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