3218   gclog_or_tty->print_cr("    Final counting total time = %8.2f s (avg = %8.2f ms).",
3219                          _total_counting_time,
3220                          (_cleanup_times.num() > 0 ? _total_counting_time * 1000.0 /
3221                           (double)_cleanup_times.num()
3222                          : 0.0));
3223   if (G1ScrubRemSets) {
3224     gclog_or_tty->print_cr("    RS scrub total time = %8.2f s (avg = %8.2f ms).",
3225                            _total_rs_scrub_time,
3226                            (_cleanup_times.num() > 0 ? _total_rs_scrub_time * 1000.0 /
3227                             (double)_cleanup_times.num()
3228                            : 0.0));
3229   }
3230   gclog_or_tty->print_cr("  Total stop_world time = %8.2f s.",
3231                          (_init_times.sum() + _remark_times.sum() +
3232                           _cleanup_times.sum())/1000.0);
3233   gclog_or_tty->print_cr("  Total concurrent time = %8.2f s "
3234                 "(%8.2f s marking).",
3235                 cmThread()->vtime_accum(),
3236                 cmThread()->vtime_mark_accum());
3237 }
3238 
3239 void ConcurrentMark::print_worker_threads_on(outputStream* st) const {
3240   if (use_parallel_marking_threads()) {
3241     _parallel_workers->print_worker_threads_on(st);
3242   }
3243 }
3244 
3245 // We take a break if someone is trying to stop the world.
3246 bool ConcurrentMark::do_yield_check(uint worker_id) {
3247   if (should_yield()) {
3248     if (worker_id == 0) {
3249       _g1h->g1_policy()->record_concurrent_pause();
3250     }
3251     cmThread()->yield();
3252     return true;
3253   } else {
3254     return false;
3255   }
3256 }
3257 
3258 bool ConcurrentMark::should_yield() {
3259   return cmThread()->should_yield();
3260 }
3261 
3262 bool ConcurrentMark::containing_card_is_marked(void* p) {
3263   size_t offset = pointer_delta(p, _g1h->reserved_region().start(), 1);
3264   return _card_bm.at(offset >> CardTableModRefBS::card_shift);
3265 }
3266 
3267 bool ConcurrentMark::containing_cards_are_marked(void* start,
3268                                                  void* last) {
3269   return containing_card_is_marked(start) &&
3270          containing_card_is_marked(last);
3271 }
3272 
3273 #ifndef PRODUCT
3274 // for debugging purposes
3275 void ConcurrentMark::print_finger() {
3276   gclog_or_tty->print_cr("heap ["PTR_FORMAT", "PTR_FORMAT"), global finger = "PTR_FORMAT,
3277                          _heap_start, _heap_end, _finger);
3278   for (uint i = 0; i < _max_worker_id; ++i) {
3279     gclog_or_tty->print("   %u: "PTR_FORMAT, i, _tasks[i]->finger());
3280   }
3281   gclog_or_tty->print_cr("");
3282 }
3283 #endif
3284 
3285 void CMTask::scan_object(oop obj) {
3286   assert(_nextMarkBitMap->isMarked((HeapWord*) obj), "invariant");
3287 
3288   if (_cm->verbose_high()) {
3289     gclog_or_tty->print_cr("[%u] we're scanning object "PTR_FORMAT,
3290                            _worker_id, (void*) obj);
3291   }
3292 
3293   size_t obj_size = obj->size();
3294   _words_scanned += obj_size;
3295 
3296   obj->oop_iterate(_cm_oop_closure);
3297   statsOnly( ++_objs_scanned );
3298   check_limits();
3299 }
3300 
3301 // Closure for iteration over bitmaps
3302 class CMBitMapClosure : public BitMapClosure {
3303 private:
3304   // the bitmap that is being iterated over
3305   CMBitMap*                   _nextMarkBitMap;
3306   ConcurrentMark*             _cm;
3307   CMTask*                     _task;
3308 
3309 public:
3310   CMBitMapClosure(CMTask *task, ConcurrentMark* cm, CMBitMap* nextMarkBitMap) :
3311     _task(task), _cm(cm), _nextMarkBitMap(nextMarkBitMap) { }
3312 
3313   bool do_bit(size_t offset) {
3314     HeapWord* addr = _nextMarkBitMap->offsetToHeapWord(offset);
3315     assert(_nextMarkBitMap->isMarked(addr), "invariant");
3316     assert( addr < _cm->finger(), "invariant");
3317 
3318     statsOnly( _task->increase_objs_found_on_bitmap() );
3319     assert(addr >= _task->finger(), "invariant");
3320 
3321     // We move that task's local finger along.
3322     _task->move_finger_to(addr);
3323 
3324     _task->scan_object(oop(addr));
3325     // we only partially drain the local queue and global stack
3326     _task->drain_local_queue(true);
3327     _task->drain_global_stack(true);
3328 
3329     // if the has_aborted flag has been raised, we need to bail out of
3330     // the iteration
3331     return !_task->has_aborted();
3332   }
3333 };
3334 
3335 // Closure for iterating over objects, currently only used for
3336 // processing SATB buffers.
3337 class CMObjectClosure : public ObjectClosure {
3338 private:
3339   CMTask* _task;
3340 
3341 public:
3342   void do_object(oop obj) {
3343     _task->deal_with_reference(obj);
3344   }
3345 
3346   CMObjectClosure(CMTask* task) : _task(task) { }
3347 };
3348 
3349 G1CMOopClosure::G1CMOopClosure(G1CollectedHeap* g1h,
3350                                ConcurrentMark* cm,
3351                                CMTask* task)
3352   : _g1h(g1h), _cm(cm), _task(task) {
3353   assert(_ref_processor == NULL, "should be initialized to NULL");
3354 
3355   if (G1UseConcMarkReferenceProcessing) {
3356     _ref_processor = g1h->ref_processor_cm();
3357     assert(_ref_processor != NULL, "should not be NULL");
3358   }
3359 }
3360 
3361 void CMTask::setup_for_region(HeapRegion* hr) {
3362   // Separated the asserts so that we know which one fires.
3363   assert(hr != NULL,
3364         "claim_region() should have filtered out continues humongous regions");
3365   assert(!hr->continuesHumongous(),
3366         "claim_region() should have filtered out continues humongous regions");
3367 
3368   if (_cm->verbose_low()) {
3369     gclog_or_tty->print_cr("[%u] setting up for region "PTR_FORMAT,
3370                            _worker_id, hr);
3371   }
3372 
3373   _curr_region  = hr;
3374   _finger       = hr->bottom();
3375   update_region_limit();
3376 }
3377 
3378 void CMTask::update_region_limit() {
3379   HeapRegion* hr            = _curr_region;
3380   HeapWord* bottom          = hr->bottom();
3381   HeapWord* limit           = hr->next_top_at_mark_start();
3382 
3383   if (limit == bottom) {
3384     if (_cm->verbose_low()) {
3385       gclog_or_tty->print_cr("[%u] found an empty region "
3386                              "["PTR_FORMAT", "PTR_FORMAT")",
3387                              _worker_id, bottom, limit);
3388     }
3389     // The region was collected underneath our feet.
3390     // We set the finger to bottom to ensure that the bitmap
3391     // iteration that will follow this will not do anything.
3392     // (this is not a condition that holds when we set the region up,
3393     // as the region is not supposed to be empty in the first place)
3394     _finger = bottom;
3395   } else if (limit >= _region_limit) {
3396     assert(limit >= _finger, "peace of mind");
3397   } else {
3398     assert(limit < _region_limit, "only way to get here");
3399     // This can happen under some pretty unusual circumstances.  An
3400     // evacuation pause empties the region underneath our feet (NTAMS
3401     // at bottom). We then do some allocation in the region (NTAMS
3402     // stays at bottom), followed by the region being used as a GC
3403     // alloc region (NTAMS will move to top() and the objects
3404     // originally below it will be grayed). All objects now marked in
3405     // the region are explicitly grayed, if below the global finger,
3406     // and we do not need in fact to scan anything else. So, we simply
3407     // set _finger to be limit to ensure that the bitmap iteration
3408     // doesn't do anything.
3409     _finger = limit;
3410   }
3411 
3412   _region_limit = limit;
3413 }
3414 
3415 void CMTask::giveup_current_region() {
3416   assert(_curr_region != NULL, "invariant");
3417   if (_cm->verbose_low()) {
3418     gclog_or_tty->print_cr("[%u] giving up region "PTR_FORMAT,
3419                            _worker_id, _curr_region);
3420   }
3421   clear_region_fields();
3422 }
3423 
3424 void CMTask::clear_region_fields() {
3425   // Values for these three fields that indicate that we're not
3426   // holding on to a region.
3427   _curr_region   = NULL;
3428   _finger        = NULL;
3429   _region_limit  = NULL;
3430 }
3431 
3432 void CMTask::set_cm_oop_closure(G1CMOopClosure* cm_oop_closure) {
3433   if (cm_oop_closure == NULL) {
3434     assert(_cm_oop_closure != NULL, "invariant");
3435   } else {
3436     assert(_cm_oop_closure == NULL, "invariant");
3437   }
3438   _cm_oop_closure = cm_oop_closure;
3439 }
3440 
3441 void CMTask::reset(CMBitMap* nextMarkBitMap) {
3442   guarantee(nextMarkBitMap != NULL, "invariant");
3443 
3444   if (_cm->verbose_low()) {
3445     gclog_or_tty->print_cr("[%u] resetting", _worker_id);
3446   }
3447 
3448   _nextMarkBitMap                = nextMarkBitMap;
3449   clear_region_fields();
3450 
3451   _calls                         = 0;
3452   _elapsed_time_ms               = 0.0;
3453   _termination_time_ms           = 0.0;
3454   _termination_start_time_ms     = 0.0;
3455 
3456 #if _MARKING_STATS_
3457   _local_pushes                  = 0;
3458   _local_pops                    = 0;
3459   _local_max_size                = 0;
3460   _objs_scanned                  = 0;
3461   _global_pushes                 = 0;
3462   _global_pops                   = 0;
3463   _global_max_size               = 0;
3464   _global_transfers_to           = 0;
3465   _global_transfers_from         = 0;
3466   _regions_claimed               = 0;
3467   _objs_found_on_bitmap          = 0;
3468   _satb_buffers_processed        = 0;
3469   _steal_attempts                = 0;
3470   _steals                        = 0;
3471   _aborted                       = 0;
3472   _aborted_overflow              = 0;
3473   _aborted_cm_aborted            = 0;
3474   _aborted_yield                 = 0;
3475   _aborted_timed_out             = 0;
3476   _aborted_satb                  = 0;
3477   _aborted_termination           = 0;
3478 #endif // _MARKING_STATS_
3479 }
3480 
3481 bool CMTask::should_exit_termination() {
3482   regular_clock_call();
3483   // This is called when we are in the termination protocol. We should
3484   // quit if, for some reason, this task wants to abort or the global
3485   // stack is not empty (this means that we can get work from it).
3486   return !_cm->mark_stack_empty() || has_aborted();
3487 }
3488 
3489 void CMTask::reached_limit() {
3490   assert(_words_scanned >= _words_scanned_limit ||
3491          _refs_reached >= _refs_reached_limit ,
3492          "shouldn't have been called otherwise");
3493   regular_clock_call();
3494 }
3495 
3496 void CMTask::regular_clock_call() {
3497   if (has_aborted()) return;
3498 
3499   // First, we need to recalculate the words scanned and refs reached
3500   // limits for the next clock call.
3501   recalculate_limits();
3502 
3503   // During the regular clock call we do the following
3504 
3505   // (1) If an overflow has been flagged, then we abort.
3506   if (_cm->has_overflown()) {
3507     set_has_aborted();
3508     return;
3509   }
3510 
3511   // If we are not concurrent (i.e. we're doing remark) we don't need
3512   // to check anything else. The other steps are only needed during
3513   // the concurrent marking phase.
3514   if (!concurrent()) return;
3515 
3516   // (2) If marking has been aborted for Full GC, then we also abort.
3517   if (_cm->has_aborted()) {
3518     set_has_aborted();
3519     statsOnly( ++_aborted_cm_aborted );
3520     return;
3521   }
3522 
3523   double curr_time_ms = os::elapsedVTime() * 1000.0;
3524 
3525   // (3) If marking stats are enabled, then we update the step history.
3526 #if _MARKING_STATS_
3527   if (_words_scanned >= _words_scanned_limit) {
3528     ++_clock_due_to_scanning;
3529   }
3530   if (_refs_reached >= _refs_reached_limit) {
3531     ++_clock_due_to_marking;
3532   }
3533 
3534   double last_interval_ms = curr_time_ms - _interval_start_time_ms;
3535   _interval_start_time_ms = curr_time_ms;
3536   _all_clock_intervals_ms.add(last_interval_ms);
3537 
3538   if (_cm->verbose_medium()) {
3539       gclog_or_tty->print_cr("[%u] regular clock, interval = %1.2lfms, "
3540                         "scanned = %d%s, refs reached = %d%s",
3541                         _worker_id, last_interval_ms,
3542                         _words_scanned,
3543                         (_words_scanned >= _words_scanned_limit) ? " (*)" : "",
3544                         _refs_reached,
3545                         (_refs_reached >= _refs_reached_limit) ? " (*)" : "");
3546   }
3547 #endif // _MARKING_STATS_
3548 
3549   // (4) We check whether we should yield. If we have to, then we abort.
3550   if (_cm->should_yield()) {
3551     // We should yield. To do this we abort the task. The caller is
3552     // responsible for yielding.
3553     set_has_aborted();
3554     statsOnly( ++_aborted_yield );
3555     return;
3556   }
3557 
3558   // (5) We check whether we've reached our time quota. If we have,
3559   // then we abort.
3560   double elapsed_time_ms = curr_time_ms - _start_time_ms;
3561   if (elapsed_time_ms > _time_target_ms) {
3562     set_has_aborted();
3563     _has_timed_out = true;
3564     statsOnly( ++_aborted_timed_out );
3565     return;
3566   }
3567 
3568   // (6) Finally, we check whether there are enough completed STAB
3569   // buffers available for processing. If there are, we abort.
3570   SATBMarkQueueSet& satb_mq_set = JavaThread::satb_mark_queue_set();
3571   if (!_draining_satb_buffers && satb_mq_set.process_completed_buffers()) {
3572     if (_cm->verbose_low()) {
3573       gclog_or_tty->print_cr("[%u] aborting to deal with pending SATB buffers",
3574                              _worker_id);
3575     }
3576     // we do need to process SATB buffers, we'll abort and restart
3577     // the marking task to do so
3578     set_has_aborted();
3579     statsOnly( ++_aborted_satb );
3580     return;
3581   }
3582 }
3583 
3584 void CMTask::recalculate_limits() {
3585   _real_words_scanned_limit = _words_scanned + words_scanned_period;
3586   _words_scanned_limit      = _real_words_scanned_limit;
3587 
3588   _real_refs_reached_limit  = _refs_reached  + refs_reached_period;
3589   _refs_reached_limit       = _real_refs_reached_limit;
3590 }
3591 
3592 void CMTask::decrease_limits() {
3593   // This is called when we believe that we're going to do an infrequent
3594   // operation which will increase the per byte scanned cost (i.e. move
3595   // entries to/from the global stack). It basically tries to decrease the
3596   // scanning limit so that the clock is called earlier.
3597 
3598   if (_cm->verbose_medium()) {
3599     gclog_or_tty->print_cr("[%u] decreasing limits", _worker_id);
3600   }
3601 
3602   _words_scanned_limit = _real_words_scanned_limit -
3603     3 * words_scanned_period / 4;
3604   _refs_reached_limit  = _real_refs_reached_limit -
3605     3 * refs_reached_period / 4;
3606 }
3607 
3608 void CMTask::move_entries_to_global_stack() {
3609   // local array where we'll store the entries that will be popped
3610   // from the local queue
3611   oop buffer[global_stack_transfer_size];
3612 
3613   int n = 0;
3614   oop obj;
3615   while (n < global_stack_transfer_size && _task_queue->pop_local(obj)) {
3616     buffer[n] = obj;
3617     ++n;
3618   }
3619 
3620   if (n > 0) {
3621     // we popped at least one entry from the local queue
3622 
3623     statsOnly( ++_global_transfers_to; _local_pops += n );
3624 
3625     if (!_cm->mark_stack_push(buffer, n)) {
3626       if (_cm->verbose_low()) {
3627         gclog_or_tty->print_cr("[%u] aborting due to global stack overflow",
3628                                _worker_id);
3629       }
3630       set_has_aborted();
3631     } else {
3632       // the transfer was successful
3633 
3634       if (_cm->verbose_medium()) {
3635         gclog_or_tty->print_cr("[%u] pushed %d entries to the global stack",
3636                                _worker_id, n);
3637       }
3638       statsOnly( int tmp_size = _cm->mark_stack_size();
3639                  if (tmp_size > _global_max_size) {
3640                    _global_max_size = tmp_size;
3641                  }
3642                  _global_pushes += n );
3643     }
3644   }
3645 
3646   // this operation was quite expensive, so decrease the limits
3647   decrease_limits();
3648 }
3649 
3650 void CMTask::get_entries_from_global_stack() {
3651   // local array where we'll store the entries that will be popped
3652   // from the global stack.
3653   oop buffer[global_stack_transfer_size];
3654   int n;
3655   _cm->mark_stack_pop(buffer, global_stack_transfer_size, &n);
3656   assert(n <= global_stack_transfer_size,
3657          "we should not pop more than the given limit");
3658   if (n > 0) {
3659     // yes, we did actually pop at least one entry
3660 
3661     statsOnly( ++_global_transfers_from; _global_pops += n );
3662     if (_cm->verbose_medium()) {
3663       gclog_or_tty->print_cr("[%u] popped %d entries from the global stack",
3664                              _worker_id, n);
3665     }
3666     for (int i = 0; i < n; ++i) {
3667       bool success = _task_queue->push(buffer[i]);
3668       // We only call this when the local queue is empty or under a
3669       // given target limit. So, we do not expect this push to fail.
3670       assert(success, "invariant");
3671     }
3672 
3673     statsOnly( int tmp_size = _task_queue->size();
3674                if (tmp_size > _local_max_size) {
3675                  _local_max_size = tmp_size;
3676                }
3677                _local_pushes += n );
3678   }
3679 
3680   // this operation was quite expensive, so decrease the limits
3681   decrease_limits();
3682 }
3683 
3684 void CMTask::drain_local_queue(bool partially) {
3685   if (has_aborted()) return;
3686 
3687   // Decide what the target size is, depending whether we're going to
3688   // drain it partially (so that other tasks can steal if they run out
3689   // of things to do) or totally (at the very end).
3690   size_t target_size;
3691   if (partially) {
3692     target_size = MIN2((size_t)_task_queue->max_elems()/3, GCDrainStackTargetSize);
3693   } else {
3694     target_size = 0;
3695   }
3696 
3697   if (_task_queue->size() > target_size) {
3698     if (_cm->verbose_high()) {
3699       gclog_or_tty->print_cr("[%u] draining local queue, target size = %d",
3700                              _worker_id, target_size);
3701     }
3702 
3703     oop obj;
3704     bool ret = _task_queue->pop_local(obj);
3705     while (ret) {
3706       statsOnly( ++_local_pops );
3707 
3708       if (_cm->verbose_high()) {
3709         gclog_or_tty->print_cr("[%u] popped "PTR_FORMAT, _worker_id,
3710                                (void*) obj);
3711       }
3712 
3713       assert(_g1h->is_in_g1_reserved((HeapWord*) obj), "invariant" );
3714       assert(!_g1h->is_on_master_free_list(
3715                   _g1h->heap_region_containing((HeapWord*) obj)), "invariant");
3716 
3717       scan_object(obj);
3718 
3719       if (_task_queue->size() <= target_size || has_aborted()) {
3720         ret = false;
3721       } else {
3722         ret = _task_queue->pop_local(obj);
3723       }
3724     }
3725 
3726     if (_cm->verbose_high()) {
3727       gclog_or_tty->print_cr("[%u] drained local queue, size = %d",
3728                              _worker_id, _task_queue->size());
3729     }
3730   }
3731 }
3732 
3733 void CMTask::drain_global_stack(bool partially) {
3734   if (has_aborted()) return;
3735 
3736   // We have a policy to drain the local queue before we attempt to
3737   // drain the global stack.
3738   assert(partially || _task_queue->size() == 0, "invariant");
3739 
3740   // Decide what the target size is, depending whether we're going to
3741   // drain it partially (so that other tasks can steal if they run out
3742   // of things to do) or totally (at the very end).  Notice that,
3743   // because we move entries from the global stack in chunks or
3744   // because another task might be doing the same, we might in fact
3745   // drop below the target. But, this is not a problem.
3746   size_t target_size;
3747   if (partially) {
3748     target_size = _cm->partial_mark_stack_size_target();
3749   } else {
3750     target_size = 0;
3751   }
3752 
3753   if (_cm->mark_stack_size() > target_size) {
3754     if (_cm->verbose_low()) {
3755       gclog_or_tty->print_cr("[%u] draining global_stack, target size %d",
3756                              _worker_id, target_size);
3757     }
3758 
3759     while (!has_aborted() && _cm->mark_stack_size() > target_size) {
3760       get_entries_from_global_stack();
3761       drain_local_queue(partially);
3762     }
3763 
3764     if (_cm->verbose_low()) {
3765       gclog_or_tty->print_cr("[%u] drained global stack, size = %d",
3766                              _worker_id, _cm->mark_stack_size());
3767     }
3768   }
3769 }
3770 
3771 // SATB Queue has several assumptions on whether to call the par or
3772 // non-par versions of the methods. this is why some of the code is
3773 // replicated. We should really get rid of the single-threaded version
3774 // of the code to simplify things.
3775 void CMTask::drain_satb_buffers() {
3776   if (has_aborted()) return;
3777 
3778   // We set this so that the regular clock knows that we're in the
3779   // middle of draining buffers and doesn't set the abort flag when it
3780   // notices that SATB buffers are available for draining. It'd be
3781   // very counter productive if it did that. :-)
3782   _draining_satb_buffers = true;
3783 
3784   CMObjectClosure oc(this);
3785   SATBMarkQueueSet& satb_mq_set = JavaThread::satb_mark_queue_set();
3786   if (G1CollectedHeap::use_parallel_gc_threads()) {
3787     satb_mq_set.set_par_closure(_worker_id, &oc);
3788   } else {
3789     satb_mq_set.set_closure(&oc);
3790   }
3791 
3792   // This keeps claiming and applying the closure to completed buffers
3793   // until we run out of buffers or we need to abort.
3794   if (G1CollectedHeap::use_parallel_gc_threads()) {
3795     while (!has_aborted() &&
3796            satb_mq_set.par_apply_closure_to_completed_buffer(_worker_id)) {
3797       if (_cm->verbose_medium()) {
3798         gclog_or_tty->print_cr("[%u] processed an SATB buffer", _worker_id);
3799       }
3800       statsOnly( ++_satb_buffers_processed );
3801       regular_clock_call();
3802     }
3803   } else {
3804     while (!has_aborted() &&
3805            satb_mq_set.apply_closure_to_completed_buffer()) {
3806       if (_cm->verbose_medium()) {
3807         gclog_or_tty->print_cr("[%u] processed an SATB buffer", _worker_id);
3808       }
3809       statsOnly( ++_satb_buffers_processed );
3810       regular_clock_call();
3811     }
3812   }
3813 
3814   if (!concurrent() && !has_aborted()) {
3815     // We should only do this during remark.
3816     if (G1CollectedHeap::use_parallel_gc_threads()) {
3817       satb_mq_set.par_iterate_closure_all_threads(_worker_id);
3818     } else {
3819       satb_mq_set.iterate_closure_all_threads();
3820     }
3821   }
3822 
3823   _draining_satb_buffers = false;
3824 
3825   assert(has_aborted() ||
3826          concurrent() ||
3827          satb_mq_set.completed_buffers_num() == 0, "invariant");
3828 
3829   if (G1CollectedHeap::use_parallel_gc_threads()) {
3830     satb_mq_set.set_par_closure(_worker_id, NULL);
3831   } else {
3832     satb_mq_set.set_closure(NULL);
3833   }
3834 
3835   // again, this was a potentially expensive operation, decrease the
3836   // limits to get the regular clock call early
3837   decrease_limits();
3838 }
3839 
3840 void CMTask::print_stats() {
3841   gclog_or_tty->print_cr("Marking Stats, task = %u, calls = %d",
3842                          _worker_id, _calls);
3843   gclog_or_tty->print_cr("  Elapsed time = %1.2lfms, Termination time = %1.2lfms",
3844                          _elapsed_time_ms, _termination_time_ms);
3845   gclog_or_tty->print_cr("  Step Times (cum): num = %d, avg = %1.2lfms, sd = %1.2lfms",
3846                          _step_times_ms.num(), _step_times_ms.avg(),
3847                          _step_times_ms.sd());
3848   gclog_or_tty->print_cr("                    max = %1.2lfms, total = %1.2lfms",
3849                          _step_times_ms.maximum(), _step_times_ms.sum());
3850 
3851 #if _MARKING_STATS_
3852   gclog_or_tty->print_cr("  Clock Intervals (cum): num = %d, avg = %1.2lfms, sd = %1.2lfms",
3853                          _all_clock_intervals_ms.num(), _all_clock_intervals_ms.avg(),
3854                          _all_clock_intervals_ms.sd());
3855   gclog_or_tty->print_cr("                         max = %1.2lfms, total = %1.2lfms",
3856                          _all_clock_intervals_ms.maximum(),
3857                          _all_clock_intervals_ms.sum());
3858   gclog_or_tty->print_cr("  Clock Causes (cum): scanning = %d, marking = %d",
3859                          _clock_due_to_scanning, _clock_due_to_marking);
3860   gclog_or_tty->print_cr("  Objects: scanned = %d, found on the bitmap = %d",
3861                          _objs_scanned, _objs_found_on_bitmap);
3862   gclog_or_tty->print_cr("  Local Queue:  pushes = %d, pops = %d, max size = %d",
3863                          _local_pushes, _local_pops, _local_max_size);
3864   gclog_or_tty->print_cr("  Global Stack: pushes = %d, pops = %d, max size = %d",
3865                          _global_pushes, _global_pops, _global_max_size);
3866   gclog_or_tty->print_cr("                transfers to = %d, transfers from = %d",
3867                          _global_transfers_to,_global_transfers_from);
3868   gclog_or_tty->print_cr("  Regions: claimed = %d", _regions_claimed);
3869   gclog_or_tty->print_cr("  SATB buffers: processed = %d", _satb_buffers_processed);
3870   gclog_or_tty->print_cr("  Steals: attempts = %d, successes = %d",
3871                          _steal_attempts, _steals);
3872   gclog_or_tty->print_cr("  Aborted: %d, due to", _aborted);
3873   gclog_or_tty->print_cr("    overflow: %d, global abort: %d, yield: %d",
3874                          _aborted_overflow, _aborted_cm_aborted, _aborted_yield);
3875   gclog_or_tty->print_cr("    time out: %d, SATB: %d, termination: %d",
3876                          _aborted_timed_out, _aborted_satb, _aborted_termination);
3877 #endif // _MARKING_STATS_
3878 }
3879 
3880 /*****************************************************************************
3881 
3882     The do_marking_step(time_target_ms, ...) method is the building
3883     block of the parallel marking framework. It can be called in parallel
3884     with other invocations of do_marking_step() on different tasks
3885     (but only one per task, obviously) and concurrently with the
3886     mutator threads, or during remark, hence it eliminates the need
3887     for two versions of the code. When called during remark, it will
3888     pick up from where the task left off during the concurrent marking
3889     phase. Interestingly, tasks are also claimable during evacuation
3890     pauses too, since do_marking_step() ensures that it aborts before
3891     it needs to yield.
3892 
3893     The data structures that it uses to do marking work are the
3894     following:
3895 
3896       (1) Marking Bitmap. If there are gray objects that appear only
3897       on the bitmap (this happens either when dealing with an overflow
3898       or when the initial marking phase has simply marked the roots
3899       and didn't push them on the stack), then tasks claim heap
3900       regions whose bitmap they then scan to find gray objects. A
3901       global finger indicates where the end of the last claimed region
3902       is. A local finger indicates how far into the region a task has
3903       scanned. The two fingers are used to determine how to gray an
3904       object (i.e. whether simply marking it is OK, as it will be
3905       visited by a task in the future, or whether it needs to be also
3906       pushed on a stack).
3907 
3908       (2) Local Queue. The local queue of the task which is accessed
3909       reasonably efficiently by the task. Other tasks can steal from
3910       it when they run out of work. Throughout the marking phase, a
3911       task attempts to keep its local queue short but not totally
3912       empty, so that entries are available for stealing by other
3913       tasks. Only when there is no more work, a task will totally
3914       drain its local queue.
3915 
3916       (3) Global Mark Stack. This handles local queue overflow. During
3917       marking only sets of entries are moved between it and the local
3918       queues, as access to it requires a mutex and more fine-grain
3919       interaction with it which might cause contention. If it
3920       overflows, then the marking phase should restart and iterate
3921       over the bitmap to identify gray objects. Throughout the marking
3922       phase, tasks attempt to keep the global mark stack at a small
3923       length but not totally empty, so that entries are available for
3924       popping by other tasks. Only when there is no more work, tasks
3925       will totally drain the global mark stack.
3926 
3927       (4) SATB Buffer Queue. This is where completed SATB buffers are
3928       made available. Buffers are regularly removed from this queue
3929       and scanned for roots, so that the queue doesn't get too
3930       long. During remark, all completed buffers are processed, as
3931       well as the filled in parts of any uncompleted buffers.
3932 
3933     The do_marking_step() method tries to abort when the time target
3934     has been reached. There are a few other cases when the
3935     do_marking_step() method also aborts:
3936 
3937       (1) When the marking phase has been aborted (after a Full GC).
3938 
3939       (2) When a global overflow (on the global stack) has been
3940       triggered. Before the task aborts, it will actually sync up with
3941       the other tasks to ensure that all the marking data structures
3942       (local queues, stacks, fingers etc.)  are re-initialised so that
3943       when do_marking_step() completes, the marking phase can
3944       immediately restart.
3945 
3946       (3) When enough completed SATB buffers are available. The
3947       do_marking_step() method only tries to drain SATB buffers right
3948       at the beginning. So, if enough buffers are available, the
3949       marking step aborts and the SATB buffers are processed at
3950       the beginning of the next invocation.
3951 
3952       (4) To yield. when we have to yield then we abort and yield
3953       right at the end of do_marking_step(). This saves us from a lot
3954       of hassle as, by yielding we might allow a Full GC. If this
3955       happens then objects will be compacted underneath our feet, the
3956       heap might shrink, etc. We save checking for this by just
3957       aborting and doing the yield right at the end.
3958 
3959     From the above it follows that the do_marking_step() method should
3960     be called in a loop (or, otherwise, regularly) until it completes.
3961 
3962     If a marking step completes without its has_aborted() flag being
3963     true, it means it has completed the current marking phase (and
3964     also all other marking tasks have done so and have all synced up).
3965 
3966     A method called regular_clock_call() is invoked "regularly" (in
3967     sub ms intervals) throughout marking. It is this clock method that
3968     checks all the abort conditions which were mentioned above and
3969     decides when the task should abort. A work-based scheme is used to
3970     trigger this clock method: when the number of object words the
3971     marking phase has scanned or the number of references the marking
3972     phase has visited reach a given limit. Additional invocations to
3973     the method clock have been planted in a few other strategic places
3974     too. The initial reason for the clock method was to avoid calling
3975     vtime too regularly, as it is quite expensive. So, once it was in
3976     place, it was natural to piggy-back all the other conditions on it
3977     too and not constantly check them throughout the code.
3978 
3979     If do_termination is true then do_marking_step will enter its
3980     termination protocol.
3981 
3982     The value of is_serial must be true when do_marking_step is being
3983     called serially (i.e. by the VMThread) and do_marking_step should
3984     skip any synchronization in the termination and overflow code.
3985     Examples include the serial remark code and the serial reference
3986     processing closures.
3987 
3988     The value of is_serial must be false when do_marking_step is
3989     being called by any of the worker threads in a work gang.
3990     Examples include the concurrent marking code (CMMarkingTask),
3991     the MT remark code, and the MT reference processing closures.
3992 
3993  *****************************************************************************/
3994 
3995 void CMTask::do_marking_step(double time_target_ms,
3996                              bool do_termination,
3997                              bool is_serial) {
3998   assert(time_target_ms >= 1.0, "minimum granularity is 1ms");
3999   assert(concurrent() == _cm->concurrent(), "they should be the same");
4000 
4001   G1CollectorPolicy* g1_policy = _g1h->g1_policy();
4002   assert(_task_queues != NULL, "invariant");
4003   assert(_task_queue != NULL, "invariant");
4004   assert(_task_queues->queue(_worker_id) == _task_queue, "invariant");
4005 
4006   assert(!_claimed,
4007          "only one thread should claim this task at any one time");
4008 
4009   // OK, this doesn't safeguard again all possible scenarios, as it is
4010   // possible for two threads to set the _claimed flag at the same
4011   // time. But it is only for debugging purposes anyway and it will
4012   // catch most problems.
4013   _claimed = true;
4014 
4015   _start_time_ms = os::elapsedVTime() * 1000.0;
4016   statsOnly( _interval_start_time_ms = _start_time_ms );
4017 
4018   // If do_stealing is true then do_marking_step will attempt to
4019   // steal work from the other CMTasks. It only makes sense to
4020   // enable stealing when the termination protocol is enabled
4021   // and do_marking_step() is not being called serially.
4022   bool do_stealing = do_termination && !is_serial;
4023 
4024   double diff_prediction_ms =
4025     g1_policy->get_new_prediction(&_marking_step_diffs_ms);
4026   _time_target_ms = time_target_ms - diff_prediction_ms;
4027 
4028   // set up the variables that are used in the work-based scheme to
4029   // call the regular clock method
4030   _words_scanned = 0;
4031   _refs_reached  = 0;
4032   recalculate_limits();
4033 
4034   // clear all flags
4035   clear_has_aborted();
4036   _has_timed_out = false;
4037   _draining_satb_buffers = false;
4038 
4039   ++_calls;
4040 
4041   if (_cm->verbose_low()) {
4042     gclog_or_tty->print_cr("[%u] >>>>>>>>>> START, call = %d, "
4043                            "target = %1.2lfms >>>>>>>>>>",
4044                            _worker_id, _calls, _time_target_ms);
4045   }
4046 
4047   // Set up the bitmap and oop closures. Anything that uses them is
4048   // eventually called from this method, so it is OK to allocate these
4049   // statically.
4050   CMBitMapClosure bitmap_closure(this, _cm, _nextMarkBitMap);
4051   G1CMOopClosure  cm_oop_closure(_g1h, _cm, this);
4052   set_cm_oop_closure(&cm_oop_closure);
4053 
4054   if (_cm->has_overflown()) {
4055     // This can happen if the mark stack overflows during a GC pause
4056     // and this task, after a yield point, restarts. We have to abort
4057     // as we need to get into the overflow protocol which happens
4058     // right at the end of this task.
4059     set_has_aborted();
4060   }
4061 
4062   // First drain any available SATB buffers. After this, we will not
4063   // look at SATB buffers before the next invocation of this method.
4064   // If enough completed SATB buffers are queued up, the regular clock
4065   // will abort this task so that it restarts.
4066   drain_satb_buffers();
4067   // ...then partially drain the local queue and the global stack
4068   drain_local_queue(true);
4069   drain_global_stack(true);
4070 
4071   do {
4072     if (!has_aborted() && _curr_region != NULL) {
4073       // This means that we're already holding on to a region.
4074       assert(_finger != NULL, "if region is not NULL, then the finger "
4075              "should not be NULL either");
4076 
4077       // We might have restarted this task after an evacuation pause
4078       // which might have evacuated the region we're holding on to
4079       // underneath our feet. Let's read its limit again to make sure
4080       // that we do not iterate over a region of the heap that
4081       // contains garbage (update_region_limit() will also move
4082       // _finger to the start of the region if it is found empty).
4083       update_region_limit();
4084       // We will start from _finger not from the start of the region,
4085       // as we might be restarting this task after aborting half-way
4086       // through scanning this region. In this case, _finger points to
4087       // the address where we last found a marked object. If this is a
4088       // fresh region, _finger points to start().
4089       MemRegion mr = MemRegion(_finger, _region_limit);
4090 
4091       if (_cm->verbose_low()) {
4092         gclog_or_tty->print_cr("[%u] we're scanning part "
4093                                "["PTR_FORMAT", "PTR_FORMAT") "
4094                                "of region "HR_FORMAT,
4095                                _worker_id, _finger, _region_limit,
4096                                HR_FORMAT_PARAMS(_curr_region));
4097       }
4098 
4099       assert(!_curr_region->isHumongous() || mr.start() == _curr_region->bottom(),
4100              "humongous regions should go around loop once only");
4101 
4102       // Some special cases:
4103       // If the memory region is empty, we can just give up the region.
4104       // If the current region is humongous then we only need to check
4105       // the bitmap for the bit associated with the start of the object,
4106       // scan the object if it's live, and give up the region.
4107       // Otherwise, let's iterate over the bitmap of the part of the region
4108       // that is left.
4109       // If the iteration is successful, give up the region.
4110       if (mr.is_empty()) {
4111         giveup_current_region();
4112         regular_clock_call();
4113       } else if (_curr_region->isHumongous() && mr.start() == _curr_region->bottom()) {
4114         if (_nextMarkBitMap->isMarked(mr.start())) {
4115           // The object is marked - apply the closure
4116           BitMap::idx_t offset = _nextMarkBitMap->heapWordToOffset(mr.start());
4117           bitmap_closure.do_bit(offset);
4118         }
4119         // Even if this task aborted while scanning the humongous object
4120         // we can (and should) give up the current region.
4121         giveup_current_region();
4122         regular_clock_call();
4123       } else if (_nextMarkBitMap->iterate(&bitmap_closure, mr)) {
4124         giveup_current_region();
4125         regular_clock_call();
4126       } else {
4127         assert(has_aborted(), "currently the only way to do so");
4128         // The only way to abort the bitmap iteration is to return
4129         // false from the do_bit() method. However, inside the
4130         // do_bit() method we move the _finger to point to the
4131         // object currently being looked at. So, if we bail out, we
4132         // have definitely set _finger to something non-null.
4133         assert(_finger != NULL, "invariant");
4134 
4135         // Region iteration was actually aborted. So now _finger
4136         // points to the address of the object we last scanned. If we
4137         // leave it there, when we restart this task, we will rescan
4138         // the object. It is easy to avoid this. We move the finger by
4139         // enough to point to the next possible object header (the
4140         // bitmap knows by how much we need to move it as it knows its
4141         // granularity).
4142         assert(_finger < _region_limit, "invariant");
4143         HeapWord* new_finger = _nextMarkBitMap->nextObject(_finger);
4144         // Check if bitmap iteration was aborted while scanning the last object
4145         if (new_finger >= _region_limit) {
4146           giveup_current_region();
4147         } else {
4148           move_finger_to(new_finger);
4149         }
4150       }
4151     }
4152     // At this point we have either completed iterating over the
4153     // region we were holding on to, or we have aborted.
4154 
4155     // We then partially drain the local queue and the global stack.
4156     // (Do we really need this?)
4157     drain_local_queue(true);
4158     drain_global_stack(true);
4159 
4160     // Read the note on the claim_region() method on why it might
4161     // return NULL with potentially more regions available for
4162     // claiming and why we have to check out_of_regions() to determine
4163     // whether we're done or not.
4164     while (!has_aborted() && _curr_region == NULL && !_cm->out_of_regions()) {
4165       // We are going to try to claim a new region. We should have
4166       // given up on the previous one.
4167       // Separated the asserts so that we know which one fires.
4168       assert(_curr_region  == NULL, "invariant");
4169       assert(_finger       == NULL, "invariant");
4170       assert(_region_limit == NULL, "invariant");
4171       if (_cm->verbose_low()) {
4172         gclog_or_tty->print_cr("[%u] trying to claim a new region", _worker_id);
4173       }
4174       HeapRegion* claimed_region = _cm->claim_region(_worker_id);
4175       if (claimed_region != NULL) {
4176         // Yes, we managed to claim one
4177         statsOnly( ++_regions_claimed );
4178 
4179         if (_cm->verbose_low()) {
4180           gclog_or_tty->print_cr("[%u] we successfully claimed "
4181                                  "region "PTR_FORMAT,
4182                                  _worker_id, claimed_region);
4183         }
4184 
4185         setup_for_region(claimed_region);
4186         assert(_curr_region == claimed_region, "invariant");
4187       }
4188       // It is important to call the regular clock here. It might take
4189       // a while to claim a region if, for example, we hit a large
4190       // block of empty regions. So we need to call the regular clock
4191       // method once round the loop to make sure it's called
4192       // frequently enough.
4193       regular_clock_call();
4194     }
4195 
4196     if (!has_aborted() && _curr_region == NULL) {
4197       assert(_cm->out_of_regions(),
4198              "at this point we should be out of regions");
4199     }
4200   } while ( _curr_region != NULL && !has_aborted());
4201 
4202   if (!has_aborted()) {
4203     // We cannot check whether the global stack is empty, since other
4204     // tasks might be pushing objects to it concurrently.
4205     assert(_cm->out_of_regions(),
4206            "at this point we should be out of regions");
4207 
4208     if (_cm->verbose_low()) {
4209       gclog_or_tty->print_cr("[%u] all regions claimed", _worker_id);
4210     }
4211 
4212     // Try to reduce the number of available SATB buffers so that
4213     // remark has less work to do.
4214     drain_satb_buffers();
4215   }
4216 
4217   // Since we've done everything else, we can now totally drain the
4218   // local queue and global stack.
4219   drain_local_queue(false);
4220   drain_global_stack(false);
4221 
4222   // Attempt at work stealing from other task's queues.
4223   if (do_stealing && !has_aborted()) {
4224     // We have not aborted. This means that we have finished all that
4225     // we could. Let's try to do some stealing...
4226 
4227     // We cannot check whether the global stack is empty, since other
4228     // tasks might be pushing objects to it concurrently.
4229     assert(_cm->out_of_regions() && _task_queue->size() == 0,
4230            "only way to reach here");
4231 
4232     if (_cm->verbose_low()) {
4233       gclog_or_tty->print_cr("[%u] starting to steal", _worker_id);
4234     }
4235 
4236     while (!has_aborted()) {
4237       oop obj;
4238       statsOnly( ++_steal_attempts );
4239 
4240       if (_cm->try_stealing(_worker_id, &_hash_seed, obj)) {
4241         if (_cm->verbose_medium()) {
4242           gclog_or_tty->print_cr("[%u] stolen "PTR_FORMAT" successfully",
4243                                  _worker_id, (void*) obj);
4244         }
4245 
4246         statsOnly( ++_steals );
4247 
4248         assert(_nextMarkBitMap->isMarked((HeapWord*) obj),
4249                "any stolen object should be marked");
4250         scan_object(obj);
4251 
4252         // And since we're towards the end, let's totally drain the
4253         // local queue and global stack.
4254         drain_local_queue(false);
4255         drain_global_stack(false);
4256       } else {
4257         break;
4258       }
4259     }
4260   }
4261 
4262   // If we are about to wrap up and go into termination, check if we
4263   // should raise the overflow flag.
4264   if (do_termination && !has_aborted()) {
4265     if (_cm->force_overflow()->should_force()) {
4266       _cm->set_has_overflown();
4267       regular_clock_call();
4268     }
4269   }
4270 
4271   // We still haven't aborted. Now, let's try to get into the
4272   // termination protocol.
4273   if (do_termination && !has_aborted()) {
4274     // We cannot check whether the global stack is empty, since other
4275     // tasks might be concurrently pushing objects on it.
4276     // Separated the asserts so that we know which one fires.
4277     assert(_cm->out_of_regions(), "only way to reach here");
4278     assert(_task_queue->size() == 0, "only way to reach here");
4279 
4280     if (_cm->verbose_low()) {
4281       gclog_or_tty->print_cr("[%u] starting termination protocol", _worker_id);
4282     }
4283 
4284     _termination_start_time_ms = os::elapsedVTime() * 1000.0;
4285 
4286     // The CMTask class also extends the TerminatorTerminator class,
4287     // hence its should_exit_termination() method will also decide
4288     // whether to exit the termination protocol or not.
4289     bool finished = (is_serial ||
4290                      _cm->terminator()->offer_termination(this));
4291     double termination_end_time_ms = os::elapsedVTime() * 1000.0;
4292     _termination_time_ms +=
4293       termination_end_time_ms - _termination_start_time_ms;
4294 
4295     if (finished) {
4296       // We're all done.
4297 
4298       if (_worker_id == 0) {
4299         // let's allow task 0 to do this
4300         if (concurrent()) {
4301           assert(_cm->concurrent_marking_in_progress(), "invariant");
4302           // we need to set this to false before the next
4303           // safepoint. This way we ensure that the marking phase
4304           // doesn't observe any more heap expansions.
4305           _cm->clear_concurrent_marking_in_progress();
4306         }
4307       }
4308 
4309       // We can now guarantee that the global stack is empty, since
4310       // all other tasks have finished. We separated the guarantees so
4311       // that, if a condition is false, we can immediately find out
4312       // which one.
4313       guarantee(_cm->out_of_regions(), "only way to reach here");
4314       guarantee(_cm->mark_stack_empty(), "only way to reach here");
4315       guarantee(_task_queue->size() == 0, "only way to reach here");
4316       guarantee(!_cm->has_overflown(), "only way to reach here");
4317       guarantee(!_cm->mark_stack_overflow(), "only way to reach here");
4318 
4319       if (_cm->verbose_low()) {
4320         gclog_or_tty->print_cr("[%u] all tasks terminated", _worker_id);
4321       }
4322     } else {
4323       // Apparently there's more work to do. Let's abort this task. It
4324       // will restart it and we can hopefully find more things to do.
4325 
4326       if (_cm->verbose_low()) {
4327         gclog_or_tty->print_cr("[%u] apparently there is more work to do",
4328                                _worker_id);
4329       }
4330 
4331       set_has_aborted();
4332       statsOnly( ++_aborted_termination );
4333     }
4334   }
4335 
4336   // Mainly for debugging purposes to make sure that a pointer to the
4337   // closure which was statically allocated in this frame doesn't
4338   // escape it by accident.
4339   set_cm_oop_closure(NULL);
4340   double end_time_ms = os::elapsedVTime() * 1000.0;
4341   double elapsed_time_ms = end_time_ms - _start_time_ms;
4342   // Update the step history.
4343   _step_times_ms.add(elapsed_time_ms);
4344 
4345   if (has_aborted()) {
4346     // The task was aborted for some reason.
4347 
4348     statsOnly( ++_aborted );
4349 
4350     if (_has_timed_out) {
4351       double diff_ms = elapsed_time_ms - _time_target_ms;
4352       // Keep statistics of how well we did with respect to hitting
4353       // our target only if we actually timed out (if we aborted for
4354       // other reasons, then the results might get skewed).
4355       _marking_step_diffs_ms.add(diff_ms);
4356     }
4357 
4358     if (_cm->has_overflown()) {
4359       // This is the interesting one. We aborted because a global
4360       // overflow was raised. This means we have to restart the
4361       // marking phase and start iterating over regions. However, in
4362       // order to do this we have to make sure that all tasks stop
4363       // what they are doing and re-initialise in a safe manner. We
4364       // will achieve this with the use of two barrier sync points.
4365 
4366       if (_cm->verbose_low()) {
4367         gclog_or_tty->print_cr("[%u] detected overflow", _worker_id);
4368       }
4369 
4370       if (!is_serial) {
4371         // We only need to enter the sync barrier if being called
4372         // from a parallel context
4373         _cm->enter_first_sync_barrier(_worker_id);
4374         
4375         // When we exit this sync barrier we know that all tasks have
4376         // stopped doing marking work. So, it's now safe to
4377         // re-initialise our data structures. At the end of this method,
4378         // task 0 will clear the global data structures.
4379       }
4380 
4381       statsOnly( ++_aborted_overflow );
4382 
4383       // We clear the local state of this task...
4384       clear_region_fields();
4385 
4386       if (!is_serial) {
4387         // ...and enter the second barrier.
4388         _cm->enter_second_sync_barrier(_worker_id);
4389       }
4390       // At this point everything has bee re-initialised and we're
4391       // ready to restart.
4392     }
4393 
4394     if (_cm->verbose_low()) {
4395       gclog_or_tty->print_cr("[%u] <<<<<<<<<< ABORTING, target = %1.2lfms, "
4396                              "elapsed = %1.2lfms <<<<<<<<<<",
4397                              _worker_id, _time_target_ms, elapsed_time_ms);
4398       if (_cm->has_aborted()) {
4399         gclog_or_tty->print_cr("[%u] ========== MARKING ABORTED ==========",
4400                                _worker_id);
4401       }
4402     }
4403   } else {
4404     if (_cm->verbose_low()) {
4405       gclog_or_tty->print_cr("[%u] <<<<<<<<<< FINISHED, target = %1.2lfms, "
4406                              "elapsed = %1.2lfms <<<<<<<<<<",
4407                              _worker_id, _time_target_ms, elapsed_time_ms);
4408     }
4409   }
4410 
4411   _claimed = false;
4412 }
4413 
4414 CMTask::CMTask(uint worker_id,
4415                ConcurrentMark* cm,
4416                size_t* marked_bytes,
4417                BitMap* card_bm,
4418                CMTaskQueue* task_queue,
4419                CMTaskQueueSet* task_queues)
4420   : _g1h(G1CollectedHeap::heap()),
4421     _worker_id(worker_id), _cm(cm),
4422     _claimed(false),
4423     _nextMarkBitMap(NULL), _hash_seed(17),
4424     _task_queue(task_queue),
4425     _task_queues(task_queues),
4426     _cm_oop_closure(NULL),
4427     _marked_bytes_array(marked_bytes),
4428     _card_bm(card_bm) {
4429   guarantee(task_queue != NULL, "invariant");
4430   guarantee(task_queues != NULL, "invariant");
4431 
4432   statsOnly( _clock_due_to_scanning = 0;
4433              _clock_due_to_marking  = 0 );
4434 
4435   _marking_step_diffs_ms.add(0.5);
4436 }
4437 
4438 // These are formatting macros that are used below to ensure
4439 // consistent formatting. The *_H_* versions are used to format the
4440 // header for a particular value and they should be kept consistent
4441 // with the corresponding macro. Also note that most of the macros add
4442 // the necessary white space (as a prefix) which makes them a bit
4443 // easier to compose.
4444 
4445 // All the output lines are prefixed with this string to be able to
4446 // identify them easily in a large log file.
4447 #define G1PPRL_LINE_PREFIX            "###"
4448 
4449 #define G1PPRL_ADDR_BASE_FORMAT    " "PTR_FORMAT"-"PTR_FORMAT
4450 #ifdef _LP64
4451 #define G1PPRL_ADDR_BASE_H_FORMAT  " %37s"
4452 #else // _LP64
4453 #define G1PPRL_ADDR_BASE_H_FORMAT  " %21s"
4454 #endif // _LP64
4455 
4456 // For per-region info
4457 #define G1PPRL_TYPE_FORMAT            "   %-4s"
4458 #define G1PPRL_TYPE_H_FORMAT          "   %4s"
4459 #define G1PPRL_BYTE_FORMAT            "  "SIZE_FORMAT_W(9)
4460 #define G1PPRL_BYTE_H_FORMAT          "  %9s"
4461 #define G1PPRL_DOUBLE_FORMAT          "  %14.1f"
4462 #define G1PPRL_DOUBLE_H_FORMAT        "  %14s"
4463 
4464 // For summary info
4465 #define G1PPRL_SUM_ADDR_FORMAT(tag)    "  "tag":"G1PPRL_ADDR_BASE_FORMAT
4466 #define G1PPRL_SUM_BYTE_FORMAT(tag)    "  "tag": "SIZE_FORMAT
4467 #define G1PPRL_SUM_MB_FORMAT(tag)      "  "tag": %1.2f MB"
4468 #define G1PPRL_SUM_MB_PERC_FORMAT(tag) G1PPRL_SUM_MB_FORMAT(tag)" / %1.2f %%"
4469 
4470 G1PrintRegionLivenessInfoClosure::
4471 G1PrintRegionLivenessInfoClosure(outputStream* out, const char* phase_name)
4472   : _out(out),
4473     _total_used_bytes(0), _total_capacity_bytes(0),
4474     _total_prev_live_bytes(0), _total_next_live_bytes(0),
4475     _hum_used_bytes(0), _hum_capacity_bytes(0),
4476     _hum_prev_live_bytes(0), _hum_next_live_bytes(0) {
4477   G1CollectedHeap* g1h = G1CollectedHeap::heap();
4478   MemRegion g1_committed = g1h->g1_committed();
4479   MemRegion g1_reserved = g1h->g1_reserved();
4480   double now = os::elapsedTime();
4481 
4482   // Print the header of the output.
4483   _out->cr();
4484   _out->print_cr(G1PPRL_LINE_PREFIX" PHASE %s @ %1.3f", phase_name, now);
4485   _out->print_cr(G1PPRL_LINE_PREFIX" HEAP"
4486                  G1PPRL_SUM_ADDR_FORMAT("committed")
4487                  G1PPRL_SUM_ADDR_FORMAT("reserved")
4488                  G1PPRL_SUM_BYTE_FORMAT("region-size"),
4489                  g1_committed.start(), g1_committed.end(),
4490                  g1_reserved.start(), g1_reserved.end(),
4491                  HeapRegion::GrainBytes);
4492   _out->print_cr(G1PPRL_LINE_PREFIX);
4493   _out->print_cr(G1PPRL_LINE_PREFIX
4494                  G1PPRL_TYPE_H_FORMAT
4495                  G1PPRL_ADDR_BASE_H_FORMAT
4496                  G1PPRL_BYTE_H_FORMAT
4497                  G1PPRL_BYTE_H_FORMAT
4498                  G1PPRL_BYTE_H_FORMAT
4499                  G1PPRL_DOUBLE_H_FORMAT,
4500                  "type", "address-range",
4501                  "used", "prev-live", "next-live", "gc-eff");
4502   _out->print_cr(G1PPRL_LINE_PREFIX
4503                  G1PPRL_TYPE_H_FORMAT
4504                  G1PPRL_ADDR_BASE_H_FORMAT
4505                  G1PPRL_BYTE_H_FORMAT
4506                  G1PPRL_BYTE_H_FORMAT
4507                  G1PPRL_BYTE_H_FORMAT
4508                  G1PPRL_DOUBLE_H_FORMAT,
4509                  "", "",
4510                  "(bytes)", "(bytes)", "(bytes)", "(bytes/ms)");
4511 }
4512 
4513 // It takes as a parameter a reference to one of the _hum_* fields, it
4514 // deduces the corresponding value for a region in a humongous region
4515 // series (either the region size, or what's left if the _hum_* field
4516 // is < the region size), and updates the _hum_* field accordingly.
4517 size_t G1PrintRegionLivenessInfoClosure::get_hum_bytes(size_t* hum_bytes) {
4518   size_t bytes = 0;
4519   // The > 0 check is to deal with the prev and next live bytes which
4520   // could be 0.
4521   if (*hum_bytes > 0) {
4522     bytes = MIN2(HeapRegion::GrainBytes, *hum_bytes);
4523     *hum_bytes -= bytes;
4524   }
4525   return bytes;
4526 }
4527 
4528 // It deduces the values for a region in a humongous region series
4529 // from the _hum_* fields and updates those accordingly. It assumes
4530 // that that _hum_* fields have already been set up from the "starts
4531 // humongous" region and we visit the regions in address order.
4532 void G1PrintRegionLivenessInfoClosure::get_hum_bytes(size_t* used_bytes,
4533                                                      size_t* capacity_bytes,
4534                                                      size_t* prev_live_bytes,
4535                                                      size_t* next_live_bytes) {
4536   assert(_hum_used_bytes > 0 && _hum_capacity_bytes > 0, "pre-condition");
4537   *used_bytes      = get_hum_bytes(&_hum_used_bytes);
4538   *capacity_bytes  = get_hum_bytes(&_hum_capacity_bytes);
4539   *prev_live_bytes = get_hum_bytes(&_hum_prev_live_bytes);
4540   *next_live_bytes = get_hum_bytes(&_hum_next_live_bytes);
4541 }
4542 
4543 bool G1PrintRegionLivenessInfoClosure::doHeapRegion(HeapRegion* r) {
4544   const char* type = "";
4545   HeapWord* bottom       = r->bottom();
4546   HeapWord* end          = r->end();
4547   size_t capacity_bytes  = r->capacity();
4548   size_t used_bytes      = r->used();
4549   size_t prev_live_bytes = r->live_bytes();
4550   size_t next_live_bytes = r->next_live_bytes();
4551   double gc_eff          = r->gc_efficiency();
4552   if (r->used() == 0) {
4553     type = "FREE";
4554   } else if (r->is_survivor()) {
4555     type = "SURV";
4556   } else if (r->is_young()) {
4557     type = "EDEN";
4558   } else if (r->startsHumongous()) {
4559     type = "HUMS";
4560 
4561     assert(_hum_used_bytes == 0 && _hum_capacity_bytes == 0 &&
4562            _hum_prev_live_bytes == 0 && _hum_next_live_bytes == 0,
4563            "they should have been zeroed after the last time we used them");
4564     // Set up the _hum_* fields.
4565     _hum_capacity_bytes  = capacity_bytes;
4566     _hum_used_bytes      = used_bytes;
4567     _hum_prev_live_bytes = prev_live_bytes;
4568     _hum_next_live_bytes = next_live_bytes;
4569     get_hum_bytes(&used_bytes, &capacity_bytes,
4570                   &prev_live_bytes, &next_live_bytes);
4571     end = bottom + HeapRegion::GrainWords;
4572   } else if (r->continuesHumongous()) {
4573     type = "HUMC";
4574     get_hum_bytes(&used_bytes, &capacity_bytes,
4575                   &prev_live_bytes, &next_live_bytes);
4576     assert(end == bottom + HeapRegion::GrainWords, "invariant");
4577   } else {
4578     type = "OLD";
4579   }
4580 
4581   _total_used_bytes      += used_bytes;
4582   _total_capacity_bytes  += capacity_bytes;
4583   _total_prev_live_bytes += prev_live_bytes;
4584   _total_next_live_bytes += next_live_bytes;
4585 
4586   // Print a line for this particular region.
4587   _out->print_cr(G1PPRL_LINE_PREFIX
4588                  G1PPRL_TYPE_FORMAT
4589                  G1PPRL_ADDR_BASE_FORMAT
4590                  G1PPRL_BYTE_FORMAT
4591                  G1PPRL_BYTE_FORMAT
4592                  G1PPRL_BYTE_FORMAT
4593                  G1PPRL_DOUBLE_FORMAT,
4594                  type, bottom, end,
4595                  used_bytes, prev_live_bytes, next_live_bytes, gc_eff);
4596 
4597   return false;
4598 }
4599 
4600 G1PrintRegionLivenessInfoClosure::~G1PrintRegionLivenessInfoClosure() {
4601   // Print the footer of the output.
4602   _out->print_cr(G1PPRL_LINE_PREFIX);
4603   _out->print_cr(G1PPRL_LINE_PREFIX
4604                  " SUMMARY"
4605                  G1PPRL_SUM_MB_FORMAT("capacity")
4606                  G1PPRL_SUM_MB_PERC_FORMAT("used")
4607                  G1PPRL_SUM_MB_PERC_FORMAT("prev-live")
4608                  G1PPRL_SUM_MB_PERC_FORMAT("next-live"),
4609                  bytes_to_mb(_total_capacity_bytes),
4610                  bytes_to_mb(_total_used_bytes),
4611                  perc(_total_used_bytes, _total_capacity_bytes),
4612                  bytes_to_mb(_total_prev_live_bytes),
4613                  perc(_total_prev_live_bytes, _total_capacity_bytes),
4614                  bytes_to_mb(_total_next_live_bytes),
4615                  perc(_total_next_live_bytes, _total_capacity_bytes));
4616   _out->cr();
4617 }