1 /*
   2  * Copyright (c) 2001, 2010, 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/parGCAllocBuffer.hpp"
  28 #include "gc_implementation/parNew/parNewGeneration.hpp"
  29 #include "gc_implementation/parNew/parOopClosures.inline.hpp"
  30 #include "gc_implementation/shared/adaptiveSizePolicy.hpp"
  31 #include "gc_implementation/shared/ageTable.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>* 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>* 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>*             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(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 };
 326 
 327 
 328 ParScanThreadStateSet::ParScanThreadStateSet(
 329   int num_threads, Space& to_space, ParNewGeneration& gen,
 330   Generation& old_gen, ObjToScanQueueSet& queue_set,
 331   Stack<oop>* overflow_stacks,
 332   size_t desired_plab_sz, ParallelTaskTerminator& term)
 333   : ResourceArray(sizeof(ParScanThreadState), num_threads),
 334     _gen(gen), _next_gen(old_gen), _term(term)
 335 {
 336   assert(num_threads > 0, "sanity check!");
 337   assert(ParGCUseLocalOverflow == (overflow_stacks != NULL),
 338          "overflow_stack allocation mismatch");
 339   // Initialize states.
 340   for (int i = 0; i < num_threads; ++i) {
 341     new ((ParScanThreadState*)_data + i)
 342         ParScanThreadState(&to_space, &gen, &old_gen, i, &queue_set,
 343                            overflow_stacks, desired_plab_sz, term);
 344   }
 345 }
 346 
 347 inline ParScanThreadState& ParScanThreadStateSet::thread_state(int i)
 348 {
 349   assert(i >= 0 && i < length(), "sanity check!");
 350   return ((ParScanThreadState*)_data)[i];
 351 }
 352 
 353 
 354 void ParScanThreadStateSet::reset(bool promotion_failed)
 355 {
 356   _term.reset_for_reuse();
 357   if (promotion_failed) {
 358     for (int i = 0; i < length(); ++i) {
 359       thread_state(i).print_and_clear_promotion_failure_size();
 360     }
 361   }
 362 }
 363 
 364 #if TASKQUEUE_STATS
 365 void
 366 ParScanThreadState::reset_stats()
 367 {
 368   taskqueue_stats().reset();
 369   _term_attempts = 0;
 370   _overflow_refills = 0;
 371   _overflow_refill_objs = 0;
 372 }
 373 
 374 void ParScanThreadStateSet::reset_stats()
 375 {
 376   for (int i = 0; i < length(); ++i) {
 377     thread_state(i).reset_stats();
 378   }
 379 }
 380 
 381 void
 382 ParScanThreadStateSet::print_termination_stats_hdr(outputStream* const st)
 383 {
 384   st->print_raw_cr("GC Termination Stats");
 385   st->print_raw_cr("     elapsed  --strong roots-- "
 386                    "-------termination-------");
 387   st->print_raw_cr("thr     ms        ms       %   "
 388                    "    ms       %   attempts");
 389   st->print_raw_cr("--- --------- --------- ------ "
 390                    "--------- ------ --------");
 391 }
 392 
 393 void ParScanThreadStateSet::print_termination_stats(outputStream* const st)
 394 {
 395   print_termination_stats_hdr(st);
 396 
 397   for (int i = 0; i < length(); ++i) {
 398     const ParScanThreadState & pss = thread_state(i);
 399     const double elapsed_ms = pss.elapsed_time() * 1000.0;
 400     const double s_roots_ms = pss.strong_roots_time() * 1000.0;
 401     const double term_ms = pss.term_time() * 1000.0;
 402     st->print_cr("%3d %9.2f %9.2f %6.2f "
 403                  "%9.2f %6.2f " SIZE_FORMAT_W(8),
 404                  i, elapsed_ms, s_roots_ms, s_roots_ms * 100 / elapsed_ms,
 405                  term_ms, term_ms * 100 / elapsed_ms, pss.term_attempts());
 406   }
 407 }
 408 
 409 // Print stats related to work queue activity.
 410 void ParScanThreadStateSet::print_taskqueue_stats_hdr(outputStream* const st)
 411 {
 412   st->print_raw_cr("GC Task Stats");
 413   st->print_raw("thr "); TaskQueueStats::print_header(1, st); st->cr();
 414   st->print_raw("--- "); TaskQueueStats::print_header(2, st); st->cr();
 415 }
 416 
 417 void ParScanThreadStateSet::print_taskqueue_stats(outputStream* const st)
 418 {
 419   print_taskqueue_stats_hdr(st);
 420 
 421   TaskQueueStats totals;
 422   for (int i = 0; i < length(); ++i) {
 423     const ParScanThreadState & pss = thread_state(i);
 424     const TaskQueueStats & stats = pss.taskqueue_stats();
 425     st->print("%3d ", i); stats.print(st); st->cr();
 426     totals += stats;
 427 
 428     if (pss.overflow_refills() > 0) {
 429       st->print_cr("    " SIZE_FORMAT_W(10) " overflow refills    "
 430                    SIZE_FORMAT_W(10) " overflow objects",
 431                    pss.overflow_refills(), pss.overflow_refill_objs());
 432     }
 433   }
 434   st->print("tot "); totals.print(st); st->cr();
 435 
 436   DEBUG_ONLY(totals.verify());
 437 }
 438 #endif // TASKQUEUE_STATS
 439 
 440 void ParScanThreadStateSet::flush()
 441 {
 442   // Work in this loop should be kept as lightweight as
 443   // possible since this might otherwise become a bottleneck
 444   // to scaling. Should we add heavy-weight work into this
 445   // loop, consider parallelizing the loop into the worker threads.
 446   for (int i = 0; i < length(); ++i) {
 447     ParScanThreadState& par_scan_state = thread_state(i);
 448 
 449     // Flush stats related to To-space PLAB activity and
 450     // retire the last buffer.
 451     par_scan_state.to_space_alloc_buffer()->
 452       flush_stats_and_retire(_gen.plab_stats(),
 453                              false /* !retain */);
 454 
 455     // Every thread has its own age table.  We need to merge
 456     // them all into one.
 457     ageTable *local_table = par_scan_state.age_table();
 458     _gen.age_table()->merge(local_table);
 459 
 460     // Inform old gen that we're done.
 461     _next_gen.par_promote_alloc_done(i);
 462     _next_gen.par_oop_since_save_marks_iterate_done(i);
 463   }
 464 
 465   if (UseConcMarkSweepGC && ParallelGCThreads > 0) {
 466     // We need to call this even when ResizeOldPLAB is disabled
 467     // so as to avoid breaking some asserts. While we may be able
 468     // to avoid this by reorganizing the code a bit, I am loathe
 469     // to do that unless we find cases where ergo leads to bad
 470     // performance.
 471     CFLS_LAB::compute_desired_plab_size();
 472   }
 473 }
 474 
 475 ParScanClosure::ParScanClosure(ParNewGeneration* g,
 476                                ParScanThreadState* par_scan_state) :
 477   OopsInGenClosure(g), _par_scan_state(par_scan_state), _g(g)
 478 {
 479   assert(_g->level() == 0, "Optimized for youngest generation");
 480   _boundary = _g->reserved().end();
 481 }
 482 
 483 void ParScanWithBarrierClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, true, false); }
 484 void ParScanWithBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, false); }
 485 
 486 void ParScanWithoutBarrierClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, false, false); }
 487 void ParScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, false); }
 488 
 489 void ParRootScanWithBarrierTwoGensClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, true, true); }
 490 void ParRootScanWithBarrierTwoGensClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, true); }
 491 
 492 void ParRootScanWithoutBarrierClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, false, true); }
 493 void ParRootScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, true); }
 494 
 495 ParScanWeakRefClosure::ParScanWeakRefClosure(ParNewGeneration* g,
 496                                              ParScanThreadState* par_scan_state)
 497   : ScanWeakRefClosure(g), _par_scan_state(par_scan_state)
 498 {}
 499 
 500 void ParScanWeakRefClosure::do_oop(oop* p)       { ParScanWeakRefClosure::do_oop_work(p); }
 501 void ParScanWeakRefClosure::do_oop(narrowOop* p) { ParScanWeakRefClosure::do_oop_work(p); }
 502 
 503 #ifdef WIN32
 504 #pragma warning(disable: 4786) /* identifier was truncated to '255' characters in the browser information */
 505 #endif
 506 
 507 ParEvacuateFollowersClosure::ParEvacuateFollowersClosure(
 508     ParScanThreadState* par_scan_state_,
 509     ParScanWithoutBarrierClosure* to_space_closure_,
 510     ParScanWithBarrierClosure* old_gen_closure_,
 511     ParRootScanWithoutBarrierClosure* to_space_root_closure_,
 512     ParNewGeneration* par_gen_,
 513     ParRootScanWithBarrierTwoGensClosure* old_gen_root_closure_,
 514     ObjToScanQueueSet* task_queues_,
 515     ParallelTaskTerminator* terminator_) :
 516 
 517     _par_scan_state(par_scan_state_),
 518     _to_space_closure(to_space_closure_),
 519     _old_gen_closure(old_gen_closure_),
 520     _to_space_root_closure(to_space_root_closure_),
 521     _old_gen_root_closure(old_gen_root_closure_),
 522     _par_gen(par_gen_),
 523     _task_queues(task_queues_),
 524     _terminator(terminator_)
 525 {}
 526 
 527 void ParEvacuateFollowersClosure::do_void() {
 528   ObjToScanQueue* work_q = par_scan_state()->work_queue();
 529 
 530   while (true) {
 531 
 532     // Scan to-space and old-gen objs until we run out of both.
 533     oop obj_to_scan;
 534     par_scan_state()->trim_queues(0);
 535 
 536     // We have no local work, attempt to steal from other threads.
 537 
 538     // attempt to steal work from promoted.
 539     if (task_queues()->steal(par_scan_state()->thread_num(),
 540                              par_scan_state()->hash_seed(),
 541                              obj_to_scan)) {
 542       bool res = work_q->push(obj_to_scan);
 543       assert(res, "Empty queue should have room for a push.");
 544 
 545       //   if successful, goto Start.
 546       continue;
 547 
 548       // try global overflow list.
 549     } else if (par_gen()->take_from_overflow_list(par_scan_state())) {
 550       continue;
 551     }
 552 
 553     // Otherwise, offer termination.
 554     par_scan_state()->start_term_time();
 555     if (terminator()->offer_termination()) break;
 556     par_scan_state()->end_term_time();
 557   }
 558   assert(par_gen()->_overflow_list == NULL && par_gen()->_num_par_pushes == 0,
 559          "Broken overflow list?");
 560   // Finish the last termination pause.
 561   par_scan_state()->end_term_time();
 562 }
 563 
 564 ParNewGenTask::ParNewGenTask(ParNewGeneration* gen, Generation* next_gen,
 565                 HeapWord* young_old_boundary, ParScanThreadStateSet* state_set) :
 566     AbstractGangTask("ParNewGeneration collection"),
 567     _gen(gen), _next_gen(next_gen),
 568     _young_old_boundary(young_old_boundary),
 569     _state_set(state_set)
 570   {}
 571 
 572 void ParNewGenTask::work(int i) {
 573   GenCollectedHeap* gch = GenCollectedHeap::heap();
 574   // Since this is being done in a separate thread, need new resource
 575   // and handle marks.
 576   ResourceMark rm;
 577   HandleMark hm;
 578   // We would need multiple old-gen queues otherwise.
 579   assert(gch->n_gens() == 2, "Par young collection currently only works with one older gen.");
 580 
 581   Generation* old_gen = gch->next_gen(_gen);
 582 
 583   ParScanThreadState& par_scan_state = _state_set->thread_state(i);
 584   par_scan_state.set_young_old_boundary(_young_old_boundary);
 585 
 586   par_scan_state.start_strong_roots();
 587   gch->gen_process_strong_roots(_gen->level(),
 588                                 true,  // Process younger gens, if any,
 589                                        // as strong roots.
 590                                 false, // no scope; this is parallel code
 591                                 false, // not collecting perm generation.
 592                                 SharedHeap::SO_AllClasses,
 593                                 &par_scan_state.to_space_root_closure(),
 594                                 true,   // walk *all* scavengable nmethods
 595                                 &par_scan_state.older_gen_closure());
 596   par_scan_state.end_strong_roots();
 597 
 598   // "evacuate followers".
 599   par_scan_state.evacuate_followers_closure().do_void();
 600 }
 601 
 602 #ifdef _MSC_VER
 603 #pragma warning( push )
 604 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list
 605 #endif
 606 ParNewGeneration::
 607 ParNewGeneration(ReservedSpace rs, size_t initial_byte_size, int level)
 608   : DefNewGeneration(rs, initial_byte_size, level, "PCopy"),
 609   _overflow_list(NULL),
 610   _is_alive_closure(this),
 611   _plab_stats(YoungPLABSize, PLABWeight)
 612 {
 613   NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;)
 614   NOT_PRODUCT(_num_par_pushes = 0;)
 615   _task_queues = new ObjToScanQueueSet(ParallelGCThreads);
 616   guarantee(_task_queues != NULL, "task_queues allocation failure.");
 617 
 618   for (uint i1 = 0; i1 < ParallelGCThreads; i1++) {
 619     ObjToScanQueue *q = new ObjToScanQueue();
 620     guarantee(q != NULL, "work_queue Allocation failure.");
 621     _task_queues->register_queue(i1, q);
 622   }
 623 
 624   for (uint i2 = 0; i2 < ParallelGCThreads; i2++)
 625     _task_queues->queue(i2)->initialize();
 626 
 627   _overflow_stacks = NULL;
 628   if (ParGCUseLocalOverflow) {
 629     _overflow_stacks = NEW_C_HEAP_ARRAY(Stack<oop>, ParallelGCThreads);
 630     for (size_t i = 0; i < ParallelGCThreads; ++i) {
 631       new (_overflow_stacks + i) Stack<oop>();
 632     }
 633   }
 634 
 635   if (UsePerfData) {
 636     EXCEPTION_MARK;
 637     ResourceMark rm;
 638 
 639     const char* cname =
 640          PerfDataManager::counter_name(_gen_counters->name_space(), "threads");
 641     PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None,
 642                                      ParallelGCThreads, CHECK);
 643   }
 644 }
 645 #ifdef _MSC_VER
 646 #pragma warning( pop )
 647 #endif
 648 
 649 // ParNewGeneration::
 650 ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) :
 651   DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {}
 652 
 653 template <class T>
 654 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) {
 655 #ifdef ASSERT
 656   {
 657     assert(!oopDesc::is_null(*p), "expected non-null ref");
 658     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 659     // We never expect to see a null reference being processed
 660     // as a weak reference.
 661     assert(obj->is_oop(), "expected an oop while scanning weak refs");
 662   }
 663 #endif // ASSERT
 664 
 665   _par_cl->do_oop_nv(p);
 666 
 667   if (Universe::heap()->is_in_reserved(p)) {
 668     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 669     _rs->write_ref_field_gc_par(p, obj);
 670   }
 671 }
 672 
 673 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(oop* p)       { ParKeepAliveClosure::do_oop_work(p); }
 674 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(narrowOop* p) { ParKeepAliveClosure::do_oop_work(p); }
 675 
 676 // ParNewGeneration::
 677 KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) :
 678   DefNewGeneration::KeepAliveClosure(cl) {}
 679 
 680 template <class T>
 681 void /*ParNewGeneration::*/KeepAliveClosure::do_oop_work(T* p) {
 682 #ifdef ASSERT
 683   {
 684     assert(!oopDesc::is_null(*p), "expected non-null ref");
 685     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 686     // We never expect to see a null reference being processed
 687     // as a weak reference.
 688     assert(obj->is_oop(), "expected an oop while scanning weak refs");
 689   }
 690 #endif // ASSERT
 691 
 692   _cl->do_oop_nv(p);
 693 
 694   if (Universe::heap()->is_in_reserved(p)) {
 695     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 696     _rs->write_ref_field_gc_par(p, obj);
 697   }
 698 }
 699 
 700 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(oop* p)       { KeepAliveClosure::do_oop_work(p); }
 701 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(narrowOop* p) { KeepAliveClosure::do_oop_work(p); }
 702 
 703 template <class T> void ScanClosureWithParBarrier::do_oop_work(T* p) {
 704   T heap_oop = oopDesc::load_heap_oop(p);
 705   if (!oopDesc::is_null(heap_oop)) {
 706     oop obj = oopDesc::decode_heap_oop_not_null(heap_oop);
 707     if ((HeapWord*)obj < _boundary) {
 708       assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?");
 709       oop new_obj = obj->is_forwarded()
 710                       ? obj->forwardee()
 711                       : _g->DefNewGeneration::copy_to_survivor_space(obj);
 712       oopDesc::encode_store_heap_oop_not_null(p, new_obj);
 713     }
 714     if (_gc_barrier) {
 715       // If p points to a younger generation, mark the card.
 716       if ((HeapWord*)obj < _gen_boundary) {
 717         _rs->write_ref_field_gc_par(p, obj);
 718       }
 719     }
 720   }
 721 }
 722 
 723 void ScanClosureWithParBarrier::do_oop(oop* p)       { ScanClosureWithParBarrier::do_oop_work(p); }
 724 void ScanClosureWithParBarrier::do_oop(narrowOop* p) { ScanClosureWithParBarrier::do_oop_work(p); }
 725 
 726 class ParNewRefProcTaskProxy: public AbstractGangTask {
 727   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
 728 public:
 729   ParNewRefProcTaskProxy(ProcessTask& task, ParNewGeneration& gen,
 730                          Generation& next_gen,
 731                          HeapWord* young_old_boundary,
 732                          ParScanThreadStateSet& state_set);
 733 
 734 private:
 735   virtual void work(int i);
 736 
 737 private:
 738   ParNewGeneration&      _gen;
 739   ProcessTask&           _task;
 740   Generation&            _next_gen;
 741   HeapWord*              _young_old_boundary;
 742   ParScanThreadStateSet& _state_set;
 743 };
 744 
 745 ParNewRefProcTaskProxy::ParNewRefProcTaskProxy(
 746     ProcessTask& task, ParNewGeneration& gen,
 747     Generation& next_gen,
 748     HeapWord* young_old_boundary,
 749     ParScanThreadStateSet& state_set)
 750   : AbstractGangTask("ParNewGeneration parallel reference processing"),
 751     _gen(gen),
 752     _task(task),
 753     _next_gen(next_gen),
 754     _young_old_boundary(young_old_boundary),
 755     _state_set(state_set)
 756 {
 757 }
 758 
 759 void ParNewRefProcTaskProxy::work(int i)
 760 {
 761   ResourceMark rm;
 762   HandleMark hm;
 763   ParScanThreadState& par_scan_state = _state_set.thread_state(i);
 764   par_scan_state.set_young_old_boundary(_young_old_boundary);
 765   _task.work(i, par_scan_state.is_alive_closure(),
 766              par_scan_state.keep_alive_closure(),
 767              par_scan_state.evacuate_followers_closure());
 768 }
 769 
 770 class ParNewRefEnqueueTaskProxy: public AbstractGangTask {
 771   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
 772   EnqueueTask& _task;
 773 
 774 public:
 775   ParNewRefEnqueueTaskProxy(EnqueueTask& task)
 776     : AbstractGangTask("ParNewGeneration parallel reference enqueue"),
 777       _task(task)
 778   { }
 779 
 780   virtual void work(int i)
 781   {
 782     _task.work(i);
 783   }
 784 };
 785 
 786 
 787 void ParNewRefProcTaskExecutor::execute(ProcessTask& task)
 788 {
 789   GenCollectedHeap* gch = GenCollectedHeap::heap();
 790   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
 791          "not a generational heap");
 792   WorkGang* workers = gch->workers();
 793   assert(workers != NULL, "Need parallel worker threads.");
 794   ParNewRefProcTaskProxy rp_task(task, _generation, *_generation.next_gen(),
 795                                  _generation.reserved().end(), _state_set);
 796   workers->run_task(&rp_task);
 797   _state_set.reset(_generation.promotion_failed());
 798 }
 799 
 800 void ParNewRefProcTaskExecutor::execute(EnqueueTask& task)
 801 {
 802   GenCollectedHeap* gch = GenCollectedHeap::heap();
 803   WorkGang* workers = gch->workers();
 804   assert(workers != NULL, "Need parallel worker threads.");
 805   ParNewRefEnqueueTaskProxy enq_task(task);
 806   workers->run_task(&enq_task);
 807 }
 808 
 809 void ParNewRefProcTaskExecutor::set_single_threaded_mode()
 810 {
 811   _state_set.flush();
 812   GenCollectedHeap* gch = GenCollectedHeap::heap();
 813   gch->set_par_threads(0);  // 0 ==> non-parallel.
 814   gch->save_marks();
 815 }
 816 
 817 ScanClosureWithParBarrier::
 818 ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) :
 819   ScanClosure(g, gc_barrier) {}
 820 
 821 EvacuateFollowersClosureGeneral::
 822 EvacuateFollowersClosureGeneral(GenCollectedHeap* gch, int level,
 823                                 OopsInGenClosure* cur,
 824                                 OopsInGenClosure* older) :
 825   _gch(gch), _level(level),
 826   _scan_cur_or_nonheap(cur), _scan_older(older)
 827 {}
 828 
 829 void EvacuateFollowersClosureGeneral::do_void() {
 830   do {
 831     // Beware: this call will lead to closure applications via virtual
 832     // calls.
 833     _gch->oop_since_save_marks_iterate(_level,
 834                                        _scan_cur_or_nonheap,
 835                                        _scan_older);
 836   } while (!_gch->no_allocs_since_save_marks(_level));
 837 }
 838 
 839 
 840 bool ParNewGeneration::_avoid_promotion_undo = false;
 841 
 842 void ParNewGeneration::adjust_desired_tenuring_threshold() {
 843   // Set the desired survivor size to half the real survivor space
 844   _tenuring_threshold =
 845     age_table()->compute_tenuring_threshold(to()->capacity()/HeapWordSize);
 846 }
 847 
 848 // A Generation that does parallel young-gen collection.
 849 
 850 void ParNewGeneration::collect(bool   full,
 851                                bool   clear_all_soft_refs,
 852                                size_t size,
 853                                bool   is_tlab) {
 854   assert(full || size > 0, "otherwise we don't want to collect");
 855   GenCollectedHeap* gch = GenCollectedHeap::heap();
 856   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
 857     "not a CMS generational heap");
 858   AdaptiveSizePolicy* size_policy = gch->gen_policy()->size_policy();
 859   WorkGang* workers = gch->workers();
 860   _next_gen = gch->next_gen(this);
 861   assert(_next_gen != NULL,
 862     "This must be the youngest gen, and not the only gen");
 863   assert(gch->n_gens() == 2,
 864          "Par collection currently only works with single older gen.");
 865   // Do we have to avoid promotion_undo?
 866   if (gch->collector_policy()->is_concurrent_mark_sweep_policy()) {
 867     set_avoid_promotion_undo(true);
 868   }
 869 
 870   // If the next generation is too full to accomodate worst-case promotion
 871   // from this generation, pass on collection; let the next generation
 872   // do it.
 873   if (!collection_attempt_is_safe()) {
 874     gch->set_incremental_collection_failed();  // slight lie, in that we did not even attempt one
 875     return;
 876   }
 877   assert(to()->is_empty(), "Else not collection_attempt_is_safe");
 878 
 879   init_assuming_no_promotion_failure();
 880 
 881   if (UseAdaptiveSizePolicy) {
 882     set_survivor_overflow(false);
 883     size_policy->minor_collection_begin();
 884   }
 885 
 886   TraceTime t1("GC", PrintGC && !PrintGCDetails, true, gclog_or_tty);
 887   // Capture heap used before collection (for printing).
 888   size_t gch_prev_used = gch->used();
 889 
 890   SpecializationStats::clear();
 891 
 892   age_table()->clear();
 893   to()->clear(SpaceDecorator::Mangle);
 894 
 895   gch->save_marks();
 896   assert(workers != NULL, "Need parallel worker threads.");
 897   ParallelTaskTerminator _term(workers->total_workers(), task_queues());
 898   ParScanThreadStateSet thread_state_set(workers->total_workers(),
 899                                          *to(), *this, *_next_gen, *task_queues(),
 900                                          _overflow_stacks, desired_plab_sz(), _term);
 901 
 902   ParNewGenTask tsk(this, _next_gen, reserved().end(), &thread_state_set);
 903   int n_workers = workers->total_workers();
 904   gch->set_par_threads(n_workers);
 905   gch->rem_set()->prepare_for_younger_refs_iterate(true);
 906   // It turns out that even when we're using 1 thread, doing the work in a
 907   // separate thread causes wide variance in run times.  We can't help this
 908   // in the multi-threaded case, but we special-case n=1 here to get
 909   // repeatable measurements of the 1-thread overhead of the parallel code.
 910   if (n_workers > 1) {
 911     GenCollectedHeap::StrongRootsScope srs(gch);
 912     workers->run_task(&tsk);
 913   } else {
 914     GenCollectedHeap::StrongRootsScope srs(gch);
 915     tsk.work(0);
 916   }
 917   thread_state_set.reset(promotion_failed());
 918 
 919   // Process (weak) reference objects found during scavenge.
 920   ReferenceProcessor* rp = ref_processor();
 921   IsAliveClosure is_alive(this);
 922   ScanWeakRefClosure scan_weak_ref(this);
 923   KeepAliveClosure keep_alive(&scan_weak_ref);
 924   ScanClosure               scan_without_gc_barrier(this, false);
 925   ScanClosureWithParBarrier scan_with_gc_barrier(this, true);
 926   set_promo_failure_scan_stack_closure(&scan_without_gc_barrier);
 927   EvacuateFollowersClosureGeneral evacuate_followers(gch, _level,
 928     &scan_without_gc_barrier, &scan_with_gc_barrier);
 929   rp->setup_policy(clear_all_soft_refs);
 930   if (rp->processing_is_mt()) {
 931     ParNewRefProcTaskExecutor task_executor(*this, thread_state_set);
 932     rp->process_discovered_references(&is_alive, &keep_alive,
 933                                       &evacuate_followers, &task_executor);
 934   } else {
 935     thread_state_set.flush();
 936     gch->set_par_threads(0);  // 0 ==> non-parallel.
 937     gch->save_marks();
 938     rp->process_discovered_references(&is_alive, &keep_alive,
 939                                       &evacuate_followers, NULL);
 940   }
 941   if (!promotion_failed()) {
 942     // Swap the survivor spaces.
 943     eden()->clear(SpaceDecorator::Mangle);
 944     from()->clear(SpaceDecorator::Mangle);
 945     if (ZapUnusedHeapArea) {
 946       // This is now done here because of the piece-meal mangling which
 947       // can check for valid mangling at intermediate points in the
 948       // collection(s).  When a minor collection fails to collect
 949       // sufficient space resizing of the young generation can occur
 950       // an redistribute the spaces in the young generation.  Mangle
 951       // here so that unzapped regions don't get distributed to
 952       // other spaces.
 953       to()->mangle_unused_area();
 954     }
 955     swap_spaces();
 956 
 957     // A successful scavenge should restart the GC time limit count which is
 958     // for full GC's.
 959     size_policy->reset_gc_overhead_limit_count();
 960 
 961     assert(to()->is_empty(), "to space should be empty now");
 962   } else {
 963     assert(_promo_failure_scan_stack.is_empty(), "post condition");
 964     _promo_failure_scan_stack.clear(true); // Clear cached segments.
 965 
 966     remove_forwarding_pointers();
 967     if (PrintGCDetails) {
 968       gclog_or_tty->print(" (promotion failed)");
 969     }
 970     // All the spaces are in play for mark-sweep.
 971     swap_spaces();  // Make life simpler for CMS || rescan; see 6483690.
 972     from()->set_next_compaction_space(to());
 973     gch->set_incremental_collection_failed();
 974     // Inform the next generation that a promotion failure occurred.
 975     _next_gen->promotion_failure_occurred();
 976 
 977     // Reset the PromotionFailureALot counters.
 978     NOT_PRODUCT(Universe::heap()->reset_promotion_should_fail();)
 979   }
 980   // set new iteration safe limit for the survivor spaces
 981   from()->set_concurrent_iteration_safe_limit(from()->top());
 982   to()->set_concurrent_iteration_safe_limit(to()->top());
 983 
 984   adjust_desired_tenuring_threshold();
 985   if (ResizePLAB) {
 986     plab_stats()->adjust_desired_plab_sz();
 987   }
 988 
 989   if (PrintGC && !PrintGCDetails) {
 990     gch->print_heap_change(gch_prev_used);
 991   }
 992 
 993   if (PrintGCDetails && ParallelGCVerbose) {
 994     TASKQUEUE_STATS_ONLY(thread_state_set.print_termination_stats());
 995     TASKQUEUE_STATS_ONLY(thread_state_set.print_taskqueue_stats());
 996   }
 997 
 998   if (UseAdaptiveSizePolicy) {
 999     size_policy->minor_collection_end(gch->gc_cause());
1000     size_policy->avg_survived()->sample(from()->used());
1001   }
1002 
1003   update_time_of_last_gc(os::javaTimeMillis());
1004 
1005   SpecializationStats::print();
1006 
1007   rp->set_enqueuing_is_done(true);
1008   if (rp->processing_is_mt()) {
1009     ParNewRefProcTaskExecutor task_executor(*this, thread_state_set);
1010     rp->enqueue_discovered_references(&task_executor);
1011   } else {
1012     rp->enqueue_discovered_references(NULL);
1013   }
1014   rp->verify_no_references_recorded();
1015 }
1016 
1017 static int sum;
1018 void ParNewGeneration::waste_some_time() {
1019   for (int i = 0; i < 100; i++) {
1020     sum += i;
1021   }
1022 }
1023 
1024 static const oop ClaimedForwardPtr = oop(0x4);
1025 
1026 // Because of concurrency, there are times where an object for which
1027 // "is_forwarded()" is true contains an "interim" forwarding pointer
1028 // value.  Such a value will soon be overwritten with a real value.
1029 // This method requires "obj" to have a forwarding pointer, and waits, if
1030 // necessary for a real one to be inserted, and returns it.
1031 
1032 oop ParNewGeneration::real_forwardee(oop obj) {
1033   oop forward_ptr = obj->forwardee();
1034   if (forward_ptr != ClaimedForwardPtr) {
1035     return forward_ptr;
1036   } else {
1037     return real_forwardee_slow(obj);
1038   }
1039 }
1040 
1041 oop ParNewGeneration::real_forwardee_slow(oop obj) {
1042   // Spin-read if it is claimed but not yet written by another thread.
1043   oop forward_ptr = obj->forwardee();
1044   while (forward_ptr == ClaimedForwardPtr) {
1045     waste_some_time();
1046     assert(obj->is_forwarded(), "precondition");
1047     forward_ptr = obj->forwardee();
1048   }
1049   return forward_ptr;
1050 }
1051 
1052 #ifdef ASSERT
1053 bool ParNewGeneration::is_legal_forward_ptr(oop p) {
1054   return
1055     (_avoid_promotion_undo && p == ClaimedForwardPtr)
1056     || Universe::heap()->is_in_reserved(p);
1057 }
1058 #endif
1059 
1060 void ParNewGeneration::preserve_mark_if_necessary(oop obj, markOop m) {
1061   if (m->must_be_preserved_for_promotion_failure(obj)) {
1062     // We should really have separate per-worker stacks, rather
1063     // than use locking of a common pair of stacks.
1064     MutexLocker ml(ParGCRareEvent_lock);
1065     preserve_mark(obj, m);
1066   }
1067 }
1068 
1069 // Multiple GC threads may try to promote an object.  If the object
1070 // is successfully promoted, a forwarding pointer will be installed in
1071 // the object in the young generation.  This method claims the right
1072 // to install the forwarding pointer before it copies the object,
1073 // thus avoiding the need to undo the copy as in
1074 // copy_to_survivor_space_avoiding_with_undo.
1075 
1076 oop ParNewGeneration::copy_to_survivor_space_avoiding_promotion_undo(
1077         ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) {
1078   // In the sequential version, this assert also says that the object is
1079   // not forwarded.  That might not be the case here.  It is the case that
1080   // the caller observed it to be not forwarded at some time in the past.
1081   assert(is_in_reserved(old), "shouldn't be scavenging this oop");
1082 
1083   // The sequential code read "old->age()" below.  That doesn't work here,
1084   // since the age is in the mark word, and that might be overwritten with
1085   // a forwarding pointer by a parallel thread.  So we must save the mark
1086   // word in a local and then analyze it.
1087   oopDesc dummyOld;
1088   dummyOld.set_mark(m);
1089   assert(!dummyOld.is_forwarded(),
1090          "should not be called with forwarding pointer mark word.");
1091 
1092   oop new_obj = NULL;
1093   oop forward_ptr;
1094 
1095   // Try allocating obj in to-space (unless too old)
1096   if (dummyOld.age() < tenuring_threshold()) {
1097     new_obj = (oop)par_scan_state->alloc_in_to_space(sz);
1098     if (new_obj == NULL) {
1099       set_survivor_overflow(true);
1100     }
1101   }
1102 
1103   if (new_obj == NULL) {
1104     // Either to-space is full or we decided to promote
1105     // try allocating obj tenured
1106 
1107     // Attempt to install a null forwarding pointer (atomically),
1108     // to claim the right to install the real forwarding pointer.
1109     forward_ptr = old->forward_to_atomic(ClaimedForwardPtr);
1110     if (forward_ptr != NULL) {
1111       // someone else beat us to it.
1112         return real_forwardee(old);
1113     }
1114 
1115     new_obj = _next_gen->par_promote(par_scan_state->thread_num(),
1116                                        old, m, sz);
1117 
1118     if (new_obj == NULL) {
1119       // promotion failed, forward to self
1120       _promotion_failed = true;
1121       new_obj = old;
1122 
1123       preserve_mark_if_necessary(old, m);
1124       // Log the size of the maiden promotion failure
1125       par_scan_state->log_promotion_failure(sz);
1126     }
1127 
1128     old->forward_to(new_obj);
1129     forward_ptr = NULL;
1130   } else {
1131     // Is in to-space; do copying ourselves.
1132     Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz);
1133     forward_ptr = old->forward_to_atomic(new_obj);
1134     // Restore the mark word copied above.
1135     new_obj->set_mark(m);
1136     // Increment age if obj still in new generation
1137     new_obj->incr_age();
1138     par_scan_state->age_table()->add(new_obj, sz);
1139   }
1140   assert(new_obj != NULL, "just checking");
1141 
1142   if (forward_ptr == NULL) {
1143     oop obj_to_push = new_obj;
1144     if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) {
1145       // Length field used as index of next element to be scanned.
1146       // Real length can be obtained from real_forwardee()
1147       arrayOop(old)->set_length(0);
1148       obj_to_push = old;
1149       assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push,
1150              "push forwarded object");
1151     }
1152     // Push it on one of the queues of to-be-scanned objects.
1153     bool simulate_overflow = false;
1154     NOT_PRODUCT(
1155       if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) {
1156         // simulate a stack overflow
1157         simulate_overflow = true;
1158       }
1159     )
1160     if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) {
1161       // Add stats for overflow pushes.
1162       if (Verbose && PrintGCDetails) {
1163         gclog_or_tty->print("queue overflow!\n");
1164       }
1165       push_on_overflow_list(old, par_scan_state);
1166       TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0));
1167     }
1168 
1169     return new_obj;
1170   }
1171 
1172   // Oops.  Someone beat us to it.  Undo the allocation.  Where did we
1173   // allocate it?
1174   if (is_in_reserved(new_obj)) {
1175     // Must be in to_space.
1176     assert(to()->is_in_reserved(new_obj), "Checking");
1177     if (forward_ptr == ClaimedForwardPtr) {
1178       // Wait to get the real forwarding pointer value.
1179       forward_ptr = real_forwardee(old);
1180     }
1181     par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz);
1182   }
1183 
1184   return forward_ptr;
1185 }
1186 
1187 
1188 // Multiple GC threads may try to promote the same object.  If two
1189 // or more GC threads copy the object, only one wins the race to install
1190 // the forwarding pointer.  The other threads have to undo their copy.
1191 
1192 oop ParNewGeneration::copy_to_survivor_space_with_undo(
1193         ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) {
1194 
1195   // In the sequential version, this assert also says that the object is
1196   // not forwarded.  That might not be the case here.  It is the case that
1197   // the caller observed it to be not forwarded at some time in the past.
1198   assert(is_in_reserved(old), "shouldn't be scavenging this oop");
1199 
1200   // The sequential code read "old->age()" below.  That doesn't work here,
1201   // since the age is in the mark word, and that might be overwritten with
1202   // a forwarding pointer by a parallel thread.  So we must save the mark
1203   // word here, install it in a local oopDesc, and then analyze it.
1204   oopDesc dummyOld;
1205   dummyOld.set_mark(m);
1206   assert(!dummyOld.is_forwarded(),
1207          "should not be called with forwarding pointer mark word.");
1208 
1209   bool failed_to_promote = false;
1210   oop new_obj = NULL;
1211   oop forward_ptr;
1212 
1213   // Try allocating obj in to-space (unless too old)
1214   if (dummyOld.age() < tenuring_threshold()) {
1215     new_obj = (oop)par_scan_state->alloc_in_to_space(sz);
1216     if (new_obj == NULL) {
1217       set_survivor_overflow(true);
1218     }
1219   }
1220 
1221   if (new_obj == NULL) {
1222     // Either to-space is full or we decided to promote
1223     // try allocating obj tenured
1224     new_obj = _next_gen->par_promote(par_scan_state->thread_num(),
1225                                        old, m, sz);
1226 
1227     if (new_obj == NULL) {
1228       // promotion failed, forward to self
1229       forward_ptr = old->forward_to_atomic(old);
1230       new_obj = old;
1231 
1232       if (forward_ptr != NULL) {
1233         return forward_ptr;   // someone else succeeded
1234       }
1235 
1236       _promotion_failed = true;
1237       failed_to_promote = true;
1238 
1239       preserve_mark_if_necessary(old, m);
1240       // Log the size of the maiden promotion failure
1241       par_scan_state->log_promotion_failure(sz);
1242     }
1243   } else {
1244     // Is in to-space; do copying ourselves.
1245     Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz);
1246     // Restore the mark word copied above.
1247     new_obj->set_mark(m);
1248     // Increment age if new_obj still in new generation
1249     new_obj->incr_age();
1250     par_scan_state->age_table()->add(new_obj, sz);
1251   }
1252   assert(new_obj != NULL, "just checking");
1253 
1254   // Now attempt to install the forwarding pointer (atomically).
1255   // We have to copy the mark word before overwriting with forwarding
1256   // ptr, so we can restore it below in the copy.
1257   if (!failed_to_promote) {
1258     forward_ptr = old->forward_to_atomic(new_obj);
1259   }
1260 
1261   if (forward_ptr == NULL) {
1262     oop obj_to_push = new_obj;
1263     if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) {
1264       // Length field used as index of next element to be scanned.
1265       // Real length can be obtained from real_forwardee()
1266       arrayOop(old)->set_length(0);
1267       obj_to_push = old;
1268       assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push,
1269              "push forwarded object");
1270     }
1271     // Push it on one of the queues of to-be-scanned objects.
1272     bool simulate_overflow = false;
1273     NOT_PRODUCT(
1274       if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) {
1275         // simulate a stack overflow
1276         simulate_overflow = true;
1277       }
1278     )
1279     if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) {
1280       // Add stats for overflow pushes.
1281       push_on_overflow_list(old, par_scan_state);
1282       TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0));
1283     }
1284 
1285     return new_obj;
1286   }
1287 
1288   // Oops.  Someone beat us to it.  Undo the allocation.  Where did we
1289   // allocate it?
1290   if (is_in_reserved(new_obj)) {
1291     // Must be in to_space.
1292     assert(to()->is_in_reserved(new_obj), "Checking");
1293     par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz);
1294   } else {
1295     assert(!_avoid_promotion_undo, "Should not be here if avoiding.");
1296     _next_gen->par_promote_alloc_undo(par_scan_state->thread_num(),
1297                                       (HeapWord*)new_obj, sz);
1298   }
1299 
1300   return forward_ptr;
1301 }
1302 
1303 #ifndef PRODUCT
1304 // It's OK to call this multi-threaded;  the worst thing
1305 // that can happen is that we'll get a bunch of closely
1306 // spaced simulated oveflows, but that's OK, in fact
1307 // probably good as it would exercise the overflow code
1308 // under contention.
1309 bool ParNewGeneration::should_simulate_overflow() {
1310   if (_overflow_counter-- <= 0) { // just being defensive
1311     _overflow_counter = ParGCWorkQueueOverflowInterval;
1312     return true;
1313   } else {
1314     return false;
1315   }
1316 }
1317 #endif
1318 
1319 // In case we are using compressed oops, we need to be careful.
1320 // If the object being pushed is an object array, then its length
1321 // field keeps track of the "grey boundary" at which the next
1322 // incremental scan will be done (see ParGCArrayScanChunk).
1323 // When using compressed oops, this length field is kept in the
1324 // lower 32 bits of the erstwhile klass word and cannot be used
1325 // for the overflow chaining pointer (OCP below). As such the OCP
1326 // would itself need to be compressed into the top 32-bits in this
1327 // case. Unfortunately, see below, in the event that we have a
1328 // promotion failure, the node to be pushed on the list can be
1329 // outside of the Java heap, so the heap-based pointer compression
1330 // would not work (we would have potential aliasing between C-heap
1331 // and Java-heap pointers). For this reason, when using compressed
1332 // oops, we simply use a worker-thread-local, non-shared overflow
1333 // list in the form of a growable array, with a slightly different
1334 // overflow stack draining strategy. If/when we start using fat
1335 // stacks here, we can go back to using (fat) pointer chains
1336 // (although some performance comparisons would be useful since
1337 // single global lists have their own performance disadvantages
1338 // as we were made painfully aware not long ago, see 6786503).
1339 #define BUSY (oop(0x1aff1aff))
1340 void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) {
1341   assert(is_in_reserved(from_space_obj), "Should be from this generation");
1342   if (ParGCUseLocalOverflow) {
1343     // In the case of compressed oops, we use a private, not-shared
1344     // overflow stack.
1345     par_scan_state->push_on_overflow_stack(from_space_obj);
1346   } else {
1347     assert(!UseCompressedOops, "Error");
1348     // if the object has been forwarded to itself, then we cannot
1349     // use the klass pointer for the linked list.  Instead we have
1350     // to allocate an oopDesc in the C-Heap and use that for the linked list.
1351     // XXX This is horribly inefficient when a promotion failure occurs
1352     // and should be fixed. XXX FIX ME !!!
1353 #ifndef PRODUCT
1354     Atomic::inc_ptr(&_num_par_pushes);
1355     assert(_num_par_pushes > 0, "Tautology");
1356 #endif
1357     if (from_space_obj->forwardee() == from_space_obj) {
1358       oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1);
1359       listhead->forward_to(from_space_obj);
1360       from_space_obj = listhead;
1361     }
1362     oop observed_overflow_list = _overflow_list;
1363     oop cur_overflow_list;
1364     do {
1365       cur_overflow_list = observed_overflow_list;
1366       if (cur_overflow_list != BUSY) {
1367         from_space_obj->set_klass_to_list_ptr(cur_overflow_list);
1368       } else {
1369         from_space_obj->set_klass_to_list_ptr(NULL);
1370       }
1371       observed_overflow_list =
1372         (oop)Atomic::cmpxchg_ptr(from_space_obj, &_overflow_list, cur_overflow_list);
1373     } while (cur_overflow_list != observed_overflow_list);
1374   }
1375 }
1376 
1377 bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) {
1378   bool res;
1379 
1380   if (ParGCUseLocalOverflow) {
1381     res = par_scan_state->take_from_overflow_stack();
1382   } else {
1383     assert(!UseCompressedOops, "Error");
1384     res = take_from_overflow_list_work(par_scan_state);
1385   }
1386   return res;
1387 }
1388 
1389 
1390 // *NOTE*: The overflow list manipulation code here and
1391 // in CMSCollector:: are very similar in shape,
1392 // except that in the CMS case we thread the objects
1393 // directly into the list via their mark word, and do
1394 // not need to deal with special cases below related
1395 // to chunking of object arrays and promotion failure
1396 // handling.
1397 // CR 6797058 has been filed to attempt consolidation of
1398 // the common code.
1399 // Because of the common code, if you make any changes in
1400 // the code below, please check the CMS version to see if
1401 // similar changes might be needed.
1402 // See CMSCollector::par_take_from_overflow_list() for
1403 // more extensive documentation comments.
1404 bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) {
1405   ObjToScanQueue* work_q = par_scan_state->work_queue();
1406   // How many to take?
1407   size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
1408                                  (size_t)ParGCDesiredObjsFromOverflowList);
1409 
1410   assert(!UseCompressedOops, "Error");
1411   assert(par_scan_state->overflow_stack() == NULL, "Error");
1412   if (_overflow_list == NULL) return false;
1413 
1414   // Otherwise, there was something there; try claiming the list.
1415   oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
1416   // Trim off a prefix of at most objsFromOverflow items
1417   Thread* tid = Thread::current();
1418   size_t spin_count = (size_t)ParallelGCThreads;
1419   size_t sleep_time_millis = MAX2((size_t)1, objsFromOverflow/100);
1420   for (size_t spin = 0; prefix == BUSY && spin < spin_count; spin++) {
1421     // someone grabbed it before we did ...
1422     // ... we spin for a short while...
1423     os::sleep(tid, sleep_time_millis, false);
1424     if (_overflow_list == NULL) {
1425       // nothing left to take
1426       return false;
1427     } else if (_overflow_list != BUSY) {
1428      // try and grab the prefix
1429      prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
1430     }
1431   }
1432   if (prefix == NULL || prefix == BUSY) {
1433      // Nothing to take or waited long enough
1434      if (prefix == NULL) {
1435        // Write back the NULL in case we overwrote it with BUSY above
1436        // and it is still the same value.
1437        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
1438      }
1439      return false;
1440   }
1441   assert(prefix != NULL && prefix != BUSY, "Error");
1442   size_t i = 1;
1443   oop cur = prefix;
1444   while (i < objsFromOverflow && cur->klass_or_null() != NULL) {
1445     i++; cur = oop(cur->klass());
1446   }
1447 
1448   // Reattach remaining (suffix) to overflow list
1449   if (cur->klass_or_null() == NULL) {
1450     // Write back the NULL in lieu of the BUSY we wrote
1451     // above and it is still the same value.
1452     if (_overflow_list == BUSY) {
1453       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
1454     }
1455   } else {
1456     assert(cur->klass_or_null() != BUSY, "Error");
1457     oop suffix = oop(cur->klass());       // suffix will be put back on global list
1458     cur->set_klass_to_list_ptr(NULL);     // break off suffix
1459     // It's possible that the list is still in the empty(busy) state
1460     // we left it in a short while ago; in that case we may be
1461     // able to place back the suffix.
1462     oop observed_overflow_list = _overflow_list;
1463     oop cur_overflow_list = observed_overflow_list;
1464     bool attached = false;
1465     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
1466       observed_overflow_list =
1467         (oop) Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);
1468       if (cur_overflow_list == observed_overflow_list) {
1469         attached = true;
1470         break;
1471       } else cur_overflow_list = observed_overflow_list;
1472     }
1473     if (!attached) {
1474       // Too bad, someone else got in in between; we'll need to do a splice.
1475       // Find the last item of suffix list
1476       oop last = suffix;
1477       while (last->klass_or_null() != NULL) {
1478         last = oop(last->klass());
1479       }
1480       // Atomically prepend suffix to current overflow list
1481       observed_overflow_list = _overflow_list;
1482       do {
1483         cur_overflow_list = observed_overflow_list;
1484         if (cur_overflow_list != BUSY) {
1485           // Do the splice ...
1486           last->set_klass_to_list_ptr(cur_overflow_list);
1487         } else { // cur_overflow_list == BUSY
1488           last->set_klass_to_list_ptr(NULL);
1489         }
1490         observed_overflow_list =
1491           (oop)Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);
1492       } while (cur_overflow_list != observed_overflow_list);
1493     }
1494   }
1495 
1496   // Push objects on prefix list onto this thread's work queue
1497   assert(prefix != NULL && prefix != BUSY, "program logic");
1498   cur = prefix;
1499   ssize_t n = 0;
1500   while (cur != NULL) {
1501     oop obj_to_push = cur->forwardee();
1502     oop next        = oop(cur->klass_or_null());
1503     cur->set_klass(obj_to_push->klass());
1504     // This may be an array object that is self-forwarded. In that case, the list pointer
1505     // space, cur, is not in the Java heap, but rather in the C-heap and should be freed.
1506     if (!is_in_reserved(cur)) {
1507       // This can become a scaling bottleneck when there is work queue overflow coincident
1508       // with promotion failure.
1509       oopDesc* f = cur;
1510       FREE_C_HEAP_ARRAY(oopDesc, f);
1511     } else if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) {
1512       assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");
1513       obj_to_push = cur;
1514     }
1515     bool ok = work_q->push(obj_to_push);
1516     assert(ok, "Should have succeeded");
1517     cur = next;
1518     n++;
1519   }
1520   TASKQUEUE_STATS_ONLY(par_scan_state->note_overflow_refill(n));
1521 #ifndef PRODUCT
1522   assert(_num_par_pushes >= n, "Too many pops?");
1523   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
1524 #endif
1525   return true;
1526 }
1527 #undef BUSY
1528 
1529 void ParNewGeneration::ref_processor_init()
1530 {
1531   if (_ref_processor == NULL) {
1532     // Allocate and initialize a reference processor
1533     _ref_processor =
1534       new ReferenceProcessor(_reserved,                  // span
1535                              ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing
1536                              ParallelGCThreads,          // mt processing degree
1537                              refs_discovery_is_mt(),     // mt discovery
1538                              ParallelGCThreads,          // mt discovery degree
1539                              refs_discovery_is_atomic(), // atomic_discovery
1540                              NULL,                       // is_alive_non_header
1541                              false);                     // write barrier for next field updates
1542   }
1543 }
1544 
1545 const char* ParNewGeneration::name() const {
1546   return "par new generation";
1547 }
1548 
1549 bool ParNewGeneration::in_use() {
1550   return UseParNewGC && ParallelGCThreads > 0;
1551 }