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_word_size(buf_size);
 252         plab->set_buf(buf_space);
 253         record_survivor_plab(buf_space, buf_size);
 254         obj = plab->allocate_aligned(word_sz, SurvivorAlignmentInBytes);
 255         // Note that we cannot compare buf_size < word_sz below
 256         // because of AlignmentReserve (see PLAB::allocate()).
 257         assert(obj != NULL || plab->words_remaining() < word_sz,
 258                "Else should have been able to allocate");
 259         // It's conceivable that we may be able to use the
 260         // buffer we just grabbed for subsequent small requests
 261         // even if not for this one.
 262       } else {
 263         // We're used up.
 264         _to_space_full = true;
 265       }
 266 
 267     } else {
 268       // Too large; allocate the object individually.
 269       obj = sp->par_allocate(word_sz);
 270     }
 271   }
 272   return obj;
 273 }
 274 
 275 
 276 void ParScanThreadState::undo_alloc_in_to_space(HeapWord* obj, size_t word_sz) {
 277   to_space_alloc_buffer()->undo_allocation(obj, word_sz);
 278 }
 279 
 280 void ParScanThreadState::print_promotion_failure_size() {
 281   if (_promotion_failed_info.has_failed() && PrintPromotionFailure) {
 282     gclog_or_tty->print(" (%d: promotion failure size = " SIZE_FORMAT ") ",
 283                         _thread_num, _promotion_failed_info.first_size());
 284   }
 285 }
 286 
 287 class ParScanThreadStateSet: private ResourceArray {
 288 public:
 289   // Initializes states for the specified number of threads;
 290   ParScanThreadStateSet(int                     num_threads,
 291                         Space&                  to_space,
 292                         ParNewGeneration&       gen,
 293                         Generation&             old_gen,
 294                         ObjToScanQueueSet&      queue_set,
 295                         Stack<oop, mtGC>*       overflow_stacks_,
 296                         size_t                  desired_plab_sz,
 297                         ParallelTaskTerminator& term);
 298 
 299   ~ParScanThreadStateSet() { TASKQUEUE_STATS_ONLY(reset_stats()); }
 300 
 301   inline ParScanThreadState& thread_state(int i);
 302 
 303   void trace_promotion_failed(const YoungGCTracer* gc_tracer);
 304   void reset(uint active_workers, bool promotion_failed);
 305   void flush();
 306 
 307   #if TASKQUEUE_STATS
 308   static void
 309     print_termination_stats_hdr(outputStream* const st = gclog_or_tty);
 310   void print_termination_stats(outputStream* const st = gclog_or_tty);
 311   static void
 312     print_taskqueue_stats_hdr(outputStream* const st = gclog_or_tty);
 313   void print_taskqueue_stats(outputStream* const st = gclog_or_tty);
 314   void reset_stats();
 315   #endif // TASKQUEUE_STATS
 316 
 317 private:
 318   ParallelTaskTerminator& _term;
 319   ParNewGeneration&       _gen;
 320   Generation&             _old_gen;
 321  public:
 322   bool is_valid(int id) const { return id < length(); }
 323   ParallelTaskTerminator* terminator() { return &_term; }
 324 };
 325 
 326 
 327 ParScanThreadStateSet::ParScanThreadStateSet(
 328   int num_threads, Space& to_space, ParNewGeneration& gen,
 329   Generation& old_gen, ObjToScanQueueSet& queue_set,
 330   Stack<oop, mtGC>* overflow_stacks,
 331   size_t desired_plab_sz, ParallelTaskTerminator& term)
 332   : ResourceArray(sizeof(ParScanThreadState), num_threads),
 333     _gen(gen), _old_gen(old_gen), _term(term)
 334 {
 335   assert(num_threads > 0, "sanity check!");
 336   assert(ParGCUseLocalOverflow == (overflow_stacks != NULL),
 337          "overflow_stack allocation mismatch");
 338   // Initialize states.
 339   for (int i = 0; i < num_threads; ++i) {
 340     new ((ParScanThreadState*)_data + i)
 341         ParScanThreadState(&to_space, &gen, &old_gen, i, &queue_set,
 342                            overflow_stacks, desired_plab_sz, term);
 343   }
 344 }
 345 
 346 inline ParScanThreadState& ParScanThreadStateSet::thread_state(int i)
 347 {
 348   assert(i >= 0 && i < length(), "sanity check!");
 349   return ((ParScanThreadState*)_data)[i];
 350 }
 351 
 352 void ParScanThreadStateSet::trace_promotion_failed(const YoungGCTracer* gc_tracer) {
 353   for (int i = 0; i < length(); ++i) {
 354     if (thread_state(i).promotion_failed()) {
 355       gc_tracer->report_promotion_failed(thread_state(i).promotion_failed_info());
 356       thread_state(i).promotion_failed_info().reset();
 357     }
 358   }
 359 }
 360 
 361 void ParScanThreadStateSet::reset(uint active_threads, bool promotion_failed)
 362 {
 363   _term.reset_for_reuse(active_threads);
 364   if (promotion_failed) {
 365     for (int i = 0; i < length(); ++i) {
 366       thread_state(i).print_promotion_failure_size();
 367     }
 368   }
 369 }
 370 
 371 #if TASKQUEUE_STATS
 372 void
 373 ParScanThreadState::reset_stats()
 374 {
 375   taskqueue_stats().reset();
 376   _term_attempts = 0;
 377   _overflow_refills = 0;
 378   _overflow_refill_objs = 0;
 379 }
 380 
 381 void ParScanThreadStateSet::reset_stats()
 382 {
 383   for (int i = 0; i < length(); ++i) {
 384     thread_state(i).reset_stats();
 385   }
 386 }
 387 
 388 void
 389 ParScanThreadStateSet::print_termination_stats_hdr(outputStream* const st)
 390 {
 391   st->print_raw_cr("GC Termination Stats");
 392   st->print_raw_cr("     elapsed  --strong roots-- "
 393                    "-------termination-------");
 394   st->print_raw_cr("thr     ms        ms       %   "
 395                    "    ms       %   attempts");
 396   st->print_raw_cr("--- --------- --------- ------ "
 397                    "--------- ------ --------");
 398 }
 399 
 400 void ParScanThreadStateSet::print_termination_stats(outputStream* const st)
 401 {
 402   print_termination_stats_hdr(st);
 403 
 404   for (int i = 0; i < length(); ++i) {
 405     const ParScanThreadState & pss = thread_state(i);
 406     const double elapsed_ms = pss.elapsed_time() * 1000.0;
 407     const double s_roots_ms = pss.strong_roots_time() * 1000.0;
 408     const double term_ms = pss.term_time() * 1000.0;
 409     st->print_cr("%3d %9.2f %9.2f %6.2f "
 410                  "%9.2f %6.2f " SIZE_FORMAT_W(8),
 411                  i, elapsed_ms, s_roots_ms, s_roots_ms * 100 / elapsed_ms,
 412                  term_ms, term_ms * 100 / elapsed_ms, pss.term_attempts());
 413   }
 414 }
 415 
 416 // Print stats related to work queue activity.
 417 void ParScanThreadStateSet::print_taskqueue_stats_hdr(outputStream* const st)
 418 {
 419   st->print_raw_cr("GC Task Stats");
 420   st->print_raw("thr "); TaskQueueStats::print_header(1, st); st->cr();
 421   st->print_raw("--- "); TaskQueueStats::print_header(2, st); st->cr();
 422 }
 423 
 424 void ParScanThreadStateSet::print_taskqueue_stats(outputStream* const st)
 425 {
 426   print_taskqueue_stats_hdr(st);
 427 
 428   TaskQueueStats totals;
 429   for (int i = 0; i < length(); ++i) {
 430     const ParScanThreadState & pss = thread_state(i);
 431     const TaskQueueStats & stats = pss.taskqueue_stats();
 432     st->print("%3d ", i); stats.print(st); st->cr();
 433     totals += stats;
 434 
 435     if (pss.overflow_refills() > 0) {
 436       st->print_cr("    " SIZE_FORMAT_W(10) " overflow refills    "
 437                    SIZE_FORMAT_W(10) " overflow objects",
 438                    pss.overflow_refills(), pss.overflow_refill_objs());
 439     }
 440   }
 441   st->print("tot "); totals.print(st); st->cr();
 442 
 443   DEBUG_ONLY(totals.verify());
 444 }
 445 #endif // TASKQUEUE_STATS
 446 
 447 void ParScanThreadStateSet::flush()
 448 {
 449   // Work in this loop should be kept as lightweight as
 450   // possible since this might otherwise become a bottleneck
 451   // to scaling. Should we add heavy-weight work into this
 452   // loop, consider parallelizing the loop into the worker threads.
 453   for (int i = 0; i < length(); ++i) {
 454     ParScanThreadState& par_scan_state = thread_state(i);
 455 
 456     // Flush stats related to To-space PLAB activity and
 457     // retire the last buffer.
 458     par_scan_state.to_space_alloc_buffer()->flush_and_retire_stats(_gen.plab_stats());
 459 
 460     // Every thread has its own age table.  We need to merge
 461     // them all into one.
 462     ageTable *local_table = par_scan_state.age_table();
 463     _gen.age_table()->merge(local_table);
 464 
 465     // Inform old gen that we're done.
 466     _old_gen.par_promote_alloc_done(i);
 467     _old_gen.par_oop_since_save_marks_iterate_done(i);
 468   }
 469 
 470   if (UseConcMarkSweepGC) {
 471     // We need to call this even when ResizeOldPLAB is disabled
 472     // so as to avoid breaking some asserts. While we may be able
 473     // to avoid this by reorganizing the code a bit, I am loathe
 474     // to do that unless we find cases where ergo leads to bad
 475     // performance.
 476     CFLS_LAB::compute_desired_plab_size();
 477   }
 478 }
 479 
 480 ParScanClosure::ParScanClosure(ParNewGeneration* g,
 481                                ParScanThreadState* par_scan_state) :
 482   OopsInKlassOrGenClosure(g), _par_scan_state(par_scan_state), _g(g)
 483 {
 484   _boundary = _g->reserved().end();
 485 }
 486 
 487 void ParScanWithBarrierClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, true, false); }
 488 void ParScanWithBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, false); }
 489 
 490 void ParScanWithoutBarrierClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, false, false); }
 491 void ParScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, false); }
 492 
 493 void ParRootScanWithBarrierTwoGensClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, true, true); }
 494 void ParRootScanWithBarrierTwoGensClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, true); }
 495 
 496 void ParRootScanWithoutBarrierClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, false, true); }
 497 void ParRootScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, true); }
 498 
 499 ParScanWeakRefClosure::ParScanWeakRefClosure(ParNewGeneration* g,
 500                                              ParScanThreadState* par_scan_state)
 501   : ScanWeakRefClosure(g), _par_scan_state(par_scan_state)
 502 {}
 503 
 504 void ParScanWeakRefClosure::do_oop(oop* p)       { ParScanWeakRefClosure::do_oop_work(p); }
 505 void ParScanWeakRefClosure::do_oop(narrowOop* p) { ParScanWeakRefClosure::do_oop_work(p); }
 506 
 507 #ifdef WIN32
 508 #pragma warning(disable: 4786) /* identifier was truncated to '255' characters in the browser information */
 509 #endif
 510 
 511 ParEvacuateFollowersClosure::ParEvacuateFollowersClosure(
 512     ParScanThreadState* par_scan_state_,
 513     ParScanWithoutBarrierClosure* to_space_closure_,
 514     ParScanWithBarrierClosure* old_gen_closure_,
 515     ParRootScanWithoutBarrierClosure* to_space_root_closure_,
 516     ParNewGeneration* par_gen_,
 517     ParRootScanWithBarrierTwoGensClosure* old_gen_root_closure_,
 518     ObjToScanQueueSet* task_queues_,
 519     ParallelTaskTerminator* terminator_) :
 520 
 521     _par_scan_state(par_scan_state_),
 522     _to_space_closure(to_space_closure_),
 523     _old_gen_closure(old_gen_closure_),
 524     _to_space_root_closure(to_space_root_closure_),
 525     _old_gen_root_closure(old_gen_root_closure_),
 526     _par_gen(par_gen_),
 527     _task_queues(task_queues_),
 528     _terminator(terminator_)
 529 {}
 530 
 531 void ParEvacuateFollowersClosure::do_void() {
 532   ObjToScanQueue* work_q = par_scan_state()->work_queue();
 533 
 534   while (true) {
 535 
 536     // Scan to-space and old-gen objs until we run out of both.
 537     oop obj_to_scan;
 538     par_scan_state()->trim_queues(0);
 539 
 540     // We have no local work, attempt to steal from other threads.
 541 
 542     // attempt to steal work from promoted.
 543     if (task_queues()->steal(par_scan_state()->thread_num(),
 544                              par_scan_state()->hash_seed(),
 545                              obj_to_scan)) {
 546       bool res = work_q->push(obj_to_scan);
 547       assert(res, "Empty queue should have room for a push.");
 548 
 549       //   if successful, goto Start.
 550       continue;
 551 
 552       // try global overflow list.
 553     } else if (par_gen()->take_from_overflow_list(par_scan_state())) {
 554       continue;
 555     }
 556 
 557     // Otherwise, offer termination.
 558     par_scan_state()->start_term_time();
 559     if (terminator()->offer_termination()) break;
 560     par_scan_state()->end_term_time();
 561   }
 562   assert(par_gen()->_overflow_list == NULL && par_gen()->_num_par_pushes == 0,
 563          "Broken overflow list?");
 564   // Finish the last termination pause.
 565   par_scan_state()->end_term_time();
 566 }
 567 
 568 ParNewGenTask::ParNewGenTask(ParNewGeneration* young_gen, Generation* old_gen,
 569                              HeapWord* young_old_boundary, ParScanThreadStateSet* state_set,
 570                              StrongRootsScope* strong_roots_scope) :
 571     AbstractGangTask("ParNewGeneration collection"),
 572     _young_gen(young_gen), _old_gen(old_gen),
 573     _young_old_boundary(young_old_boundary),
 574     _state_set(state_set),
 575     _strong_roots_scope(strong_roots_scope)
 576   {}
 577 
 578 void ParNewGenTask::work(uint worker_id) {
 579   GenCollectedHeap* gch = GenCollectedHeap::heap();
 580   // Since this is being done in a separate thread, need new resource
 581   // and handle marks.
 582   ResourceMark rm;
 583   HandleMark hm;
 584 
 585   ParScanThreadState& par_scan_state = _state_set->thread_state(worker_id);
 586   assert(_state_set->is_valid(worker_id), "Should not have been called");
 587 
 588   par_scan_state.set_young_old_boundary(_young_old_boundary);
 589 
 590   KlassScanClosure klass_scan_closure(&par_scan_state.to_space_root_closure(),
 591                                       gch->rem_set()->klass_rem_set());
 592   CLDToKlassAndOopClosure cld_scan_closure(&klass_scan_closure,
 593                                            &par_scan_state.to_space_root_closure(),
 594                                            false);
 595 
 596   par_scan_state.start_strong_roots();
 597   gch->gen_process_roots(_strong_roots_scope,
 598                          GenCollectedHeap::YoungGen,
 599                          true,  // Process younger gens, if any,
 600                                 // as strong roots.
 601                          GenCollectedHeap::SO_ScavengeCodeCache,
 602                          GenCollectedHeap::StrongAndWeakRoots,
 603                          &par_scan_state.to_space_root_closure(),
 604                          &par_scan_state.older_gen_closure(),
 605                          &cld_scan_closure);
 606 
 607   par_scan_state.end_strong_roots();
 608 
 609   // "evacuate followers".
 610   par_scan_state.evacuate_followers_closure().do_void();
 611 }
 612 
 613 #ifdef _MSC_VER
 614 #pragma warning( push )
 615 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list
 616 #endif
 617 ParNewGeneration::
 618 ParNewGeneration(ReservedSpace rs, size_t initial_byte_size)
 619   : DefNewGeneration(rs, initial_byte_size, "PCopy"),
 620   _overflow_list(NULL),
 621   _is_alive_closure(this),
 622   _plab_stats(YoungPLABSize, PLABWeight)
 623 {
 624   NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;)
 625   NOT_PRODUCT(_num_par_pushes = 0;)
 626   _task_queues = new ObjToScanQueueSet(ParallelGCThreads);
 627   guarantee(_task_queues != NULL, "task_queues allocation failure.");
 628 
 629   for (uint i1 = 0; i1 < ParallelGCThreads; i1++) {
 630     ObjToScanQueue *q = new ObjToScanQueue();
 631     guarantee(q != NULL, "work_queue Allocation failure.");
 632     _task_queues->register_queue(i1, q);
 633   }
 634 
 635   for (uint i2 = 0; i2 < ParallelGCThreads; i2++)
 636     _task_queues->queue(i2)->initialize();
 637 
 638   _overflow_stacks = NULL;
 639   if (ParGCUseLocalOverflow) {
 640 
 641     // typedef to workaround NEW_C_HEAP_ARRAY macro, which can not deal
 642     // with ','
 643     typedef Stack<oop, mtGC> GCOopStack;
 644 
 645     _overflow_stacks = NEW_C_HEAP_ARRAY(GCOopStack, ParallelGCThreads, mtGC);
 646     for (size_t i = 0; i < ParallelGCThreads; ++i) {
 647       new (_overflow_stacks + i) Stack<oop, mtGC>();
 648     }
 649   }
 650 
 651   if (UsePerfData) {
 652     EXCEPTION_MARK;
 653     ResourceMark rm;
 654 
 655     const char* cname =
 656          PerfDataManager::counter_name(_gen_counters->name_space(), "threads");
 657     PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None,
 658                                      ParallelGCThreads, CHECK);
 659   }
 660 }
 661 #ifdef _MSC_VER
 662 #pragma warning( pop )
 663 #endif
 664 
 665 // ParNewGeneration::
 666 ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) :
 667   DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {}
 668 
 669 template <class T>
 670 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) {
 671 #ifdef ASSERT
 672   {
 673     assert(!oopDesc::is_null(*p), "expected non-null ref");
 674     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 675     // We never expect to see a null reference being processed
 676     // as a weak reference.
 677     assert(obj->is_oop(), "expected an oop while scanning weak refs");
 678   }
 679 #endif // ASSERT
 680 
 681   _par_cl->do_oop_nv(p);
 682 
 683   if (GenCollectedHeap::heap()->is_in_reserved(p)) {
 684     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 685     _rs->write_ref_field_gc_par(p, obj);
 686   }
 687 }
 688 
 689 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(oop* p)       { ParKeepAliveClosure::do_oop_work(p); }
 690 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(narrowOop* p) { ParKeepAliveClosure::do_oop_work(p); }
 691 
 692 // ParNewGeneration::
 693 KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) :
 694   DefNewGeneration::KeepAliveClosure(cl) {}
 695 
 696 template <class T>
 697 void /*ParNewGeneration::*/KeepAliveClosure::do_oop_work(T* p) {
 698 #ifdef ASSERT
 699   {
 700     assert(!oopDesc::is_null(*p), "expected non-null ref");
 701     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 702     // We never expect to see a null reference being processed
 703     // as a weak reference.
 704     assert(obj->is_oop(), "expected an oop while scanning weak refs");
 705   }
 706 #endif // ASSERT
 707 
 708   _cl->do_oop_nv(p);
 709 
 710   if (GenCollectedHeap::heap()->is_in_reserved(p)) {
 711     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 712     _rs->write_ref_field_gc_par(p, obj);
 713   }
 714 }
 715 
 716 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(oop* p)       { KeepAliveClosure::do_oop_work(p); }
 717 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(narrowOop* p) { KeepAliveClosure::do_oop_work(p); }
 718 
 719 template <class T> void ScanClosureWithParBarrier::do_oop_work(T* p) {
 720   T heap_oop = oopDesc::load_heap_oop(p);
 721   if (!oopDesc::is_null(heap_oop)) {
 722     oop obj = oopDesc::decode_heap_oop_not_null(heap_oop);
 723     if ((HeapWord*)obj < _boundary) {
 724       assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?");
 725       oop new_obj = obj->is_forwarded()
 726                       ? obj->forwardee()
 727                       : _g->DefNewGeneration::copy_to_survivor_space(obj);
 728       oopDesc::encode_store_heap_oop_not_null(p, new_obj);
 729     }
 730     if (_gc_barrier) {
 731       // If p points to a younger generation, mark the card.
 732       if ((HeapWord*)obj < _gen_boundary) {
 733         _rs->write_ref_field_gc_par(p, obj);
 734       }
 735     }
 736   }
 737 }
 738 
 739 void ScanClosureWithParBarrier::do_oop(oop* p)       { ScanClosureWithParBarrier::do_oop_work(p); }
 740 void ScanClosureWithParBarrier::do_oop(narrowOop* p) { ScanClosureWithParBarrier::do_oop_work(p); }
 741 
 742 class ParNewRefProcTaskProxy: public AbstractGangTask {
 743   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
 744 public:
 745   ParNewRefProcTaskProxy(ProcessTask& task,
 746                          ParNewGeneration& gen,
 747                          Generation& old_gen,
 748                          HeapWord* young_old_boundary,
 749                          ParScanThreadStateSet& state_set);
 750 
 751 private:
 752   virtual void work(uint worker_id);
 753 private:
 754   ParNewGeneration&      _young_gen;
 755   ProcessTask&           _task;
 756   Generation&            _old_gen;
 757   HeapWord*              _young_old_boundary;
 758   ParScanThreadStateSet& _state_set;
 759 };
 760 
 761 ParNewRefProcTaskProxy::ParNewRefProcTaskProxy(ProcessTask& task,
 762                                                ParNewGeneration& young_gen,
 763                                                Generation& old_gen,
 764                                                HeapWord* young_old_boundary,
 765                                                ParScanThreadStateSet& state_set)
 766   : AbstractGangTask("ParNewGeneration parallel reference processing"),
 767     _young_gen(young_gen),
 768     _task(task),
 769     _old_gen(old_gen),
 770     _young_old_boundary(young_old_boundary),
 771     _state_set(state_set)
 772 {
 773 }
 774 
 775 void ParNewRefProcTaskProxy::work(uint worker_id)
 776 {
 777   ResourceMark rm;
 778   HandleMark hm;
 779   ParScanThreadState& par_scan_state = _state_set.thread_state(worker_id);
 780   par_scan_state.set_young_old_boundary(_young_old_boundary);
 781   _task.work(worker_id, par_scan_state.is_alive_closure(),
 782              par_scan_state.keep_alive_closure(),
 783              par_scan_state.evacuate_followers_closure());
 784 }
 785 
 786 class ParNewRefEnqueueTaskProxy: public AbstractGangTask {
 787   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
 788   EnqueueTask& _task;
 789 
 790 public:
 791   ParNewRefEnqueueTaskProxy(EnqueueTask& task)
 792     : AbstractGangTask("ParNewGeneration parallel reference enqueue"),
 793       _task(task)
 794   { }
 795 
 796   virtual void work(uint worker_id)
 797   {
 798     _task.work(worker_id);
 799   }
 800 };
 801 
 802 
 803 void ParNewRefProcTaskExecutor::execute(ProcessTask& task)
 804 {
 805   GenCollectedHeap* gch = GenCollectedHeap::heap();
 806   WorkGang* workers = gch->workers();
 807   assert(workers != NULL, "Need parallel worker threads.");
 808   _state_set.reset(workers->active_workers(), _young_gen.promotion_failed());
 809   ParNewRefProcTaskProxy rp_task(task, _young_gen, _old_gen,
 810                                  _young_gen.reserved().end(), _state_set);
 811   workers->run_task(&rp_task);
 812   _state_set.reset(0 /* bad value in debug if not reset */,
 813                    _young_gen.promotion_failed());
 814 }
 815 
 816 void ParNewRefProcTaskExecutor::execute(EnqueueTask& task)
 817 {
 818   GenCollectedHeap* gch = GenCollectedHeap::heap();
 819   WorkGang* workers = gch->workers();
 820   assert(workers != NULL, "Need parallel worker threads.");
 821   ParNewRefEnqueueTaskProxy enq_task(task);
 822   workers->run_task(&enq_task);
 823 }
 824 
 825 void ParNewRefProcTaskExecutor::set_single_threaded_mode()
 826 {
 827   _state_set.flush();
 828   GenCollectedHeap* gch = GenCollectedHeap::heap();
 829   gch->save_marks();
 830 }
 831 
 832 ScanClosureWithParBarrier::
 833 ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) :
 834   ScanClosure(g, gc_barrier) {}
 835 
 836 EvacuateFollowersClosureGeneral::
 837 EvacuateFollowersClosureGeneral(GenCollectedHeap* gch,
 838                                 OopsInGenClosure* cur,
 839                                 OopsInGenClosure* older) :
 840   _gch(gch),
 841   _scan_cur_or_nonheap(cur), _scan_older(older)
 842 {}
 843 
 844 void EvacuateFollowersClosureGeneral::do_void() {
 845   do {
 846     // Beware: this call will lead to closure applications via virtual
 847     // calls.
 848     _gch->oop_since_save_marks_iterate(GenCollectedHeap::YoungGen,
 849                                        _scan_cur_or_nonheap,
 850                                        _scan_older);
 851   } while (!_gch->no_allocs_since_save_marks());
 852 }
 853 
 854 
 855 // A Generation that does parallel young-gen collection.
 856 
 857 void ParNewGeneration::handle_promotion_failed(GenCollectedHeap* gch, ParScanThreadStateSet& thread_state_set) {
 858   assert(_promo_failure_scan_stack.is_empty(), "post condition");
 859   _promo_failure_scan_stack.clear(true); // Clear cached segments.
 860 
 861   remove_forwarding_pointers();
 862   if (PrintGCDetails) {
 863     gclog_or_tty->print(" (promotion failed)");
 864   }
 865   // All the spaces are in play for mark-sweep.
 866   swap_spaces();  // Make life simpler for CMS || rescan; see 6483690.
 867   from()->set_next_compaction_space(to());
 868   gch->set_incremental_collection_failed();
 869   // Inform the next generation that a promotion failure occurred.
 870   _old_gen->promotion_failure_occurred();
 871 
 872   // Trace promotion failure in the parallel GC threads
 873   thread_state_set.trace_promotion_failed(gc_tracer());
 874   // Single threaded code may have reported promotion failure to the global state
 875   if (_promotion_failed_info.has_failed()) {
 876     _gc_tracer.report_promotion_failed(_promotion_failed_info);
 877   }
 878   // Reset the PromotionFailureALot counters.
 879   NOT_PRODUCT(gch->reset_promotion_should_fail();)
 880 }
 881 
 882 void ParNewGeneration::collect(bool   full,
 883                                bool   clear_all_soft_refs,
 884                                size_t size,
 885                                bool   is_tlab) {
 886   assert(full || size > 0, "otherwise we don't want to collect");
 887 
 888   GenCollectedHeap* gch = GenCollectedHeap::heap();
 889 
 890   _gc_timer->register_gc_start();
 891 
 892   AdaptiveSizePolicy* size_policy = gch->gen_policy()->size_policy();
 893   WorkGang* workers = gch->workers();
 894   assert(workers != NULL, "Need workgang for parallel work");
 895   uint active_workers =
 896        AdaptiveSizePolicy::calc_active_workers(workers->total_workers(),
 897                                                workers->active_workers(),
 898                                                Threads::number_of_non_daemon_threads());
 899   workers->set_active_workers(active_workers);
 900   _old_gen = gch->old_gen();
 901 
 902   // If the next generation is too full to accommodate worst-case promotion
 903   // from this generation, pass on collection; let the next generation
 904   // do it.
 905   if (!collection_attempt_is_safe()) {
 906     gch->set_incremental_collection_failed();  // slight lie, in that we did not even attempt one
 907     return;
 908   }
 909   assert(to()->is_empty(), "Else not collection_attempt_is_safe");
 910 
 911   _gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start());
 912   gch->trace_heap_before_gc(gc_tracer());
 913 
 914   init_assuming_no_promotion_failure();
 915 
 916   if (UseAdaptiveSizePolicy) {
 917     set_survivor_overflow(false);
 918     size_policy->minor_collection_begin();
 919   }
 920 
 921   GCTraceTime t1(GCCauseString("GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL, _gc_tracer.gc_id());
 922   // Capture heap used before collection (for printing).
 923   size_t gch_prev_used = gch->used();
 924 
 925   age_table()->clear();
 926   to()->clear(SpaceDecorator::Mangle);
 927 
 928   gch->save_marks();
 929 
 930   // Set the correct parallelism (number of queues) in the reference processor
 931   ref_processor()->set_active_mt_degree(active_workers);
 932 
 933   // Always set the terminator for the active number of workers
 934   // because only those workers go through the termination protocol.
 935   ParallelTaskTerminator _term(active_workers, task_queues());
 936   ParScanThreadStateSet thread_state_set(active_workers,
 937                                          *to(), *this, *_old_gen, *task_queues(),
 938                                          _overflow_stacks, desired_plab_sz(), _term);
 939 
 940   thread_state_set.reset(active_workers, promotion_failed());
 941 
 942   {
 943     StrongRootsScope srs(active_workers);
 944 
 945     ParNewGenTask tsk(this, _old_gen, reserved().end(), &thread_state_set, &srs);
 946     gch->rem_set()->prepare_for_younger_refs_iterate(true);
 947     // It turns out that even when we're using 1 thread, doing the work in a
 948     // separate thread causes wide variance in run times.  We can't help this
 949     // in the multi-threaded case, but we special-case n=1 here to get
 950     // repeatable measurements of the 1-thread overhead of the parallel code.
 951     if (active_workers > 1) {
 952       workers->run_task(&tsk);
 953     } else {
 954       tsk.work(0);
 955     }
 956   }
 957 
 958   thread_state_set.reset(0 /* Bad value in debug if not reset */,
 959                          promotion_failed());
 960 
 961   // Trace and reset failed promotion info.
 962   if (promotion_failed()) {
 963     thread_state_set.trace_promotion_failed(gc_tracer());
 964   }
 965 
 966   // Process (weak) reference objects found during scavenge.
 967   ReferenceProcessor* rp = ref_processor();
 968   IsAliveClosure is_alive(this);
 969   ScanWeakRefClosure scan_weak_ref(this);
 970   KeepAliveClosure keep_alive(&scan_weak_ref);
 971   ScanClosure               scan_without_gc_barrier(this, false);
 972   ScanClosureWithParBarrier scan_with_gc_barrier(this, true);
 973   set_promo_failure_scan_stack_closure(&scan_without_gc_barrier);
 974   EvacuateFollowersClosureGeneral evacuate_followers(gch,
 975     &scan_without_gc_barrier, &scan_with_gc_barrier);
 976   rp->setup_policy(clear_all_soft_refs);
 977   // Can  the mt_degree be set later (at run_task() time would be best)?
 978   rp->set_active_mt_degree(active_workers);
 979   ReferenceProcessorStats stats;
 980   if (rp->processing_is_mt()) {
 981     ParNewRefProcTaskExecutor task_executor(*this, *_old_gen, thread_state_set);
 982     stats = rp->process_discovered_references(&is_alive, &keep_alive,
 983                                               &evacuate_followers, &task_executor,
 984                                               _gc_timer, _gc_tracer.gc_id());
 985   } else {
 986     thread_state_set.flush();
 987     gch->save_marks();
 988     stats = rp->process_discovered_references(&is_alive, &keep_alive,
 989                                               &evacuate_followers, NULL,
 990                                               _gc_timer, _gc_tracer.gc_id());
 991   }
 992   _gc_tracer.report_gc_reference_stats(stats);
 993   if (!promotion_failed()) {
 994     // Swap the survivor spaces.
 995     eden()->clear(SpaceDecorator::Mangle);
 996     from()->clear(SpaceDecorator::Mangle);
 997     if (ZapUnusedHeapArea) {
 998       // This is now done here because of the piece-meal mangling which
 999       // can check for valid mangling at intermediate points in the
1000       // collection(s).  When a minor collection fails to collect
1001       // sufficient space resizing of the young generation can occur
1002       // an redistribute the spaces in the young generation.  Mangle
1003       // here so that unzapped regions don't get distributed to
1004       // other spaces.
1005       to()->mangle_unused_area();
1006     }
1007     swap_spaces();
1008 
1009     // A successful scavenge should restart the GC time limit count which is
1010     // for full GC's.
1011     size_policy->reset_gc_overhead_limit_count();
1012 
1013     assert(to()->is_empty(), "to space should be empty now");
1014 
1015     adjust_desired_tenuring_threshold();
1016   } else {
1017     handle_promotion_failed(gch, thread_state_set);
1018   }
1019   // set new iteration safe limit for the survivor spaces
1020   from()->set_concurrent_iteration_safe_limit(from()->top());
1021   to()->set_concurrent_iteration_safe_limit(to()->top());
1022 
1023   if (ResizePLAB) {
1024     plab_stats()->adjust_desired_plab_sz();
1025   }
1026 
1027   if (PrintGC && !PrintGCDetails) {
1028     gch->print_heap_change(gch_prev_used);
1029   }
1030 
1031   TASKQUEUE_STATS_ONLY(if (PrintTerminationStats) thread_state_set.print_termination_stats());
1032   TASKQUEUE_STATS_ONLY(if (PrintTaskqueue) thread_state_set.print_taskqueue_stats());
1033 
1034   if (UseAdaptiveSizePolicy) {
1035     size_policy->minor_collection_end(gch->gc_cause());
1036     size_policy->avg_survived()->sample(from()->used());
1037   }
1038 
1039   // We need to use a monotonically non-decreasing time in ms
1040   // or we will see time-warp warnings and os::javaTimeMillis()
1041   // does not guarantee monotonicity.
1042   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
1043   update_time_of_last_gc(now);
1044 
1045   rp->set_enqueuing_is_done(true);
1046   if (rp->processing_is_mt()) {
1047     ParNewRefProcTaskExecutor task_executor(*this, *_old_gen, thread_state_set);
1048     rp->enqueue_discovered_references(&task_executor);
1049   } else {
1050     rp->enqueue_discovered_references(NULL);
1051   }
1052   rp->verify_no_references_recorded();
1053 
1054   gch->trace_heap_after_gc(gc_tracer());
1055   _gc_tracer.report_tenuring_threshold(tenuring_threshold());
1056 
1057   _gc_timer->register_gc_end();
1058 
1059   _gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions());
1060 }
1061 
1062 size_t ParNewGeneration::desired_plab_sz() {
1063   return _plab_stats.desired_plab_sz(GenCollectedHeap::heap()->workers()->active_workers());
1064 }
1065 
1066 static int sum;
1067 void ParNewGeneration::waste_some_time() {
1068   for (int i = 0; i < 100; i++) {
1069     sum += i;
1070   }
1071 }
1072 
1073 static const oop ClaimedForwardPtr = cast_to_oop<intptr_t>(0x4);
1074 
1075 // Because of concurrency, there are times where an object for which
1076 // "is_forwarded()" is true contains an "interim" forwarding pointer
1077 // value.  Such a value will soon be overwritten with a real value.
1078 // This method requires "obj" to have a forwarding pointer, and waits, if
1079 // necessary for a real one to be inserted, and returns it.
1080 
1081 oop ParNewGeneration::real_forwardee(oop obj) {
1082   oop forward_ptr = obj->forwardee();
1083   if (forward_ptr != ClaimedForwardPtr) {
1084     return forward_ptr;
1085   } else {
1086     return real_forwardee_slow(obj);
1087   }
1088 }
1089 
1090 oop ParNewGeneration::real_forwardee_slow(oop obj) {
1091   // Spin-read if it is claimed but not yet written by another thread.
1092   oop forward_ptr = obj->forwardee();
1093   while (forward_ptr == ClaimedForwardPtr) {
1094     waste_some_time();
1095     assert(obj->is_forwarded(), "precondition");
1096     forward_ptr = obj->forwardee();
1097   }
1098   return forward_ptr;
1099 }
1100 
1101 void ParNewGeneration::preserve_mark_if_necessary(oop obj, markOop m) {
1102   if (m->must_be_preserved_for_promotion_failure(obj)) {
1103     // We should really have separate per-worker stacks, rather
1104     // than use locking of a common pair of stacks.
1105     MutexLocker ml(ParGCRareEvent_lock);
1106     preserve_mark(obj, m);
1107   }
1108 }
1109 
1110 // Multiple GC threads may try to promote an object.  If the object
1111 // is successfully promoted, a forwarding pointer will be installed in
1112 // the object in the young generation.  This method claims the right
1113 // to install the forwarding pointer before it copies the object,
1114 // thus avoiding the need to undo the copy as in
1115 // copy_to_survivor_space_avoiding_with_undo.
1116 
1117 oop ParNewGeneration::copy_to_survivor_space(
1118         ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) {
1119   // In the sequential version, this assert also says that the object is
1120   // not forwarded.  That might not be the case here.  It is the case that
1121   // the caller observed it to be not forwarded at some time in the past.
1122   assert(is_in_reserved(old), "shouldn't be scavenging this oop");
1123 
1124   // The sequential code read "old->age()" below.  That doesn't work here,
1125   // since the age is in the mark word, and that might be overwritten with
1126   // a forwarding pointer by a parallel thread.  So we must save the mark
1127   // word in a local and then analyze it.
1128   oopDesc dummyOld;
1129   dummyOld.set_mark(m);
1130   assert(!dummyOld.is_forwarded(),
1131          "should not be called with forwarding pointer mark word.");
1132 
1133   oop new_obj = NULL;
1134   oop forward_ptr;
1135 
1136   // Try allocating obj in to-space (unless too old)
1137   if (dummyOld.age() < tenuring_threshold()) {
1138     new_obj = (oop)par_scan_state->alloc_in_to_space(sz);
1139     if (new_obj == NULL) {
1140       set_survivor_overflow(true);
1141     }
1142   }
1143 
1144   if (new_obj == NULL) {
1145     // Either to-space is full or we decided to promote
1146     // try allocating obj tenured
1147 
1148     // Attempt to install a null forwarding pointer (atomically),
1149     // to claim the right to install the real forwarding pointer.
1150     forward_ptr = old->forward_to_atomic(ClaimedForwardPtr);
1151     if (forward_ptr != NULL) {
1152       // someone else beat us to it.
1153         return real_forwardee(old);
1154     }
1155 
1156     if (!_promotion_failed) {
1157       new_obj = _old_gen->par_promote(par_scan_state->thread_num(),
1158                                       old, m, sz);
1159     }
1160 
1161     if (new_obj == NULL) {
1162       // promotion failed, forward to self
1163       _promotion_failed = true;
1164       new_obj = old;
1165 
1166       preserve_mark_if_necessary(old, m);
1167       par_scan_state->register_promotion_failure(sz);
1168     }
1169 
1170     old->forward_to(new_obj);
1171     forward_ptr = NULL;
1172   } else {
1173     // Is in to-space; do copying ourselves.
1174     Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz);
1175     assert(GenCollectedHeap::heap()->is_in_reserved(new_obj), "illegal forwarding pointer value.");
1176     forward_ptr = old->forward_to_atomic(new_obj);
1177     // Restore the mark word copied above.
1178     new_obj->set_mark(m);
1179     // Increment age if obj still in new generation
1180     new_obj->incr_age();
1181     par_scan_state->age_table()->add(new_obj, sz);
1182   }
1183   assert(new_obj != NULL, "just checking");
1184 
1185 #ifndef PRODUCT
1186   // This code must come after the CAS test, or it will print incorrect
1187   // information.
1188   if (TraceScavenge) {
1189     gclog_or_tty->print_cr("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}",
1190        is_in_reserved(new_obj) ? "copying" : "tenuring",
1191        new_obj->klass()->internal_name(), p2i(old), p2i(new_obj), new_obj->size());
1192   }
1193 #endif
1194 
1195   if (forward_ptr == NULL) {
1196     oop obj_to_push = new_obj;
1197     if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) {
1198       // Length field used as index of next element to be scanned.
1199       // Real length can be obtained from real_forwardee()
1200       arrayOop(old)->set_length(0);
1201       obj_to_push = old;
1202       assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push,
1203              "push forwarded object");
1204     }
1205     // Push it on one of the queues of to-be-scanned objects.
1206     bool simulate_overflow = false;
1207     NOT_PRODUCT(
1208       if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) {
1209         // simulate a stack overflow
1210         simulate_overflow = true;
1211       }
1212     )
1213     if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) {
1214       // Add stats for overflow pushes.
1215       if (Verbose && PrintGCDetails) {
1216         gclog_or_tty->print("queue overflow!\n");
1217       }
1218       push_on_overflow_list(old, par_scan_state);
1219       TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0));
1220     }
1221 
1222     return new_obj;
1223   }
1224 
1225   // Oops.  Someone beat us to it.  Undo the allocation.  Where did we
1226   // allocate it?
1227   if (is_in_reserved(new_obj)) {
1228     // Must be in to_space.
1229     assert(to()->is_in_reserved(new_obj), "Checking");
1230     if (forward_ptr == ClaimedForwardPtr) {
1231       // Wait to get the real forwarding pointer value.
1232       forward_ptr = real_forwardee(old);
1233     }
1234     par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz);
1235   }
1236 
1237   return forward_ptr;
1238 }
1239 
1240 #ifndef PRODUCT
1241 // It's OK to call this multi-threaded;  the worst thing
1242 // that can happen is that we'll get a bunch of closely
1243 // spaced simulated overflows, but that's OK, in fact
1244 // probably good as it would exercise the overflow code
1245 // under contention.
1246 bool ParNewGeneration::should_simulate_overflow() {
1247   if (_overflow_counter-- <= 0) { // just being defensive
1248     _overflow_counter = ParGCWorkQueueOverflowInterval;
1249     return true;
1250   } else {
1251     return false;
1252   }
1253 }
1254 #endif
1255 
1256 // In case we are using compressed oops, we need to be careful.
1257 // If the object being pushed is an object array, then its length
1258 // field keeps track of the "grey boundary" at which the next
1259 // incremental scan will be done (see ParGCArrayScanChunk).
1260 // When using compressed oops, this length field is kept in the
1261 // lower 32 bits of the erstwhile klass word and cannot be used
1262 // for the overflow chaining pointer (OCP below). As such the OCP
1263 // would itself need to be compressed into the top 32-bits in this
1264 // case. Unfortunately, see below, in the event that we have a
1265 // promotion failure, the node to be pushed on the list can be
1266 // outside of the Java heap, so the heap-based pointer compression
1267 // would not work (we would have potential aliasing between C-heap
1268 // and Java-heap pointers). For this reason, when using compressed
1269 // oops, we simply use a worker-thread-local, non-shared overflow
1270 // list in the form of a growable array, with a slightly different
1271 // overflow stack draining strategy. If/when we start using fat
1272 // stacks here, we can go back to using (fat) pointer chains
1273 // (although some performance comparisons would be useful since
1274 // single global lists have their own performance disadvantages
1275 // as we were made painfully aware not long ago, see 6786503).
1276 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
1277 void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) {
1278   assert(is_in_reserved(from_space_obj), "Should be from this generation");
1279   if (ParGCUseLocalOverflow) {
1280     // In the case of compressed oops, we use a private, not-shared
1281     // overflow stack.
1282     par_scan_state->push_on_overflow_stack(from_space_obj);
1283   } else {
1284     assert(!UseCompressedOops, "Error");
1285     // if the object has been forwarded to itself, then we cannot
1286     // use the klass pointer for the linked list.  Instead we have
1287     // to allocate an oopDesc in the C-Heap and use that for the linked list.
1288     // XXX This is horribly inefficient when a promotion failure occurs
1289     // and should be fixed. XXX FIX ME !!!
1290 #ifndef PRODUCT
1291     Atomic::inc_ptr(&_num_par_pushes);
1292     assert(_num_par_pushes > 0, "Tautology");
1293 #endif
1294     if (from_space_obj->forwardee() == from_space_obj) {
1295       oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1, mtGC);
1296       listhead->forward_to(from_space_obj);
1297       from_space_obj = listhead;
1298     }
1299     oop observed_overflow_list = _overflow_list;
1300     oop cur_overflow_list;
1301     do {
1302       cur_overflow_list = observed_overflow_list;
1303       if (cur_overflow_list != BUSY) {
1304         from_space_obj->set_klass_to_list_ptr(cur_overflow_list);
1305       } else {
1306         from_space_obj->set_klass_to_list_ptr(NULL);
1307       }
1308       observed_overflow_list =
1309         (oop)Atomic::cmpxchg_ptr(from_space_obj, &_overflow_list, cur_overflow_list);
1310     } while (cur_overflow_list != observed_overflow_list);
1311   }
1312 }
1313 
1314 bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) {
1315   bool res;
1316 
1317   if (ParGCUseLocalOverflow) {
1318     res = par_scan_state->take_from_overflow_stack();
1319   } else {
1320     assert(!UseCompressedOops, "Error");
1321     res = take_from_overflow_list_work(par_scan_state);
1322   }
1323   return res;
1324 }
1325 
1326 
1327 // *NOTE*: The overflow list manipulation code here and
1328 // in CMSCollector:: are very similar in shape,
1329 // except that in the CMS case we thread the objects
1330 // directly into the list via their mark word, and do
1331 // not need to deal with special cases below related
1332 // to chunking of object arrays and promotion failure
1333 // handling.
1334 // CR 6797058 has been filed to attempt consolidation of
1335 // the common code.
1336 // Because of the common code, if you make any changes in
1337 // the code below, please check the CMS version to see if
1338 // similar changes might be needed.
1339 // See CMSCollector::par_take_from_overflow_list() for
1340 // more extensive documentation comments.
1341 bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) {
1342   ObjToScanQueue* work_q = par_scan_state->work_queue();
1343   // How many to take?
1344   size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
1345                                  (size_t)ParGCDesiredObjsFromOverflowList);
1346 
1347   assert(!UseCompressedOops, "Error");
1348   assert(par_scan_state->overflow_stack() == NULL, "Error");
1349   if (_overflow_list == NULL) return false;
1350 
1351   // Otherwise, there was something there; try claiming the list.
1352   oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
1353   // Trim off a prefix of at most objsFromOverflow items
1354   Thread* tid = Thread::current();
1355   size_t spin_count = ParallelGCThreads;
1356   size_t sleep_time_millis = MAX2((size_t)1, objsFromOverflow/100);
1357   for (size_t spin = 0; prefix == BUSY && spin < spin_count; spin++) {
1358     // someone grabbed it before we did ...
1359     // ... we spin for a short while...
1360     os::sleep(tid, sleep_time_millis, false);
1361     if (_overflow_list == NULL) {
1362       // nothing left to take
1363       return false;
1364     } else if (_overflow_list != BUSY) {
1365      // try and grab the prefix
1366      prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
1367     }
1368   }
1369   if (prefix == NULL || prefix == BUSY) {
1370      // Nothing to take or waited long enough
1371      if (prefix == NULL) {
1372        // Write back the NULL in case we overwrote it with BUSY above
1373        // and it is still the same value.
1374        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
1375      }
1376      return false;
1377   }
1378   assert(prefix != NULL && prefix != BUSY, "Error");
1379   size_t i = 1;
1380   oop cur = prefix;
1381   while (i < objsFromOverflow && cur->klass_or_null() != NULL) {
1382     i++; cur = cur->list_ptr_from_klass();
1383   }
1384 
1385   // Reattach remaining (suffix) to overflow list
1386   if (cur->klass_or_null() == NULL) {
1387     // Write back the NULL in lieu of the BUSY we wrote
1388     // above and it is still the same value.
1389     if (_overflow_list == BUSY) {
1390       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
1391     }
1392   } else {
1393     assert(cur->klass_or_null() != (Klass*)(address)BUSY, "Error");
1394     oop suffix = cur->list_ptr_from_klass();       // suffix will be put back on global list
1395     cur->set_klass_to_list_ptr(NULL);     // break off suffix
1396     // It's possible that the list is still in the empty(busy) state
1397     // we left it in a short while ago; in that case we may be
1398     // able to place back the suffix.
1399     oop observed_overflow_list = _overflow_list;
1400     oop cur_overflow_list = observed_overflow_list;
1401     bool attached = false;
1402     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
1403       observed_overflow_list =
1404         (oop) Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);
1405       if (cur_overflow_list == observed_overflow_list) {
1406         attached = true;
1407         break;
1408       } else cur_overflow_list = observed_overflow_list;
1409     }
1410     if (!attached) {
1411       // Too bad, someone else got in in between; we'll need to do a splice.
1412       // Find the last item of suffix list
1413       oop last = suffix;
1414       while (last->klass_or_null() != NULL) {
1415         last = last->list_ptr_from_klass();
1416       }
1417       // Atomically prepend suffix to current overflow list
1418       observed_overflow_list = _overflow_list;
1419       do {
1420         cur_overflow_list = observed_overflow_list;
1421         if (cur_overflow_list != BUSY) {
1422           // Do the splice ...
1423           last->set_klass_to_list_ptr(cur_overflow_list);
1424         } else { // cur_overflow_list == BUSY
1425           last->set_klass_to_list_ptr(NULL);
1426         }
1427         observed_overflow_list =
1428           (oop)Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);
1429       } while (cur_overflow_list != observed_overflow_list);
1430     }
1431   }
1432 
1433   // Push objects on prefix list onto this thread's work queue
1434   assert(prefix != NULL && prefix != BUSY, "program logic");
1435   cur = prefix;
1436   ssize_t n = 0;
1437   while (cur != NULL) {
1438     oop obj_to_push = cur->forwardee();
1439     oop next        = cur->list_ptr_from_klass();
1440     cur->set_klass(obj_to_push->klass());
1441     // This may be an array object that is self-forwarded. In that case, the list pointer
1442     // space, cur, is not in the Java heap, but rather in the C-heap and should be freed.
1443     if (!is_in_reserved(cur)) {
1444       // This can become a scaling bottleneck when there is work queue overflow coincident
1445       // with promotion failure.
1446       oopDesc* f = cur;
1447       FREE_C_HEAP_ARRAY(oopDesc, f);
1448     } else if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) {
1449       assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");
1450       obj_to_push = cur;
1451     }
1452     bool ok = work_q->push(obj_to_push);
1453     assert(ok, "Should have succeeded");
1454     cur = next;
1455     n++;
1456   }
1457   TASKQUEUE_STATS_ONLY(par_scan_state->note_overflow_refill(n));
1458 #ifndef PRODUCT
1459   assert(_num_par_pushes >= n, "Too many pops?");
1460   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
1461 #endif
1462   return true;
1463 }
1464 #undef BUSY
1465 
1466 void ParNewGeneration::ref_processor_init() {
1467   if (_ref_processor == NULL) {
1468     // Allocate and initialize a reference processor
1469     _ref_processor =
1470       new ReferenceProcessor(_reserved,                  // span
1471                              ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing
1472                              ParallelGCThreads,          // mt processing degree
1473                              refs_discovery_is_mt(),     // mt discovery
1474                              ParallelGCThreads,          // mt discovery degree
1475                              refs_discovery_is_atomic(), // atomic_discovery
1476                              NULL);                      // is_alive_non_header
1477   }
1478 }
1479 
1480 const char* ParNewGeneration::name() const {
1481   return "par new generation";
1482 }