1 /*
   2  * Copyright (c) 2001, 2015, 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/cms/compactibleFreeListSpace.hpp"
  27 #include "gc/cms/concurrentMarkSweepGeneration.hpp"
  28 #include "gc/cms/parNewGeneration.inline.hpp"
  29 #include "gc/cms/parOopClosures.inline.hpp"
  30 #include "gc/serial/defNewGeneration.inline.hpp"
  31 #include "gc/shared/adaptiveSizePolicy.hpp"
  32 #include "gc/shared/ageTable.hpp"
  33 #include "gc/shared/copyFailedInfo.hpp"
  34 #include "gc/shared/gcHeapSummary.hpp"
  35 #include "gc/shared/gcTimer.hpp"
  36 #include "gc/shared/gcTrace.hpp"
  37 #include "gc/shared/gcTraceTime.hpp"
  38 #include "gc/shared/genCollectedHeap.hpp"
  39 #include "gc/shared/genOopClosures.inline.hpp"
  40 #include "gc/shared/generation.hpp"
  41 #include "gc/shared/plab.inline.hpp"
  42 #include "gc/shared/referencePolicy.hpp"
  43 #include "gc/shared/space.hpp"
  44 #include "gc/shared/spaceDecorator.hpp"
  45 #include "gc/shared/strongRootsScope.hpp"
  46 #include "gc/shared/taskqueue.inline.hpp"
  47 #include "gc/shared/workgroup.hpp"
  48 #include "memory/resourceArea.hpp"
  49 #include "oops/objArrayOop.hpp"
  50 #include "oops/oop.inline.hpp"
  51 #include "runtime/atomic.inline.hpp"
  52 #include "runtime/handles.hpp"
  53 #include "runtime/handles.inline.hpp"
  54 #include "runtime/java.hpp"
  55 #include "runtime/thread.inline.hpp"
  56 #include "utilities/copy.hpp"
  57 #include "utilities/globalDefinitions.hpp"
  58 #include "utilities/stack.inline.hpp"
  59 
  60 #ifdef _MSC_VER
  61 #pragma warning( push )
  62 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list
  63 #endif
  64 ParScanThreadState::ParScanThreadState(Space* to_space_,
  65                                        ParNewGeneration* young_gen_,
  66                                        Generation* old_gen_,
  67                                        int thread_num_,
  68                                        ObjToScanQueueSet* work_queue_set_,
  69                                        Stack<oop, mtGC>* overflow_stacks_,
  70                                        size_t desired_plab_sz_,
  71                                        ParallelTaskTerminator& term_) :
  72   _to_space(to_space_), _old_gen(old_gen_), _young_gen(young_gen_), _thread_num(thread_num_),
  73   _work_queue(work_queue_set_->queue(thread_num_)), _to_space_full(false),
  74   _overflow_stack(overflow_stacks_ ? overflow_stacks_ + thread_num_ : NULL),
  75   _ageTable(false), // false ==> not the global age table, no perf data.
  76   _to_space_alloc_buffer(desired_plab_sz_),
  77   _to_space_closure(young_gen_, this), _old_gen_closure(young_gen_, this),
  78   _to_space_root_closure(young_gen_, this), _old_gen_root_closure(young_gen_, this),
  79   _older_gen_closure(young_gen_, this),
  80   _evacuate_followers(this, &_to_space_closure, &_old_gen_closure,
  81                       &_to_space_root_closure, young_gen_, &_old_gen_root_closure,
  82                       work_queue_set_, &term_),
  83   _is_alive_closure(young_gen_), _scan_weak_ref_closure(young_gen_, this),
  84   _keep_alive_closure(&_scan_weak_ref_closure),
  85   _strong_roots_time(0.0), _term_time(0.0)
  86 {
  87   #if TASKQUEUE_STATS
  88   _term_attempts = 0;
  89   _overflow_refills = 0;
  90   _overflow_refill_objs = 0;
  91   #endif // TASKQUEUE_STATS
  92 
  93   _survivor_chunk_array =
  94     (ChunkArray*) old_gen()->get_data_recorder(thread_num());
  95   _hash_seed = 17;  // Might want to take time-based random value.
  96   _start = os::elapsedTime();
  97   _old_gen_closure.set_generation(old_gen_);
  98   _old_gen_root_closure.set_generation(old_gen_);
  99 }
 100 #ifdef _MSC_VER
 101 #pragma warning( pop )
 102 #endif
 103 
 104 void ParScanThreadState::record_survivor_plab(HeapWord* plab_start,
 105                                               size_t plab_word_size) {
 106   ChunkArray* sca = survivor_chunk_array();
 107   if (sca != NULL) {
 108     // A non-null SCA implies that we want the PLAB data recorded.
 109     sca->record_sample(plab_start, plab_word_size);
 110   }
 111 }
 112 
 113 bool ParScanThreadState::should_be_partially_scanned(oop new_obj, oop old_obj) const {
 114   return new_obj->is_objArray() &&
 115          arrayOop(new_obj)->length() > ParGCArrayScanChunk &&
 116          new_obj != old_obj;
 117 }
 118 
 119 void ParScanThreadState::scan_partial_array_and_push_remainder(oop old) {
 120   assert(old->is_objArray(), "must be obj array");
 121   assert(old->is_forwarded(), "must be forwarded");
 122   assert(GenCollectedHeap::heap()->is_in_reserved(old), "must be in heap.");
 123   assert(!old_gen()->is_in(old), "must be in young generation.");
 124 
 125   objArrayOop obj = objArrayOop(old->forwardee());
 126   // Process ParGCArrayScanChunk elements now
 127   // and push the remainder back onto queue
 128   int start     = arrayOop(old)->length();
 129   int end       = obj->length();
 130   int remainder = end - start;
 131   assert(start <= end, "just checking");
 132   if (remainder > 2 * ParGCArrayScanChunk) {
 133     // Test above combines last partial chunk with a full chunk
 134     end = start + ParGCArrayScanChunk;
 135     arrayOop(old)->set_length(end);
 136     // Push remainder.
 137     bool ok = work_queue()->push(old);
 138     assert(ok, "just popped, push must be okay");
 139   } else {
 140     // Restore length so that it can be used if there
 141     // is a promotion failure and forwarding pointers
 142     // must be removed.
 143     arrayOop(old)->set_length(end);
 144   }
 145 
 146   // process our set of indices (include header in first chunk)
 147   // should make sure end is even (aligned to HeapWord in case of compressed oops)
 148   if ((HeapWord *)obj < young_old_boundary()) {
 149     // object is in to_space
 150     obj->oop_iterate_range(&_to_space_closure, start, end);
 151   } else {
 152     // object is in old generation
 153     obj->oop_iterate_range(&_old_gen_closure, start, end);
 154   }
 155 }
 156 
 157 
 158 void ParScanThreadState::trim_queues(int max_size) {
 159   ObjToScanQueue* queue = work_queue();
 160   do {
 161     while (queue->size() > (juint)max_size) {
 162       oop obj_to_scan;
 163       if (queue->pop_local(obj_to_scan)) {
 164         if ((HeapWord *)obj_to_scan < young_old_boundary()) {
 165           if (obj_to_scan->is_objArray() &&
 166               obj_to_scan->is_forwarded() &&
 167               obj_to_scan->forwardee() != obj_to_scan) {
 168             scan_partial_array_and_push_remainder(obj_to_scan);
 169           } else {
 170             // object is in to_space
 171             obj_to_scan->oop_iterate(&_to_space_closure);
 172           }
 173         } else {
 174           // object is in old generation
 175           obj_to_scan->oop_iterate(&_old_gen_closure);
 176         }
 177       }
 178     }
 179     // For the  case of compressed oops, we have a private, non-shared
 180     // overflow stack, so we eagerly drain it so as to more evenly
 181     // distribute load early. Note: this may be good to do in
 182     // general rather than delay for the final stealing phase.
 183     // If applicable, we'll transfer a set of objects over to our
 184     // work queue, allowing them to be stolen and draining our
 185     // private overflow stack.
 186   } while (ParGCTrimOverflow && young_gen()->take_from_overflow_list(this));
 187 }
 188 
 189 bool ParScanThreadState::take_from_overflow_stack() {
 190   assert(ParGCUseLocalOverflow, "Else should not call");
 191   assert(young_gen()->overflow_list() == NULL, "Error");
 192   ObjToScanQueue* queue = work_queue();
 193   Stack<oop, mtGC>* const of_stack = overflow_stack();
 194   const size_t num_overflow_elems = of_stack->size();
 195   const size_t space_available = queue->max_elems() - queue->size();
 196   const size_t num_take_elems = MIN3(space_available / 4,
 197                                      ParGCDesiredObjsFromOverflowList,
 198                                      num_overflow_elems);
 199   // Transfer the most recent num_take_elems from the overflow
 200   // stack to our work queue.
 201   for (size_t i = 0; i != num_take_elems; i++) {
 202     oop cur = of_stack->pop();
 203     oop obj_to_push = cur->forwardee();
 204     assert(GenCollectedHeap::heap()->is_in_reserved(cur), "Should be in heap");
 205     assert(!old_gen()->is_in_reserved(cur), "Should be in young gen");
 206     assert(GenCollectedHeap::heap()->is_in_reserved(obj_to_push), "Should be in heap");
 207     if (should_be_partially_scanned(obj_to_push, cur)) {
 208       assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");
 209       obj_to_push = cur;
 210     }
 211     bool ok = queue->push(obj_to_push);
 212     assert(ok, "Should have succeeded");
 213   }
 214   assert(young_gen()->overflow_list() == NULL, "Error");
 215   return num_take_elems > 0;  // was something transferred?
 216 }
 217 
 218 void ParScanThreadState::push_on_overflow_stack(oop p) {
 219   assert(ParGCUseLocalOverflow, "Else should not call");
 220   overflow_stack()->push(p);
 221   assert(young_gen()->overflow_list() == NULL, "Error");
 222 }
 223 
 224 HeapWord* ParScanThreadState::alloc_in_to_space_slow(size_t word_sz) {
 225 
 226   // Otherwise, if the object is small enough, try to reallocate the
 227   // buffer.
 228   HeapWord* obj = NULL;
 229   if (!_to_space_full) {
 230     PLAB* const plab = to_space_alloc_buffer();
 231     Space*            const sp   = to_space();
 232     if (word_sz * 100 <
 233         ParallelGCBufferWastePct * plab->word_sz()) {
 234       // Is small enough; abandon this buffer and start a new one.
 235       plab->retire();
 236       size_t buf_size = plab->word_sz();
 237       HeapWord* buf_space = sp->par_allocate(buf_size);
 238       if (buf_space == NULL) {
 239         const size_t min_bytes =
 240           PLAB::min_size() << LogHeapWordSize;
 241         size_t free_bytes = sp->free();
 242         while(buf_space == NULL && free_bytes >= min_bytes) {
 243           buf_size = free_bytes >> LogHeapWordSize;
 244           assert(buf_size == (size_t)align_object_size(buf_size),
 245                  "Invariant");
 246           buf_space  = sp->par_allocate(buf_size);
 247           free_bytes = sp->free();
 248         }
 249       }
 250       if (buf_space != NULL) {
 251         plab->set_buf(buf_space, buf_size);
 252         record_survivor_plab(buf_space, buf_size);
 253         obj = plab->allocate_aligned(word_sz, SurvivorAlignmentInBytes);
 254         // Note that we cannot compare buf_size < word_sz below
 255         // because of AlignmentReserve (see PLAB::allocate()).
 256         assert(obj != NULL || plab->words_remaining() < word_sz,
 257                "Else should have been able to allocate");
 258         // It's conceivable that we may be able to use the
 259         // buffer we just grabbed for subsequent small requests
 260         // even if not for this one.
 261       } else {
 262         // We're used up.
 263         _to_space_full = true;
 264       }
 265 
 266     } else {
 267       // Too large; allocate the object individually.
 268       obj = sp->par_allocate(word_sz);
 269     }
 270   }
 271   return obj;
 272 }
 273 
 274 
 275 void ParScanThreadState::undo_alloc_in_to_space(HeapWord* obj, size_t word_sz) {
 276   to_space_alloc_buffer()->undo_allocation(obj, word_sz);
 277 }
 278 
 279 void ParScanThreadState::print_promotion_failure_size() {
 280   if (_promotion_failed_info.has_failed() && PrintPromotionFailure) {
 281     gclog_or_tty->print(" (%d: promotion failure size = " SIZE_FORMAT ") ",
 282                         _thread_num, _promotion_failed_info.first_size());
 283   }
 284 }
 285 
 286 class ParScanThreadStateSet: private ResourceArray {
 287 public:
 288   // Initializes states for the specified number of threads;
 289   ParScanThreadStateSet(int                     num_threads,
 290                         Space&                  to_space,
 291                         ParNewGeneration&       gen,
 292                         Generation&             old_gen,
 293                         ObjToScanQueueSet&      queue_set,
 294                         Stack<oop, mtGC>*       overflow_stacks_,
 295                         size_t                  desired_plab_sz,
 296                         ParallelTaskTerminator& term);
 297 
 298   ~ParScanThreadStateSet() { TASKQUEUE_STATS_ONLY(reset_stats()); }
 299 
 300   inline ParScanThreadState& thread_state(int i);
 301 
 302   void trace_promotion_failed(const YoungGCTracer* gc_tracer);
 303   void reset(uint active_workers, bool promotion_failed);
 304   void flush();
 305 
 306   #if TASKQUEUE_STATS
 307   static void
 308     print_termination_stats_hdr(outputStream* const st = gclog_or_tty);
 309   void print_termination_stats(outputStream* const st = gclog_or_tty);
 310   static void
 311     print_taskqueue_stats_hdr(outputStream* const st = gclog_or_tty);
 312   void print_taskqueue_stats(outputStream* const st = gclog_or_tty);
 313   void reset_stats();
 314   #endif // TASKQUEUE_STATS
 315 
 316 private:
 317   ParallelTaskTerminator& _term;
 318   ParNewGeneration&       _gen;
 319   Generation&             _old_gen;
 320  public:
 321   bool is_valid(int id) const { return id < length(); }
 322   ParallelTaskTerminator* terminator() { return &_term; }
 323 };
 324 
 325 
 326 ParScanThreadStateSet::ParScanThreadStateSet(
 327   int num_threads, Space& to_space, ParNewGeneration& gen,
 328   Generation& old_gen, ObjToScanQueueSet& queue_set,
 329   Stack<oop, mtGC>* overflow_stacks,
 330   size_t desired_plab_sz, ParallelTaskTerminator& term)
 331   : ResourceArray(sizeof(ParScanThreadState), num_threads),
 332     _gen(gen), _old_gen(old_gen), _term(term)
 333 {
 334   assert(num_threads > 0, "sanity check!");
 335   assert(ParGCUseLocalOverflow == (overflow_stacks != NULL),
 336          "overflow_stack allocation mismatch");
 337   // Initialize states.
 338   for (int i = 0; i < num_threads; ++i) {
 339     new ((ParScanThreadState*)_data + i)
 340         ParScanThreadState(&to_space, &gen, &old_gen, i, &queue_set,
 341                            overflow_stacks, desired_plab_sz, term);
 342   }
 343 }
 344 
 345 inline ParScanThreadState& ParScanThreadStateSet::thread_state(int i)
 346 {
 347   assert(i >= 0 && i < length(), "sanity check!");
 348   return ((ParScanThreadState*)_data)[i];
 349 }
 350 
 351 void ParScanThreadStateSet::trace_promotion_failed(const YoungGCTracer* gc_tracer) {
 352   for (int i = 0; i < length(); ++i) {
 353     if (thread_state(i).promotion_failed()) {
 354       gc_tracer->report_promotion_failed(thread_state(i).promotion_failed_info());
 355       thread_state(i).promotion_failed_info().reset();
 356     }
 357   }
 358 }
 359 
 360 void ParScanThreadStateSet::reset(uint active_threads, bool promotion_failed)
 361 {
 362   _term.reset_for_reuse(active_threads);
 363   if (promotion_failed) {
 364     for (int i = 0; i < length(); ++i) {
 365       thread_state(i).print_promotion_failure_size();
 366     }
 367   }
 368 }
 369 
 370 #if TASKQUEUE_STATS
 371 void
 372 ParScanThreadState::reset_stats()
 373 {
 374   taskqueue_stats().reset();
 375   _term_attempts = 0;
 376   _overflow_refills = 0;
 377   _overflow_refill_objs = 0;
 378 }
 379 
 380 void ParScanThreadStateSet::reset_stats()
 381 {
 382   for (int i = 0; i < length(); ++i) {
 383     thread_state(i).reset_stats();
 384   }
 385 }
 386 
 387 void
 388 ParScanThreadStateSet::print_termination_stats_hdr(outputStream* const st)
 389 {
 390   st->print_raw_cr("GC Termination Stats");
 391   st->print_raw_cr("     elapsed  --strong roots-- "
 392                    "-------termination-------");
 393   st->print_raw_cr("thr     ms        ms       %   "
 394                    "    ms       %   attempts");
 395   st->print_raw_cr("--- --------- --------- ------ "
 396                    "--------- ------ --------");
 397 }
 398 
 399 void ParScanThreadStateSet::print_termination_stats(outputStream* const st)
 400 {
 401   print_termination_stats_hdr(st);
 402 
 403   for (int i = 0; i < length(); ++i) {
 404     const ParScanThreadState & pss = thread_state(i);
 405     const double elapsed_ms = pss.elapsed_time() * 1000.0;
 406     const double s_roots_ms = pss.strong_roots_time() * 1000.0;
 407     const double term_ms = pss.term_time() * 1000.0;
 408     st->print_cr("%3d %9.2f %9.2f %6.2f "
 409                  "%9.2f %6.2f " SIZE_FORMAT_W(8),
 410                  i, elapsed_ms, s_roots_ms, s_roots_ms * 100 / elapsed_ms,
 411                  term_ms, term_ms * 100 / elapsed_ms, pss.term_attempts());
 412   }
 413 }
 414 
 415 // Print stats related to work queue activity.
 416 void ParScanThreadStateSet::print_taskqueue_stats_hdr(outputStream* const st)
 417 {
 418   st->print_raw_cr("GC Task Stats");
 419   st->print_raw("thr "); TaskQueueStats::print_header(1, st); st->cr();
 420   st->print_raw("--- "); TaskQueueStats::print_header(2, st); st->cr();
 421 }
 422 
 423 void ParScanThreadStateSet::print_taskqueue_stats(outputStream* const st)
 424 {
 425   print_taskqueue_stats_hdr(st);
 426 
 427   TaskQueueStats totals;
 428   for (int i = 0; i < length(); ++i) {
 429     const ParScanThreadState & pss = thread_state(i);
 430     const TaskQueueStats & stats = pss.taskqueue_stats();
 431     st->print("%3d ", i); stats.print(st); st->cr();
 432     totals += stats;
 433 
 434     if (pss.overflow_refills() > 0) {
 435       st->print_cr("    " SIZE_FORMAT_W(10) " overflow refills    "
 436                    SIZE_FORMAT_W(10) " overflow objects",
 437                    pss.overflow_refills(), pss.overflow_refill_objs());
 438     }
 439   }
 440   st->print("tot "); totals.print(st); st->cr();
 441 
 442   DEBUG_ONLY(totals.verify());
 443 }
 444 #endif // TASKQUEUE_STATS
 445 
 446 void ParScanThreadStateSet::flush()
 447 {
 448   // Work in this loop should be kept as lightweight as
 449   // possible since this might otherwise become a bottleneck
 450   // to scaling. Should we add heavy-weight work into this
 451   // loop, consider parallelizing the loop into the worker threads.
 452   for (int i = 0; i < length(); ++i) {
 453     ParScanThreadState& par_scan_state = thread_state(i);
 454 
 455     // Flush stats related to To-space PLAB activity and
 456     // retire the last buffer.
 457     par_scan_state.to_space_alloc_buffer()->flush_and_retire_stats(_gen.plab_stats());
 458 
 459     // Every thread has its own age table.  We need to merge
 460     // them all into one.
 461     ageTable *local_table = par_scan_state.age_table();
 462     _gen.age_table()->merge(local_table);
 463 
 464     // Inform old gen that we're done.
 465     _old_gen.par_promote_alloc_done(i);
 466     _old_gen.par_oop_since_save_marks_iterate_done(i);
 467   }
 468 
 469   if (UseConcMarkSweepGC) {
 470     // We need to call this even when ResizeOldPLAB is disabled
 471     // so as to avoid breaking some asserts. While we may be able
 472     // to avoid this by reorganizing the code a bit, I am loathe
 473     // to do that unless we find cases where ergo leads to bad
 474     // performance.
 475     CFLS_LAB::compute_desired_plab_size();
 476   }
 477 }
 478 
 479 ParScanClosure::ParScanClosure(ParNewGeneration* g,
 480                                ParScanThreadState* par_scan_state) :
 481   OopsInKlassOrGenClosure(g), _par_scan_state(par_scan_state), _g(g)
 482 {
 483   _boundary = _g->reserved().end();
 484 }
 485 
 486 void ParScanWithBarrierClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, true, false); }
 487 void ParScanWithBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, false); }
 488 
 489 void ParScanWithoutBarrierClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, false, false); }
 490 void ParScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, false); }
 491 
 492 void ParRootScanWithBarrierTwoGensClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, true, true); }
 493 void ParRootScanWithBarrierTwoGensClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, true); }
 494 
 495 void ParRootScanWithoutBarrierClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, false, true); }
 496 void ParRootScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, true); }
 497 
 498 ParScanWeakRefClosure::ParScanWeakRefClosure(ParNewGeneration* g,
 499                                              ParScanThreadState* par_scan_state)
 500   : ScanWeakRefClosure(g), _par_scan_state(par_scan_state)
 501 {}
 502 
 503 void ParScanWeakRefClosure::do_oop(oop* p)       { ParScanWeakRefClosure::do_oop_work(p); }
 504 void ParScanWeakRefClosure::do_oop(narrowOop* p) { ParScanWeakRefClosure::do_oop_work(p); }
 505 
 506 #ifdef WIN32
 507 #pragma warning(disable: 4786) /* identifier was truncated to '255' characters in the browser information */
 508 #endif
 509 
 510 ParEvacuateFollowersClosure::ParEvacuateFollowersClosure(
 511     ParScanThreadState* par_scan_state_,
 512     ParScanWithoutBarrierClosure* to_space_closure_,
 513     ParScanWithBarrierClosure* old_gen_closure_,
 514     ParRootScanWithoutBarrierClosure* to_space_root_closure_,
 515     ParNewGeneration* par_gen_,
 516     ParRootScanWithBarrierTwoGensClosure* old_gen_root_closure_,
 517     ObjToScanQueueSet* task_queues_,
 518     ParallelTaskTerminator* terminator_) :
 519 
 520     _par_scan_state(par_scan_state_),
 521     _to_space_closure(to_space_closure_),
 522     _old_gen_closure(old_gen_closure_),
 523     _to_space_root_closure(to_space_root_closure_),
 524     _old_gen_root_closure(old_gen_root_closure_),
 525     _par_gen(par_gen_),
 526     _task_queues(task_queues_),
 527     _terminator(terminator_)
 528 {}
 529 
 530 void ParEvacuateFollowersClosure::do_void() {
 531   ObjToScanQueue* work_q = par_scan_state()->work_queue();
 532 
 533   while (true) {
 534 
 535     // Scan to-space and old-gen objs until we run out of both.
 536     oop obj_to_scan;
 537     par_scan_state()->trim_queues(0);
 538 
 539     // We have no local work, attempt to steal from other threads.
 540 
 541     // attempt to steal work from promoted.
 542     if (task_queues()->steal(par_scan_state()->thread_num(),
 543                              par_scan_state()->hash_seed(),
 544                              obj_to_scan)) {
 545       bool res = work_q->push(obj_to_scan);
 546       assert(res, "Empty queue should have room for a push.");
 547 
 548       //   if successful, goto Start.
 549       continue;
 550 
 551       // try global overflow list.
 552     } else if (par_gen()->take_from_overflow_list(par_scan_state())) {
 553       continue;
 554     }
 555 
 556     // Otherwise, offer termination.
 557     par_scan_state()->start_term_time();
 558     if (terminator()->offer_termination()) break;
 559     par_scan_state()->end_term_time();
 560   }
 561   assert(par_gen()->_overflow_list == NULL && par_gen()->_num_par_pushes == 0,
 562          "Broken overflow list?");
 563   // Finish the last termination pause.
 564   par_scan_state()->end_term_time();
 565 }
 566 
 567 ParNewGenTask::ParNewGenTask(ParNewGeneration* young_gen, Generation* old_gen,
 568                              HeapWord* young_old_boundary, ParScanThreadStateSet* state_set,
 569                              StrongRootsScope* strong_roots_scope) :
 570     AbstractGangTask("ParNewGeneration collection"),
 571     _young_gen(young_gen), _old_gen(old_gen),
 572     _young_old_boundary(young_old_boundary),
 573     _state_set(state_set),
 574     _strong_roots_scope(strong_roots_scope)
 575   {}
 576 
 577 void ParNewGenTask::work(uint worker_id) {
 578   GenCollectedHeap* gch = GenCollectedHeap::heap();
 579   // Since this is being done in a separate thread, need new resource
 580   // and handle marks.
 581   ResourceMark rm;
 582   HandleMark hm;
 583 
 584   ParScanThreadState& par_scan_state = _state_set->thread_state(worker_id);
 585   assert(_state_set->is_valid(worker_id), "Should not have been called");
 586 
 587   par_scan_state.set_young_old_boundary(_young_old_boundary);
 588 
 589   KlassScanClosure klass_scan_closure(&par_scan_state.to_space_root_closure(),
 590                                       gch->rem_set()->klass_rem_set());
 591   CLDToKlassAndOopClosure cld_scan_closure(&klass_scan_closure,
 592                                            &par_scan_state.to_space_root_closure(),
 593                                            false);
 594 
 595   par_scan_state.start_strong_roots();
 596   gch->gen_process_roots(_strong_roots_scope,
 597                          GenCollectedHeap::YoungGen,
 598                          true,  // Process younger gens, if any,
 599                                 // as strong roots.
 600                          GenCollectedHeap::SO_ScavengeCodeCache,
 601                          GenCollectedHeap::StrongAndWeakRoots,
 602                          &par_scan_state.to_space_root_closure(),
 603                          &par_scan_state.older_gen_closure(),
 604                          &cld_scan_closure);
 605 
 606   par_scan_state.end_strong_roots();
 607 
 608   // "evacuate followers".
 609   par_scan_state.evacuate_followers_closure().do_void();
 610 }
 611 
 612 #ifdef _MSC_VER
 613 #pragma warning( push )
 614 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list
 615 #endif
 616 ParNewGeneration::
 617 ParNewGeneration(ReservedSpace rs, size_t initial_byte_size)
 618   : DefNewGeneration(rs, initial_byte_size, "PCopy"),
 619   _overflow_list(NULL),
 620   _is_alive_closure(this),
 621   _plab_stats(YoungPLABSize, PLABWeight)
 622 {
 623   NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;)
 624   NOT_PRODUCT(_num_par_pushes = 0;)
 625   _task_queues = new ObjToScanQueueSet(ParallelGCThreads);
 626   guarantee(_task_queues != NULL, "task_queues allocation failure.");
 627 
 628   for (uint i1 = 0; i1 < ParallelGCThreads; i1++) {
 629     ObjToScanQueue *q = new ObjToScanQueue();
 630     guarantee(q != NULL, "work_queue Allocation failure.");
 631     _task_queues->register_queue(i1, q);
 632   }
 633 
 634   for (uint i2 = 0; i2 < ParallelGCThreads; i2++)
 635     _task_queues->queue(i2)->initialize();
 636 
 637   _overflow_stacks = NULL;
 638   if (ParGCUseLocalOverflow) {
 639 
 640     // typedef to workaround NEW_C_HEAP_ARRAY macro, which can not deal
 641     // with ','
 642     typedef Stack<oop, mtGC> GCOopStack;
 643 
 644     _overflow_stacks = NEW_C_HEAP_ARRAY(GCOopStack, ParallelGCThreads, mtGC);
 645     for (size_t i = 0; i < ParallelGCThreads; ++i) {
 646       new (_overflow_stacks + i) Stack<oop, mtGC>();
 647     }
 648   }
 649 
 650   if (UsePerfData) {
 651     EXCEPTION_MARK;
 652     ResourceMark rm;
 653 
 654     const char* cname =
 655          PerfDataManager::counter_name(_gen_counters->name_space(), "threads");
 656     PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None,
 657                                      ParallelGCThreads, CHECK);
 658   }
 659 }
 660 #ifdef _MSC_VER
 661 #pragma warning( pop )
 662 #endif
 663 
 664 // ParNewGeneration::
 665 ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) :
 666   DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {}
 667 
 668 template <class T>
 669 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) {
 670 #ifdef ASSERT
 671   {
 672     assert(!oopDesc::is_null(*p), "expected non-null ref");
 673     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 674     // We never expect to see a null reference being processed
 675     // as a weak reference.
 676     assert(obj->is_oop(), "expected an oop while scanning weak refs");
 677   }
 678 #endif // ASSERT
 679 
 680   _par_cl->do_oop_nv(p);
 681 
 682   if (GenCollectedHeap::heap()->is_in_reserved(p)) {
 683     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 684     _rs->write_ref_field_gc_par(p, obj);
 685   }
 686 }
 687 
 688 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(oop* p)       { ParKeepAliveClosure::do_oop_work(p); }
 689 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(narrowOop* p) { ParKeepAliveClosure::do_oop_work(p); }
 690 
 691 // ParNewGeneration::
 692 KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) :
 693   DefNewGeneration::KeepAliveClosure(cl) {}
 694 
 695 template <class T>
 696 void /*ParNewGeneration::*/KeepAliveClosure::do_oop_work(T* p) {
 697 #ifdef ASSERT
 698   {
 699     assert(!oopDesc::is_null(*p), "expected non-null ref");
 700     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 701     // We never expect to see a null reference being processed
 702     // as a weak reference.
 703     assert(obj->is_oop(), "expected an oop while scanning weak refs");
 704   }
 705 #endif // ASSERT
 706 
 707   _cl->do_oop_nv(p);
 708 
 709   if (GenCollectedHeap::heap()->is_in_reserved(p)) {
 710     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 711     _rs->write_ref_field_gc_par(p, obj);
 712   }
 713 }
 714 
 715 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(oop* p)       { KeepAliveClosure::do_oop_work(p); }
 716 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(narrowOop* p) { KeepAliveClosure::do_oop_work(p); }
 717 
 718 template <class T> void ScanClosureWithParBarrier::do_oop_work(T* p) {
 719   T heap_oop = oopDesc::load_heap_oop(p);
 720   if (!oopDesc::is_null(heap_oop)) {
 721     oop obj = oopDesc::decode_heap_oop_not_null(heap_oop);
 722     if ((HeapWord*)obj < _boundary) {
 723       assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?");
 724       oop new_obj = obj->is_forwarded()
 725                       ? obj->forwardee()
 726                       : _g->DefNewGeneration::copy_to_survivor_space(obj);
 727       oopDesc::encode_store_heap_oop_not_null(p, new_obj);
 728     }
 729     if (_gc_barrier) {
 730       // If p points to a younger generation, mark the card.
 731       if ((HeapWord*)obj < _gen_boundary) {
 732         _rs->write_ref_field_gc_par(p, obj);
 733       }
 734     }
 735   }
 736 }
 737 
 738 void ScanClosureWithParBarrier::do_oop(oop* p)       { ScanClosureWithParBarrier::do_oop_work(p); }
 739 void ScanClosureWithParBarrier::do_oop(narrowOop* p) { ScanClosureWithParBarrier::do_oop_work(p); }
 740 
 741 class ParNewRefProcTaskProxy: public AbstractGangTask {
 742   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
 743 public:
 744   ParNewRefProcTaskProxy(ProcessTask& task,
 745                          ParNewGeneration& gen,
 746                          Generation& old_gen,
 747                          HeapWord* young_old_boundary,
 748                          ParScanThreadStateSet& state_set);
 749 
 750 private:
 751   virtual void work(uint worker_id);
 752 private:
 753   ParNewGeneration&      _young_gen;
 754   ProcessTask&           _task;
 755   Generation&            _old_gen;
 756   HeapWord*              _young_old_boundary;
 757   ParScanThreadStateSet& _state_set;
 758 };
 759 
 760 ParNewRefProcTaskProxy::ParNewRefProcTaskProxy(ProcessTask& task,
 761                                                ParNewGeneration& young_gen,
 762                                                Generation& old_gen,
 763                                                HeapWord* young_old_boundary,
 764                                                ParScanThreadStateSet& state_set)
 765   : AbstractGangTask("ParNewGeneration parallel reference processing"),
 766     _young_gen(young_gen),
 767     _task(task),
 768     _old_gen(old_gen),
 769     _young_old_boundary(young_old_boundary),
 770     _state_set(state_set)
 771 {
 772 }
 773 
 774 void ParNewRefProcTaskProxy::work(uint worker_id)
 775 {
 776   ResourceMark rm;
 777   HandleMark hm;
 778   ParScanThreadState& par_scan_state = _state_set.thread_state(worker_id);
 779   par_scan_state.set_young_old_boundary(_young_old_boundary);
 780   _task.work(worker_id, par_scan_state.is_alive_closure(),
 781              par_scan_state.keep_alive_closure(),
 782              par_scan_state.evacuate_followers_closure());
 783 }
 784 
 785 class ParNewRefEnqueueTaskProxy: public AbstractGangTask {
 786   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
 787   EnqueueTask& _task;
 788 
 789 public:
 790   ParNewRefEnqueueTaskProxy(EnqueueTask& task)
 791     : AbstractGangTask("ParNewGeneration parallel reference enqueue"),
 792       _task(task)
 793   { }
 794 
 795   virtual void work(uint worker_id)
 796   {
 797     _task.work(worker_id);
 798   }
 799 };
 800 
 801 
 802 void ParNewRefProcTaskExecutor::execute(ProcessTask& task)
 803 {
 804   GenCollectedHeap* gch = GenCollectedHeap::heap();
 805   WorkGang* workers = gch->workers();
 806   assert(workers != NULL, "Need parallel worker threads.");
 807   _state_set.reset(workers->active_workers(), _young_gen.promotion_failed());
 808   ParNewRefProcTaskProxy rp_task(task, _young_gen, _old_gen,
 809                                  _young_gen.reserved().end(), _state_set);
 810   workers->run_task(&rp_task);
 811   _state_set.reset(0 /* bad value in debug if not reset */,
 812                    _young_gen.promotion_failed());
 813 }
 814 
 815 void ParNewRefProcTaskExecutor::execute(EnqueueTask& task)
 816 {
 817   GenCollectedHeap* gch = GenCollectedHeap::heap();
 818   WorkGang* workers = gch->workers();
 819   assert(workers != NULL, "Need parallel worker threads.");
 820   ParNewRefEnqueueTaskProxy enq_task(task);
 821   workers->run_task(&enq_task);
 822 }
 823 
 824 void ParNewRefProcTaskExecutor::set_single_threaded_mode()
 825 {
 826   _state_set.flush();
 827   GenCollectedHeap* gch = GenCollectedHeap::heap();
 828   gch->save_marks();
 829 }
 830 
 831 ScanClosureWithParBarrier::
 832 ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) :
 833   ScanClosure(g, gc_barrier) {}
 834 
 835 EvacuateFollowersClosureGeneral::
 836 EvacuateFollowersClosureGeneral(GenCollectedHeap* gch,
 837                                 OopsInGenClosure* cur,
 838                                 OopsInGenClosure* older) :
 839   _gch(gch),
 840   _scan_cur_or_nonheap(cur), _scan_older(older)
 841 {}
 842 
 843 void EvacuateFollowersClosureGeneral::do_void() {
 844   do {
 845     // Beware: this call will lead to closure applications via virtual
 846     // calls.
 847     _gch->oop_since_save_marks_iterate(GenCollectedHeap::YoungGen,
 848                                        _scan_cur_or_nonheap,
 849                                        _scan_older);
 850   } while (!_gch->no_allocs_since_save_marks());
 851 }
 852 
 853 
 854 // A Generation that does parallel young-gen collection.
 855 
 856 void ParNewGeneration::handle_promotion_failed(GenCollectedHeap* gch, ParScanThreadStateSet& thread_state_set) {
 857   assert(_promo_failure_scan_stack.is_empty(), "post condition");
 858   _promo_failure_scan_stack.clear(true); // Clear cached segments.
 859 
 860   remove_forwarding_pointers();
 861   if (PrintGCDetails) {
 862     gclog_or_tty->print(" (promotion failed)");
 863   }
 864   // All the spaces are in play for mark-sweep.
 865   swap_spaces();  // Make life simpler for CMS || rescan; see 6483690.
 866   from()->set_next_compaction_space(to());
 867   gch->set_incremental_collection_failed();
 868   // Inform the next generation that a promotion failure occurred.
 869   _old_gen->promotion_failure_occurred();
 870 
 871   // Trace promotion failure in the parallel GC threads
 872   thread_state_set.trace_promotion_failed(gc_tracer());
 873   // Single threaded code may have reported promotion failure to the global state
 874   if (_promotion_failed_info.has_failed()) {
 875     _gc_tracer.report_promotion_failed(_promotion_failed_info);
 876   }
 877   // Reset the PromotionFailureALot counters.
 878   NOT_PRODUCT(gch->reset_promotion_should_fail();)
 879 }
 880 
 881 void ParNewGeneration::collect(bool   full,
 882                                bool   clear_all_soft_refs,
 883                                size_t size,
 884                                bool   is_tlab) {
 885   assert(full || size > 0, "otherwise we don't want to collect");
 886 
 887   GenCollectedHeap* gch = GenCollectedHeap::heap();
 888 
 889   _gc_timer->register_gc_start();
 890 
 891   AdaptiveSizePolicy* size_policy = gch->gen_policy()->size_policy();
 892   WorkGang* workers = gch->workers();
 893   assert(workers != NULL, "Need workgang for parallel work");
 894   uint active_workers =
 895        AdaptiveSizePolicy::calc_active_workers(workers->total_workers(),
 896                                                workers->active_workers(),
 897                                                Threads::number_of_non_daemon_threads());
 898   workers->set_active_workers(active_workers);
 899   _old_gen = gch->old_gen();
 900 
 901   // If the next generation is too full to accommodate worst-case promotion
 902   // from this generation, pass on collection; let the next generation
 903   // do it.
 904   if (!collection_attempt_is_safe()) {
 905     gch->set_incremental_collection_failed();  // slight lie, in that we did not even attempt one
 906     return;
 907   }
 908   assert(to()->is_empty(), "Else not collection_attempt_is_safe");
 909 
 910   _gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start());
 911   gch->trace_heap_before_gc(gc_tracer());
 912 
 913   init_assuming_no_promotion_failure();
 914 
 915   if (UseAdaptiveSizePolicy) {
 916     set_survivor_overflow(false);
 917     size_policy->minor_collection_begin();
 918   }
 919 
 920   GCTraceTime t1(GCCauseString("GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL, _gc_tracer.gc_id());
 921   // Capture heap used before collection (for printing).
 922   size_t gch_prev_used = gch->used();
 923 
 924   age_table()->clear();
 925   to()->clear(SpaceDecorator::Mangle);
 926 
 927   gch->save_marks();
 928 
 929   // Set the correct parallelism (number of queues) in the reference processor
 930   ref_processor()->set_active_mt_degree(active_workers);
 931 
 932   // Always set the terminator for the active number of workers
 933   // because only those workers go through the termination protocol.
 934   ParallelTaskTerminator _term(active_workers, task_queues());
 935   ParScanThreadStateSet thread_state_set(active_workers,
 936                                          *to(), *this, *_old_gen, *task_queues(),
 937                                          _overflow_stacks, desired_plab_sz(), _term);
 938 
 939   thread_state_set.reset(active_workers, promotion_failed());
 940 
 941   {
 942     StrongRootsScope srs(active_workers);
 943 
 944     ParNewGenTask tsk(this, _old_gen, reserved().end(), &thread_state_set, &srs);
 945     gch->rem_set()->prepare_for_younger_refs_iterate(true);
 946     // It turns out that even when we're using 1 thread, doing the work in a
 947     // separate thread causes wide variance in run times.  We can't help this
 948     // in the multi-threaded case, but we special-case n=1 here to get
 949     // repeatable measurements of the 1-thread overhead of the parallel code.
 950     if (active_workers > 1) {
 951       workers->run_task(&tsk);
 952     } else {
 953       tsk.work(0);
 954     }
 955   }
 956 
 957   thread_state_set.reset(0 /* Bad value in debug if not reset */,
 958                          promotion_failed());
 959 
 960   // Trace and reset failed promotion info.
 961   if (promotion_failed()) {
 962     thread_state_set.trace_promotion_failed(gc_tracer());
 963   }
 964 
 965   // Process (weak) reference objects found during scavenge.
 966   ReferenceProcessor* rp = ref_processor();
 967   IsAliveClosure is_alive(this);
 968   ScanWeakRefClosure scan_weak_ref(this);
 969   KeepAliveClosure keep_alive(&scan_weak_ref);
 970   ScanClosure               scan_without_gc_barrier(this, false);
 971   ScanClosureWithParBarrier scan_with_gc_barrier(this, true);
 972   set_promo_failure_scan_stack_closure(&scan_without_gc_barrier);
 973   EvacuateFollowersClosureGeneral evacuate_followers(gch,
 974     &scan_without_gc_barrier, &scan_with_gc_barrier);
 975   rp->setup_policy(clear_all_soft_refs);
 976   // Can  the mt_degree be set later (at run_task() time would be best)?
 977   rp->set_active_mt_degree(active_workers);
 978   ReferenceProcessorStats stats;
 979   if (rp->processing_is_mt()) {
 980     ParNewRefProcTaskExecutor task_executor(*this, *_old_gen, thread_state_set);
 981     stats = rp->process_discovered_references(&is_alive, &keep_alive,
 982                                               &evacuate_followers, &task_executor,
 983                                               _gc_timer, _gc_tracer.gc_id());
 984   } else {
 985     thread_state_set.flush();
 986     gch->save_marks();
 987     stats = rp->process_discovered_references(&is_alive, &keep_alive,
 988                                               &evacuate_followers, NULL,
 989                                               _gc_timer, _gc_tracer.gc_id());
 990   }
 991   _gc_tracer.report_gc_reference_stats(stats);
 992   if (!promotion_failed()) {
 993     // Swap the survivor spaces.
 994     eden()->clear(SpaceDecorator::Mangle);
 995     from()->clear(SpaceDecorator::Mangle);
 996     if (ZapUnusedHeapArea) {
 997       // This is now done here because of the piece-meal mangling which
 998       // can check for valid mangling at intermediate points in the
 999       // collection(s).  When a minor collection fails to collect
1000       // sufficient space resizing of the young generation can occur
1001       // an redistribute the spaces in the young generation.  Mangle
1002       // here so that unzapped regions don't get distributed to
1003       // other spaces.
1004       to()->mangle_unused_area();
1005     }
1006     swap_spaces();
1007 
1008     // A successful scavenge should restart the GC time limit count which is
1009     // for full GC's.
1010     size_policy->reset_gc_overhead_limit_count();
1011 
1012     assert(to()->is_empty(), "to space should be empty now");
1013 
1014     adjust_desired_tenuring_threshold();
1015   } else {
1016     handle_promotion_failed(gch, thread_state_set);
1017   }
1018   // set new iteration safe limit for the survivor spaces
1019   from()->set_concurrent_iteration_safe_limit(from()->top());
1020   to()->set_concurrent_iteration_safe_limit(to()->top());
1021 
1022   if (ResizePLAB) {
1023     plab_stats()->adjust_desired_plab_sz();
1024   }
1025 
1026   if (PrintGC && !PrintGCDetails) {
1027     gch->print_heap_change(gch_prev_used);
1028   }
1029 
1030   TASKQUEUE_STATS_ONLY(if (PrintTerminationStats) thread_state_set.print_termination_stats());
1031   TASKQUEUE_STATS_ONLY(if (PrintTaskqueue) thread_state_set.print_taskqueue_stats());
1032 
1033   if (UseAdaptiveSizePolicy) {
1034     size_policy->minor_collection_end(gch->gc_cause());
1035     size_policy->avg_survived()->sample(from()->used());
1036   }
1037 
1038   // We need to use a monotonically non-decreasing time in ms
1039   // or we will see time-warp warnings and os::javaTimeMillis()
1040   // does not guarantee monotonicity.
1041   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
1042   update_time_of_last_gc(now);
1043 
1044   rp->set_enqueuing_is_done(true);
1045   if (rp->processing_is_mt()) {
1046     ParNewRefProcTaskExecutor task_executor(*this, *_old_gen, thread_state_set);
1047     rp->enqueue_discovered_references(&task_executor);
1048   } else {
1049     rp->enqueue_discovered_references(NULL);
1050   }
1051   rp->verify_no_references_recorded();
1052 
1053   gch->trace_heap_after_gc(gc_tracer());
1054   _gc_tracer.report_tenuring_threshold(tenuring_threshold());
1055 
1056   _gc_timer->register_gc_end();
1057 
1058   _gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions());
1059 }
1060 
1061 size_t ParNewGeneration::desired_plab_sz() {
1062   return _plab_stats.desired_plab_sz(GenCollectedHeap::heap()->workers()->active_workers());
1063 }
1064 
1065 static int sum;
1066 void ParNewGeneration::waste_some_time() {
1067   for (int i = 0; i < 100; i++) {
1068     sum += i;
1069   }
1070 }
1071 
1072 static const oop ClaimedForwardPtr = cast_to_oop<intptr_t>(0x4);
1073 
1074 // Because of concurrency, there are times where an object for which
1075 // "is_forwarded()" is true contains an "interim" forwarding pointer
1076 // value.  Such a value will soon be overwritten with a real value.
1077 // This method requires "obj" to have a forwarding pointer, and waits, if
1078 // necessary for a real one to be inserted, and returns it.
1079 
1080 oop ParNewGeneration::real_forwardee(oop obj) {
1081   oop forward_ptr = obj->forwardee();
1082   if (forward_ptr != ClaimedForwardPtr) {
1083     return forward_ptr;
1084   } else {
1085     return real_forwardee_slow(obj);
1086   }
1087 }
1088 
1089 oop ParNewGeneration::real_forwardee_slow(oop obj) {
1090   // Spin-read if it is claimed but not yet written by another thread.
1091   oop forward_ptr = obj->forwardee();
1092   while (forward_ptr == ClaimedForwardPtr) {
1093     waste_some_time();
1094     assert(obj->is_forwarded(), "precondition");
1095     forward_ptr = obj->forwardee();
1096   }
1097   return forward_ptr;
1098 }
1099 
1100 void ParNewGeneration::preserve_mark_if_necessary(oop obj, markOop m) {
1101   if (m->must_be_preserved_for_promotion_failure(obj)) {
1102     // We should really have separate per-worker stacks, rather
1103     // than use locking of a common pair of stacks.
1104     MutexLocker ml(ParGCRareEvent_lock);
1105     preserve_mark(obj, m);
1106   }
1107 }
1108 
1109 // Multiple GC threads may try to promote an object.  If the object
1110 // is successfully promoted, a forwarding pointer will be installed in
1111 // the object in the young generation.  This method claims the right
1112 // to install the forwarding pointer before it copies the object,
1113 // thus avoiding the need to undo the copy as in
1114 // copy_to_survivor_space_avoiding_with_undo.
1115 
1116 oop ParNewGeneration::copy_to_survivor_space(
1117         ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) {
1118   // In the sequential version, this assert also says that the object is
1119   // not forwarded.  That might not be the case here.  It is the case that
1120   // the caller observed it to be not forwarded at some time in the past.
1121   assert(is_in_reserved(old), "shouldn't be scavenging this oop");
1122 
1123   // The sequential code read "old->age()" below.  That doesn't work here,
1124   // since the age is in the mark word, and that might be overwritten with
1125   // a forwarding pointer by a parallel thread.  So we must save the mark
1126   // word in a local and then analyze it.
1127   oopDesc dummyOld;
1128   dummyOld.set_mark(m);
1129   assert(!dummyOld.is_forwarded(),
1130          "should not be called with forwarding pointer mark word.");
1131 
1132   oop new_obj = NULL;
1133   oop forward_ptr;
1134 
1135   // Try allocating obj in to-space (unless too old)
1136   if (dummyOld.age() < tenuring_threshold()) {
1137     new_obj = (oop)par_scan_state->alloc_in_to_space(sz);
1138     if (new_obj == NULL) {
1139       set_survivor_overflow(true);
1140     }
1141   }
1142 
1143   if (new_obj == NULL) {
1144     // Either to-space is full or we decided to promote
1145     // try allocating obj tenured
1146 
1147     // Attempt to install a null forwarding pointer (atomically),
1148     // to claim the right to install the real forwarding pointer.
1149     forward_ptr = old->forward_to_atomic(ClaimedForwardPtr);
1150     if (forward_ptr != NULL) {
1151       // someone else beat us to it.
1152         return real_forwardee(old);
1153     }
1154 
1155     if (!_promotion_failed) {
1156       new_obj = _old_gen->par_promote(par_scan_state->thread_num(),
1157                                       old, m, sz);
1158     }
1159 
1160     if (new_obj == NULL) {
1161       // promotion failed, forward to self
1162       _promotion_failed = true;
1163       new_obj = old;
1164 
1165       preserve_mark_if_necessary(old, m);
1166       par_scan_state->register_promotion_failure(sz);
1167     }
1168 
1169     old->forward_to(new_obj);
1170     forward_ptr = NULL;
1171   } else {
1172     // Is in to-space; do copying ourselves.
1173     Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz);
1174     assert(GenCollectedHeap::heap()->is_in_reserved(new_obj), "illegal forwarding pointer value.");
1175     forward_ptr = old->forward_to_atomic(new_obj);
1176     // Restore the mark word copied above.
1177     new_obj->set_mark(m);
1178     // Increment age if obj still in new generation
1179     new_obj->incr_age();
1180     par_scan_state->age_table()->add(new_obj, sz);
1181   }
1182   assert(new_obj != NULL, "just checking");
1183 
1184 #ifndef PRODUCT
1185   // This code must come after the CAS test, or it will print incorrect
1186   // information.
1187   if (TraceScavenge) {
1188     gclog_or_tty->print_cr("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}",
1189        is_in_reserved(new_obj) ? "copying" : "tenuring",
1190        new_obj->klass()->internal_name(), p2i(old), p2i(new_obj), new_obj->size());
1191   }
1192 #endif
1193 
1194   if (forward_ptr == NULL) {
1195     oop obj_to_push = new_obj;
1196     if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) {
1197       // Length field used as index of next element to be scanned.
1198       // Real length can be obtained from real_forwardee()
1199       arrayOop(old)->set_length(0);
1200       obj_to_push = old;
1201       assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push,
1202              "push forwarded object");
1203     }
1204     // Push it on one of the queues of to-be-scanned objects.
1205     bool simulate_overflow = false;
1206     NOT_PRODUCT(
1207       if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) {
1208         // simulate a stack overflow
1209         simulate_overflow = true;
1210       }
1211     )
1212     if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) {
1213       // Add stats for overflow pushes.
1214       if (Verbose && PrintGCDetails) {
1215         gclog_or_tty->print("queue overflow!\n");
1216       }
1217       push_on_overflow_list(old, par_scan_state);
1218       TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0));
1219     }
1220 
1221     return new_obj;
1222   }
1223 
1224   // Oops.  Someone beat us to it.  Undo the allocation.  Where did we
1225   // allocate it?
1226   if (is_in_reserved(new_obj)) {
1227     // Must be in to_space.
1228     assert(to()->is_in_reserved(new_obj), "Checking");
1229     if (forward_ptr == ClaimedForwardPtr) {
1230       // Wait to get the real forwarding pointer value.
1231       forward_ptr = real_forwardee(old);
1232     }
1233     par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz);
1234   }
1235 
1236   return forward_ptr;
1237 }
1238 
1239 #ifndef PRODUCT
1240 // It's OK to call this multi-threaded;  the worst thing
1241 // that can happen is that we'll get a bunch of closely
1242 // spaced simulated overflows, but that's OK, in fact
1243 // probably good as it would exercise the overflow code
1244 // under contention.
1245 bool ParNewGeneration::should_simulate_overflow() {
1246   if (_overflow_counter-- <= 0) { // just being defensive
1247     _overflow_counter = ParGCWorkQueueOverflowInterval;
1248     return true;
1249   } else {
1250     return false;
1251   }
1252 }
1253 #endif
1254 
1255 // In case we are using compressed oops, we need to be careful.
1256 // If the object being pushed is an object array, then its length
1257 // field keeps track of the "grey boundary" at which the next
1258 // incremental scan will be done (see ParGCArrayScanChunk).
1259 // When using compressed oops, this length field is kept in the
1260 // lower 32 bits of the erstwhile klass word and cannot be used
1261 // for the overflow chaining pointer (OCP below). As such the OCP
1262 // would itself need to be compressed into the top 32-bits in this
1263 // case. Unfortunately, see below, in the event that we have a
1264 // promotion failure, the node to be pushed on the list can be
1265 // outside of the Java heap, so the heap-based pointer compression
1266 // would not work (we would have potential aliasing between C-heap
1267 // and Java-heap pointers). For this reason, when using compressed
1268 // oops, we simply use a worker-thread-local, non-shared overflow
1269 // list in the form of a growable array, with a slightly different
1270 // overflow stack draining strategy. If/when we start using fat
1271 // stacks here, we can go back to using (fat) pointer chains
1272 // (although some performance comparisons would be useful since
1273 // single global lists have their own performance disadvantages
1274 // as we were made painfully aware not long ago, see 6786503).
1275 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
1276 void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) {
1277   assert(is_in_reserved(from_space_obj), "Should be from this generation");
1278   if (ParGCUseLocalOverflow) {
1279     // In the case of compressed oops, we use a private, not-shared
1280     // overflow stack.
1281     par_scan_state->push_on_overflow_stack(from_space_obj);
1282   } else {
1283     assert(!UseCompressedOops, "Error");
1284     // if the object has been forwarded to itself, then we cannot
1285     // use the klass pointer for the linked list.  Instead we have
1286     // to allocate an oopDesc in the C-Heap and use that for the linked list.
1287     // XXX This is horribly inefficient when a promotion failure occurs
1288     // and should be fixed. XXX FIX ME !!!
1289 #ifndef PRODUCT
1290     Atomic::inc_ptr(&_num_par_pushes);
1291     assert(_num_par_pushes > 0, "Tautology");
1292 #endif
1293     if (from_space_obj->forwardee() == from_space_obj) {
1294       oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1, mtGC);
1295       listhead->forward_to(from_space_obj);
1296       from_space_obj = listhead;
1297     }
1298     oop observed_overflow_list = _overflow_list;
1299     oop cur_overflow_list;
1300     do {
1301       cur_overflow_list = observed_overflow_list;
1302       if (cur_overflow_list != BUSY) {
1303         from_space_obj->set_klass_to_list_ptr(cur_overflow_list);
1304       } else {
1305         from_space_obj->set_klass_to_list_ptr(NULL);
1306       }
1307       observed_overflow_list =
1308         (oop)Atomic::cmpxchg_ptr(from_space_obj, &_overflow_list, cur_overflow_list);
1309     } while (cur_overflow_list != observed_overflow_list);
1310   }
1311 }
1312 
1313 bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) {
1314   bool res;
1315 
1316   if (ParGCUseLocalOverflow) {
1317     res = par_scan_state->take_from_overflow_stack();
1318   } else {
1319     assert(!UseCompressedOops, "Error");
1320     res = take_from_overflow_list_work(par_scan_state);
1321   }
1322   return res;
1323 }
1324 
1325 
1326 // *NOTE*: The overflow list manipulation code here and
1327 // in CMSCollector:: are very similar in shape,
1328 // except that in the CMS case we thread the objects
1329 // directly into the list via their mark word, and do
1330 // not need to deal with special cases below related
1331 // to chunking of object arrays and promotion failure
1332 // handling.
1333 // CR 6797058 has been filed to attempt consolidation of
1334 // the common code.
1335 // Because of the common code, if you make any changes in
1336 // the code below, please check the CMS version to see if
1337 // similar changes might be needed.
1338 // See CMSCollector::par_take_from_overflow_list() for
1339 // more extensive documentation comments.
1340 bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) {
1341   ObjToScanQueue* work_q = par_scan_state->work_queue();
1342   // How many to take?
1343   size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
1344                                  (size_t)ParGCDesiredObjsFromOverflowList);
1345 
1346   assert(!UseCompressedOops, "Error");
1347   assert(par_scan_state->overflow_stack() == NULL, "Error");
1348   if (_overflow_list == NULL) return false;
1349 
1350   // Otherwise, there was something there; try claiming the list.
1351   oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
1352   // Trim off a prefix of at most objsFromOverflow items
1353   Thread* tid = Thread::current();
1354   size_t spin_count = ParallelGCThreads;
1355   size_t sleep_time_millis = MAX2((size_t)1, objsFromOverflow/100);
1356   for (size_t spin = 0; prefix == BUSY && spin < spin_count; spin++) {
1357     // someone grabbed it before we did ...
1358     // ... we spin for a short while...
1359     os::sleep(tid, sleep_time_millis, false);
1360     if (_overflow_list == NULL) {
1361       // nothing left to take
1362       return false;
1363     } else if (_overflow_list != BUSY) {
1364      // try and grab the prefix
1365      prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
1366     }
1367   }
1368   if (prefix == NULL || prefix == BUSY) {
1369      // Nothing to take or waited long enough
1370      if (prefix == NULL) {
1371        // Write back the NULL in case we overwrote it with BUSY above
1372        // and it is still the same value.
1373        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
1374      }
1375      return false;
1376   }
1377   assert(prefix != NULL && prefix != BUSY, "Error");
1378   size_t i = 1;
1379   oop cur = prefix;
1380   while (i < objsFromOverflow && cur->klass_or_null() != NULL) {
1381     i++; cur = cur->list_ptr_from_klass();
1382   }
1383 
1384   // Reattach remaining (suffix) to overflow list
1385   if (cur->klass_or_null() == NULL) {
1386     // Write back the NULL in lieu of the BUSY we wrote
1387     // above and it is still the same value.
1388     if (_overflow_list == BUSY) {
1389       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
1390     }
1391   } else {
1392     assert(cur->klass_or_null() != (Klass*)(address)BUSY, "Error");
1393     oop suffix = cur->list_ptr_from_klass();       // suffix will be put back on global list
1394     cur->set_klass_to_list_ptr(NULL);     // break off suffix
1395     // It's possible that the list is still in the empty(busy) state
1396     // we left it in a short while ago; in that case we may be
1397     // able to place back the suffix.
1398     oop observed_overflow_list = _overflow_list;
1399     oop cur_overflow_list = observed_overflow_list;
1400     bool attached = false;
1401     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
1402       observed_overflow_list =
1403         (oop) Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);
1404       if (cur_overflow_list == observed_overflow_list) {
1405         attached = true;
1406         break;
1407       } else cur_overflow_list = observed_overflow_list;
1408     }
1409     if (!attached) {
1410       // Too bad, someone else got in in between; we'll need to do a splice.
1411       // Find the last item of suffix list
1412       oop last = suffix;
1413       while (last->klass_or_null() != NULL) {
1414         last = last->list_ptr_from_klass();
1415       }
1416       // Atomically prepend suffix to current overflow list
1417       observed_overflow_list = _overflow_list;
1418       do {
1419         cur_overflow_list = observed_overflow_list;
1420         if (cur_overflow_list != BUSY) {
1421           // Do the splice ...
1422           last->set_klass_to_list_ptr(cur_overflow_list);
1423         } else { // cur_overflow_list == BUSY
1424           last->set_klass_to_list_ptr(NULL);
1425         }
1426         observed_overflow_list =
1427           (oop)Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);
1428       } while (cur_overflow_list != observed_overflow_list);
1429     }
1430   }
1431 
1432   // Push objects on prefix list onto this thread's work queue
1433   assert(prefix != NULL && prefix != BUSY, "program logic");
1434   cur = prefix;
1435   ssize_t n = 0;
1436   while (cur != NULL) {
1437     oop obj_to_push = cur->forwardee();
1438     oop next        = cur->list_ptr_from_klass();
1439     cur->set_klass(obj_to_push->klass());
1440     // This may be an array object that is self-forwarded. In that case, the list pointer
1441     // space, cur, is not in the Java heap, but rather in the C-heap and should be freed.
1442     if (!is_in_reserved(cur)) {
1443       // This can become a scaling bottleneck when there is work queue overflow coincident
1444       // with promotion failure.
1445       oopDesc* f = cur;
1446       FREE_C_HEAP_ARRAY(oopDesc, f);
1447     } else if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) {
1448       assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");
1449       obj_to_push = cur;
1450     }
1451     bool ok = work_q->push(obj_to_push);
1452     assert(ok, "Should have succeeded");
1453     cur = next;
1454     n++;
1455   }
1456   TASKQUEUE_STATS_ONLY(par_scan_state->note_overflow_refill(n));
1457 #ifndef PRODUCT
1458   assert(_num_par_pushes >= n, "Too many pops?");
1459   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
1460 #endif
1461   return true;
1462 }
1463 #undef BUSY
1464 
1465 void ParNewGeneration::ref_processor_init() {
1466   if (_ref_processor == NULL) {
1467     // Allocate and initialize a reference processor
1468     _ref_processor =
1469       new ReferenceProcessor(_reserved,                  // span
1470                              ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing
1471                              ParallelGCThreads,          // mt processing degree
1472                              refs_discovery_is_mt(),     // mt discovery
1473                              ParallelGCThreads,          // mt discovery degree
1474                              refs_discovery_is_atomic(), // atomic_discovery
1475                              NULL);                      // is_alive_non_header
1476   }
1477 }
1478 
1479 const char* ParNewGeneration::name() const {
1480   return "par new generation";
1481 }