1 /*
   2  * Copyright (c) 2001, 2012, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp"
  27 #include "gc_implementation/parNew/parNewGeneration.hpp"
  28 #include "gc_implementation/parNew/parOopClosures.inline.hpp"
  29 #include "gc_implementation/shared/adaptiveSizePolicy.hpp"
  30 #include "gc_implementation/shared/ageTable.hpp"
  31 #include "gc_implementation/shared/parGCAllocBuffer.hpp"
  32 #include "gc_implementation/shared/spaceDecorator.hpp"
  33 #include "memory/defNewGeneration.inline.hpp"
  34 #include "memory/genCollectedHeap.hpp"
  35 #include "memory/genOopClosures.inline.hpp"
  36 #include "memory/generation.hpp"
  37 #include "memory/generation.inline.hpp"
  38 #include "memory/referencePolicy.hpp"
  39 #include "memory/resourceArea.hpp"
  40 #include "memory/sharedHeap.hpp"
  41 #include "memory/space.hpp"
  42 #include "oops/objArrayOop.hpp"
  43 #include "oops/oop.inline.hpp"
  44 #include "oops/oop.pcgc.inline.hpp"
  45 #include "runtime/handles.hpp"
  46 #include "runtime/handles.inline.hpp"
  47 #include "runtime/java.hpp"
  48 #include "runtime/thread.hpp"
  49 #include "utilities/copy.hpp"
  50 #include "utilities/globalDefinitions.hpp"
  51 #include "utilities/workgroup.hpp"
  52 
  53 #ifdef _MSC_VER
  54 #pragma warning( push )
  55 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list
  56 #endif
  57 ParScanThreadState::ParScanThreadState(Space* to_space_,
  58                                        ParNewGeneration* gen_,
  59                                        Generation* old_gen_,
  60                                        int thread_num_,
  61                                        ObjToScanQueueSet* work_queue_set_,
  62                                        Stack<oop, mtGC>* overflow_stacks_,
  63                                        size_t desired_plab_sz_,
  64                                        ParallelTaskTerminator& term_) :
  65   _to_space(to_space_), _old_gen(old_gen_), _young_gen(gen_), _thread_num(thread_num_),
  66   _work_queue(work_queue_set_->queue(thread_num_)), _to_space_full(false),
  67   _overflow_stack(overflow_stacks_ ? overflow_stacks_ + thread_num_ : NULL),
  68   _ageTable(false), // false ==> not the global age table, no perf data.
  69   _to_space_alloc_buffer(desired_plab_sz_),
  70   _to_space_closure(gen_, this), _old_gen_closure(gen_, this),
  71   _to_space_root_closure(gen_, this), _old_gen_root_closure(gen_, this),
  72   _older_gen_closure(gen_, this),
  73   _evacuate_followers(this, &_to_space_closure, &_old_gen_closure,
  74                       &_to_space_root_closure, gen_, &_old_gen_root_closure,
  75                       work_queue_set_, &term_),
  76   _is_alive_closure(gen_), _scan_weak_ref_closure(gen_, this),
  77   _keep_alive_closure(&_scan_weak_ref_closure),
  78   _promotion_failure_size(0),
  79   _strong_roots_time(0.0), _term_time(0.0)
  80 {
  81   #if TASKQUEUE_STATS
  82   _term_attempts = 0;
  83   _overflow_refills = 0;
  84   _overflow_refill_objs = 0;
  85   #endif // TASKQUEUE_STATS
  86 
  87   _survivor_chunk_array =
  88     (ChunkArray*) old_gen()->get_data_recorder(thread_num());
  89   _hash_seed = 17;  // Might want to take time-based random value.
  90   _start = os::elapsedTime();
  91   _old_gen_closure.set_generation(old_gen_);
  92   _old_gen_root_closure.set_generation(old_gen_);
  93 }
  94 #ifdef _MSC_VER
  95 #pragma warning( pop )
  96 #endif
  97 
  98 void ParScanThreadState::record_survivor_plab(HeapWord* plab_start,
  99                                               size_t plab_word_size) {
 100   ChunkArray* sca = survivor_chunk_array();
 101   if (sca != NULL) {
 102     // A non-null SCA implies that we want the PLAB data recorded.
 103     sca->record_sample(plab_start, plab_word_size);
 104   }
 105 }
 106 
 107 bool ParScanThreadState::should_be_partially_scanned(oop new_obj, oop old_obj) const {
 108   return new_obj->is_objArray() &&
 109          arrayOop(new_obj)->length() > ParGCArrayScanChunk &&
 110          new_obj != old_obj;
 111 }
 112 
 113 void ParScanThreadState::scan_partial_array_and_push_remainder(oop old) {
 114   assert(old->is_objArray(), "must be obj array");
 115   assert(old->is_forwarded(), "must be forwarded");
 116   assert(Universe::heap()->is_in_reserved(old), "must be in heap.");
 117   assert(!old_gen()->is_in(old), "must be in young generation.");
 118 
 119   objArrayOop obj = objArrayOop(old->forwardee());
 120   // Process ParGCArrayScanChunk elements now
 121   // and push the remainder back onto queue
 122   int start     = arrayOop(old)->length();
 123   int end       = obj->length();
 124   int remainder = end - start;
 125   assert(start <= end, "just checking");
 126   if (remainder > 2 * ParGCArrayScanChunk) {
 127     // Test above combines last partial chunk with a full chunk
 128     end = start + ParGCArrayScanChunk;
 129     arrayOop(old)->set_length(end);
 130     // Push remainder.
 131     bool ok = work_queue()->push(old);
 132     assert(ok, "just popped, push must be okay");
 133   } else {
 134     // Restore length so that it can be used if there
 135     // is a promotion failure and forwarding pointers
 136     // must be removed.
 137     arrayOop(old)->set_length(end);
 138   }
 139 
 140   // process our set of indices (include header in first chunk)
 141   // should make sure end is even (aligned to HeapWord in case of compressed oops)
 142   if ((HeapWord *)obj < young_old_boundary()) {
 143     // object is in to_space
 144     obj->oop_iterate_range(&_to_space_closure, start, end);
 145   } else {
 146     // object is in old generation
 147     obj->oop_iterate_range(&_old_gen_closure, start, end);
 148   }
 149 }
 150 
 151 
 152 void ParScanThreadState::trim_queues(int max_size) {
 153   ObjToScanQueue* queue = work_queue();
 154   do {
 155     while (queue->size() > (juint)max_size) {
 156       oop obj_to_scan;
 157       if (queue->pop_local(obj_to_scan)) {
 158         if ((HeapWord *)obj_to_scan < young_old_boundary()) {
 159           if (obj_to_scan->is_objArray() &&
 160               obj_to_scan->is_forwarded() &&
 161               obj_to_scan->forwardee() != obj_to_scan) {
 162             scan_partial_array_and_push_remainder(obj_to_scan);
 163           } else {
 164             // object is in to_space
 165             obj_to_scan->oop_iterate(&_to_space_closure);
 166           }
 167         } else {
 168           // object is in old generation
 169           obj_to_scan->oop_iterate(&_old_gen_closure);
 170         }
 171       }
 172     }
 173     // For the  case of compressed oops, we have a private, non-shared
 174     // overflow stack, so we eagerly drain it so as to more evenly
 175     // distribute load early. Note: this may be good to do in
 176     // general rather than delay for the final stealing phase.
 177     // If applicable, we'll transfer a set of objects over to our
 178     // work queue, allowing them to be stolen and draining our
 179     // private overflow stack.
 180   } while (ParGCTrimOverflow && young_gen()->take_from_overflow_list(this));
 181 }
 182 
 183 bool ParScanThreadState::take_from_overflow_stack() {
 184   assert(ParGCUseLocalOverflow, "Else should not call");
 185   assert(young_gen()->overflow_list() == NULL, "Error");
 186   ObjToScanQueue* queue = work_queue();
 187   Stack<oop, mtGC>* const of_stack = overflow_stack();
 188   const size_t num_overflow_elems = of_stack->size();
 189   const size_t space_available = queue->max_elems() - queue->size();
 190   const size_t num_take_elems = MIN3(space_available / 4,
 191                                      ParGCDesiredObjsFromOverflowList,
 192                                      num_overflow_elems);
 193   // Transfer the most recent num_take_elems from the overflow
 194   // stack to our work queue.
 195   for (size_t i = 0; i != num_take_elems; i++) {
 196     oop cur = of_stack->pop();
 197     oop obj_to_push = cur->forwardee();
 198     assert(Universe::heap()->is_in_reserved(cur), "Should be in heap");
 199     assert(!old_gen()->is_in_reserved(cur), "Should be in young gen");
 200     assert(Universe::heap()->is_in_reserved(obj_to_push), "Should be in heap");
 201     if (should_be_partially_scanned(obj_to_push, cur)) {
 202       assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");
 203       obj_to_push = cur;
 204     }
 205     bool ok = queue->push(obj_to_push);
 206     assert(ok, "Should have succeeded");
 207   }
 208   assert(young_gen()->overflow_list() == NULL, "Error");
 209   return num_take_elems > 0;  // was something transferred?
 210 }
 211 
 212 void ParScanThreadState::push_on_overflow_stack(oop p) {
 213   assert(ParGCUseLocalOverflow, "Else should not call");
 214   overflow_stack()->push(p);
 215   assert(young_gen()->overflow_list() == NULL, "Error");
 216 }
 217 
 218 HeapWord* ParScanThreadState::alloc_in_to_space_slow(size_t word_sz) {
 219 
 220   // Otherwise, if the object is small enough, try to reallocate the
 221   // buffer.
 222   HeapWord* obj = NULL;
 223   if (!_to_space_full) {
 224     ParGCAllocBuffer* const plab = to_space_alloc_buffer();
 225     Space*            const sp   = to_space();
 226     if (word_sz * 100 <
 227         ParallelGCBufferWastePct * plab->word_sz()) {
 228       // Is small enough; abandon this buffer and start a new one.
 229       plab->retire(false, false);
 230       size_t buf_size = plab->word_sz();
 231       HeapWord* buf_space = sp->par_allocate(buf_size);
 232       if (buf_space == NULL) {
 233         const size_t min_bytes =
 234           ParGCAllocBuffer::min_size() << LogHeapWordSize;
 235         size_t free_bytes = sp->free();
 236         while(buf_space == NULL && free_bytes >= min_bytes) {
 237           buf_size = free_bytes >> LogHeapWordSize;
 238           assert(buf_size == (size_t)align_object_size(buf_size),
 239                  "Invariant");
 240           buf_space  = sp->par_allocate(buf_size);
 241           free_bytes = sp->free();
 242         }
 243       }
 244       if (buf_space != NULL) {
 245         plab->set_word_size(buf_size);
 246         plab->set_buf(buf_space);
 247         record_survivor_plab(buf_space, buf_size);
 248         obj = plab->allocate(word_sz);
 249         // Note that we cannot compare buf_size < word_sz below
 250         // because of AlignmentReserve (see ParGCAllocBuffer::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 
 261     } else {
 262       // Too large; allocate the object individually.
 263       obj = sp->par_allocate(word_sz);
 264     }
 265   }
 266   return obj;
 267 }
 268 
 269 
 270 void ParScanThreadState::undo_alloc_in_to_space(HeapWord* obj,
 271                                                 size_t word_sz) {
 272   // Is the alloc in the current alloc buffer?
 273   if (to_space_alloc_buffer()->contains(obj)) {
 274     assert(to_space_alloc_buffer()->contains(obj + word_sz - 1),
 275            "Should contain whole object.");
 276     to_space_alloc_buffer()->undo_allocation(obj, word_sz);
 277   } else {
 278     CollectedHeap::fill_with_object(obj, word_sz);
 279   }
 280 }
 281 
 282 void ParScanThreadState::print_and_clear_promotion_failure_size() {
 283   if (_promotion_failure_size != 0) {
 284     if (PrintPromotionFailure) {
 285       gclog_or_tty->print(" (%d: promotion failure size = " SIZE_FORMAT ") ",
 286         _thread_num, _promotion_failure_size);
 287     }
 288     _promotion_failure_size = 0;
 289   }
 290 }
 291 
 292 class ParScanThreadStateSet: private ResourceArray {
 293 public:
 294   // Initializes states for the specified number of threads;
 295   ParScanThreadStateSet(int                     num_threads,
 296                         Space&                  to_space,
 297                         ParNewGeneration&       gen,
 298                         Generation&             old_gen,
 299                         ObjToScanQueueSet&      queue_set,
 300                         Stack<oop, mtGC>*       overflow_stacks_,
 301                         size_t                  desired_plab_sz,
 302                         ParallelTaskTerminator& term);
 303 
 304   ~ParScanThreadStateSet() { TASKQUEUE_STATS_ONLY(reset_stats()); }
 305 
 306   inline ParScanThreadState& thread_state(int i);
 307 
 308   void reset(int active_workers, bool promotion_failed);
 309   void flush();
 310 
 311   #if TASKQUEUE_STATS
 312   static void
 313     print_termination_stats_hdr(outputStream* const st = gclog_or_tty);
 314   void print_termination_stats(outputStream* const st = gclog_or_tty);
 315   static void
 316     print_taskqueue_stats_hdr(outputStream* const st = gclog_or_tty);
 317   void print_taskqueue_stats(outputStream* const st = gclog_or_tty);
 318   void reset_stats();
 319   #endif // TASKQUEUE_STATS
 320 
 321 private:
 322   ParallelTaskTerminator& _term;
 323   ParNewGeneration&       _gen;
 324   Generation&             _next_gen;
 325  public:
 326   bool is_valid(int id) const { return id < length(); }
 327   ParallelTaskTerminator* terminator() { return &_term; }
 328 };
 329 
 330 
 331 ParScanThreadStateSet::ParScanThreadStateSet(
 332   int num_threads, Space& to_space, ParNewGeneration& gen,
 333   Generation& old_gen, ObjToScanQueueSet& queue_set,
 334   Stack<oop, mtGC>* overflow_stacks,
 335   size_t desired_plab_sz, ParallelTaskTerminator& term)
 336   : ResourceArray(sizeof(ParScanThreadState), num_threads),
 337     _gen(gen), _next_gen(old_gen), _term(term)
 338 {
 339   assert(num_threads > 0, "sanity check!");
 340   assert(ParGCUseLocalOverflow == (overflow_stacks != NULL),
 341          "overflow_stack allocation mismatch");
 342   // Initialize states.
 343   for (int i = 0; i < num_threads; ++i) {
 344     new ((ParScanThreadState*)_data + i)
 345         ParScanThreadState(&to_space, &gen, &old_gen, i, &queue_set,
 346                            overflow_stacks, desired_plab_sz, term);
 347   }
 348 }
 349 
 350 inline ParScanThreadState& ParScanThreadStateSet::thread_state(int i)
 351 {
 352   assert(i >= 0 && i < length(), "sanity check!");
 353   return ((ParScanThreadState*)_data)[i];
 354 }
 355 
 356 
 357 void ParScanThreadStateSet::reset(int active_threads, bool promotion_failed)
 358 {
 359   _term.reset_for_reuse(active_threads);
 360   if (promotion_failed) {
 361     for (int i = 0; i < length(); ++i) {
 362       thread_state(i).print_and_clear_promotion_failure_size();
 363     }
 364   }
 365 }
 366 
 367 #if TASKQUEUE_STATS
 368 void
 369 ParScanThreadState::reset_stats()
 370 {
 371   taskqueue_stats().reset();
 372   _term_attempts = 0;
 373   _overflow_refills = 0;
 374   _overflow_refill_objs = 0;
 375 }
 376 
 377 void ParScanThreadStateSet::reset_stats()
 378 {
 379   for (int i = 0; i < length(); ++i) {
 380     thread_state(i).reset_stats();
 381   }
 382 }
 383 
 384 void
 385 ParScanThreadStateSet::print_termination_stats_hdr(outputStream* const st)
 386 {
 387   st->print_raw_cr("GC Termination Stats");
 388   st->print_raw_cr("     elapsed  --strong roots-- "
 389                    "-------termination-------");
 390   st->print_raw_cr("thr     ms        ms       %   "
 391                    "    ms       %   attempts");
 392   st->print_raw_cr("--- --------- --------- ------ "
 393                    "--------- ------ --------");
 394 }
 395 
 396 void ParScanThreadStateSet::print_termination_stats(outputStream* const st)
 397 {
 398   print_termination_stats_hdr(st);
 399 
 400   for (int i = 0; i < length(); ++i) {
 401     const ParScanThreadState & pss = thread_state(i);
 402     const double elapsed_ms = pss.elapsed_time() * 1000.0;
 403     const double s_roots_ms = pss.strong_roots_time() * 1000.0;
 404     const double term_ms = pss.term_time() * 1000.0;
 405     st->print_cr("%3d %9.2f %9.2f %6.2f "
 406                  "%9.2f %6.2f " SIZE_FORMAT_W(8),
 407                  i, elapsed_ms, s_roots_ms, s_roots_ms * 100 / elapsed_ms,
 408                  term_ms, term_ms * 100 / elapsed_ms, pss.term_attempts());
 409   }
 410 }
 411 
 412 // Print stats related to work queue activity.
 413 void ParScanThreadStateSet::print_taskqueue_stats_hdr(outputStream* const st)
 414 {
 415   st->print_raw_cr("GC Task Stats");
 416   st->print_raw("thr "); TaskQueueStats::print_header(1, st); st->cr();
 417   st->print_raw("--- "); TaskQueueStats::print_header(2, st); st->cr();
 418 }
 419 
 420 void ParScanThreadStateSet::print_taskqueue_stats(outputStream* const st)
 421 {
 422   print_taskqueue_stats_hdr(st);
 423 
 424   TaskQueueStats totals;
 425   for (int i = 0; i < length(); ++i) {
 426     const ParScanThreadState & pss = thread_state(i);
 427     const TaskQueueStats & stats = pss.taskqueue_stats();
 428     st->print("%3d ", i); stats.print(st); st->cr();
 429     totals += stats;
 430 
 431     if (pss.overflow_refills() > 0) {
 432       st->print_cr("    " SIZE_FORMAT_W(10) " overflow refills    "
 433                    SIZE_FORMAT_W(10) " overflow objects",
 434                    pss.overflow_refills(), pss.overflow_refill_objs());
 435     }
 436   }
 437   st->print("tot "); totals.print(st); st->cr();
 438 
 439   DEBUG_ONLY(totals.verify());
 440 }
 441 #endif // TASKQUEUE_STATS
 442 
 443 void ParScanThreadStateSet::flush()
 444 {
 445   // Work in this loop should be kept as lightweight as
 446   // possible since this might otherwise become a bottleneck
 447   // to scaling. Should we add heavy-weight work into this
 448   // loop, consider parallelizing the loop into the worker threads.
 449   for (int i = 0; i < length(); ++i) {
 450     ParScanThreadState& par_scan_state = thread_state(i);
 451 
 452     // Flush stats related to To-space PLAB activity and
 453     // retire the last buffer.
 454     par_scan_state.to_space_alloc_buffer()->
 455       flush_stats_and_retire(_gen.plab_stats(),
 456                              true /* end_of_gc */,
 457                              false /* retain */);
 458 
 459     // Every thread has its own age table.  We need to merge
 460     // them all into one.
 461     ageTable *local_table = par_scan_state.age_table();
 462     _gen.age_table()->merge(local_table);
 463 
 464     // Inform old gen that we're done.
 465     _next_gen.par_promote_alloc_done(i);
 466     _next_gen.par_oop_since_save_marks_iterate_done(i);
 467   }
 468 
 469   if (UseConcMarkSweepGC && ParallelGCThreads > 0) {
 470     // We need to call this even when ResizeOldPLAB is disabled
 471     // so as to avoid breaking some asserts. While we may be able
 472     // to avoid this by reorganizing the code a bit, I am loathe
 473     // to do that unless we find cases where ergo leads to bad
 474     // performance.
 475     CFLS_LAB::compute_desired_plab_size();
 476   }
 477 }
 478 
 479 ParScanClosure::ParScanClosure(ParNewGeneration* g,
 480                                ParScanThreadState* par_scan_state) :
 481   OopsInKlassOrGenClosure(g), _par_scan_state(par_scan_state), _g(g)
 482 {
 483   assert(_g->level() == 0, "Optimized for youngest generation");
 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* gen, Generation* next_gen,
 569                 HeapWord* young_old_boundary, ParScanThreadStateSet* state_set) :
 570     AbstractGangTask("ParNewGeneration collection"),
 571     _gen(gen), _next_gen(next_gen),
 572     _young_old_boundary(young_old_boundary),
 573     _state_set(state_set)
 574   {}
 575 
 576 // Reset the terminator for the given number of
 577 // active threads.
 578 void ParNewGenTask::set_for_termination(int active_workers) {
 579   _state_set->reset(active_workers, _gen->promotion_failed());
 580   // Should the heap be passed in?  There's only 1 for now so
 581   // grab it instead.
 582   GenCollectedHeap* gch = GenCollectedHeap::heap();
 583   gch->set_n_termination(active_workers);
 584 }
 585 
 586 // The "i" passed to this method is the part of the work for
 587 // this thread.  It is not the worker ID.  The "i" is derived
 588 // from _started_workers which is incremented in internal_note_start()
 589 // called in GangWorker loop() and which is called under the
 590 // which is  called under the protection of the gang monitor and is
 591 // called after a task is started.  So "i" is based on
 592 // first-come-first-served.
 593 
 594 void ParNewGenTask::work(uint worker_id) {
 595   GenCollectedHeap* gch = GenCollectedHeap::heap();
 596   // Since this is being done in a separate thread, need new resource
 597   // and handle marks.
 598   ResourceMark rm;
 599   HandleMark hm;
 600   // We would need multiple old-gen queues otherwise.
 601   assert(gch->n_gens() == 2, "Par young collection currently only works with one older gen.");
 602 
 603   Generation* old_gen = gch->next_gen(_gen);
 604 
 605   ParScanThreadState& par_scan_state = _state_set->thread_state(worker_id);
 606   assert(_state_set->is_valid(worker_id), "Should not have been called");
 607 
 608   par_scan_state.set_young_old_boundary(_young_old_boundary);
 609 
 610   KlassScanClosure klass_scan_closure(&par_scan_state.to_space_root_closure(),
 611                                       gch->rem_set()->klass_rem_set());
 612 
 613   int so = SharedHeap::SO_AllClasses | SharedHeap::SO_Strings | SharedHeap::SO_CodeCache;
 614 
 615   par_scan_state.start_strong_roots();
 616   gch->gen_process_strong_roots(_gen->level(),
 617                                 true,  // Process younger gens, if any,
 618                                        // as strong roots.
 619                                 false, // no scope; this is parallel code
 620                                 true,  // is scavenging
 621                                 SharedHeap::ScanningOption(so),
 622                                 &par_scan_state.to_space_root_closure(),
 623                                 true,   // walk *all* scavengable nmethods
 624                                 &par_scan_state.older_gen_closure(),
 625                                 &klass_scan_closure);
 626   par_scan_state.end_strong_roots();
 627 
 628   // "evacuate followers".
 629   par_scan_state.evacuate_followers_closure().do_void();
 630 }
 631 
 632 #ifdef _MSC_VER
 633 #pragma warning( push )
 634 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list
 635 #endif
 636 ParNewGeneration::
 637 ParNewGeneration(ReservedSpace rs, size_t initial_byte_size, int level)
 638   : DefNewGeneration(rs, initial_byte_size, level, "PCopy"),
 639   _overflow_list(NULL),
 640   _is_alive_closure(this),
 641   _plab_stats(YoungPLABSize, PLABWeight)
 642 {
 643   NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;)
 644   NOT_PRODUCT(_num_par_pushes = 0;)
 645   _task_queues = new ObjToScanQueueSet(ParallelGCThreads);
 646   guarantee(_task_queues != NULL, "task_queues allocation failure.");
 647 
 648   for (uint i1 = 0; i1 < ParallelGCThreads; i1++) {
 649     ObjToScanQueue *q = new ObjToScanQueue();
 650     guarantee(q != NULL, "work_queue Allocation failure.");
 651     _task_queues->register_queue(i1, q);
 652   }
 653 
 654   for (uint i2 = 0; i2 < ParallelGCThreads; i2++)
 655     _task_queues->queue(i2)->initialize();
 656 
 657   _overflow_stacks = NULL;
 658   if (ParGCUseLocalOverflow) {
 659 
 660     // typedef to workaround NEW_C_HEAP_ARRAY macro, which can not deal
 661     // with ','
 662     typedef Stack<oop, mtGC> GCOopStack;
 663 
 664     _overflow_stacks = NEW_C_HEAP_ARRAY(GCOopStack, ParallelGCThreads, mtGC);
 665     for (size_t i = 0; i < ParallelGCThreads; ++i) {
 666       new (_overflow_stacks + i) Stack<oop, mtGC>();
 667     }
 668   }
 669 
 670   if (UsePerfData) {
 671     EXCEPTION_MARK;
 672     ResourceMark rm;
 673 
 674     const char* cname =
 675          PerfDataManager::counter_name(_gen_counters->name_space(), "threads");
 676     PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None,
 677                                      ParallelGCThreads, CHECK);
 678   }
 679 }
 680 #ifdef _MSC_VER
 681 #pragma warning( pop )
 682 #endif
 683 
 684 // ParNewGeneration::
 685 ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) :
 686   DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {}
 687 
 688 template <class T>
 689 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) {
 690 #ifdef ASSERT
 691   {
 692     assert(!oopDesc::is_null(*p), "expected non-null ref");
 693     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 694     // We never expect to see a null reference being processed
 695     // as a weak reference.
 696     assert(obj->is_oop(), "expected an oop while scanning weak refs");
 697   }
 698 #endif // ASSERT
 699 
 700   _par_cl->do_oop_nv(p);
 701 
 702   if (Universe::heap()->is_in_reserved(p)) {
 703     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 704     _rs->write_ref_field_gc_par(p, obj);
 705   }
 706 }
 707 
 708 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(oop* p)       { ParKeepAliveClosure::do_oop_work(p); }
 709 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(narrowOop* p) { ParKeepAliveClosure::do_oop_work(p); }
 710 
 711 // ParNewGeneration::
 712 KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) :
 713   DefNewGeneration::KeepAliveClosure(cl) {}
 714 
 715 template <class T>
 716 void /*ParNewGeneration::*/KeepAliveClosure::do_oop_work(T* p) {
 717 #ifdef ASSERT
 718   {
 719     assert(!oopDesc::is_null(*p), "expected non-null ref");
 720     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 721     // We never expect to see a null reference being processed
 722     // as a weak reference.
 723     assert(obj->is_oop(), "expected an oop while scanning weak refs");
 724   }
 725 #endif // ASSERT
 726 
 727   _cl->do_oop_nv(p);
 728 
 729   if (Universe::heap()->is_in_reserved(p)) {
 730     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 731     _rs->write_ref_field_gc_par(p, obj);
 732   }
 733 }
 734 
 735 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(oop* p)       { KeepAliveClosure::do_oop_work(p); }
 736 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(narrowOop* p) { KeepAliveClosure::do_oop_work(p); }
 737 
 738 template <class T> void ScanClosureWithParBarrier::do_oop_work(T* p) {
 739   T heap_oop = oopDesc::load_heap_oop(p);
 740   if (!oopDesc::is_null(heap_oop)) {
 741     oop obj = oopDesc::decode_heap_oop_not_null(heap_oop);
 742     if ((HeapWord*)obj < _boundary) {
 743       assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?");
 744       oop new_obj = obj->is_forwarded()
 745                       ? obj->forwardee()
 746                       : _g->DefNewGeneration::copy_to_survivor_space(obj);
 747       oopDesc::encode_store_heap_oop_not_null(p, new_obj);
 748     }
 749     if (_gc_barrier) {
 750       // If p points to a younger generation, mark the card.
 751       if ((HeapWord*)obj < _gen_boundary) {
 752         _rs->write_ref_field_gc_par(p, obj);
 753       }
 754     }
 755   }
 756 }
 757 
 758 void ScanClosureWithParBarrier::do_oop(oop* p)       { ScanClosureWithParBarrier::do_oop_work(p); }
 759 void ScanClosureWithParBarrier::do_oop(narrowOop* p) { ScanClosureWithParBarrier::do_oop_work(p); }
 760 
 761 class ParNewRefProcTaskProxy: public AbstractGangTask {
 762   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
 763 public:
 764   ParNewRefProcTaskProxy(ProcessTask& task, ParNewGeneration& gen,
 765                          Generation& next_gen,
 766                          HeapWord* young_old_boundary,
 767                          ParScanThreadStateSet& state_set);
 768 
 769 private:
 770   virtual void work(uint worker_id);
 771   virtual void set_for_termination(int active_workers) {
 772     _state_set.terminator()->reset_for_reuse(active_workers);
 773   }
 774 private:
 775   ParNewGeneration&      _gen;
 776   ProcessTask&           _task;
 777   Generation&            _next_gen;
 778   HeapWord*              _young_old_boundary;
 779   ParScanThreadStateSet& _state_set;
 780 };
 781 
 782 ParNewRefProcTaskProxy::ParNewRefProcTaskProxy(
 783     ProcessTask& task, ParNewGeneration& gen,
 784     Generation& next_gen,
 785     HeapWord* young_old_boundary,
 786     ParScanThreadStateSet& state_set)
 787   : AbstractGangTask("ParNewGeneration parallel reference processing"),
 788     _gen(gen),
 789     _task(task),
 790     _next_gen(next_gen),
 791     _young_old_boundary(young_old_boundary),
 792     _state_set(state_set)
 793 {
 794 }
 795 
 796 void ParNewRefProcTaskProxy::work(uint worker_id)
 797 {
 798   ResourceMark rm;
 799   HandleMark hm;
 800   ParScanThreadState& par_scan_state = _state_set.thread_state(worker_id);
 801   par_scan_state.set_young_old_boundary(_young_old_boundary);
 802   _task.work(worker_id, par_scan_state.is_alive_closure(),
 803              par_scan_state.keep_alive_closure(),
 804              par_scan_state.evacuate_followers_closure());
 805 }
 806 
 807 class ParNewRefEnqueueTaskProxy: public AbstractGangTask {
 808   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
 809   EnqueueTask& _task;
 810 
 811 public:
 812   ParNewRefEnqueueTaskProxy(EnqueueTask& task)
 813     : AbstractGangTask("ParNewGeneration parallel reference enqueue"),
 814       _task(task)
 815   { }
 816 
 817   virtual void work(uint worker_id)
 818   {
 819     _task.work(worker_id);
 820   }
 821 };
 822 
 823 
 824 void ParNewRefProcTaskExecutor::execute(ProcessTask& task)
 825 {
 826   GenCollectedHeap* gch = GenCollectedHeap::heap();
 827   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
 828          "not a generational heap");
 829   FlexibleWorkGang* workers = gch->workers();
 830   assert(workers != NULL, "Need parallel worker threads.");
 831   _state_set.reset(workers->active_workers(), _generation.promotion_failed());
 832   ParNewRefProcTaskProxy rp_task(task, _generation, *_generation.next_gen(),
 833                                  _generation.reserved().end(), _state_set);
 834   workers->run_task(&rp_task);
 835   _state_set.reset(0 /* bad value in debug if not reset */,
 836                    _generation.promotion_failed());
 837 }
 838 
 839 void ParNewRefProcTaskExecutor::execute(EnqueueTask& task)
 840 {
 841   GenCollectedHeap* gch = GenCollectedHeap::heap();
 842   FlexibleWorkGang* workers = gch->workers();
 843   assert(workers != NULL, "Need parallel worker threads.");
 844   ParNewRefEnqueueTaskProxy enq_task(task);
 845   workers->run_task(&enq_task);
 846 }
 847 
 848 void ParNewRefProcTaskExecutor::set_single_threaded_mode()
 849 {
 850   _state_set.flush();
 851   GenCollectedHeap* gch = GenCollectedHeap::heap();
 852   gch->set_par_threads(0);  // 0 ==> non-parallel.
 853   gch->save_marks();
 854 }
 855 
 856 ScanClosureWithParBarrier::
 857 ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) :
 858   ScanClosure(g, gc_barrier) {}
 859 
 860 EvacuateFollowersClosureGeneral::
 861 EvacuateFollowersClosureGeneral(GenCollectedHeap* gch, int level,
 862                                 OopsInGenClosure* cur,
 863                                 OopsInGenClosure* older) :
 864   _gch(gch), _level(level),
 865   _scan_cur_or_nonheap(cur), _scan_older(older)
 866 {}
 867 
 868 void EvacuateFollowersClosureGeneral::do_void() {
 869   do {
 870     // Beware: this call will lead to closure applications via virtual
 871     // calls.
 872     _gch->oop_since_save_marks_iterate(_level,
 873                                        _scan_cur_or_nonheap,
 874                                        _scan_older);
 875   } while (!_gch->no_allocs_since_save_marks(_level));
 876 }
 877 
 878 
 879 bool ParNewGeneration::_avoid_promotion_undo = false;
 880 
 881 void ParNewGeneration::adjust_desired_tenuring_threshold() {
 882   // Set the desired survivor size to half the real survivor space
 883   _tenuring_threshold =
 884     age_table()->compute_tenuring_threshold(to()->capacity()/HeapWordSize);
 885 }
 886 
 887 // A Generation that does parallel young-gen collection.
 888 
 889 void ParNewGeneration::collect(bool   full,
 890                                bool   clear_all_soft_refs,
 891                                size_t size,
 892                                bool   is_tlab) {
 893   assert(full || size > 0, "otherwise we don't want to collect");
 894   GenCollectedHeap* gch = GenCollectedHeap::heap();
 895   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
 896     "not a CMS generational heap");
 897   AdaptiveSizePolicy* size_policy = gch->gen_policy()->size_policy();
 898   FlexibleWorkGang* workers = gch->workers();
 899   assert(workers != NULL, "Need workgang for parallel work");
 900   int active_workers =
 901       AdaptiveSizePolicy::calc_active_workers(workers->total_workers(),
 902                                    workers->active_workers(),
 903                                    Threads::number_of_non_daemon_threads());
 904   workers->set_active_workers(active_workers);
 905   _next_gen = gch->next_gen(this);
 906   assert(_next_gen != NULL,
 907     "This must be the youngest gen, and not the only gen");
 908   assert(gch->n_gens() == 2,
 909          "Par collection currently only works with single older gen.");
 910   // Do we have to avoid promotion_undo?
 911   if (gch->collector_policy()->is_concurrent_mark_sweep_policy()) {
 912     set_avoid_promotion_undo(true);
 913   }
 914 
 915   // If the next generation is too full to accomodate worst-case promotion
 916   // from this generation, pass on collection; let the next generation
 917   // do it.
 918   if (!collection_attempt_is_safe()) {
 919     gch->set_incremental_collection_failed();  // slight lie, in that we did not even attempt one
 920     return;
 921   }
 922   assert(to()->is_empty(), "Else not collection_attempt_is_safe");
 923 
 924   init_assuming_no_promotion_failure();
 925 
 926   if (UseAdaptiveSizePolicy) {
 927     set_survivor_overflow(false);
 928     size_policy->minor_collection_begin();
 929   }
 930 
 931   TraceTime t1(GCCauseString("GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, gclog_or_tty);
 932   // Capture heap used before collection (for printing).
 933   size_t gch_prev_used = gch->used();
 934 
 935   SpecializationStats::clear();
 936 
 937   age_table()->clear();
 938   to()->clear(SpaceDecorator::Mangle);
 939 
 940   gch->save_marks();
 941   assert(workers != NULL, "Need parallel worker threads.");
 942   int n_workers = active_workers;
 943 
 944   // Set the correct parallelism (number of queues) in the reference processor
 945   ref_processor()->set_active_mt_degree(n_workers);
 946 
 947   // Always set the terminator for the active number of workers
 948   // because only those workers go through the termination protocol.
 949   ParallelTaskTerminator _term(n_workers, task_queues());
 950   ParScanThreadStateSet thread_state_set(workers->active_workers(),
 951                                          *to(), *this, *_next_gen, *task_queues(),
 952                                          _overflow_stacks, desired_plab_sz(), _term);
 953 
 954   ParNewGenTask tsk(this, _next_gen, reserved().end(), &thread_state_set);
 955   gch->set_par_threads(n_workers);
 956   gch->rem_set()->prepare_for_younger_refs_iterate(true);
 957   // It turns out that even when we're using 1 thread, doing the work in a
 958   // separate thread causes wide variance in run times.  We can't help this
 959   // in the multi-threaded case, but we special-case n=1 here to get
 960   // repeatable measurements of the 1-thread overhead of the parallel code.
 961   if (n_workers > 1) {
 962     GenCollectedHeap::StrongRootsScope srs(gch);
 963     workers->run_task(&tsk);
 964   } else {
 965     GenCollectedHeap::StrongRootsScope srs(gch);
 966     tsk.work(0);
 967   }
 968   thread_state_set.reset(0 /* Bad value in debug if not reset */,
 969                          promotion_failed());
 970 
 971   // Process (weak) reference objects found during scavenge.
 972   ReferenceProcessor* rp = ref_processor();
 973   IsAliveClosure is_alive(this);
 974   ScanWeakRefClosure scan_weak_ref(this);
 975   KeepAliveClosure keep_alive(&scan_weak_ref);
 976   ScanClosure               scan_without_gc_barrier(this, false);
 977   ScanClosureWithParBarrier scan_with_gc_barrier(this, true);
 978   set_promo_failure_scan_stack_closure(&scan_without_gc_barrier);
 979   EvacuateFollowersClosureGeneral evacuate_followers(gch, _level,
 980     &scan_without_gc_barrier, &scan_with_gc_barrier);
 981   rp->setup_policy(clear_all_soft_refs);
 982   // Can  the mt_degree be set later (at run_task() time would be best)?
 983   rp->set_active_mt_degree(active_workers);
 984   if (rp->processing_is_mt()) {
 985     ParNewRefProcTaskExecutor task_executor(*this, thread_state_set);
 986     rp->process_discovered_references(&is_alive, &keep_alive,
 987                                       &evacuate_followers, &task_executor);
 988   } else {
 989     thread_state_set.flush();
 990     gch->set_par_threads(0);  // 0 ==> non-parallel.
 991     gch->save_marks();
 992     rp->process_discovered_references(&is_alive, &keep_alive,
 993                                       &evacuate_followers, NULL);
 994   }
 995   if (!promotion_failed()) {
 996     // Swap the survivor spaces.
 997     eden()->clear(SpaceDecorator::Mangle);
 998     from()->clear(SpaceDecorator::Mangle);
 999     if (ZapUnusedHeapArea) {
1000       // This is now done here because of the piece-meal mangling which
1001       // can check for valid mangling at intermediate points in the
1002       // collection(s).  When a minor collection fails to collect
1003       // sufficient space resizing of the young generation can occur
1004       // an redistribute the spaces in the young generation.  Mangle
1005       // here so that unzapped regions don't get distributed to
1006       // other spaces.
1007       to()->mangle_unused_area();
1008     }
1009     swap_spaces();
1010 
1011     // A successful scavenge should restart the GC time limit count which is
1012     // for full GC's.
1013     size_policy->reset_gc_overhead_limit_count();
1014 
1015     assert(to()->is_empty(), "to space should be empty now");
1016   } else {
1017     assert(_promo_failure_scan_stack.is_empty(), "post condition");
1018     _promo_failure_scan_stack.clear(true); // Clear cached segments.
1019 
1020     remove_forwarding_pointers();
1021     if (PrintGCDetails) {
1022       gclog_or_tty->print(" (promotion failed)");
1023     }
1024     // All the spaces are in play for mark-sweep.
1025     swap_spaces();  // Make life simpler for CMS || rescan; see 6483690.
1026     from()->set_next_compaction_space(to());
1027     gch->set_incremental_collection_failed();
1028     // Inform the next generation that a promotion failure occurred.
1029     _next_gen->promotion_failure_occurred();
1030 
1031     // Reset the PromotionFailureALot counters.
1032     NOT_PRODUCT(Universe::heap()->reset_promotion_should_fail();)
1033   }
1034   // set new iteration safe limit for the survivor spaces
1035   from()->set_concurrent_iteration_safe_limit(from()->top());
1036   to()->set_concurrent_iteration_safe_limit(to()->top());
1037 
1038   adjust_desired_tenuring_threshold();
1039   if (ResizePLAB) {
1040     plab_stats()->adjust_desired_plab_sz(n_workers);
1041   }
1042 
1043   if (PrintGC && !PrintGCDetails) {
1044     gch->print_heap_change(gch_prev_used);
1045   }
1046 
1047   if (PrintGCDetails && ParallelGCVerbose) {
1048     TASKQUEUE_STATS_ONLY(thread_state_set.print_termination_stats());
1049     TASKQUEUE_STATS_ONLY(thread_state_set.print_taskqueue_stats());
1050   }
1051 
1052   if (UseAdaptiveSizePolicy) {
1053     size_policy->minor_collection_end(gch->gc_cause());
1054     size_policy->avg_survived()->sample(from()->used());
1055   }
1056 
1057   // We need to use a monotonically non-deccreasing time in ms
1058   // or we will see time-warp warnings and os::javaTimeMillis()
1059   // does not guarantee monotonicity.
1060   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
1061   update_time_of_last_gc(now);
1062 
1063   SpecializationStats::print();
1064 
1065   rp->set_enqueuing_is_done(true);
1066   if (rp->processing_is_mt()) {
1067     ParNewRefProcTaskExecutor task_executor(*this, thread_state_set);
1068     rp->enqueue_discovered_references(&task_executor);
1069   } else {
1070     rp->enqueue_discovered_references(NULL);
1071   }
1072   rp->verify_no_references_recorded();
1073 }
1074 
1075 static int sum;
1076 void ParNewGeneration::waste_some_time() {
1077   for (int i = 0; i < 100; i++) {
1078     sum += i;
1079   }
1080 }
1081 
1082 static const oop ClaimedForwardPtr = oop(0x4);
1083 
1084 // Because of concurrency, there are times where an object for which
1085 // "is_forwarded()" is true contains an "interim" forwarding pointer
1086 // value.  Such a value will soon be overwritten with a real value.
1087 // This method requires "obj" to have a forwarding pointer, and waits, if
1088 // necessary for a real one to be inserted, and returns it.
1089 
1090 oop ParNewGeneration::real_forwardee(oop obj) {
1091   oop forward_ptr = obj->forwardee();
1092   if (forward_ptr != ClaimedForwardPtr) {
1093     return forward_ptr;
1094   } else {
1095     return real_forwardee_slow(obj);
1096   }
1097 }
1098 
1099 oop ParNewGeneration::real_forwardee_slow(oop obj) {
1100   // Spin-read if it is claimed but not yet written by another thread.
1101   oop forward_ptr = obj->forwardee();
1102   while (forward_ptr == ClaimedForwardPtr) {
1103     waste_some_time();
1104     assert(obj->is_forwarded(), "precondition");
1105     forward_ptr = obj->forwardee();
1106   }
1107   return forward_ptr;
1108 }
1109 
1110 #ifdef ASSERT
1111 bool ParNewGeneration::is_legal_forward_ptr(oop p) {
1112   return
1113     (_avoid_promotion_undo && p == ClaimedForwardPtr)
1114     || Universe::heap()->is_in_reserved(p);
1115 }
1116 #endif
1117 
1118 void ParNewGeneration::preserve_mark_if_necessary(oop obj, markOop m) {
1119   if (m->must_be_preserved_for_promotion_failure(obj)) {
1120     // We should really have separate per-worker stacks, rather
1121     // than use locking of a common pair of stacks.
1122     MutexLocker ml(ParGCRareEvent_lock);
1123     preserve_mark(obj, m);
1124   }
1125 }
1126 
1127 // Multiple GC threads may try to promote an object.  If the object
1128 // is successfully promoted, a forwarding pointer will be installed in
1129 // the object in the young generation.  This method claims the right
1130 // to install the forwarding pointer before it copies the object,
1131 // thus avoiding the need to undo the copy as in
1132 // copy_to_survivor_space_avoiding_with_undo.
1133 
1134 oop ParNewGeneration::copy_to_survivor_space_avoiding_promotion_undo(
1135         ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) {
1136   // In the sequential version, this assert also says that the object is
1137   // not forwarded.  That might not be the case here.  It is the case that
1138   // the caller observed it to be not forwarded at some time in the past.
1139   assert(is_in_reserved(old), "shouldn't be scavenging this oop");
1140 
1141   // The sequential code read "old->age()" below.  That doesn't work here,
1142   // since the age is in the mark word, and that might be overwritten with
1143   // a forwarding pointer by a parallel thread.  So we must save the mark
1144   // word in a local and then analyze it.
1145   oopDesc dummyOld;
1146   dummyOld.set_mark(m);
1147   assert(!dummyOld.is_forwarded(),
1148          "should not be called with forwarding pointer mark word.");
1149 
1150   oop new_obj = NULL;
1151   oop forward_ptr;
1152 
1153   // Try allocating obj in to-space (unless too old)
1154   if (dummyOld.age() < tenuring_threshold()) {
1155     new_obj = (oop)par_scan_state->alloc_in_to_space(sz);
1156     if (new_obj == NULL) {
1157       set_survivor_overflow(true);
1158     }
1159   }
1160 
1161   if (new_obj == NULL) {
1162     // Either to-space is full or we decided to promote
1163     // try allocating obj tenured
1164 
1165     // Attempt to install a null forwarding pointer (atomically),
1166     // to claim the right to install the real forwarding pointer.
1167     forward_ptr = old->forward_to_atomic(ClaimedForwardPtr);
1168     if (forward_ptr != NULL) {
1169       // someone else beat us to it.
1170         return real_forwardee(old);
1171     }
1172 
1173     new_obj = _next_gen->par_promote(par_scan_state->thread_num(),
1174                                        old, m, sz);
1175 
1176     if (new_obj == NULL) {
1177       // promotion failed, forward to self
1178       _promotion_failed = true;
1179       new_obj = old;
1180 
1181       preserve_mark_if_necessary(old, m);
1182       // Log the size of the maiden promotion failure
1183       par_scan_state->log_promotion_failure(sz);
1184     }
1185 
1186     old->forward_to(new_obj);
1187     forward_ptr = NULL;
1188   } else {
1189     // Is in to-space; do copying ourselves.
1190     Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz);
1191     forward_ptr = old->forward_to_atomic(new_obj);
1192     // Restore the mark word copied above.
1193     new_obj->set_mark(m);
1194     // Increment age if obj still in new generation
1195     new_obj->incr_age();
1196     par_scan_state->age_table()->add(new_obj, sz);
1197   }
1198   assert(new_obj != NULL, "just checking");
1199 
1200 #ifndef PRODUCT
1201   // This code must come after the CAS test, or it will print incorrect
1202   // information.
1203   if (TraceScavenge) {
1204     gclog_or_tty->print_cr("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}",
1205        is_in_reserved(new_obj) ? "copying" : "tenuring",
1206        new_obj->klass()->internal_name(), old, new_obj, new_obj->size());
1207   }
1208 #endif
1209 
1210   if (forward_ptr == NULL) {
1211     oop obj_to_push = new_obj;
1212     if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) {
1213       // Length field used as index of next element to be scanned.
1214       // Real length can be obtained from real_forwardee()
1215       arrayOop(old)->set_length(0);
1216       obj_to_push = old;
1217       assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push,
1218              "push forwarded object");
1219     }
1220     // Push it on one of the queues of to-be-scanned objects.
1221     bool simulate_overflow = false;
1222     NOT_PRODUCT(
1223       if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) {
1224         // simulate a stack overflow
1225         simulate_overflow = true;
1226       }
1227     )
1228     if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) {
1229       // Add stats for overflow pushes.
1230       if (Verbose && PrintGCDetails) {
1231         gclog_or_tty->print("queue overflow!\n");
1232       }
1233       push_on_overflow_list(old, par_scan_state);
1234       TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0));
1235     }
1236 
1237     return new_obj;
1238   }
1239 
1240   // Oops.  Someone beat us to it.  Undo the allocation.  Where did we
1241   // allocate it?
1242   if (is_in_reserved(new_obj)) {
1243     // Must be in to_space.
1244     assert(to()->is_in_reserved(new_obj), "Checking");
1245     if (forward_ptr == ClaimedForwardPtr) {
1246       // Wait to get the real forwarding pointer value.
1247       forward_ptr = real_forwardee(old);
1248     }
1249     par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz);
1250   }
1251 
1252   return forward_ptr;
1253 }
1254 
1255 
1256 // Multiple GC threads may try to promote the same object.  If two
1257 // or more GC threads copy the object, only one wins the race to install
1258 // the forwarding pointer.  The other threads have to undo their copy.
1259 
1260 oop ParNewGeneration::copy_to_survivor_space_with_undo(
1261         ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) {
1262 
1263   // In the sequential version, this assert also says that the object is
1264   // not forwarded.  That might not be the case here.  It is the case that
1265   // the caller observed it to be not forwarded at some time in the past.
1266   assert(is_in_reserved(old), "shouldn't be scavenging this oop");
1267 
1268   // The sequential code read "old->age()" below.  That doesn't work here,
1269   // since the age is in the mark word, and that might be overwritten with
1270   // a forwarding pointer by a parallel thread.  So we must save the mark
1271   // word here, install it in a local oopDesc, and then analyze it.
1272   oopDesc dummyOld;
1273   dummyOld.set_mark(m);
1274   assert(!dummyOld.is_forwarded(),
1275          "should not be called with forwarding pointer mark word.");
1276 
1277   bool failed_to_promote = false;
1278   oop new_obj = NULL;
1279   oop forward_ptr;
1280 
1281   // Try allocating obj in to-space (unless too old)
1282   if (dummyOld.age() < tenuring_threshold()) {
1283     new_obj = (oop)par_scan_state->alloc_in_to_space(sz);
1284     if (new_obj == NULL) {
1285       set_survivor_overflow(true);
1286     }
1287   }
1288 
1289   if (new_obj == NULL) {
1290     // Either to-space is full or we decided to promote
1291     // try allocating obj tenured
1292     new_obj = _next_gen->par_promote(par_scan_state->thread_num(),
1293                                        old, m, sz);
1294 
1295     if (new_obj == NULL) {
1296       // promotion failed, forward to self
1297       forward_ptr = old->forward_to_atomic(old);
1298       new_obj = old;
1299 
1300       if (forward_ptr != NULL) {
1301         return forward_ptr;   // someone else succeeded
1302       }
1303 
1304       _promotion_failed = true;
1305       failed_to_promote = true;
1306 
1307       preserve_mark_if_necessary(old, m);
1308       // Log the size of the maiden promotion failure
1309       par_scan_state->log_promotion_failure(sz);
1310     }
1311   } else {
1312     // Is in to-space; do copying ourselves.
1313     Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz);
1314     // Restore the mark word copied above.
1315     new_obj->set_mark(m);
1316     // Increment age if new_obj still in new generation
1317     new_obj->incr_age();
1318     par_scan_state->age_table()->add(new_obj, sz);
1319   }
1320   assert(new_obj != NULL, "just checking");
1321 
1322 #ifndef PRODUCT
1323   // This code must come after the CAS test, or it will print incorrect
1324   // information.
1325   if (TraceScavenge) {
1326     gclog_or_tty->print_cr("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}",
1327        is_in_reserved(new_obj) ? "copying" : "tenuring",
1328        new_obj->klass()->internal_name(), old, new_obj, new_obj->size());
1329   }
1330 #endif
1331 
1332   // Now attempt to install the forwarding pointer (atomically).
1333   // We have to copy the mark word before overwriting with forwarding
1334   // ptr, so we can restore it below in the copy.
1335   if (!failed_to_promote) {
1336     forward_ptr = old->forward_to_atomic(new_obj);
1337   }
1338 
1339   if (forward_ptr == NULL) {
1340     oop obj_to_push = new_obj;
1341     if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) {
1342       // Length field used as index of next element to be scanned.
1343       // Real length can be obtained from real_forwardee()
1344       arrayOop(old)->set_length(0);
1345       obj_to_push = old;
1346       assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push,
1347              "push forwarded object");
1348     }
1349     // Push it on one of the queues of to-be-scanned objects.
1350     bool simulate_overflow = false;
1351     NOT_PRODUCT(
1352       if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) {
1353         // simulate a stack overflow
1354         simulate_overflow = true;
1355       }
1356     )
1357     if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) {
1358       // Add stats for overflow pushes.
1359       push_on_overflow_list(old, par_scan_state);
1360       TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0));
1361     }
1362 
1363     return new_obj;
1364   }
1365 
1366   // Oops.  Someone beat us to it.  Undo the allocation.  Where did we
1367   // allocate it?
1368   if (is_in_reserved(new_obj)) {
1369     // Must be in to_space.
1370     assert(to()->is_in_reserved(new_obj), "Checking");
1371     par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz);
1372   } else {
1373     assert(!_avoid_promotion_undo, "Should not be here if avoiding.");
1374     _next_gen->par_promote_alloc_undo(par_scan_state->thread_num(),
1375                                       (HeapWord*)new_obj, sz);
1376   }
1377 
1378   return forward_ptr;
1379 }
1380 
1381 #ifndef PRODUCT
1382 // It's OK to call this multi-threaded;  the worst thing
1383 // that can happen is that we'll get a bunch of closely
1384 // spaced simulated oveflows, but that's OK, in fact
1385 // probably good as it would exercise the overflow code
1386 // under contention.
1387 bool ParNewGeneration::should_simulate_overflow() {
1388   if (_overflow_counter-- <= 0) { // just being defensive
1389     _overflow_counter = ParGCWorkQueueOverflowInterval;
1390     return true;
1391   } else {
1392     return false;
1393   }
1394 }
1395 #endif
1396 
1397 // In case we are using compressed oops, we need to be careful.
1398 // If the object being pushed is an object array, then its length
1399 // field keeps track of the "grey boundary" at which the next
1400 // incremental scan will be done (see ParGCArrayScanChunk).
1401 // When using compressed oops, this length field is kept in the
1402 // lower 32 bits of the erstwhile klass word and cannot be used
1403 // for the overflow chaining pointer (OCP below). As such the OCP
1404 // would itself need to be compressed into the top 32-bits in this
1405 // case. Unfortunately, see below, in the event that we have a
1406 // promotion failure, the node to be pushed on the list can be
1407 // outside of the Java heap, so the heap-based pointer compression
1408 // would not work (we would have potential aliasing between C-heap
1409 // and Java-heap pointers). For this reason, when using compressed
1410 // oops, we simply use a worker-thread-local, non-shared overflow
1411 // list in the form of a growable array, with a slightly different
1412 // overflow stack draining strategy. If/when we start using fat
1413 // stacks here, we can go back to using (fat) pointer chains
1414 // (although some performance comparisons would be useful since
1415 // single global lists have their own performance disadvantages
1416 // as we were made painfully aware not long ago, see 6786503).
1417 #define BUSY (oop(0x1aff1aff))
1418 void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) {
1419   assert(is_in_reserved(from_space_obj), "Should be from this generation");
1420   if (ParGCUseLocalOverflow) {
1421     // In the case of compressed oops, we use a private, not-shared
1422     // overflow stack.
1423     par_scan_state->push_on_overflow_stack(from_space_obj);
1424   } else {
1425     assert(!UseCompressedOops, "Error");
1426     // if the object has been forwarded to itself, then we cannot
1427     // use the klass pointer for the linked list.  Instead we have
1428     // to allocate an oopDesc in the C-Heap and use that for the linked list.
1429     // XXX This is horribly inefficient when a promotion failure occurs
1430     // and should be fixed. XXX FIX ME !!!
1431 #ifndef PRODUCT
1432     Atomic::inc_ptr(&_num_par_pushes);
1433     assert(_num_par_pushes > 0, "Tautology");
1434 #endif
1435     if (from_space_obj->forwardee() == from_space_obj) {
1436       oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1, mtGC);
1437       listhead->forward_to(from_space_obj);
1438       from_space_obj = listhead;
1439     }
1440     oop observed_overflow_list = _overflow_list;
1441     oop cur_overflow_list;
1442     do {
1443       cur_overflow_list = observed_overflow_list;
1444       if (cur_overflow_list != BUSY) {
1445         from_space_obj->set_klass_to_list_ptr(cur_overflow_list);
1446       } else {
1447         from_space_obj->set_klass_to_list_ptr(NULL);
1448       }
1449       observed_overflow_list =
1450         (oop)Atomic::cmpxchg_ptr(from_space_obj, &_overflow_list, cur_overflow_list);
1451     } while (cur_overflow_list != observed_overflow_list);
1452   }
1453 }
1454 
1455 bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) {
1456   bool res;
1457 
1458   if (ParGCUseLocalOverflow) {
1459     res = par_scan_state->take_from_overflow_stack();
1460   } else {
1461     assert(!UseCompressedOops, "Error");
1462     res = take_from_overflow_list_work(par_scan_state);
1463   }
1464   return res;
1465 }
1466 
1467 
1468 // *NOTE*: The overflow list manipulation code here and
1469 // in CMSCollector:: are very similar in shape,
1470 // except that in the CMS case we thread the objects
1471 // directly into the list via their mark word, and do
1472 // not need to deal with special cases below related
1473 // to chunking of object arrays and promotion failure
1474 // handling.
1475 // CR 6797058 has been filed to attempt consolidation of
1476 // the common code.
1477 // Because of the common code, if you make any changes in
1478 // the code below, please check the CMS version to see if
1479 // similar changes might be needed.
1480 // See CMSCollector::par_take_from_overflow_list() for
1481 // more extensive documentation comments.
1482 bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) {
1483   ObjToScanQueue* work_q = par_scan_state->work_queue();
1484   // How many to take?
1485   size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
1486                                  (size_t)ParGCDesiredObjsFromOverflowList);
1487 
1488   assert(!UseCompressedOops, "Error");
1489   assert(par_scan_state->overflow_stack() == NULL, "Error");
1490   if (_overflow_list == NULL) return false;
1491 
1492   // Otherwise, there was something there; try claiming the list.
1493   oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
1494   // Trim off a prefix of at most objsFromOverflow items
1495   Thread* tid = Thread::current();
1496   size_t spin_count = (size_t)ParallelGCThreads;
1497   size_t sleep_time_millis = MAX2((size_t)1, objsFromOverflow/100);
1498   for (size_t spin = 0; prefix == BUSY && spin < spin_count; spin++) {
1499     // someone grabbed it before we did ...
1500     // ... we spin for a short while...
1501     os::sleep(tid, sleep_time_millis, false);
1502     if (_overflow_list == NULL) {
1503       // nothing left to take
1504       return false;
1505     } else if (_overflow_list != BUSY) {
1506      // try and grab the prefix
1507      prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
1508     }
1509   }
1510   if (prefix == NULL || prefix == BUSY) {
1511      // Nothing to take or waited long enough
1512      if (prefix == NULL) {
1513        // Write back the NULL in case we overwrote it with BUSY above
1514        // and it is still the same value.
1515        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
1516      }
1517      return false;
1518   }
1519   assert(prefix != NULL && prefix != BUSY, "Error");
1520   size_t i = 1;
1521   oop cur = prefix;
1522   while (i < objsFromOverflow && cur->klass_or_null() != NULL) {
1523     i++; cur = cur->list_ptr_from_klass();
1524   }
1525 
1526   // Reattach remaining (suffix) to overflow list
1527   if (cur->klass_or_null() == NULL) {
1528     // Write back the NULL in lieu of the BUSY we wrote
1529     // above and it is still the same value.
1530     if (_overflow_list == BUSY) {
1531       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
1532     }
1533   } else {
1534     assert(cur->klass_or_null() != (Klass*)(address)BUSY, "Error");
1535     oop suffix = cur->list_ptr_from_klass();       // suffix will be put back on global list
1536     cur->set_klass_to_list_ptr(NULL);     // break off suffix
1537     // It's possible that the list is still in the empty(busy) state
1538     // we left it in a short while ago; in that case we may be
1539     // able to place back the suffix.
1540     oop observed_overflow_list = _overflow_list;
1541     oop cur_overflow_list = observed_overflow_list;
1542     bool attached = false;
1543     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
1544       observed_overflow_list =
1545         (oop) Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);
1546       if (cur_overflow_list == observed_overflow_list) {
1547         attached = true;
1548         break;
1549       } else cur_overflow_list = observed_overflow_list;
1550     }
1551     if (!attached) {
1552       // Too bad, someone else got in in between; we'll need to do a splice.
1553       // Find the last item of suffix list
1554       oop last = suffix;
1555       while (last->klass_or_null() != NULL) {
1556         last = last->list_ptr_from_klass();
1557       }
1558       // Atomically prepend suffix to current overflow list
1559       observed_overflow_list = _overflow_list;
1560       do {
1561         cur_overflow_list = observed_overflow_list;
1562         if (cur_overflow_list != BUSY) {
1563           // Do the splice ...
1564           last->set_klass_to_list_ptr(cur_overflow_list);
1565         } else { // cur_overflow_list == BUSY
1566           last->set_klass_to_list_ptr(NULL);
1567         }
1568         observed_overflow_list =
1569           (oop)Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);
1570       } while (cur_overflow_list != observed_overflow_list);
1571     }
1572   }
1573 
1574   // Push objects on prefix list onto this thread's work queue
1575   assert(prefix != NULL && prefix != BUSY, "program logic");
1576   cur = prefix;
1577   ssize_t n = 0;
1578   while (cur != NULL) {
1579     oop obj_to_push = cur->forwardee();
1580     oop next        = cur->list_ptr_from_klass();
1581     cur->set_klass(obj_to_push->klass());
1582     // This may be an array object that is self-forwarded. In that case, the list pointer
1583     // space, cur, is not in the Java heap, but rather in the C-heap and should be freed.
1584     if (!is_in_reserved(cur)) {
1585       // This can become a scaling bottleneck when there is work queue overflow coincident
1586       // with promotion failure.
1587       oopDesc* f = cur;
1588       FREE_C_HEAP_ARRAY(oopDesc, f, mtGC);
1589     } else if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) {
1590       assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");
1591       obj_to_push = cur;
1592     }
1593     bool ok = work_q->push(obj_to_push);
1594     assert(ok, "Should have succeeded");
1595     cur = next;
1596     n++;
1597   }
1598   TASKQUEUE_STATS_ONLY(par_scan_state->note_overflow_refill(n));
1599 #ifndef PRODUCT
1600   assert(_num_par_pushes >= n, "Too many pops?");
1601   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
1602 #endif
1603   return true;
1604 }
1605 #undef BUSY
1606 
1607 void ParNewGeneration::ref_processor_init()
1608 {
1609   if (_ref_processor == NULL) {
1610     // Allocate and initialize a reference processor
1611     _ref_processor =
1612       new ReferenceProcessor(_reserved,                  // span
1613                              ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing
1614                              (int) ParallelGCThreads,    // mt processing degree
1615                              refs_discovery_is_mt(),     // mt discovery
1616                              (int) ParallelGCThreads,    // mt discovery degree
1617                              refs_discovery_is_atomic(), // atomic_discovery
1618                              NULL,                       // is_alive_non_header
1619                              false);                     // write barrier for next field updates
1620   }
1621 }
1622 
1623 const char* ParNewGeneration::name() const {
1624   return "par new generation";
1625 }




--- EOF ---