1 /*
   2  * Copyright (c) 2001, 2014, 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 "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp"
  27 #include "gc_implementation/parNew/parNewGeneration.hpp"
  28 #include "gc_implementation/parNew/parOopClosures.inline.hpp"
  29 #include "gc_implementation/shared/adaptiveSizePolicy.hpp"
  30 #include "gc_implementation/shared/ageTable.hpp"
  31 #include "gc_implementation/shared/copyFailedInfo.hpp"
  32 #include "gc_implementation/shared/gcHeapSummary.hpp"
  33 #include "gc_implementation/shared/gcTimer.hpp"
  34 #include "gc_implementation/shared/gcTrace.hpp"
  35 #include "gc_implementation/shared/gcTraceTime.hpp"
  36 #include "gc_implementation/shared/parGCAllocBuffer.inline.hpp"
  37 #include "gc_implementation/shared/spaceDecorator.hpp"
  38 #include "memory/defNewGeneration.inline.hpp"
  39 #include "memory/genCollectedHeap.hpp"
  40 #include "memory/genOopClosures.inline.hpp"
  41 #include "memory/generation.hpp"
  42 #include "memory/generation.inline.hpp"
  43 #include "memory/referencePolicy.hpp"
  44 #include "memory/resourceArea.hpp"
  45 #include "memory/sharedHeap.hpp"
  46 #include "memory/space.hpp"
  47 #include "oops/objArrayOop.hpp"
  48 #include "oops/oop.inline.hpp"
  49 #include "oops/oop.pcgc.inline.hpp"
  50 #include "runtime/atomic.inline.hpp"
  51 #include "runtime/handles.hpp"
  52 #include "runtime/handles.inline.hpp"
  53 #include "runtime/java.hpp"
  54 #include "runtime/thread.inline.hpp"
  55 #include "utilities/copy.hpp"
  56 #include "utilities/globalDefinitions.hpp"
  57 #include "utilities/workgroup.hpp"
  58 
  59 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
  60 
  61 #ifdef _MSC_VER
  62 #pragma warning( push )
  63 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list
  64 #endif
  65 ParScanThreadState::ParScanThreadState(Space* to_space_,
  66                                        ParNewGeneration* young_gen_,
  67                                        Generation* old_gen_,
  68                                        int thread_num_,
  69                                        ObjToScanQueueSet* work_queue_set_,
  70                                        Stack<oop, mtGC>* overflow_stacks_,
  71                                        size_t desired_plab_sz_,
  72                                        ParallelTaskTerminator& term_) :
  73   _to_space(to_space_), _old_gen(old_gen_), _young_gen(young_gen_), _thread_num(thread_num_),
  74   _work_queue(work_queue_set_->queue(thread_num_)), _to_space_full(false),
  75   _overflow_stack(overflow_stacks_ ? overflow_stacks_ + thread_num_ : NULL),
  76   _ageTable(false), // false ==> not the global age table, no perf data.
  77   _to_space_alloc_buffer(desired_plab_sz_),
  78   _to_space_closure(young_gen_, this), _old_gen_closure(young_gen_, this),
  79   _to_space_root_closure(young_gen_, this), _old_gen_root_closure(young_gen_, this),
  80   _older_gen_closure(young_gen_, this),
  81   _evacuate_followers(this, &_to_space_closure, &_old_gen_closure,
  82                       &_to_space_root_closure, young_gen_, &_old_gen_root_closure,
  83                       work_queue_set_, &term_),
  84   _is_alive_closure(young_gen_), _scan_weak_ref_closure(young_gen_, this),
  85   _keep_alive_closure(&_scan_weak_ref_closure),
  86   _strong_roots_time(0.0), _term_time(0.0)
  87 {
  88   #if TASKQUEUE_STATS
  89   _term_attempts = 0;
  90   _overflow_refills = 0;
  91   _overflow_refill_objs = 0;
  92   #endif // TASKQUEUE_STATS
  93 
  94   _survivor_chunk_array =
  95     (ChunkArray*) old_gen()->get_data_recorder(thread_num());
  96   _hash_seed = 17;  // Might want to take time-based random value.
  97   _start = os::elapsedTime();
  98   _old_gen_closure.set_generation(old_gen_);
  99   _old_gen_root_closure.set_generation(old_gen_);
 100 }
 101 #ifdef _MSC_VER
 102 #pragma warning( pop )
 103 #endif
 104 
 105 void ParScanThreadState::record_survivor_plab(HeapWord* plab_start,
 106                                               size_t plab_word_size) {
 107   ChunkArray* sca = survivor_chunk_array();
 108   if (sca != NULL) {
 109     // A non-null SCA implies that we want the PLAB data recorded.
 110     sca->record_sample(plab_start, plab_word_size);
 111   }
 112 }
 113 
 114 bool ParScanThreadState::should_be_partially_scanned(oop new_obj, oop old_obj) const {
 115   return new_obj->is_objArray() &&
 116          arrayOop(new_obj)->length() > ParGCArrayScanChunk &&
 117          new_obj != old_obj;
 118 }
 119 
 120 void ParScanThreadState::scan_partial_array_and_push_remainder(oop old) {
 121   assert(old->is_objArray(), "must be obj array");
 122   assert(old->is_forwarded(), "must be forwarded");
 123   assert(Universe::heap()->is_in_reserved(old), "must be in heap.");
 124   assert(!old_gen()->is_in(old), "must be in young generation.");
 125 
 126   objArrayOop obj = objArrayOop(old->forwardee());
 127   // Process ParGCArrayScanChunk elements now
 128   // and push the remainder back onto queue
 129   int start     = arrayOop(old)->length();
 130   int end       = obj->length();
 131   int remainder = end - start;
 132   assert(start <= end, "just checking");
 133   if (remainder > 2 * ParGCArrayScanChunk) {
 134     // Test above combines last partial chunk with a full chunk
 135     end = start + ParGCArrayScanChunk;
 136     arrayOop(old)->set_length(end);
 137     // Push remainder.
 138     bool ok = work_queue()->push(old);
 139     assert(ok, "just popped, push must be okay");
 140   } else {
 141     // Restore length so that it can be used if there
 142     // is a promotion failure and forwarding pointers
 143     // must be removed.
 144     arrayOop(old)->set_length(end);
 145   }
 146 
 147   // process our set of indices (include header in first chunk)
 148   // should make sure end is even (aligned to HeapWord in case of compressed oops)
 149   if ((HeapWord *)obj < young_old_boundary()) {
 150     // object is in to_space
 151     obj->oop_iterate_range(&_to_space_closure, start, end);
 152   } else {
 153     // object is in old generation
 154     obj->oop_iterate_range(&_old_gen_closure, start, end);
 155   }
 156 }
 157 
 158 
 159 void ParScanThreadState::trim_queues(int max_size) {
 160   ObjToScanQueue* queue = work_queue();
 161   do {
 162     while (queue->size() > (juint)max_size) {
 163       oop obj_to_scan;
 164       if (queue->pop_local(obj_to_scan)) {
 165         if ((HeapWord *)obj_to_scan < young_old_boundary()) {
 166           if (obj_to_scan->is_objArray() &&
 167               obj_to_scan->is_forwarded() &&
 168               obj_to_scan->forwardee() != obj_to_scan) {
 169             scan_partial_array_and_push_remainder(obj_to_scan);
 170           } else {
 171             // object is in to_space
 172             obj_to_scan->oop_iterate(&_to_space_closure);
 173           }
 174         } else {
 175           // object is in old generation
 176           obj_to_scan->oop_iterate(&_old_gen_closure);
 177         }
 178       }
 179     }
 180     // For the  case of compressed oops, we have a private, non-shared
 181     // overflow stack, so we eagerly drain it so as to more evenly
 182     // distribute load early. Note: this may be good to do in
 183     // general rather than delay for the final stealing phase.
 184     // If applicable, we'll transfer a set of objects over to our
 185     // work queue, allowing them to be stolen and draining our
 186     // private overflow stack.
 187   } while (ParGCTrimOverflow && young_gen()->take_from_overflow_list(this));
 188 }
 189 
 190 bool ParScanThreadState::take_from_overflow_stack() {
 191   assert(ParGCUseLocalOverflow, "Else should not call");
 192   assert(young_gen()->overflow_list() == NULL, "Error");
 193   ObjToScanQueue* queue = work_queue();
 194   Stack<oop, mtGC>* const of_stack = overflow_stack();
 195   const size_t num_overflow_elems = of_stack->size();
 196   const size_t space_available = queue->max_elems() - queue->size();
 197   const size_t num_take_elems = MIN3(space_available / 4,
 198                                      ParGCDesiredObjsFromOverflowList,
 199                                      num_overflow_elems);
 200   // Transfer the most recent num_take_elems from the overflow
 201   // stack to our work queue.
 202   for (size_t i = 0; i != num_take_elems; i++) {
 203     oop cur = of_stack->pop();
 204     oop obj_to_push = cur->forwardee();
 205     assert(Universe::heap()->is_in_reserved(cur), "Should be in heap");
 206     assert(!old_gen()->is_in_reserved(cur), "Should be in young gen");
 207     assert(Universe::heap()->is_in_reserved(obj_to_push), "Should be in heap");
 208     if (should_be_partially_scanned(obj_to_push, cur)) {
 209       assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");
 210       obj_to_push = cur;
 211     }
 212     bool ok = queue->push(obj_to_push);
 213     assert(ok, "Should have succeeded");
 214   }
 215   assert(young_gen()->overflow_list() == NULL, "Error");
 216   return num_take_elems > 0;  // was something transferred?
 217 }
 218 
 219 void ParScanThreadState::push_on_overflow_stack(oop p) {
 220   assert(ParGCUseLocalOverflow, "Else should not call");
 221   overflow_stack()->push(p);
 222   assert(young_gen()->overflow_list() == NULL, "Error");
 223 }
 224 
 225 HeapWord* ParScanThreadState::alloc_in_to_space_slow(size_t word_sz) {
 226 
 227   // Otherwise, if the object is small enough, try to reallocate the
 228   // buffer.
 229   HeapWord* obj = NULL;
 230   if (!_to_space_full) {
 231     ParGCAllocBuffer* const plab = to_space_alloc_buffer();
 232     Space*            const sp   = to_space();
 233     if (word_sz * 100 <
 234         ParallelGCBufferWastePct * plab->word_sz()) {
 235       // Is small enough; abandon this buffer and start a new one.
 236       plab->retire(false, false);
 237       size_t buf_size = plab->word_sz();
 238       HeapWord* buf_space = sp->par_allocate(buf_size);
 239       if (buf_space == NULL) {
 240         const size_t min_bytes =
 241           ParGCAllocBuffer::min_size() << LogHeapWordSize;
 242         size_t free_bytes = sp->free();
 243         while(buf_space == NULL && free_bytes >= min_bytes) {
 244           buf_size = free_bytes >> LogHeapWordSize;
 245           assert(buf_size == (size_t)align_object_size(buf_size),
 246                  "Invariant");
 247           buf_space  = sp->par_allocate(buf_size);
 248           free_bytes = sp->free();
 249         }
 250       }
 251       if (buf_space != NULL) {
 252         plab->set_word_size(buf_size);
 253         plab->set_buf(buf_space);
 254         record_survivor_plab(buf_space, buf_size);
 255         obj = plab->allocate_aligned(word_sz, SurvivorAlignmentInBytes);
 256         // Note that we cannot compare buf_size < word_sz below
 257         // because of AlignmentReserve (see ParGCAllocBuffer::allocate()).
 258         assert(obj != NULL || plab->words_remaining() < word_sz,
 259                "Else should have been able to allocate");
 260         // It's conceivable that we may be able to use the
 261         // buffer we just grabbed for subsequent small requests
 262         // even if not for this one.
 263       } else {
 264         // We're used up.
 265         _to_space_full = true;
 266       }
 267 
 268     } else {
 269       // Too large; allocate the object individually.
 270       obj = sp->par_allocate(word_sz);
 271     }
 272   }
 273   return obj;
 274 }
 275 
 276 
 277 void ParScanThreadState::undo_alloc_in_to_space(HeapWord* obj,
 278                                                 size_t word_sz) {
 279   // Is the alloc in the current alloc buffer?
 280   if (to_space_alloc_buffer()->contains(obj)) {
 281     assert(to_space_alloc_buffer()->contains(obj + word_sz - 1),
 282            "Should contain whole object.");
 283     to_space_alloc_buffer()->undo_allocation(obj, word_sz);
 284   } else {
 285     CollectedHeap::fill_with_object(obj, word_sz);
 286   }
 287 }
 288 
 289 void ParScanThreadState::print_promotion_failure_size() {
 290   if (_promotion_failed_info.has_failed() && PrintPromotionFailure) {
 291     gclog_or_tty->print(" (%d: promotion failure size = " SIZE_FORMAT ") ",
 292                         _thread_num, _promotion_failed_info.first_size());
 293   }
 294 }
 295 
 296 class ParScanThreadStateSet: private ResourceArray {
 297 public:
 298   // Initializes states for the specified number of threads;
 299   ParScanThreadStateSet(int                     num_threads,
 300                         Space&                  to_space,
 301                         ParNewGeneration&       gen,
 302                         Generation&             old_gen,
 303                         ObjToScanQueueSet&      queue_set,
 304                         Stack<oop, mtGC>*       overflow_stacks_,
 305                         size_t                  desired_plab_sz,
 306                         ParallelTaskTerminator& term);
 307 
 308   ~ParScanThreadStateSet() { TASKQUEUE_STATS_ONLY(reset_stats()); }
 309 
 310   inline ParScanThreadState& thread_state(int i);
 311 
 312   void trace_promotion_failed(YoungGCTracer& gc_tracer);
 313   void reset(int active_workers, bool promotion_failed);
 314   void flush();
 315 
 316   #if TASKQUEUE_STATS
 317   static void
 318     print_termination_stats_hdr(outputStream* const st = gclog_or_tty);
 319   void print_termination_stats(outputStream* const st = gclog_or_tty);
 320   static void
 321     print_taskqueue_stats_hdr(outputStream* const st = gclog_or_tty);
 322   void print_taskqueue_stats(outputStream* const st = gclog_or_tty);
 323   void reset_stats();
 324   #endif // TASKQUEUE_STATS
 325 
 326 private:
 327   ParallelTaskTerminator& _term;
 328   ParNewGeneration&       _gen;
 329   Generation&             _old_gen;
 330  public:
 331   bool is_valid(int id) const { return id < length(); }
 332   ParallelTaskTerminator* terminator() { return &_term; }
 333 };
 334 
 335 
 336 ParScanThreadStateSet::ParScanThreadStateSet(
 337   int num_threads, Space& to_space, ParNewGeneration& gen,
 338   Generation& old_gen, ObjToScanQueueSet& queue_set,
 339   Stack<oop, mtGC>* overflow_stacks,
 340   size_t desired_plab_sz, ParallelTaskTerminator& term)
 341   : ResourceArray(sizeof(ParScanThreadState), num_threads),
 342     _gen(gen), _old_gen(old_gen), _term(term)
 343 {
 344   assert(num_threads > 0, "sanity check!");
 345   assert(ParGCUseLocalOverflow == (overflow_stacks != NULL),
 346          "overflow_stack allocation mismatch");
 347   // Initialize states.
 348   for (int i = 0; i < num_threads; ++i) {
 349     new ((ParScanThreadState*)_data + i)
 350         ParScanThreadState(&to_space, &gen, &old_gen, i, &queue_set,
 351                            overflow_stacks, desired_plab_sz, term);
 352   }
 353 }
 354 
 355 inline ParScanThreadState& ParScanThreadStateSet::thread_state(int i)
 356 {
 357   assert(i >= 0 && i < length(), "sanity check!");
 358   return ((ParScanThreadState*)_data)[i];
 359 }
 360 
 361 void ParScanThreadStateSet::trace_promotion_failed(YoungGCTracer& gc_tracer) {
 362   for (int i = 0; i < length(); ++i) {
 363     if (thread_state(i).promotion_failed()) {
 364       gc_tracer.report_promotion_failed(thread_state(i).promotion_failed_info());
 365       thread_state(i).promotion_failed_info().reset();
 366     }
 367   }
 368 }
 369 
 370 void ParScanThreadStateSet::reset(int active_threads, bool promotion_failed)
 371 {
 372   _term.reset_for_reuse(active_threads);
 373   if (promotion_failed) {
 374     for (int i = 0; i < length(); ++i) {
 375       thread_state(i).print_promotion_failure_size();
 376     }
 377   }
 378 }
 379 
 380 #if TASKQUEUE_STATS
 381 void
 382 ParScanThreadState::reset_stats()
 383 {
 384   taskqueue_stats().reset();
 385   _term_attempts = 0;
 386   _overflow_refills = 0;
 387   _overflow_refill_objs = 0;
 388 }
 389 
 390 void ParScanThreadStateSet::reset_stats()
 391 {
 392   for (int i = 0; i < length(); ++i) {
 393     thread_state(i).reset_stats();
 394   }
 395 }
 396 
 397 void
 398 ParScanThreadStateSet::print_termination_stats_hdr(outputStream* const st)
 399 {
 400   st->print_raw_cr("GC Termination Stats");
 401   st->print_raw_cr("     elapsed  --strong roots-- "
 402                    "-------termination-------");
 403   st->print_raw_cr("thr     ms        ms       %   "
 404                    "    ms       %   attempts");
 405   st->print_raw_cr("--- --------- --------- ------ "
 406                    "--------- ------ --------");
 407 }
 408 
 409 void ParScanThreadStateSet::print_termination_stats(outputStream* const st)
 410 {
 411   print_termination_stats_hdr(st);
 412 
 413   for (int i = 0; i < length(); ++i) {
 414     const ParScanThreadState & pss = thread_state(i);
 415     const double elapsed_ms = pss.elapsed_time() * 1000.0;
 416     const double s_roots_ms = pss.strong_roots_time() * 1000.0;
 417     const double term_ms = pss.term_time() * 1000.0;
 418     st->print_cr("%3d %9.2f %9.2f %6.2f "
 419                  "%9.2f %6.2f " SIZE_FORMAT_W(8),
 420                  i, elapsed_ms, s_roots_ms, s_roots_ms * 100 / elapsed_ms,
 421                  term_ms, term_ms * 100 / elapsed_ms, pss.term_attempts());
 422   }
 423 }
 424 
 425 // Print stats related to work queue activity.
 426 void ParScanThreadStateSet::print_taskqueue_stats_hdr(outputStream* const st)
 427 {
 428   st->print_raw_cr("GC Task Stats");
 429   st->print_raw("thr "); TaskQueueStats::print_header(1, st); st->cr();
 430   st->print_raw("--- "); TaskQueueStats::print_header(2, st); st->cr();
 431 }
 432 
 433 void ParScanThreadStateSet::print_taskqueue_stats(outputStream* const st)
 434 {
 435   print_taskqueue_stats_hdr(st);
 436 
 437   TaskQueueStats totals;
 438   for (int i = 0; i < length(); ++i) {
 439     const ParScanThreadState & pss = thread_state(i);
 440     const TaskQueueStats & stats = pss.taskqueue_stats();
 441     st->print("%3d ", i); stats.print(st); st->cr();
 442     totals += stats;
 443 
 444     if (pss.overflow_refills() > 0) {
 445       st->print_cr("    " SIZE_FORMAT_W(10) " overflow refills    "
 446                    SIZE_FORMAT_W(10) " overflow objects",
 447                    pss.overflow_refills(), pss.overflow_refill_objs());
 448     }
 449   }
 450   st->print("tot "); totals.print(st); st->cr();
 451 
 452   DEBUG_ONLY(totals.verify());
 453 }
 454 #endif // TASKQUEUE_STATS
 455 
 456 void ParScanThreadStateSet::flush()
 457 {
 458   // Work in this loop should be kept as lightweight as
 459   // possible since this might otherwise become a bottleneck
 460   // to scaling. Should we add heavy-weight work into this
 461   // loop, consider parallelizing the loop into the worker threads.
 462   for (int i = 0; i < length(); ++i) {
 463     ParScanThreadState& par_scan_state = thread_state(i);
 464 
 465     // Flush stats related to To-space PLAB activity and
 466     // retire the last buffer.
 467     par_scan_state.to_space_alloc_buffer()->
 468       flush_stats_and_retire(_gen.plab_stats(),
 469                              true /* end_of_gc */,
 470                              false /* retain */);
 471 
 472     // Every thread has its own age table.  We need to merge
 473     // them all into one.
 474     ageTable *local_table = par_scan_state.age_table();
 475     _gen.age_table()->merge(local_table);
 476 
 477     // Inform old gen that we're done.
 478     _old_gen.par_promote_alloc_done(i);
 479     _old_gen.par_oop_since_save_marks_iterate_done(i);
 480   }
 481 
 482   if (UseConcMarkSweepGC && ParallelGCThreads > 0) {
 483     // We need to call this even when ResizeOldPLAB is disabled
 484     // so as to avoid breaking some asserts. While we may be able
 485     // to avoid this by reorganizing the code a bit, I am loathe
 486     // to do that unless we find cases where ergo leads to bad
 487     // performance.
 488     CFLS_LAB::compute_desired_plab_size();
 489   }
 490 }
 491 
 492 ParScanClosure::ParScanClosure(ParNewGeneration* g,
 493                                ParScanThreadState* par_scan_state) :
 494   OopsInKlassOrGenClosure(g), _par_scan_state(par_scan_state), _g(g)
 495 {
 496   _boundary = _g->reserved().end();
 497 }
 498 
 499 void ParScanWithBarrierClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, true, false); }
 500 void ParScanWithBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, false); }
 501 
 502 void ParScanWithoutBarrierClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, false, false); }
 503 void ParScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, false); }
 504 
 505 void ParRootScanWithBarrierTwoGensClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, true, true); }
 506 void ParRootScanWithBarrierTwoGensClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, true); }
 507 
 508 void ParRootScanWithoutBarrierClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, false, true); }
 509 void ParRootScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, true); }
 510 
 511 ParScanWeakRefClosure::ParScanWeakRefClosure(ParNewGeneration* g,
 512                                              ParScanThreadState* par_scan_state)
 513   : ScanWeakRefClosure(g), _par_scan_state(par_scan_state)
 514 {}
 515 
 516 void ParScanWeakRefClosure::do_oop(oop* p)       { ParScanWeakRefClosure::do_oop_work(p); }
 517 void ParScanWeakRefClosure::do_oop(narrowOop* p) { ParScanWeakRefClosure::do_oop_work(p); }
 518 
 519 #ifdef WIN32
 520 #pragma warning(disable: 4786) /* identifier was truncated to '255' characters in the browser information */
 521 #endif
 522 
 523 ParEvacuateFollowersClosure::ParEvacuateFollowersClosure(
 524     ParScanThreadState* par_scan_state_,
 525     ParScanWithoutBarrierClosure* to_space_closure_,
 526     ParScanWithBarrierClosure* old_gen_closure_,
 527     ParRootScanWithoutBarrierClosure* to_space_root_closure_,
 528     ParNewGeneration* par_gen_,
 529     ParRootScanWithBarrierTwoGensClosure* old_gen_root_closure_,
 530     ObjToScanQueueSet* task_queues_,
 531     ParallelTaskTerminator* terminator_) :
 532 
 533     _par_scan_state(par_scan_state_),
 534     _to_space_closure(to_space_closure_),
 535     _old_gen_closure(old_gen_closure_),
 536     _to_space_root_closure(to_space_root_closure_),
 537     _old_gen_root_closure(old_gen_root_closure_),
 538     _par_gen(par_gen_),
 539     _task_queues(task_queues_),
 540     _terminator(terminator_)
 541 {}
 542 
 543 void ParEvacuateFollowersClosure::do_void() {
 544   ObjToScanQueue* work_q = par_scan_state()->work_queue();
 545 
 546   while (true) {
 547 
 548     // Scan to-space and old-gen objs until we run out of both.
 549     oop obj_to_scan;
 550     par_scan_state()->trim_queues(0);
 551 
 552     // We have no local work, attempt to steal from other threads.
 553 
 554     // attempt to steal work from promoted.
 555     if (task_queues()->steal(par_scan_state()->thread_num(),
 556                              par_scan_state()->hash_seed(),
 557                              obj_to_scan)) {
 558       bool res = work_q->push(obj_to_scan);
 559       assert(res, "Empty queue should have room for a push.");
 560 
 561       //   if successful, goto Start.
 562       continue;
 563 
 564       // try global overflow list.
 565     } else if (par_gen()->take_from_overflow_list(par_scan_state())) {
 566       continue;
 567     }
 568 
 569     // Otherwise, offer termination.
 570     par_scan_state()->start_term_time();
 571     if (terminator()->offer_termination()) break;
 572     par_scan_state()->end_term_time();
 573   }
 574   assert(par_gen()->_overflow_list == NULL && par_gen()->_num_par_pushes == 0,
 575          "Broken overflow list?");
 576   // Finish the last termination pause.
 577   par_scan_state()->end_term_time();
 578 }
 579 
 580 ParNewGenTask::ParNewGenTask(ParNewGeneration* young_gen, Generation* old_gen,
 581                 HeapWord* young_old_boundary, ParScanThreadStateSet* state_set) :
 582     AbstractGangTask("ParNewGeneration collection"),
 583     _young_gen(young_gen), _old_gen(old_gen),
 584     _young_old_boundary(young_old_boundary),
 585     _state_set(state_set)
 586   {}
 587 
 588 // Reset the terminator for the given number of
 589 // active threads.
 590 void ParNewGenTask::set_for_termination(int active_workers) {
 591   _state_set->reset(active_workers, _young_gen->promotion_failed());
 592   // Should the heap be passed in?  There's only 1 for now so
 593   // grab it instead.
 594   GenCollectedHeap* gch = GenCollectedHeap::heap();
 595   gch->set_n_termination(active_workers);
 596 }
 597 
 598 void ParNewGenTask::work(uint worker_id) {
 599   GenCollectedHeap* gch = GenCollectedHeap::heap();
 600   // Since this is being done in a separate thread, need new resource
 601   // and handle marks.
 602   ResourceMark rm;
 603   HandleMark hm;
 604 
 605   Generation* old_gen = gch->old_gen();
 606 
 607   ParScanThreadState& par_scan_state = _state_set->thread_state(worker_id);
 608   assert(_state_set->is_valid(worker_id), "Should not have been called");
 609 
 610   par_scan_state.set_young_old_boundary(_young_old_boundary);
 611 
 612   KlassScanClosure klass_scan_closure(&par_scan_state.to_space_root_closure(),
 613                                       gch->rem_set()->klass_rem_set());
 614   CLDToKlassAndOopClosure cld_scan_closure(&klass_scan_closure,
 615                                            &par_scan_state.to_space_root_closure(),
 616                                            false);
 617 
 618   par_scan_state.start_strong_roots();
 619   gch->gen_process_roots(Generation::Young,
 620                          true,  // Process younger gens, if any,
 621                                 // as strong roots.
 622                          false, // no scope; this is parallel code
 623                          SharedHeap::SO_ScavengeCodeCache,
 624                          GenCollectedHeap::StrongAndWeakRoots,
 625                          &par_scan_state.to_space_root_closure(),
 626                          &par_scan_state.older_gen_closure(),
 627                          &cld_scan_closure);
 628 
 629   par_scan_state.end_strong_roots();
 630 
 631   // "evacuate followers".
 632   par_scan_state.evacuate_followers_closure().do_void();
 633 }
 634 
 635 #ifdef _MSC_VER
 636 #pragma warning( push )
 637 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list
 638 #endif
 639 ParNewGeneration::
 640 ParNewGeneration(ReservedSpace rs, size_t initial_byte_size)
 641   : DefNewGeneration(rs, initial_byte_size, "PCopy"),
 642   _overflow_list(NULL),
 643   _is_alive_closure(this),
 644   _plab_stats(YoungPLABSize, PLABWeight)
 645 {
 646   NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;)
 647   NOT_PRODUCT(_num_par_pushes = 0;)
 648   _task_queues = new ObjToScanQueueSet(ParallelGCThreads);
 649   guarantee(_task_queues != NULL, "task_queues allocation failure.");
 650 
 651   for (uint i1 = 0; i1 < ParallelGCThreads; i1++) {
 652     ObjToScanQueue *q = new ObjToScanQueue();
 653     guarantee(q != NULL, "work_queue Allocation failure.");
 654     _task_queues->register_queue(i1, q);
 655   }
 656 
 657   for (uint i2 = 0; i2 < ParallelGCThreads; i2++)
 658     _task_queues->queue(i2)->initialize();
 659 
 660   _overflow_stacks = NULL;
 661   if (ParGCUseLocalOverflow) {
 662 
 663     // typedef to workaround NEW_C_HEAP_ARRAY macro, which can not deal
 664     // with ','
 665     typedef Stack<oop, mtGC> GCOopStack;
 666 
 667     _overflow_stacks = NEW_C_HEAP_ARRAY(GCOopStack, ParallelGCThreads, mtGC);
 668     for (size_t i = 0; i < ParallelGCThreads; ++i) {
 669       new (_overflow_stacks + i) Stack<oop, mtGC>();
 670     }
 671   }
 672 
 673   if (UsePerfData) {
 674     EXCEPTION_MARK;
 675     ResourceMark rm;
 676 
 677     const char* cname =
 678          PerfDataManager::counter_name(_gen_counters->name_space(), "threads");
 679     PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None,
 680                                      ParallelGCThreads, CHECK);
 681   }
 682 }
 683 #ifdef _MSC_VER
 684 #pragma warning( pop )
 685 #endif
 686 
 687 // ParNewGeneration::
 688 ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) :
 689   DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {}
 690 
 691 template <class T>
 692 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) {
 693 #ifdef ASSERT
 694   {
 695     assert(!oopDesc::is_null(*p), "expected non-null ref");
 696     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 697     // We never expect to see a null reference being processed
 698     // as a weak reference.
 699     assert(obj->is_oop(), "expected an oop while scanning weak refs");
 700   }
 701 #endif // ASSERT
 702 
 703   _par_cl->do_oop_nv(p);
 704 
 705   if (Universe::heap()->is_in_reserved(p)) {
 706     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 707     _rs->write_ref_field_gc_par(p, obj);
 708   }
 709 }
 710 
 711 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(oop* p)       { ParKeepAliveClosure::do_oop_work(p); }
 712 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(narrowOop* p) { ParKeepAliveClosure::do_oop_work(p); }
 713 
 714 // ParNewGeneration::
 715 KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) :
 716   DefNewGeneration::KeepAliveClosure(cl) {}
 717 
 718 template <class T>
 719 void /*ParNewGeneration::*/KeepAliveClosure::do_oop_work(T* p) {
 720 #ifdef ASSERT
 721   {
 722     assert(!oopDesc::is_null(*p), "expected non-null ref");
 723     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 724     // We never expect to see a null reference being processed
 725     // as a weak reference.
 726     assert(obj->is_oop(), "expected an oop while scanning weak refs");
 727   }
 728 #endif // ASSERT
 729 
 730   _cl->do_oop_nv(p);
 731 
 732   if (Universe::heap()->is_in_reserved(p)) {
 733     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 734     _rs->write_ref_field_gc_par(p, obj);
 735   }
 736 }
 737 
 738 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(oop* p)       { KeepAliveClosure::do_oop_work(p); }
 739 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(narrowOop* p) { KeepAliveClosure::do_oop_work(p); }
 740 
 741 template <class T> void ScanClosureWithParBarrier::do_oop_work(T* p) {
 742   T heap_oop = oopDesc::load_heap_oop(p);
 743   if (!oopDesc::is_null(heap_oop)) {
 744     oop obj = oopDesc::decode_heap_oop_not_null(heap_oop);
 745     if ((HeapWord*)obj < _boundary) {
 746       assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?");
 747       oop new_obj = obj->is_forwarded()
 748                       ? obj->forwardee()
 749                       : _g->DefNewGeneration::copy_to_survivor_space(obj);
 750       oopDesc::encode_store_heap_oop_not_null(p, new_obj);
 751     }
 752     if (_gc_barrier) {
 753       // If p points to a younger generation, mark the card.
 754       if ((HeapWord*)obj < _gen_boundary) {
 755         _rs->write_ref_field_gc_par(p, obj);
 756       }
 757     }
 758   }
 759 }
 760 
 761 void ScanClosureWithParBarrier::do_oop(oop* p)       { ScanClosureWithParBarrier::do_oop_work(p); }
 762 void ScanClosureWithParBarrier::do_oop(narrowOop* p) { ScanClosureWithParBarrier::do_oop_work(p); }
 763 
 764 class ParNewRefProcTaskProxy: public AbstractGangTask {
 765   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
 766 public:
 767   ParNewRefProcTaskProxy(ProcessTask& task, ParNewGeneration& gen,
 768                          Generation& old_gen,
 769                          HeapWord* young_old_boundary,
 770                          ParScanThreadStateSet& state_set);
 771 
 772 private:
 773   virtual void work(uint worker_id);
 774   virtual void set_for_termination(int active_workers) {
 775     _state_set.terminator()->reset_for_reuse(active_workers);
 776   }
 777 private:
 778   ParNewGeneration&      _young_gen;
 779   ProcessTask&           _task;
 780   Generation&            _old_gen;
 781   HeapWord*              _young_old_boundary;
 782   ParScanThreadStateSet& _state_set;
 783 };
 784 
 785 ParNewRefProcTaskProxy::ParNewRefProcTaskProxy(
 786     ProcessTask& task, ParNewGeneration& young_gen,
 787     Generation& old_gen,
 788     HeapWord* young_old_boundary,
 789     ParScanThreadStateSet& state_set)
 790   : AbstractGangTask("ParNewGeneration parallel reference processing"),
 791     _young_gen(young_gen),
 792     _task(task),
 793     _old_gen(old_gen),
 794     _young_old_boundary(young_old_boundary),
 795     _state_set(state_set)
 796 {
 797 }
 798 
 799 void ParNewRefProcTaskProxy::work(uint worker_id)
 800 {
 801   ResourceMark rm;
 802   HandleMark hm;
 803   ParScanThreadState& par_scan_state = _state_set.thread_state(worker_id);
 804   par_scan_state.set_young_old_boundary(_young_old_boundary);
 805   _task.work(worker_id, par_scan_state.is_alive_closure(),
 806              par_scan_state.keep_alive_closure(),
 807              par_scan_state.evacuate_followers_closure());
 808 }
 809 
 810 class ParNewRefEnqueueTaskProxy: public AbstractGangTask {
 811   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
 812   EnqueueTask& _task;
 813 
 814 public:
 815   ParNewRefEnqueueTaskProxy(EnqueueTask& task)
 816     : AbstractGangTask("ParNewGeneration parallel reference enqueue"),
 817       _task(task)
 818   { }
 819 
 820   virtual void work(uint worker_id)
 821   {
 822     _task.work(worker_id);
 823   }
 824 };
 825 
 826 
 827 void ParNewRefProcTaskExecutor::execute(ProcessTask& task)
 828 {
 829   GenCollectedHeap* gch = GenCollectedHeap::heap();
 830   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
 831          "not a generational heap");
 832   FlexibleWorkGang* workers = gch->workers();
 833   assert(workers != NULL, "Need parallel worker threads.");
 834   _state_set.reset(workers->active_workers(), _generation.promotion_failed());
 835   ParNewRefProcTaskProxy rp_task(task, _generation, *(gch->old_gen()),
 836                                  _generation.reserved().end(), _state_set);
 837   workers->run_task(&rp_task);
 838   _state_set.reset(0 /* bad value in debug if not reset */,
 839                    _generation.promotion_failed());
 840 }
 841 
 842 void ParNewRefProcTaskExecutor::execute(EnqueueTask& task)
 843 {
 844   GenCollectedHeap* gch = GenCollectedHeap::heap();
 845   FlexibleWorkGang* workers = gch->workers();
 846   assert(workers != NULL, "Need parallel worker threads.");
 847   ParNewRefEnqueueTaskProxy enq_task(task);
 848   workers->run_task(&enq_task);
 849 }
 850 
 851 void ParNewRefProcTaskExecutor::set_single_threaded_mode()
 852 {
 853   _state_set.flush();
 854   GenCollectedHeap* gch = GenCollectedHeap::heap();
 855   gch->set_par_threads(0);  // 0 ==> non-parallel.
 856   gch->save_marks();
 857 }
 858 
 859 ScanClosureWithParBarrier::
 860 ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) :
 861   ScanClosure(g, gc_barrier) {}
 862 
 863 EvacuateFollowersClosureGeneral::
 864 EvacuateFollowersClosureGeneral(GenCollectedHeap* gch,
 865                                 OopsInGenClosure* cur,
 866                                 OopsInGenClosure* older) :
 867   _gch(gch),
 868   _scan_cur_or_nonheap(cur), _scan_older(older)
 869 {}
 870 
 871 void EvacuateFollowersClosureGeneral::do_void() {
 872   do {
 873     // Beware: this call will lead to closure applications via virtual
 874     // calls.
 875     _gch->oop_since_save_marks_iterate(Generation::Young,
 876                                        _scan_cur_or_nonheap,
 877                                        _scan_older);
 878   } while (!_gch->no_allocs_since_save_marks(true /* include_young */));
 879 }
 880 
 881 
 882 // A Generation that does parallel young-gen collection.
 883 
 884 bool ParNewGeneration::_avoid_promotion_undo = false;
 885 
 886 void ParNewGeneration::handle_promotion_failed(GenCollectedHeap* gch, ParScanThreadStateSet& thread_state_set, ParNewTracer& gc_tracer) {
 887   assert(_promo_failure_scan_stack.is_empty(), "post condition");
 888   _promo_failure_scan_stack.clear(true); // Clear cached segments.
 889 
 890   remove_forwarding_pointers();
 891   if (PrintGCDetails) {
 892     gclog_or_tty->print(" (promotion failed)");
 893   }
 894   // All the spaces are in play for mark-sweep.
 895   swap_spaces();  // Make life simpler for CMS || rescan; see 6483690.
 896   from()->set_next_compaction_space(to());
 897   gch->set_incremental_collection_failed();
 898   // Inform the next generation that a promotion failure occurred.
 899   _old_gen->promotion_failure_occurred();
 900 
 901   // Trace promotion failure in the parallel GC threads
 902   thread_state_set.trace_promotion_failed(gc_tracer);
 903   // Single threaded code may have reported promotion failure to the global state
 904   if (_promotion_failed_info.has_failed()) {
 905     gc_tracer.report_promotion_failed(_promotion_failed_info);
 906   }
 907   // Reset the PromotionFailureALot counters.
 908   NOT_PRODUCT(Universe::heap()->reset_promotion_should_fail();)
 909 }
 910 
 911 void ParNewGeneration::collect(bool   full,
 912                                bool   clear_all_soft_refs,
 913                                size_t size,
 914                                bool   is_tlab) {
 915   assert(full || size > 0, "otherwise we don't want to collect");
 916 
 917   GenCollectedHeap* gch = GenCollectedHeap::heap();
 918 
 919   _gc_timer->register_gc_start();
 920 
 921   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
 922     "not a CMS generational heap");
 923   AdaptiveSizePolicy* size_policy = gch->gen_policy()->size_policy();
 924   FlexibleWorkGang* workers = gch->workers();
 925   assert(workers != NULL, "Need workgang for parallel work");
 926   int active_workers =
 927       AdaptiveSizePolicy::calc_active_workers(workers->total_workers(),
 928                                    workers->active_workers(),
 929                                    Threads::number_of_non_daemon_threads());
 930   workers->set_active_workers(active_workers);
 931   _old_gen = gch->old_gen();
 932   // Do we have to avoid promotion_undo?
 933   if (gch->collector_policy()->is_concurrent_mark_sweep_policy()) {
 934     set_avoid_promotion_undo(true);
 935   }
 936 
 937   // If the next generation is too full to accommodate worst-case promotion
 938   // from this generation, pass on collection; let the next generation
 939   // do it.
 940   if (!collection_attempt_is_safe()) {
 941     gch->set_incremental_collection_failed();  // slight lie, in that we did not even attempt one
 942     return;
 943   }
 944   assert(to()->is_empty(), "Else not collection_attempt_is_safe");
 945 
 946   ParNewTracer gc_tracer;
 947   gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start());
 948   gch->trace_heap_before_gc(&gc_tracer);
 949 
 950   init_assuming_no_promotion_failure();
 951 
 952   if (UseAdaptiveSizePolicy) {
 953     set_survivor_overflow(false);
 954     size_policy->minor_collection_begin();
 955   }
 956 
 957   GCTraceTime t1(GCCauseString("GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL, gc_tracer.gc_id());
 958   // Capture heap used before collection (for printing).
 959   size_t gch_prev_used = gch->used();
 960 
 961   SpecializationStats::clear();
 962 
 963   age_table()->clear();
 964   to()->clear(SpaceDecorator::Mangle);
 965 
 966   gch->save_marks();
 967   assert(workers != NULL, "Need parallel worker threads.");
 968   int n_workers = active_workers;
 969 
 970   // Set the correct parallelism (number of queues) in the reference processor
 971   ref_processor()->set_active_mt_degree(n_workers);
 972 
 973   // Always set the terminator for the active number of workers
 974   // because only those workers go through the termination protocol.
 975   ParallelTaskTerminator _term(n_workers, task_queues());
 976   ParScanThreadStateSet thread_state_set(workers->active_workers(),
 977                                          *to(), *this, *_old_gen, *task_queues(),
 978                                          _overflow_stacks, desired_plab_sz(), _term);
 979 
 980   ParNewGenTask tsk(this, _old_gen, reserved().end(), &thread_state_set);
 981   gch->set_par_threads(n_workers);
 982   gch->rem_set()->prepare_for_younger_refs_iterate(true);
 983   // It turns out that even when we're using 1 thread, doing the work in a
 984   // separate thread causes wide variance in run times.  We can't help this
 985   // in the multi-threaded case, but we special-case n=1 here to get
 986   // repeatable measurements of the 1-thread overhead of the parallel code.
 987   if (n_workers > 1) {
 988     GenCollectedHeap::StrongRootsScope srs(gch);
 989     workers->run_task(&tsk);
 990   } else {
 991     GenCollectedHeap::StrongRootsScope srs(gch);
 992     tsk.work(0);
 993   }
 994   thread_state_set.reset(0 /* Bad value in debug if not reset */,
 995                          promotion_failed());
 996 
 997   // Process (weak) reference objects found during scavenge.
 998   ReferenceProcessor* rp = ref_processor();
 999   IsAliveClosure is_alive(this);
1000   ScanWeakRefClosure scan_weak_ref(this);
1001   KeepAliveClosure keep_alive(&scan_weak_ref);
1002   ScanClosure               scan_without_gc_barrier(this, false);
1003   ScanClosureWithParBarrier scan_with_gc_barrier(this, true);
1004   set_promo_failure_scan_stack_closure(&scan_without_gc_barrier);
1005   EvacuateFollowersClosureGeneral evacuate_followers(gch,
1006     &scan_without_gc_barrier, &scan_with_gc_barrier);
1007   rp->setup_policy(clear_all_soft_refs);
1008   // Can  the mt_degree be set later (at run_task() time would be best)?
1009   rp->set_active_mt_degree(active_workers);
1010   ReferenceProcessorStats stats;
1011   if (rp->processing_is_mt()) {
1012     ParNewRefProcTaskExecutor task_executor(*this, thread_state_set);
1013     stats = rp->process_discovered_references(&is_alive, &keep_alive,
1014                                               &evacuate_followers, &task_executor,
1015                                               _gc_timer, gc_tracer.gc_id());
1016   } else {
1017     thread_state_set.flush();
1018     gch->set_par_threads(0);  // 0 ==> non-parallel.
1019     gch->save_marks();
1020     stats = rp->process_discovered_references(&is_alive, &keep_alive,
1021                                               &evacuate_followers, NULL,
1022                                               _gc_timer, gc_tracer.gc_id());
1023   }
1024   gc_tracer.report_gc_reference_stats(stats);
1025   if (!promotion_failed()) {
1026     // Swap the survivor spaces.
1027     eden()->clear(SpaceDecorator::Mangle);
1028     from()->clear(SpaceDecorator::Mangle);
1029     if (ZapUnusedHeapArea) {
1030       // This is now done here because of the piece-meal mangling which
1031       // can check for valid mangling at intermediate points in the
1032       // collection(s).  When a minor collection fails to collect
1033       // sufficient space resizing of the young generation can occur
1034       // an redistribute the spaces in the young generation.  Mangle
1035       // here so that unzapped regions don't get distributed to
1036       // other spaces.
1037       to()->mangle_unused_area();
1038     }
1039     swap_spaces();
1040 
1041     // A successful scavenge should restart the GC time limit count which is
1042     // for full GC's.
1043     size_policy->reset_gc_overhead_limit_count();
1044 
1045     assert(to()->is_empty(), "to space should be empty now");
1046 
1047     adjust_desired_tenuring_threshold();
1048   } else {
1049     handle_promotion_failed(gch, thread_state_set, gc_tracer);
1050   }
1051   // set new iteration safe limit for the survivor spaces
1052   from()->set_concurrent_iteration_safe_limit(from()->top());
1053   to()->set_concurrent_iteration_safe_limit(to()->top());
1054 
1055   if (ResizePLAB) {
1056     plab_stats()->adjust_desired_plab_sz(n_workers);
1057   }
1058 
1059   if (PrintGC && !PrintGCDetails) {
1060     gch->print_heap_change(gch_prev_used);
1061   }
1062 
1063   TASKQUEUE_STATS_ONLY(if (PrintTerminationStats) thread_state_set.print_termination_stats());
1064   TASKQUEUE_STATS_ONLY(if (PrintTaskqueue) thread_state_set.print_taskqueue_stats());
1065 
1066   if (UseAdaptiveSizePolicy) {
1067     size_policy->minor_collection_end(gch->gc_cause());
1068     size_policy->avg_survived()->sample(from()->used());
1069   }
1070 
1071   // We need to use a monotonically non-decreasing time in ms
1072   // or we will see time-warp warnings and os::javaTimeMillis()
1073   // does not guarantee monotonicity.
1074   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
1075   update_time_of_last_gc(now);
1076 
1077   SpecializationStats::print();
1078 
1079   rp->set_enqueuing_is_done(true);
1080   if (rp->processing_is_mt()) {
1081     ParNewRefProcTaskExecutor task_executor(*this, thread_state_set);
1082     rp->enqueue_discovered_references(&task_executor);
1083   } else {
1084     rp->enqueue_discovered_references(NULL);
1085   }
1086   rp->verify_no_references_recorded();
1087 
1088   gch->trace_heap_after_gc(&gc_tracer);
1089   gc_tracer.report_tenuring_threshold(tenuring_threshold());
1090 
1091   _gc_timer->register_gc_end();
1092 
1093   gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions());
1094 }
1095 
1096 static int sum;
1097 void ParNewGeneration::waste_some_time() {
1098   for (int i = 0; i < 100; i++) {
1099     sum += i;
1100   }
1101 }
1102 
1103 static const oop ClaimedForwardPtr = cast_to_oop<intptr_t>(0x4);
1104 
1105 // Because of concurrency, there are times where an object for which
1106 // "is_forwarded()" is true contains an "interim" forwarding pointer
1107 // value.  Such a value will soon be overwritten with a real value.
1108 // This method requires "obj" to have a forwarding pointer, and waits, if
1109 // necessary for a real one to be inserted, and returns it.
1110 
1111 oop ParNewGeneration::real_forwardee(oop obj) {
1112   oop forward_ptr = obj->forwardee();
1113   if (forward_ptr != ClaimedForwardPtr) {
1114     return forward_ptr;
1115   } else {
1116     return real_forwardee_slow(obj);
1117   }
1118 }
1119 
1120 oop ParNewGeneration::real_forwardee_slow(oop obj) {
1121   // Spin-read if it is claimed but not yet written by another thread.
1122   oop forward_ptr = obj->forwardee();
1123   while (forward_ptr == ClaimedForwardPtr) {
1124     waste_some_time();
1125     assert(obj->is_forwarded(), "precondition");
1126     forward_ptr = obj->forwardee();
1127   }
1128   return forward_ptr;
1129 }
1130 
1131 #ifdef ASSERT
1132 bool ParNewGeneration::is_legal_forward_ptr(oop p) {
1133   return
1134     (_avoid_promotion_undo && p == ClaimedForwardPtr)
1135     || Universe::heap()->is_in_reserved(p);
1136 }
1137 #endif
1138 
1139 void ParNewGeneration::preserve_mark_if_necessary(oop obj, markOop m) {
1140   if (m->must_be_preserved_for_promotion_failure(obj)) {
1141     // We should really have separate per-worker stacks, rather
1142     // than use locking of a common pair of stacks.
1143     MutexLocker ml(ParGCRareEvent_lock);
1144     preserve_mark(obj, m);
1145   }
1146 }
1147 
1148 // Multiple GC threads may try to promote an object.  If the object
1149 // is successfully promoted, a forwarding pointer will be installed in
1150 // the object in the young generation.  This method claims the right
1151 // to install the forwarding pointer before it copies the object,
1152 // thus avoiding the need to undo the copy as in
1153 // copy_to_survivor_space_avoiding_with_undo.
1154 
1155 oop ParNewGeneration::copy_to_survivor_space_avoiding_promotion_undo(
1156         ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) {
1157   // In the sequential version, this assert also says that the object is
1158   // not forwarded.  That might not be the case here.  It is the case that
1159   // the caller observed it to be not forwarded at some time in the past.
1160   assert(is_in_reserved(old), "shouldn't be scavenging this oop");
1161 
1162   // The sequential code read "old->age()" below.  That doesn't work here,
1163   // since the age is in the mark word, and that might be overwritten with
1164   // a forwarding pointer by a parallel thread.  So we must save the mark
1165   // word in a local and then analyze it.
1166   oopDesc dummyOld;
1167   dummyOld.set_mark(m);
1168   assert(!dummyOld.is_forwarded(),
1169          "should not be called with forwarding pointer mark word.");
1170 
1171   oop new_obj = NULL;
1172   oop forward_ptr;
1173 
1174   // Try allocating obj in to-space (unless too old)
1175   if (dummyOld.age() < tenuring_threshold()) {
1176     new_obj = (oop)par_scan_state->alloc_in_to_space(sz);
1177     if (new_obj == NULL) {
1178       set_survivor_overflow(true);
1179     }
1180   }
1181 
1182   if (new_obj == NULL) {
1183     // Either to-space is full or we decided to promote
1184     // try allocating obj tenured
1185 
1186     // Attempt to install a null forwarding pointer (atomically),
1187     // to claim the right to install the real forwarding pointer.
1188     forward_ptr = old->forward_to_atomic(ClaimedForwardPtr);
1189     if (forward_ptr != NULL) {
1190       // someone else beat us to it.
1191         return real_forwardee(old);
1192     }
1193 
1194     new_obj = _old_gen->par_promote(par_scan_state->thread_num(),
1195                                     old, m, sz);
1196 
1197     if (new_obj == NULL) {
1198       // promotion failed, forward to self
1199       _promotion_failed = true;
1200       new_obj = old;
1201 
1202       preserve_mark_if_necessary(old, m);
1203       par_scan_state->register_promotion_failure(sz);
1204     }
1205 
1206     old->forward_to(new_obj);
1207     forward_ptr = NULL;
1208   } else {
1209     // Is in to-space; do copying ourselves.
1210     Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz);
1211     forward_ptr = old->forward_to_atomic(new_obj);
1212     // Restore the mark word copied above.
1213     new_obj->set_mark(m);
1214     // Increment age if obj still in new generation
1215     new_obj->incr_age();
1216     par_scan_state->age_table()->add(new_obj, sz);
1217   }
1218   assert(new_obj != NULL, "just checking");
1219 
1220 #ifndef PRODUCT
1221   // This code must come after the CAS test, or it will print incorrect
1222   // information.
1223   if (TraceScavenge) {
1224     gclog_or_tty->print_cr("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}",
1225        is_in_reserved(new_obj) ? "copying" : "tenuring",
1226        new_obj->klass()->internal_name(), (void *)old, (void *)new_obj, new_obj->size());
1227   }
1228 #endif
1229 
1230   if (forward_ptr == NULL) {
1231     oop obj_to_push = new_obj;
1232     if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) {
1233       // Length field used as index of next element to be scanned.
1234       // Real length can be obtained from real_forwardee()
1235       arrayOop(old)->set_length(0);
1236       obj_to_push = old;
1237       assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push,
1238              "push forwarded object");
1239     }
1240     // Push it on one of the queues of to-be-scanned objects.
1241     bool simulate_overflow = false;
1242     NOT_PRODUCT(
1243       if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) {
1244         // simulate a stack overflow
1245         simulate_overflow = true;
1246       }
1247     )
1248     if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) {
1249       // Add stats for overflow pushes.
1250       if (Verbose && PrintGCDetails) {
1251         gclog_or_tty->print("queue overflow!\n");
1252       }
1253       push_on_overflow_list(old, par_scan_state);
1254       TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0));
1255     }
1256 
1257     return new_obj;
1258   }
1259 
1260   // Oops.  Someone beat us to it.  Undo the allocation.  Where did we
1261   // allocate it?
1262   if (is_in_reserved(new_obj)) {
1263     // Must be in to_space.
1264     assert(to()->is_in_reserved(new_obj), "Checking");
1265     if (forward_ptr == ClaimedForwardPtr) {
1266       // Wait to get the real forwarding pointer value.
1267       forward_ptr = real_forwardee(old);
1268     }
1269     par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz);
1270   }
1271 
1272   return forward_ptr;
1273 }
1274 
1275 
1276 // Multiple GC threads may try to promote the same object.  If two
1277 // or more GC threads copy the object, only one wins the race to install
1278 // the forwarding pointer.  The other threads have to undo their copy.
1279 
1280 oop ParNewGeneration::copy_to_survivor_space_with_undo(
1281         ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) {
1282 
1283   // In the sequential version, this assert also says that the object is
1284   // not forwarded.  That might not be the case here.  It is the case that
1285   // the caller observed it to be not forwarded at some time in the past.
1286   assert(is_in_reserved(old), "shouldn't be scavenging this oop");
1287 
1288   // The sequential code read "old->age()" below.  That doesn't work here,
1289   // since the age is in the mark word, and that might be overwritten with
1290   // a forwarding pointer by a parallel thread.  So we must save the mark
1291   // word here, install it in a local oopDesc, and then analyze it.
1292   oopDesc dummyOld;
1293   dummyOld.set_mark(m);
1294   assert(!dummyOld.is_forwarded(),
1295          "should not be called with forwarding pointer mark word.");
1296 
1297   bool failed_to_promote = false;
1298   oop new_obj = NULL;
1299   oop forward_ptr;
1300 
1301   // Try allocating obj in to-space (unless too old)
1302   if (dummyOld.age() < tenuring_threshold()) {
1303     new_obj = (oop)par_scan_state->alloc_in_to_space(sz);
1304     if (new_obj == NULL) {
1305       set_survivor_overflow(true);
1306     }
1307   }
1308 
1309   if (new_obj == NULL) {
1310     // Either to-space is full or we decided to promote
1311     // try allocating obj tenured
1312     new_obj = _old_gen->par_promote(par_scan_state->thread_num(),
1313                                     old, m, sz);
1314 
1315     if (new_obj == NULL) {
1316       // promotion failed, forward to self
1317       forward_ptr = old->forward_to_atomic(old);
1318       new_obj = old;
1319 
1320       if (forward_ptr != NULL) {
1321         return forward_ptr;   // someone else succeeded
1322       }
1323 
1324       _promotion_failed = true;
1325       failed_to_promote = true;
1326 
1327       preserve_mark_if_necessary(old, m);
1328       par_scan_state->register_promotion_failure(sz);
1329     }
1330   } else {
1331     // Is in to-space; do copying ourselves.
1332     Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz);
1333     // Restore the mark word copied above.
1334     new_obj->set_mark(m);
1335     // Increment age if new_obj still in new generation
1336     new_obj->incr_age();
1337     par_scan_state->age_table()->add(new_obj, sz);
1338   }
1339   assert(new_obj != NULL, "just checking");
1340 
1341 #ifndef PRODUCT
1342   // This code must come after the CAS test, or it will print incorrect
1343   // information.
1344   if (TraceScavenge) {
1345     gclog_or_tty->print_cr("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}",
1346        is_in_reserved(new_obj) ? "copying" : "tenuring",
1347        new_obj->klass()->internal_name(), (void *)old, (void *)new_obj, new_obj->size());
1348   }
1349 #endif
1350 
1351   // Now attempt to install the forwarding pointer (atomically).
1352   // We have to copy the mark word before overwriting with forwarding
1353   // ptr, so we can restore it below in the copy.
1354   if (!failed_to_promote) {
1355     forward_ptr = old->forward_to_atomic(new_obj);
1356   }
1357 
1358   if (forward_ptr == NULL) {
1359     oop obj_to_push = new_obj;
1360     if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) {
1361       // Length field used as index of next element to be scanned.
1362       // Real length can be obtained from real_forwardee()
1363       arrayOop(old)->set_length(0);
1364       obj_to_push = old;
1365       assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push,
1366              "push forwarded object");
1367     }
1368     // Push it on one of the queues of to-be-scanned objects.
1369     bool simulate_overflow = false;
1370     NOT_PRODUCT(
1371       if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) {
1372         // simulate a stack overflow
1373         simulate_overflow = true;
1374       }
1375     )
1376     if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) {
1377       // Add stats for overflow pushes.
1378       push_on_overflow_list(old, par_scan_state);
1379       TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0));
1380     }
1381 
1382     return new_obj;
1383   }
1384 
1385   // Oops.  Someone beat us to it.  Undo the allocation.  Where did we
1386   // allocate it?
1387   if (is_in_reserved(new_obj)) {
1388     // Must be in to_space.
1389     assert(to()->is_in_reserved(new_obj), "Checking");
1390     par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz);
1391   } else {
1392     assert(!_avoid_promotion_undo, "Should not be here if avoiding.");
1393     _old_gen->par_promote_alloc_undo(par_scan_state->thread_num(),
1394                                      (HeapWord*)new_obj, sz);
1395   }
1396 
1397   return forward_ptr;
1398 }
1399 
1400 #ifndef PRODUCT
1401 // It's OK to call this multi-threaded;  the worst thing
1402 // that can happen is that we'll get a bunch of closely
1403 // spaced simulated overflows, but that's OK, in fact
1404 // probably good as it would exercise the overflow code
1405 // under contention.
1406 bool ParNewGeneration::should_simulate_overflow() {
1407   if (_overflow_counter-- <= 0) { // just being defensive
1408     _overflow_counter = ParGCWorkQueueOverflowInterval;
1409     return true;
1410   } else {
1411     return false;
1412   }
1413 }
1414 #endif
1415 
1416 // In case we are using compressed oops, we need to be careful.
1417 // If the object being pushed is an object array, then its length
1418 // field keeps track of the "grey boundary" at which the next
1419 // incremental scan will be done (see ParGCArrayScanChunk).
1420 // When using compressed oops, this length field is kept in the
1421 // lower 32 bits of the erstwhile klass word and cannot be used
1422 // for the overflow chaining pointer (OCP below). As such the OCP
1423 // would itself need to be compressed into the top 32-bits in this
1424 // case. Unfortunately, see below, in the event that we have a
1425 // promotion failure, the node to be pushed on the list can be
1426 // outside of the Java heap, so the heap-based pointer compression
1427 // would not work (we would have potential aliasing between C-heap
1428 // and Java-heap pointers). For this reason, when using compressed
1429 // oops, we simply use a worker-thread-local, non-shared overflow
1430 // list in the form of a growable array, with a slightly different
1431 // overflow stack draining strategy. If/when we start using fat
1432 // stacks here, we can go back to using (fat) pointer chains
1433 // (although some performance comparisons would be useful since
1434 // single global lists have their own performance disadvantages
1435 // as we were made painfully aware not long ago, see 6786503).
1436 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
1437 void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) {
1438   assert(is_in_reserved(from_space_obj), "Should be from this generation");
1439   if (ParGCUseLocalOverflow) {
1440     // In the case of compressed oops, we use a private, not-shared
1441     // overflow stack.
1442     par_scan_state->push_on_overflow_stack(from_space_obj);
1443   } else {
1444     assert(!UseCompressedOops, "Error");
1445     // if the object has been forwarded to itself, then we cannot
1446     // use the klass pointer for the linked list.  Instead we have
1447     // to allocate an oopDesc in the C-Heap and use that for the linked list.
1448     // XXX This is horribly inefficient when a promotion failure occurs
1449     // and should be fixed. XXX FIX ME !!!
1450 #ifndef PRODUCT
1451     Atomic::inc_ptr(&_num_par_pushes);
1452     assert(_num_par_pushes > 0, "Tautology");
1453 #endif
1454     if (from_space_obj->forwardee() == from_space_obj) {
1455       oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1, mtGC);
1456       listhead->forward_to(from_space_obj);
1457       from_space_obj = listhead;
1458     }
1459     oop observed_overflow_list = _overflow_list;
1460     oop cur_overflow_list;
1461     do {
1462       cur_overflow_list = observed_overflow_list;
1463       if (cur_overflow_list != BUSY) {
1464         from_space_obj->set_klass_to_list_ptr(cur_overflow_list);
1465       } else {
1466         from_space_obj->set_klass_to_list_ptr(NULL);
1467       }
1468       observed_overflow_list =
1469         (oop)Atomic::cmpxchg_ptr(from_space_obj, &_overflow_list, cur_overflow_list);
1470     } while (cur_overflow_list != observed_overflow_list);
1471   }
1472 }
1473 
1474 bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) {
1475   bool res;
1476 
1477   if (ParGCUseLocalOverflow) {
1478     res = par_scan_state->take_from_overflow_stack();
1479   } else {
1480     assert(!UseCompressedOops, "Error");
1481     res = take_from_overflow_list_work(par_scan_state);
1482   }
1483   return res;
1484 }
1485 
1486 
1487 // *NOTE*: The overflow list manipulation code here and
1488 // in CMSCollector:: are very similar in shape,
1489 // except that in the CMS case we thread the objects
1490 // directly into the list via their mark word, and do
1491 // not need to deal with special cases below related
1492 // to chunking of object arrays and promotion failure
1493 // handling.
1494 // CR 6797058 has been filed to attempt consolidation of
1495 // the common code.
1496 // Because of the common code, if you make any changes in
1497 // the code below, please check the CMS version to see if
1498 // similar changes might be needed.
1499 // See CMSCollector::par_take_from_overflow_list() for
1500 // more extensive documentation comments.
1501 bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) {
1502   ObjToScanQueue* work_q = par_scan_state->work_queue();
1503   // How many to take?
1504   size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
1505                                  (size_t)ParGCDesiredObjsFromOverflowList);
1506 
1507   assert(!UseCompressedOops, "Error");
1508   assert(par_scan_state->overflow_stack() == NULL, "Error");
1509   if (_overflow_list == NULL) return false;
1510 
1511   // Otherwise, there was something there; try claiming the list.
1512   oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
1513   // Trim off a prefix of at most objsFromOverflow items
1514   Thread* tid = Thread::current();
1515   size_t spin_count = (size_t)ParallelGCThreads;
1516   size_t sleep_time_millis = MAX2((size_t)1, objsFromOverflow/100);
1517   for (size_t spin = 0; prefix == BUSY && spin < spin_count; spin++) {
1518     // someone grabbed it before we did ...
1519     // ... we spin for a short while...
1520     os::sleep(tid, sleep_time_millis, false);
1521     if (_overflow_list == NULL) {
1522       // nothing left to take
1523       return false;
1524     } else if (_overflow_list != BUSY) {
1525      // try and grab the prefix
1526      prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
1527     }
1528   }
1529   if (prefix == NULL || prefix == BUSY) {
1530      // Nothing to take or waited long enough
1531      if (prefix == NULL) {
1532        // Write back the NULL in case we overwrote it with BUSY above
1533        // and it is still the same value.
1534        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
1535      }
1536      return false;
1537   }
1538   assert(prefix != NULL && prefix != BUSY, "Error");
1539   size_t i = 1;
1540   oop cur = prefix;
1541   while (i < objsFromOverflow && cur->klass_or_null() != NULL) {
1542     i++; cur = cur->list_ptr_from_klass();
1543   }
1544 
1545   // Reattach remaining (suffix) to overflow list
1546   if (cur->klass_or_null() == NULL) {
1547     // Write back the NULL in lieu of the BUSY we wrote
1548     // above and it is still the same value.
1549     if (_overflow_list == BUSY) {
1550       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
1551     }
1552   } else {
1553     assert(cur->klass_or_null() != (Klass*)(address)BUSY, "Error");
1554     oop suffix = cur->list_ptr_from_klass();       // suffix will be put back on global list
1555     cur->set_klass_to_list_ptr(NULL);     // break off suffix
1556     // It's possible that the list is still in the empty(busy) state
1557     // we left it in a short while ago; in that case we may be
1558     // able to place back the suffix.
1559     oop observed_overflow_list = _overflow_list;
1560     oop cur_overflow_list = observed_overflow_list;
1561     bool attached = false;
1562     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
1563       observed_overflow_list =
1564         (oop) Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);
1565       if (cur_overflow_list == observed_overflow_list) {
1566         attached = true;
1567         break;
1568       } else cur_overflow_list = observed_overflow_list;
1569     }
1570     if (!attached) {
1571       // Too bad, someone else got in in between; we'll need to do a splice.
1572       // Find the last item of suffix list
1573       oop last = suffix;
1574       while (last->klass_or_null() != NULL) {
1575         last = last->list_ptr_from_klass();
1576       }
1577       // Atomically prepend suffix to current overflow list
1578       observed_overflow_list = _overflow_list;
1579       do {
1580         cur_overflow_list = observed_overflow_list;
1581         if (cur_overflow_list != BUSY) {
1582           // Do the splice ...
1583           last->set_klass_to_list_ptr(cur_overflow_list);
1584         } else { // cur_overflow_list == BUSY
1585           last->set_klass_to_list_ptr(NULL);
1586         }
1587         observed_overflow_list =
1588           (oop)Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);
1589       } while (cur_overflow_list != observed_overflow_list);
1590     }
1591   }
1592 
1593   // Push objects on prefix list onto this thread's work queue
1594   assert(prefix != NULL && prefix != BUSY, "program logic");
1595   cur = prefix;
1596   ssize_t n = 0;
1597   while (cur != NULL) {
1598     oop obj_to_push = cur->forwardee();
1599     oop next        = cur->list_ptr_from_klass();
1600     cur->set_klass(obj_to_push->klass());
1601     // This may be an array object that is self-forwarded. In that case, the list pointer
1602     // space, cur, is not in the Java heap, but rather in the C-heap and should be freed.
1603     if (!is_in_reserved(cur)) {
1604       // This can become a scaling bottleneck when there is work queue overflow coincident
1605       // with promotion failure.
1606       oopDesc* f = cur;
1607       FREE_C_HEAP_ARRAY(oopDesc, f, mtGC);
1608     } else if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) {
1609       assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");
1610       obj_to_push = cur;
1611     }
1612     bool ok = work_q->push(obj_to_push);
1613     assert(ok, "Should have succeeded");
1614     cur = next;
1615     n++;
1616   }
1617   TASKQUEUE_STATS_ONLY(par_scan_state->note_overflow_refill(n));
1618 #ifndef PRODUCT
1619   assert(_num_par_pushes >= n, "Too many pops?");
1620   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
1621 #endif
1622   return true;
1623 }
1624 #undef BUSY
1625 
1626 void ParNewGeneration::ref_processor_init() {
1627   if (_ref_processor == NULL) {
1628     // Allocate and initialize a reference processor
1629     _ref_processor =
1630       new ReferenceProcessor(_reserved,                  // span
1631                              ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing
1632                              (int) ParallelGCThreads,    // mt processing degree
1633                              refs_discovery_is_mt(),     // mt discovery
1634                              (int) ParallelGCThreads,    // mt discovery degree
1635                              refs_discovery_is_atomic(), // atomic_discovery
1636                              NULL);                      // is_alive_non_header
1637   }
1638 }
1639 
1640 const char* ParNewGeneration::name() const {
1641   return "par new generation";
1642 }