1 /*

     2  * Copyright (c) 2001, 2019, 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 "classfile/stringTable.hpp"

    27 #include "gc/cms/cmsHeap.inline.hpp"

    28 #include "gc/cms/compactibleFreeListSpace.hpp"

    29 #include "gc/cms/concurrentMarkSweepGeneration.hpp"

    30 #include "gc/cms/parNewGeneration.inline.hpp"

    31 #include "gc/cms/parOopClosures.inline.hpp"

    32 #include "gc/serial/defNewGeneration.inline.hpp"

    33 #include "gc/shared/adaptiveSizePolicy.hpp"

    34 #include "gc/shared/ageTable.inline.hpp"

    35 #include "gc/shared/copyFailedInfo.hpp"

    36 #include "gc/shared/gcHeapSummary.hpp"

    37 #include "gc/shared/gcTimer.hpp"

    38 #include "gc/shared/gcTrace.hpp"

    39 #include "gc/shared/gcTraceTime.inline.hpp"

    40 #include "gc/shared/genOopClosures.inline.hpp"

    41 #include "gc/shared/generation.hpp"

    42 #include "gc/shared/plab.inline.hpp"

    43 #include "gc/shared/preservedMarks.inline.hpp"

    44 #include "gc/shared/referencePolicy.hpp"

    45 #include "gc/shared/referenceProcessorPhaseTimes.hpp"

    46 #include "gc/shared/space.hpp"

    47 #include "gc/shared/spaceDecorator.inline.hpp"

    48 #include "gc/shared/strongRootsScope.hpp"

    49 #include "gc/shared/taskqueue.inline.hpp"

    50 #include "gc/shared/weakProcessor.hpp"

    51 #include "gc/shared/workgroup.hpp"

    52 #include "gc/shared/workerPolicy.hpp"

    53 #include "logging/log.hpp"

    54 #include "logging/logStream.hpp"

    55 #include "memory/iterator.inline.hpp"

    56 #include "memory/resourceArea.hpp"

    57 #include "oops/access.inline.hpp"

    58 #include "oops/compressedOops.inline.hpp"

    59 #include "oops/objArrayOop.hpp"

    60 #include "oops/oop.inline.hpp"

    61 #include "runtime/atomic.hpp"

    62 #include "runtime/handles.inline.hpp"

    63 #include "runtime/java.hpp"

    64 #include "runtime/thread.inline.hpp"

    65 #include "utilities/copy.hpp"

    66 #include "utilities/globalDefinitions.hpp"

    67 #include "utilities/stack.inline.hpp"

    68 

    69 ParScanThreadState::ParScanThreadState(Space* to_space_,

    70                                        ParNewGeneration* young_gen_,

    71                                        Generation* old_gen_,

    72                                        int thread_num_,

    73                                        ObjToScanQueueSet* work_queue_set_,

    74                                        Stack<oop, mtGC>* overflow_stacks_,

    75                                        PreservedMarks* preserved_marks_,

    76                                        size_t desired_plab_sz_,

    77                                        TaskTerminator& term_) :

    78   _work_queue(work_queue_set_->queue(thread_num_)),

    79   _overflow_stack(overflow_stacks_ ? overflow_stacks_ + thread_num_ : NULL),

    80   _preserved_marks(preserved_marks_),

    81   _to_space_alloc_buffer(desired_plab_sz_),

    82   _to_space_closure(young_gen_, this),

    83   _old_gen_closure(young_gen_, this),

    84   _to_space_root_closure(young_gen_, this),

    85   _older_gen_closure(young_gen_, this),

    86   _old_gen_root_closure(young_gen_, this),

    87   _evacuate_followers(this, &_to_space_closure, &_old_gen_closure,

    88                       &_to_space_root_closure, young_gen_, &_old_gen_root_closure,

    89                       work_queue_set_, term_.terminator()),

    90   _is_alive_closure(young_gen_),

    91   _scan_weak_ref_closure(young_gen_, this),

    92   _keep_alive_closure(&_scan_weak_ref_closure),

    93   _to_space(to_space_),

    94   _young_gen(young_gen_),

    95   _old_gen(old_gen_),

    96   _young_old_boundary(NULL),

    97   _thread_num(thread_num_),

    98   _ageTable(false), // false ==> not the global age table, no perf data.

    99   _to_space_full(false),

   100   _strong_roots_time(0.0),

   101   _term_time(0.0)

   102 {

   103   #if TASKQUEUE_STATS

   104   _term_attempts = 0;

   105   _overflow_refills = 0;

   106   _overflow_refill_objs = 0;

   107   #endif // TASKQUEUE_STATS

   108 

   109   _survivor_chunk_array = (ChunkArray*) old_gen()->get_data_recorder(thread_num());

   110   _start = os::elapsedTime();

   111   _old_gen_closure.set_generation(old_gen_);

   112   _old_gen_root_closure.set_generation(old_gen_);

   113 }

   114 

   115 void ParScanThreadState::record_survivor_plab(HeapWord* plab_start,

   116                                               size_t plab_word_size) {

   117   ChunkArray* sca = survivor_chunk_array();

   118   if (sca != NULL) {

   119     // A non-null SCA implies that we want the PLAB data recorded.

   120     sca->record_sample(plab_start, plab_word_size);

   121   }

   122 }

   123 

   124 bool ParScanThreadState::should_be_partially_scanned(oop new_obj, oop old_obj) const {

   125   return new_obj->is_objArray() &&

   126          arrayOop(new_obj)->length() > ParGCArrayScanChunk &&

   127          new_obj != old_obj;

   128 }

   129 

   130 void ParScanThreadState::scan_partial_array_and_push_remainder(oop old) {

   131   assert(old->is_objArray(), "must be obj array");

   132   assert(old->is_forwarded(), "must be forwarded");

   133   assert(CMSHeap::heap()->is_in_reserved(old), "must be in heap.");

   134   assert(!old_gen()->is_in(old), "must be in young generation.");

   135 

   136   objArrayOop obj = objArrayOop(old->forwardee());

   137   // Process ParGCArrayScanChunk elements now

   138   // and push the remainder back onto queue

   139   int start     = arrayOop(old)->length();

   140   int end       = obj->length();

   141   int remainder = end - start;

   142   assert(start <= end, "just checking");

   143   if (remainder > 2 * ParGCArrayScanChunk) {

   144     // Test above combines last partial chunk with a full chunk

   145     end = start + ParGCArrayScanChunk;

   146     arrayOop(old)->set_length(end);

   147     // Push remainder.

   148     bool ok = work_queue()->push(old);

   149     assert(ok, "just popped, push must be okay");

   150   } else {

   151     // Restore length so that it can be used if there

   152     // is a promotion failure and forwarding pointers

   153     // must be removed.

   154     arrayOop(old)->set_length(end);

   155   }

   156 

   157   // process our set of indices (include header in first chunk)

   158   // should make sure end is even (aligned to HeapWord in case of compressed oops)

   159   if ((HeapWord *)obj < young_old_boundary()) {

   160     // object is in to_space

   161     obj->oop_iterate_range(&_to_space_closure, start, end);

   162   } else {

   163     // object is in old generation

   164     obj->oop_iterate_range(&_old_gen_closure, start, end);

   165   }

   166 }

   167 

   168 void ParScanThreadState::trim_queues(int max_size) {

   169   ObjToScanQueue* queue = work_queue();

   170   do {

   171     while (queue->size() > (juint)max_size) {

   172       oop obj_to_scan;

   173       if (queue->pop_local(obj_to_scan)) {

   174         if ((HeapWord *)obj_to_scan < young_old_boundary()) {

   175           if (obj_to_scan->is_objArray() &&

   176               obj_to_scan->is_forwarded() &&

   177               obj_to_scan->forwardee() != obj_to_scan) {

   178             scan_partial_array_and_push_remainder(obj_to_scan);

   179           } else {

   180             // object is in to_space

   181             obj_to_scan->oop_iterate(&_to_space_closure);

   182           }

   183         } else {

   184           // object is in old generation

   185           obj_to_scan->oop_iterate(&_old_gen_closure);

   186         }

   187       }

   188     }

   189     // For the  case of compressed oops, we have a private, non-shared

   190     // overflow stack, so we eagerly drain it so as to more evenly

   191     // distribute load early. Note: this may be good to do in

   192     // general rather than delay for the final stealing phase.

   193     // If applicable, we'll transfer a set of objects over to our

   194     // work queue, allowing them to be stolen and draining our

   195     // private overflow stack.

   196   } while (ParGCTrimOverflow && young_gen()->take_from_overflow_list(this));

   197 }

   198 

   199 bool ParScanThreadState::take_from_overflow_stack() {

   200   assert(ParGCUseLocalOverflow, "Else should not call");

   201   assert(young_gen()->overflow_list() == NULL, "Error");

   202   ObjToScanQueue* queue = work_queue();

   203   Stack<oop, mtGC>* const of_stack = overflow_stack();

   204   const size_t num_overflow_elems = of_stack->size();

   205   const size_t space_available = queue->max_elems() - queue->size();

   206   const size_t num_take_elems = MIN3(space_available / 4,

   207                                      (size_t)ParGCDesiredObjsFromOverflowList,

   208                                      num_overflow_elems);

   209   // Transfer the most recent num_take_elems from the overflow

   210   // stack to our work queue.

   211   for (size_t i = 0; i != num_take_elems; i++) {

   212     oop cur = of_stack->pop();

   213     oop obj_to_push = cur->forwardee();

   214     assert(CMSHeap::heap()->is_in_reserved(cur), "Should be in heap");

   215     assert(!old_gen()->is_in_reserved(cur), "Should be in young gen");

   216     assert(CMSHeap::heap()->is_in_reserved(obj_to_push), "Should be in heap");

   217     if (should_be_partially_scanned(obj_to_push, cur)) {

   218       assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");

   219       obj_to_push = cur;

   220     }

   221     bool ok = queue->push(obj_to_push);

   222     assert(ok, "Should have succeeded");

   223   }

   224   assert(young_gen()->overflow_list() == NULL, "Error");

   225   return num_take_elems > 0;  // was something transferred?

   226 }

   227 

   228 void ParScanThreadState::push_on_overflow_stack(oop p) {

   229   assert(ParGCUseLocalOverflow, "Else should not call");

   230   overflow_stack()->push(p);

   231   assert(young_gen()->overflow_list() == NULL, "Error");

   232 }

   233 

   234 HeapWord* ParScanThreadState::alloc_in_to_space_slow(size_t word_sz) {

   235   // If the object is small enough, try to reallocate the buffer.

   236   HeapWord* obj = NULL;

   237   if (!_to_space_full) {

   238     PLAB* const plab = to_space_alloc_buffer();

   239     Space* const sp  = to_space();

   240     if (word_sz * 100 < ParallelGCBufferWastePct * plab->word_sz()) {

   241       // Is small enough; abandon this buffer and start a new one.

   242       plab->retire();

   243       // The minimum size has to be twice SurvivorAlignmentInBytes to

   244       // allow for padding used in the alignment of 1 word.  A padding

   245       // of 1 is too small for a filler word so the padding size will

   246       // be increased by SurvivorAlignmentInBytes.

   247       size_t min_usable_size = 2 * static_cast<size_t>(SurvivorAlignmentInBytes >> LogHeapWordSize);

   248       size_t buf_size = MAX2(plab->word_sz(), min_usable_size);

   249       HeapWord* buf_space = sp->par_allocate(buf_size);

   250       if (buf_space == NULL) {

   251         const size_t min_bytes = MAX2(PLAB::min_size(), min_usable_size) << LogHeapWordSize;

   252         size_t free_bytes = sp->free();

   253         while(buf_space == NULL && free_bytes >= min_bytes) {

   254           buf_size = free_bytes >> LogHeapWordSize;

   255           assert(buf_size == (size_t)align_object_size(buf_size), "Invariant");

   256           buf_space  = sp->par_allocate(buf_size);

   257           free_bytes = sp->free();

   258         }

   259       }

   260       if (buf_space != NULL) {

   261         plab->set_buf(buf_space, buf_size);

   262         record_survivor_plab(buf_space, buf_size);

   263         obj = plab->allocate_aligned(word_sz, SurvivorAlignmentInBytes);

   264         // Note that we cannot compare buf_size < word_sz below

   265         // because of AlignmentReserve (see PLAB::allocate()).

   266         assert(obj != NULL || plab->words_remaining() < word_sz,

   267                "Else should have been able to allocate requested object size "

   268                SIZE_FORMAT ", PLAB size " SIZE_FORMAT ", SurvivorAlignmentInBytes "

   269                SIZE_FORMAT ", words_remaining " SIZE_FORMAT,

   270                word_sz, buf_size, SurvivorAlignmentInBytes, plab->words_remaining());

   271         // It's conceivable that we may be able to use the

   272         // buffer we just grabbed for subsequent small requests

   273         // even if not for this one.

   274       } else {

   275         // We're used up.

   276         _to_space_full = true;

   277       }

   278     } else {

   279       // Too large; allocate the object individually.

   280       obj = sp->par_allocate(word_sz);

   281     }

   282   }

   283   return obj;

   284 }

   285 

   286 void ParScanThreadState::undo_alloc_in_to_space(HeapWord* obj, size_t word_sz) {

   287   to_space_alloc_buffer()->undo_allocation(obj, word_sz);

   288 }

   289 

   290 void ParScanThreadState::print_promotion_failure_size() {

   291   if (_promotion_failed_info.has_failed()) {

   292     log_trace(gc, promotion)(" (%d: promotion failure size = " SIZE_FORMAT ") ",

   293                              _thread_num, _promotion_failed_info.first_size());

   294   }

   295 }

   296 

   297 class ParScanThreadStateSet: StackObj {

   298 public:

   299   // Initializes states for the specified number of threads;

   300   ParScanThreadStateSet(int                     num_threads,

   301                         Space&                  to_space,

   302                         ParNewGeneration&       young_gen,

   303                         Generation&             old_gen,

   304                         ObjToScanQueueSet&      queue_set,

   305                         Stack<oop, mtGC>*       overflow_stacks_,

   306                         PreservedMarksSet&      preserved_marks_set,

   307                         size_t                  desired_plab_sz,

   308                         TaskTerminator& term);

   309 

   310   ~ParScanThreadStateSet() { TASKQUEUE_STATS_ONLY(reset_stats()); }

   311 

   312   inline ParScanThreadState& thread_state(int i);

   313 

   314   void trace_promotion_failed(const YoungGCTracer* gc_tracer);

   315   void reset(uint active_workers, bool promotion_failed);

   316   void flush();

   317 

   318   #if TASKQUEUE_STATS

   319   static void

   320     print_termination_stats_hdr(outputStream* const st);

   321   void print_termination_stats();

   322   static void

   323     print_taskqueue_stats_hdr(outputStream* const st);

   324   void print_taskqueue_stats();

   325   void reset_stats();

   326   #endif // TASKQUEUE_STATS

   327 

   328 private:

   329   TaskTerminator&         _term;

   330   ParNewGeneration&       _young_gen;

   331   Generation&             _old_gen;

   332   ParScanThreadState*     _per_thread_states;

   333   const int               _num_threads;

   334  public:

   335   bool is_valid(int id) const { return id < _num_threads; }

   336   ParallelTaskTerminator* terminator() { return _term.terminator(); }

   337 };

   338 

   339 ParScanThreadStateSet::ParScanThreadStateSet(int num_threads,

   340                                              Space& to_space,

   341                                              ParNewGeneration& young_gen,

   342                                              Generation& old_gen,

   343                                              ObjToScanQueueSet& queue_set,

   344                                              Stack<oop, mtGC>* overflow_stacks,

   345                                              PreservedMarksSet& preserved_marks_set,

   346                                              size_t desired_plab_sz,

   347                                              TaskTerminator& term)

   348   : _term(term),

   349     _young_gen(young_gen),

   350     _old_gen(old_gen),

   351     _per_thread_states(NEW_RESOURCE_ARRAY(ParScanThreadState, num_threads)),

   352     _num_threads(num_threads)

   353 {

   354   assert(num_threads > 0, "sanity check!");

   355   assert(ParGCUseLocalOverflow == (overflow_stacks != NULL),

   356          "overflow_stack allocation mismatch");

   357   // Initialize states.

   358   for (int i = 0; i < num_threads; ++i) {

   359     new(_per_thread_states + i)

   360       ParScanThreadState(&to_space, &young_gen, &old_gen, i, &queue_set,

   361                          overflow_stacks, preserved_marks_set.get(i),

   362                          desired_plab_sz, term);

   363   }

   364 }

   365 

   366 inline ParScanThreadState& ParScanThreadStateSet::thread_state(int i) {

   367   assert(i >= 0 && i < _num_threads, "sanity check!");

   368   return _per_thread_states[i];

   369 }

   370 

   371 void ParScanThreadStateSet::trace_promotion_failed(const YoungGCTracer* gc_tracer) {

   372   for (int i = 0; i < _num_threads; ++i) {

   373     if (thread_state(i).promotion_failed()) {

   374       gc_tracer->report_promotion_failed(thread_state(i).promotion_failed_info());

   375       thread_state(i).promotion_failed_info().reset();

   376     }

   377   }

   378 }

   379 

   380 void ParScanThreadStateSet::reset(uint active_threads, bool promotion_failed) {

   381   _term.terminator()->reset_for_reuse(active_threads);

   382   if (promotion_failed) {

   383     for (int i = 0; i < _num_threads; ++i) {

   384       thread_state(i).print_promotion_failure_size();

   385     }

   386   }

   387 }

   388 

   389 #if TASKQUEUE_STATS

   390 void ParScanThreadState::reset_stats() {

   391   taskqueue_stats().reset();

   392   _term_attempts = 0;

   393   _overflow_refills = 0;

   394   _overflow_refill_objs = 0;

   395 }

   396 

   397 void ParScanThreadStateSet::reset_stats() {

   398   for (int i = 0; i < _num_threads; ++i) {

   399     thread_state(i).reset_stats();

   400   }

   401 }

   402 

   403 void ParScanThreadStateSet::print_termination_stats_hdr(outputStream* const st) {

   404   st->print_raw_cr("GC Termination Stats");

   405   st->print_raw_cr("     elapsed  --strong roots-- -------termination-------");

   406   st->print_raw_cr("thr     ms        ms       %       ms       %   attempts");

   407   st->print_raw_cr("--- --------- --------- ------ --------- ------ --------");

   408 }

   409 

   410 void ParScanThreadStateSet::print_termination_stats() {

   411   Log(gc, task, stats) log;

   412   if (!log.is_debug()) {

   413     return;

   414   }

   415 

   416   ResourceMark rm;

   417   LogStream ls(log.debug());

   418   outputStream* st = &ls;

   419 

   420   print_termination_stats_hdr(st);

   421 

   422   for (int i = 0; i < _num_threads; ++i) {

   423     const ParScanThreadState & pss = thread_state(i);

   424     const double elapsed_ms = pss.elapsed_time() * 1000.0;

   425     const double s_roots_ms = pss.strong_roots_time() * 1000.0;

   426     const double term_ms = pss.term_time() * 1000.0;

   427     st->print_cr("%3d %9.2f %9.2f %6.2f %9.2f %6.2f " SIZE_FORMAT_W(8),

   428                  i, elapsed_ms, s_roots_ms, s_roots_ms * 100 / elapsed_ms,

   429                  term_ms, term_ms * 100 / elapsed_ms, pss.term_attempts());

   430   }

   431 }

   432 

   433 // Print stats related to work queue activity.

   434 void ParScanThreadStateSet::print_taskqueue_stats_hdr(outputStream* const st) {

   435   st->print_raw_cr("GC Task Stats");

   436   st->print_raw("thr "); TaskQueueStats::print_header(1, st); st->cr();

   437   st->print_raw("--- "); TaskQueueStats::print_header(2, st); st->cr();

   438 }

   439 

   440 void ParScanThreadStateSet::print_taskqueue_stats() {

   441   if (!log_is_enabled(Trace, gc, task, stats)) {

   442     return;

   443   }

   444   Log(gc, task, stats) log;

   445   ResourceMark rm;

   446   LogStream ls(log.trace());

   447   outputStream* st = &ls;

   448   print_taskqueue_stats_hdr(st);

   449 

   450   TaskQueueStats totals;

   451   for (int i = 0; i < _num_threads; ++i) {

   452     const ParScanThreadState & pss = thread_state(i);

   453     const TaskQueueStats & stats = pss.taskqueue_stats();

   454     st->print("%3d ", i); stats.print(st); st->cr();

   455     totals += stats;

   456 

   457     if (pss.overflow_refills() > 0) {

   458       st->print_cr("    " SIZE_FORMAT_W(10) " overflow refills    "

   459                    SIZE_FORMAT_W(10) " overflow objects",

   460                    pss.overflow_refills(), pss.overflow_refill_objs());

   461     }

   462   }

   463   st->print("tot "); totals.print(st); st->cr();

   464 

   465   DEBUG_ONLY(totals.verify());

   466 }

   467 #endif // TASKQUEUE_STATS

   468 

   469 void ParScanThreadStateSet::flush() {

   470   // Work in this loop should be kept as lightweight as

   471   // possible since this might otherwise become a bottleneck

   472   // to scaling. Should we add heavy-weight work into this

   473   // loop, consider parallelizing the loop into the worker threads.

   474   for (int i = 0; i < _num_threads; ++i) {

   475     ParScanThreadState& par_scan_state = thread_state(i);

   476 

   477     // Flush stats related to To-space PLAB activity and

   478     // retire the last buffer.

   479     par_scan_state.to_space_alloc_buffer()->flush_and_retire_stats(_young_gen.plab_stats());

   480 

   481     // Every thread has its own age table.  We need to merge

   482     // them all into one.

   483     AgeTable *local_table = par_scan_state.age_table();

   484     _young_gen.age_table()->merge(local_table);

   485 

   486     // Inform old gen that we're done.

   487     _old_gen.par_promote_alloc_done(i);

   488   }

   489 

   490   if (UseConcMarkSweepGC) {

   491     // We need to call this even when ResizeOldPLAB is disabled

   492     // so as to avoid breaking some asserts. While we may be able

   493     // to avoid this by reorganizing the code a bit, I am loathe

   494     // to do that unless we find cases where ergo leads to bad

   495     // performance.

   496     CompactibleFreeListSpaceLAB::compute_desired_plab_size();

   497   }

   498 }

   499 

   500 ParScanClosure::ParScanClosure(ParNewGeneration* g,

   501                                ParScanThreadState* par_scan_state) :

   502   OopsInClassLoaderDataOrGenClosure(g), _par_scan_state(par_scan_state), _g(g) {

   503   _boundary = _g->reserved().end();

   504 }

   505 

   506 void ParRootScanWithBarrierTwoGensClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, true, true); }

   507 void ParRootScanWithBarrierTwoGensClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, true); }

   508 

   509 void ParRootScanWithoutBarrierClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, false, true); }

   510 void ParRootScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, true); }

   511 

   512 ParScanWeakRefClosure::ParScanWeakRefClosure(ParNewGeneration* g,

   513                                              ParScanThreadState* par_scan_state)

   514   : ScanWeakRefClosure(g), _par_scan_state(par_scan_state)

   515 {}

   516 

   517 #ifdef WIN32

   518 #pragma warning(disable: 4786) /* identifier was truncated to '255' characters in the browser information */

   519 #endif

   520 

   521 ParEvacuateFollowersClosure::ParEvacuateFollowersClosure(

   522     ParScanThreadState* par_scan_state_,

   523     ParScanWithoutBarrierClosure* to_space_closure_,

   524     ParScanWithBarrierClosure* old_gen_closure_,

   525     ParRootScanWithoutBarrierClosure* to_space_root_closure_,

   526     ParNewGeneration* par_gen_,

   527     ParRootScanWithBarrierTwoGensClosure* old_gen_root_closure_,

   528     ObjToScanQueueSet* task_queues_,

   529     ParallelTaskTerminator* terminator_) :

   530 

   531     _par_scan_state(par_scan_state_),

   532     _to_space_closure(to_space_closure_),

   533     _to_space_root_closure(to_space_root_closure_),

   534     _old_gen_closure(old_gen_closure_),

   535     _old_gen_root_closure(old_gen_root_closure_),

   536     _par_gen(par_gen_),

   537     _task_queues(task_queues_),

   538     _terminator(terminator_)

   539 {}

   540 

   541 void ParEvacuateFollowersClosure::do_void() {

   542   ObjToScanQueue* work_q = par_scan_state()->work_queue();

   543 

   544   while (true) {

   545     // Scan to-space and old-gen objs until we run out of both.

   546     oop obj_to_scan;

   547     par_scan_state()->trim_queues(0);

   548 

   549     // We have no local work, attempt to steal from other threads.

   550 

   551     // Attempt to steal work from promoted.

   552     if (task_queues()->steal(par_scan_state()->thread_num(),

   553                              obj_to_scan)) {

   554       bool res = work_q->push(obj_to_scan);

   555       assert(res, "Empty queue should have room for a push.");

   556 

   557       // If successful, goto Start.

   558       continue;

   559 

   560       // Try global overflow list.

   561     } else if (par_gen()->take_from_overflow_list(par_scan_state())) {

   562       continue;

   563     }

   564 

   565     // Otherwise, offer termination.

   566     par_scan_state()->start_term_time();

   567     if (terminator()->offer_termination()) break;

   568     par_scan_state()->end_term_time();

   569   }

   570   assert(par_gen()->_overflow_list == NULL && par_gen()->_num_par_pushes == 0,

   571          "Broken overflow list?");

   572   // Finish the last termination pause.

   573   par_scan_state()->end_term_time();

   574 }

   575 

   576 ParNewGenTask::ParNewGenTask(ParNewGeneration* young_gen,

   577                              Generation* old_gen,

   578                              HeapWord* young_old_boundary,

   579                              ParScanThreadStateSet* state_set,

   580                              StrongRootsScope* strong_roots_scope) :

   581     AbstractGangTask("ParNewGeneration collection"),

   582     _young_gen(young_gen), _old_gen(old_gen),

   583     _young_old_boundary(young_old_boundary),

   584     _state_set(state_set),

   585     _strong_roots_scope(strong_roots_scope)

   586 {}

   587 

   588 void ParNewGenTask::work(uint worker_id) {

   589   CMSHeap* heap = CMSHeap::heap();

   590   // Since this is being done in a separate thread, need new resource

   591   // and handle marks.

   592   ResourceMark rm;

   593   HandleMark hm;

   594 

   595   ParScanThreadState& par_scan_state = _state_set->thread_state(worker_id);

   596   assert(_state_set->is_valid(worker_id), "Should not have been called");

   597 

   598   par_scan_state.set_young_old_boundary(_young_old_boundary);

   599 

   600   CLDScanClosure cld_scan_closure(&par_scan_state.to_space_root_closure(),

   601                                   heap->rem_set()->cld_rem_set()->accumulate_modified_oops());

   602 

   603   par_scan_state.start_strong_roots();

   604   heap->young_process_roots(_strong_roots_scope,

   605                            &par_scan_state.to_space_root_closure(),

   606                            &par_scan_state.older_gen_closure(),

   607                            &cld_scan_closure);

   608 

   609   par_scan_state.end_strong_roots();

   610 

   611   // "evacuate followers".

   612   par_scan_state.evacuate_followers_closure().do_void();

   613 

   614   // This will collapse this worker's promoted object list that's

   615   // created during the main ParNew parallel phase of ParNew. This has

   616   // to be called after all workers have finished promoting objects

   617   // and scanning promoted objects. It should be safe calling it from

   618   // here, given that we can only reach here after all thread have

   619   // offered termination, i.e., after there is no more work to be

   620   // done. It will also disable promotion tracking for the rest of

   621   // this GC as it's not necessary to be on during reference processing.

   622   _old_gen->par_oop_since_save_marks_iterate_done((int) worker_id);

   623 }

   624 

   625 ParNewGeneration::ParNewGeneration(ReservedSpace rs,

   626                                    size_t initial_byte_size,

   627                                    size_t min_byte_size,

   628                                    size_t max_byte_size)

   629   : DefNewGeneration(rs, initial_byte_size, min_byte_size, max_byte_size, "CMS young collection pauses"),

   630   _plab_stats("Young", YoungPLABSize, PLABWeight),

   631   _overflow_list(NULL),

   632   _is_alive_closure(this)

   633 {

   634   NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;)

   635   NOT_PRODUCT(_num_par_pushes = 0;)

   636   _task_queues = new ObjToScanQueueSet(ParallelGCThreads);

   637   guarantee(_task_queues != NULL, "task_queues allocation failure.");

   638 

   639   for (uint i = 0; i < ParallelGCThreads; i++) {

   640     ObjToScanQueue *q = new ObjToScanQueue();

   641     guarantee(q != NULL, "work_queue Allocation failure.");

   642     _task_queues->register_queue(i, q);

   643   }

   644 

   645   for (uint i = 0; i < ParallelGCThreads; i++) {

   646     _task_queues->queue(i)->initialize();

   647   }

   648 

   649   _overflow_stacks = NULL;

   650   if (ParGCUseLocalOverflow) {

   651     // typedef to workaround NEW_C_HEAP_ARRAY macro, which can not deal with ','

   652     typedef Stack<oop, mtGC> GCOopStack;

   653 

   654     _overflow_stacks = NEW_C_HEAP_ARRAY(GCOopStack, ParallelGCThreads, mtGC);

   655     for (size_t i = 0; i < ParallelGCThreads; ++i) {

   656       new (_overflow_stacks + i) Stack<oop, mtGC>();

   657     }

   658   }

   659 

   660   if (UsePerfData) {

   661     EXCEPTION_MARK;

   662     ResourceMark rm;

   663 

   664     const char* cname =

   665          PerfDataManager::counter_name(_gen_counters->name_space(), "threads");

   666     PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None,

   667                                      ParallelGCThreads, CHECK);

   668   }

   669 }

   670 

   671 // ParNewGeneration::

   672 ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) :

   673   DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {}

   674 

   675 template <class T>

   676 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) {

   677 #ifdef ASSERT

   678   {

   679     oop obj = RawAccess<IS_NOT_NULL>::oop_load(p);

   680     // We never expect to see a null reference being processed

   681     // as a weak reference.

   682     assert(oopDesc::is_oop(obj), "expected an oop while scanning weak refs");

   683   }

   684 #endif // ASSERT

   685 

   686   Devirtualizer::do_oop_no_verify(_par_cl, p);

   687 

   688   if (CMSHeap::heap()->is_in_reserved(p)) {

   689     oop obj = RawAccess<IS_NOT_NULL>::oop_load(p);;

   690     _rs->write_ref_field_gc_par(p, obj);

   691   }

   692 }

   693 

   694 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(oop* p)       { ParKeepAliveClosure::do_oop_work(p); }

   695 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(narrowOop* p) { ParKeepAliveClosure::do_oop_work(p); }

   696 

   697 // ParNewGeneration::

   698 KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) :

   699   DefNewGeneration::KeepAliveClosure(cl) {}

   700 

   701 template <class T>

   702 void /*ParNewGeneration::*/KeepAliveClosure::do_oop_work(T* p) {

   703 #ifdef ASSERT

   704   {

   705     oop obj = RawAccess<IS_NOT_NULL>::oop_load(p);

   706     // We never expect to see a null reference being processed

   707     // as a weak reference.

   708     assert(oopDesc::is_oop(obj), "expected an oop while scanning weak refs");

   709   }

   710 #endif // ASSERT

   711 

   712   Devirtualizer::do_oop_no_verify(_cl, p);

   713 

   714   if (CMSHeap::heap()->is_in_reserved(p)) {

   715     oop obj = RawAccess<IS_NOT_NULL>::oop_load(p);

   716     _rs->write_ref_field_gc_par(p, obj);

   717   }

   718 }

   719 

   720 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(oop* p)       { KeepAliveClosure::do_oop_work(p); }

   721 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(narrowOop* p) { KeepAliveClosure::do_oop_work(p); }

   722 

   723 template <class T> void ScanClosureWithParBarrier::do_oop_work(T* p) {

   724   T heap_oop = RawAccess<>::oop_load(p);

   725   if (!CompressedOops::is_null(heap_oop)) {

   726     oop obj = CompressedOops::decode_not_null(heap_oop);

   727     if ((HeapWord*)obj < _boundary) {

   728       assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?");

   729       oop new_obj = obj->is_forwarded()

   730                       ? obj->forwardee()

   731                       : _g->DefNewGeneration::copy_to_survivor_space(obj);

   732       RawAccess<IS_NOT_NULL>::oop_store(p, new_obj);

   733     }

   734     if (_gc_barrier) {

   735       // If p points to a younger generation, mark the card.

   736       if ((HeapWord*)obj < _gen_boundary) {

   737         _rs->write_ref_field_gc_par(p, obj);

   738       }

   739     }

   740   }

   741 }

   742 

   743 void ScanClosureWithParBarrier::do_oop(oop* p)       { ScanClosureWithParBarrier::do_oop_work(p); }

   744 void ScanClosureWithParBarrier::do_oop(narrowOop* p) { ScanClosureWithParBarrier::do_oop_work(p); }

   745 

   746 class ParNewRefProcTaskProxy: public AbstractGangTask {

   747   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;

   748 public:

   749   ParNewRefProcTaskProxy(ProcessTask& task,

   750                          ParNewGeneration& young_gen,

   751                          Generation& old_gen,

   752                          HeapWord* young_old_boundary,

   753                          ParScanThreadStateSet& state_set);

   754 

   755 private:

   756   virtual void work(uint worker_id);

   757 private:

   758   ParNewGeneration&      _young_gen;

   759   ProcessTask&           _task;

   760   Generation&            _old_gen;

   761   HeapWord*              _young_old_boundary;

   762   ParScanThreadStateSet& _state_set;

   763 };

   764 

   765 ParNewRefProcTaskProxy::ParNewRefProcTaskProxy(ProcessTask& task,

   766                                                ParNewGeneration& young_gen,

   767                                                Generation& old_gen,

   768                                                HeapWord* young_old_boundary,

   769                                                ParScanThreadStateSet& state_set)

   770   : AbstractGangTask("ParNewGeneration parallel reference processing"),

   771     _young_gen(young_gen),

   772     _task(task),

   773     _old_gen(old_gen),

   774     _young_old_boundary(young_old_boundary),

   775     _state_set(state_set)

   776 { }

   777 

   778 void ParNewRefProcTaskProxy::work(uint worker_id) {

   779   ResourceMark rm;

   780   HandleMark hm;

   781   ParScanThreadState& par_scan_state = _state_set.thread_state(worker_id);

   782   par_scan_state.set_young_old_boundary(_young_old_boundary);

   783   _task.work(worker_id, par_scan_state.is_alive_closure(),

   784              par_scan_state.keep_alive_closure(),

   785              par_scan_state.evacuate_followers_closure());

   786 }

   787 

   788 void ParNewRefProcTaskExecutor::execute(ProcessTask& task, uint ergo_workers) {

   789   CMSHeap* gch = CMSHeap::heap();

   790   WorkGang* workers = gch->workers();

   791   assert(workers != NULL, "Need parallel worker threads.");

   792   assert(workers->active_workers() == ergo_workers,

   793          "Ergonomically chosen workers (%u) must be equal to active workers (%u)",

   794          ergo_workers, workers->active_workers());

   795   _state_set.reset(workers->active_workers(), _young_gen.promotion_failed());

   796   ParNewRefProcTaskProxy rp_task(task, _young_gen, _old_gen,

   797                                  _young_gen.reserved().end(), _state_set);

   798   workers->run_task(&rp_task, workers->active_workers());

   799   _state_set.reset(0 /* bad value in debug if not reset */,

   800                    _young_gen.promotion_failed());

   801 }

   802 

   803 void ParNewRefProcTaskExecutor::set_single_threaded_mode() {

   804   _state_set.flush();

   805   CMSHeap* heap = CMSHeap::heap();

   806   heap->save_marks();

   807 }

   808 

   809 ScanClosureWithParBarrier::

   810 ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) :

   811   OopsInClassLoaderDataOrGenClosure(g), _g(g), _boundary(g->reserved().end()), _gc_barrier(gc_barrier)

   812 { }

   813 

   814 template <typename OopClosureType1, typename OopClosureType2>

   815 EvacuateFollowersClosureGeneral<OopClosureType1, OopClosureType2>::

   816 EvacuateFollowersClosureGeneral(CMSHeap* heap,

   817                                 OopClosureType1* cur,

   818                                 OopClosureType2* older) :

   819   _heap(heap),

   820   _scan_cur_or_nonheap(cur), _scan_older(older)

   821 { }

   822 

   823 template <typename OopClosureType1, typename OopClosureType2>

   824 void EvacuateFollowersClosureGeneral<OopClosureType1, OopClosureType2>::do_void() {

   825   do {

   826     _heap->oop_since_save_marks_iterate(_scan_cur_or_nonheap,

   827                                         _scan_older);

   828   } while (!_heap->no_allocs_since_save_marks());

   829 }

   830 

   831 // A Generation that does parallel young-gen collection.

   832 

   833 void ParNewGeneration::handle_promotion_failed(CMSHeap* gch, ParScanThreadStateSet& thread_state_set) {

   834   assert(_promo_failure_scan_stack.is_empty(), "post condition");

   835   _promo_failure_scan_stack.clear(true); // Clear cached segments.

   836 

   837   remove_forwarding_pointers();

   838   log_info(gc, promotion)("Promotion failed");

   839   // All the spaces are in play for mark-sweep.

   840   swap_spaces();  // Make life simpler for CMS || rescan; see 6483690.

   841   from()->set_next_compaction_space(to());

   842   gch->set_incremental_collection_failed();

   843   // Inform the next generation that a promotion failure occurred.

   844   _old_gen->promotion_failure_occurred();

   845 

   846   // Trace promotion failure in the parallel GC threads

   847   thread_state_set.trace_promotion_failed(gc_tracer());

   848   // Single threaded code may have reported promotion failure to the global state

   849   if (_promotion_failed_info.has_failed()) {

   850     _gc_tracer.report_promotion_failed(_promotion_failed_info);

   851   }

   852   // Reset the PromotionFailureALot counters.

   853   NOT_PRODUCT(gch->reset_promotion_should_fail();)

   854 }

   855 

   856 void ParNewGeneration::collect(bool   full,

   857                                bool   clear_all_soft_refs,

   858                                size_t size,

   859                                bool   is_tlab) {

   860   assert(full || size > 0, "otherwise we don't want to collect");

   861 

   862   CMSHeap* gch = CMSHeap::heap();

   863 

   864   _gc_timer->register_gc_start();

   865 

   866   AdaptiveSizePolicy* size_policy = gch->size_policy();

   867   WorkGang* workers = gch->workers();

   868   assert(workers != NULL, "Need workgang for parallel work");

   869   uint active_workers =

   870       WorkerPolicy::calc_active_workers(workers->total_workers(),

   871                                         workers->active_workers(),

   872                                         Threads::number_of_non_daemon_threads());

   873   active_workers = workers->update_active_workers(active_workers);

   874   log_info(gc,task)("Using %u workers of %u for evacuation", active_workers, workers->total_workers());

   875 

   876   _old_gen = gch->old_gen();

   877 

   878   // If the next generation is too full to accommodate worst-case promotion

   879   // from this generation, pass on collection; let the next generation

   880   // do it.

   881   if (!collection_attempt_is_safe()) {

   882     gch->set_incremental_collection_failed();  // slight lie, in that we did not even attempt one

   883     return;

   884   }

   885   assert(to()->is_empty(), "Else not collection_attempt_is_safe");

   886 

   887   _gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start());

   888   gch->trace_heap_before_gc(gc_tracer());

   889 

   890   init_assuming_no_promotion_failure();

   891 

   892   GCTraceTime(Trace, gc, phases) t1("ParNew", NULL, gch->gc_cause());

   893 

   894   age_table()->clear();

   895   to()->clear(SpaceDecorator::Mangle);

   896 

   897   gch->save_marks();

   898 

   899   // Set the correct parallelism (number of queues) in the reference processor

   900   ref_processor()->set_active_mt_degree(active_workers);

   901 

   902   // Need to initialize the preserved marks before the ThreadStateSet c'tor.

   903   _preserved_marks_set.init(active_workers);

   904 

   905   // Always set the terminator for the active number of workers

   906   // because only those workers go through the termination protocol.

   907   TaskTerminator _term(active_workers, task_queues());

   908   ParScanThreadStateSet thread_state_set(active_workers,

   909                                          *to(), *this, *_old_gen, *task_queues(),

   910                                          _overflow_stacks, _preserved_marks_set,

   911                                          desired_plab_sz(), _term);

   912 

   913   thread_state_set.reset(active_workers, promotion_failed());

   914 

   915   {

   916     StrongRootsScope srs(active_workers);

   917 

   918     ParNewGenTask tsk(this, _old_gen, reserved().end(), &thread_state_set, &srs);

   919     gch->rem_set()->prepare_for_younger_refs_iterate(true);

   920     // It turns out that even when we're using 1 thread, doing the work in a

   921     // separate thread causes wide variance in run times.  We can't help this

   922     // in the multi-threaded case, but we special-case n=1 here to get

   923     // repeatable measurements of the 1-thread overhead of the parallel code.

   924     // Might multiple workers ever be used?  If yes, initialization

   925     // has been done such that the single threaded path should not be used.

   926     if (workers->total_workers() > 1) {

   927       workers->run_task(&tsk);

   928     } else {

   929       tsk.work(0);

   930     }

   931   }

   932 

   933   thread_state_set.reset(0 /* Bad value in debug if not reset */,

   934                          promotion_failed());

   935 

   936   // Trace and reset failed promotion info.

   937   if (promotion_failed()) {

   938     thread_state_set.trace_promotion_failed(gc_tracer());

   939   }

   940 

   941   // Process (weak) reference objects found during scavenge.

   942   ReferenceProcessor* rp = ref_processor();

   943   IsAliveClosure is_alive(this);

   944   ScanWeakRefClosure scan_weak_ref(this);

   945   KeepAliveClosure keep_alive(&scan_weak_ref);

   946   ScanClosure               scan_without_gc_barrier(this, false);

   947   ScanClosureWithParBarrier scan_with_gc_barrier(this, true);

   948   set_promo_failure_scan_stack_closure(&scan_without_gc_barrier);

   949   EvacuateFollowersClosureGeneral<ScanClosure, ScanClosureWithParBarrier> evacuate_followers(

   950       gch, &scan_without_gc_barrier, &scan_with_gc_barrier);

   951   rp->setup_policy(clear_all_soft_refs);

   952   // Can  the mt_degree be set later (at run_task() time would be best)?

   953   rp->set_active_mt_degree(active_workers);

   954   ReferenceProcessorStats stats;

   955   ReferenceProcessorPhaseTimes pt(_gc_timer, rp->max_num_queues());

   956   if (rp->processing_is_mt()) {

   957     ParNewRefProcTaskExecutor task_executor(*this, *_old_gen, thread_state_set);

   958     stats = rp->process_discovered_references(&is_alive, &keep_alive,

   959                                               &evacuate_followers, &task_executor,

   960                                               &pt);

   961   } else {

   962     thread_state_set.flush();

   963     gch->save_marks();

   964     stats = rp->process_discovered_references(&is_alive, &keep_alive,

   965                                               &evacuate_followers, NULL,

   966                                               &pt);

   967   }

   968   _gc_tracer.report_gc_reference_stats(stats);

   969   _gc_tracer.report_tenuring_threshold(tenuring_threshold());

   970   pt.print_all_references();

   971 

   972   assert(gch->no_allocs_since_save_marks(), "evacuation should be done at this point");

   973 

   974   WeakProcessor::weak_oops_do(&is_alive, &keep_alive);

   975 

   976   // Verify that the usage of keep_alive only forwarded

   977   // the oops and did not find anything new to copy.

   978   assert(gch->no_allocs_since_save_marks(), "unexpectedly copied objects");

   979 

   980   if (!promotion_failed()) {

   981     // Swap the survivor spaces.

   982     eden()->clear(SpaceDecorator::Mangle);

   983     from()->clear(SpaceDecorator::Mangle);

   984     if (ZapUnusedHeapArea) {

   985       // This is now done here because of the piece-meal mangling which

   986       // can check for valid mangling at intermediate points in the

   987       // collection(s).  When a young collection fails to collect

   988       // sufficient space resizing of the young generation can occur

   989       // and redistribute the spaces in the young generation.  Mangle

   990       // here so that unzapped regions don't get distributed to

   991       // other spaces.

   992       to()->mangle_unused_area();

   993     }

   994     swap_spaces();

   995 

   996     // A successful scavenge should restart the GC time limit count which is

   997     // for full GC's.

   998     size_policy->reset_gc_overhead_limit_count();

   999 

  1000     assert(to()->is_empty(), "to space should be empty now");

  1001 

  1002     adjust_desired_tenuring_threshold();

  1003   } else {

  1004     handle_promotion_failed(gch, thread_state_set);

  1005   }

  1006   _preserved_marks_set.reclaim();

  1007   // set new iteration safe limit for the survivor spaces

  1008   from()->set_concurrent_iteration_safe_limit(from()->top());

  1009   to()->set_concurrent_iteration_safe_limit(to()->top());

  1010 

  1011   plab_stats()->adjust_desired_plab_sz();

  1012 

  1013   TASKQUEUE_STATS_ONLY(thread_state_set.print_termination_stats());

  1014   TASKQUEUE_STATS_ONLY(thread_state_set.print_taskqueue_stats());

  1015 

  1016   // We need to use a monotonically non-decreasing time in ms

  1017   // or we will see time-warp warnings and os::javaTimeMillis()

  1018   // does not guarantee monotonicity.

  1019   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;

  1020   update_time_of_last_gc(now);

  1021 

  1022   rp->set_enqueuing_is_done(true);

  1023   rp->verify_no_references_recorded();

  1024 

  1025   gch->trace_heap_after_gc(gc_tracer());

  1026 

  1027   _gc_timer->register_gc_end();

  1028 

  1029   _gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions());

  1030 }

  1031 

  1032 size_t ParNewGeneration::desired_plab_sz() {

  1033   return _plab_stats.desired_plab_sz(CMSHeap::heap()->workers()->active_workers());

  1034 }

  1035 

  1036 static int sum;

  1037 void ParNewGeneration::waste_some_time() {

  1038   for (int i = 0; i < 100; i++) {

  1039     sum += i;

  1040   }

  1041 }

  1042 

  1043 static const oop ClaimedForwardPtr = cast_to_oop<intptr_t>(0x4);

  1044 

  1045 // Because of concurrency, there are times where an object for which

  1046 // "is_forwarded()" is true contains an "interim" forwarding pointer

  1047 // value.  Such a value will soon be overwritten with a real value.

  1048 // This method requires "obj" to have a forwarding pointer, and waits, if

  1049 // necessary for a real one to be inserted, and returns it.

  1050 

  1051 oop ParNewGeneration::real_forwardee(oop obj) {

  1052   oop forward_ptr = obj->forwardee();

  1053   if (forward_ptr != ClaimedForwardPtr) {

  1054     return forward_ptr;

  1055   } else {

  1056     return real_forwardee_slow(obj);

  1057   }

  1058 }

  1059 

  1060 oop ParNewGeneration::real_forwardee_slow(oop obj) {

  1061   // Spin-read if it is claimed but not yet written by another thread.

  1062   oop forward_ptr = obj->forwardee();

  1063   while (forward_ptr == ClaimedForwardPtr) {

  1064     waste_some_time();

  1065     assert(obj->is_forwarded(), "precondition");

  1066     forward_ptr = obj->forwardee();

  1067   }

  1068   return forward_ptr;

  1069 }

  1070 

  1071 // Multiple GC threads may try to promote an object.  If the object

  1072 // is successfully promoted, a forwarding pointer will be installed in

  1073 // the object in the young generation.  This method claims the right

  1074 // to install the forwarding pointer before it copies the object,

  1075 // thus avoiding the need to undo the copy as in

  1076 // copy_to_survivor_space_avoiding_with_undo.

  1077 

  1078 oop ParNewGeneration::copy_to_survivor_space(ParScanThreadState* par_scan_state,

  1079                                              oop old,

  1080                                              size_t sz,

  1081                                              markWord m) {

  1082   // In the sequential version, this assert also says that the object is

  1083   // not forwarded.  That might not be the case here.  It is the case that

  1084   // the caller observed it to be not forwarded at some time in the past.

  1085   assert(is_in_reserved(old), "shouldn't be scavenging this oop");

  1086 

  1087   // The sequential code read "old->age()" below.  That doesn't work here,

  1088   // since the age is in the mark word, and that might be overwritten with

  1089   // a forwarding pointer by a parallel thread.  So we must save the mark

  1090   // word in a local and then analyze it.

  1091   oopDesc dummyOld;

  1092   dummyOld.set_mark_raw(m);

  1093   assert(!dummyOld.is_forwarded(),

  1094          "should not be called with forwarding pointer mark word.");

  1095 

  1096   oop new_obj = NULL;

  1097   oop forward_ptr;

  1098 

  1099   // Try allocating obj in to-space (unless too old)

  1100   if (dummyOld.age() < tenuring_threshold()) {

  1101     new_obj = (oop)par_scan_state->alloc_in_to_space(sz);

  1102   }

  1103 

  1104   if (new_obj == NULL) {

  1105     // Either to-space is full or we decided to promote 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, m);

  1110     if (forward_ptr != NULL) {

  1111       // someone else beat us to it.

  1112         return real_forwardee(old);

  1113     }

  1114 

  1115     if (!_promotion_failed) {

  1116       new_obj = _old_gen->par_promote(par_scan_state->thread_num(),

  1117                                       old, m, sz);

  1118     }

  1119 

  1120     if (new_obj == NULL) {

  1121       // promotion failed, forward to self

  1122       _promotion_failed = true;

  1123       new_obj = old;

  1124 

  1125       par_scan_state->preserved_marks()->push_if_necessary(old, m);

  1126       par_scan_state->register_promotion_failure(sz);

  1127     }

  1128 

  1129     old->forward_to(new_obj);

  1130     forward_ptr = NULL;

  1131   } else {

  1132     // Is in to-space; do copying ourselves.

  1133     Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz);

  1134     assert(CMSHeap::heap()->is_in_reserved(new_obj), "illegal forwarding pointer value.");