Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * Copyright (c) 2001, 2011, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

  * questions.

  *

  */

 #include "precompiled.hpp"

 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp"

 #include "gc_implementation/parNew/parGCAllocBuffer.hpp"

 #include "gc_implementation/parNew/parNewGeneration.hpp"

 #include "gc_implementation/parNew/parOopClosures.inline.hpp"

 #include "gc_implementation/shared/adaptiveSizePolicy.hpp"

 #include "gc_implementation/shared/ageTable.hpp"

 #include "gc_implementation/shared/spaceDecorator.hpp"

 #include "memory/defNewGeneration.inline.hpp"

 #include "memory/genCollectedHeap.hpp"

 #include "memory/genOopClosures.inline.hpp"

 #include "memory/generation.hpp"

 #include "memory/generation.inline.hpp"

 #include "memory/referencePolicy.hpp"

 #include "memory/resourceArea.hpp"

 #include "memory/sharedHeap.hpp"

 #include "memory/space.hpp"

 #include "oops/objArrayOop.hpp"

 #include "oops/oop.inline.hpp"

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

 #include "runtime/handles.hpp"

 #include "runtime/handles.inline.hpp"

 #include "runtime/java.hpp"

 #include "runtime/thread.hpp"

 #include "utilities/copy.hpp"

 #include "utilities/globalDefinitions.hpp"

 #include "utilities/workgroup.hpp"

 #ifdef _MSC_VER

 #pragma warning( push )

 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list

 #endif

 ParScanThreadState::ParScanThreadState(Space* to_space_,

                                        ParNewGeneration* gen_,

                                        Generation* old_gen_,

                                        int thread_num_,

                                        ObjToScanQueueSet* work_queue_set_,

                                        Stack<oop>* overflow_stacks_,

                                        size_t desired_plab_sz_,

                                        ParallelTaskTerminator& term_) :

   _to_space(to_space_), _old_gen(old_gen_), _young_gen(gen_), _thread_num(thread_num_),

   _work_queue(work_queue_set_->queue(thread_num_)), _to_space_full(false),

   _overflow_stack(overflow_stacks_ ? overflow_stacks_ + thread_num_ : NULL),

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

   _to_space_alloc_buffer(desired_plab_sz_),

   _to_space_closure(gen_, this), _old_gen_closure(gen_, this),

   _to_space_root_closure(gen_, this), _old_gen_root_closure(gen_, this),

   _older_gen_closure(gen_, this),

   _evacuate_followers(this, &_to_space_closure, &_old_gen_closure,

                       &_to_space_root_closure, gen_, &_old_gen_root_closure,

                       work_queue_set_, &term_),

   _is_alive_closure(gen_), _scan_weak_ref_closure(gen_, this),

   _keep_alive_closure(&_scan_weak_ref_closure),

   _promotion_failure_size(0),

   _strong_roots_time(0.0), _term_time(0.0)

 {

   #if TASKQUEUE_STATS

   _term_attempts = 0;

   _overflow_refills = 0;

   _overflow_refill_objs = 0;

   #endif // TASKQUEUE_STATS

   _survivor_chunk_array =

     (ChunkArray*) old_gen()->get_data_recorder(thread_num());

   _hash_seed = 17;  // Might want to take time-based random value.

   _start = os::elapsedTime();

   _old_gen_closure.set_generation(old_gen_);

   _old_gen_root_closure.set_generation(old_gen_);

 }

 #ifdef _MSC_VER

 #pragma warning( pop )

 #endif

 void ParScanThreadState::record_survivor_plab(HeapWord* plab_start,

                                               size_t plab_word_size) {

   ChunkArray* sca = survivor_chunk_array();

   if (sca != NULL) {

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

     sca->record_sample(plab_start, plab_word_size);

   }

 }

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

   return new_obj->is_objArray() &&

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

          new_obj != old_obj;

 }

 void ParScanThreadState::scan_partial_array_and_push_remainder(oop old) {

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

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

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

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

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

   // Process ParGCArrayScanChunk elements now

   // and push the remainder back onto queue

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

   int end       = obj->length();

   int remainder = end - start;

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

   if (remainder > 2 * ParGCArrayScanChunk) {

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

     end = start + ParGCArrayScanChunk;

     arrayOop(old)->set_length(end);

     // Push remainder.

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

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

   } else {

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

     // is a promotion failure and forwarding pointers

     // must be removed.

     arrayOop(old)->set_length(end);

   }

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

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

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

     // object is in to_space

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

   } else {

     // object is in old generation

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

   }

 }

 void ParScanThreadState::trim_queues(int max_size) {

   ObjToScanQueue* queue = work_queue();

   do {

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

       oop obj_to_scan;

       if (queue->pop_local(obj_to_scan)) {

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

           if (obj_to_scan->is_objArray() &&

               obj_to_scan->is_forwarded() &&

               obj_to_scan->forwardee() != obj_to_scan) {

             scan_partial_array_and_push_remainder(obj_to_scan);

           } else {

             // object is in to_space

             obj_to_scan->oop_iterate(&_to_space_closure);

           }

         } else {

           // object is in old generation

           obj_to_scan->oop_iterate(&_old_gen_closure);

         }

       }

     }

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

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

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

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

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

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

     // private overflow stack.

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

 }

 bool ParScanThreadState::take_from_overflow_stack() {

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

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

   ObjToScanQueue* queue = work_queue();

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

   const size_t num_overflow_elems = of_stack->size();

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

   const size_t num_take_elems = MIN3(space_available / 4,

                                      ParGCDesiredObjsFromOverflowList,

                                      num_overflow_elems);

   // Transfer the most recent num_take_elems from the overflow

   // stack to our work queue.

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

     oop cur = of_stack->pop();

     oop obj_to_push = cur->forwardee();

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

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

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

     if (should_be_partially_scanned(obj_to_push, cur)) {

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

       obj_to_push = cur;

     }

     bool ok = queue->push(obj_to_push);

     assert(ok, "Should have succeeded");

   }

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

   return num_take_elems > 0;  // was something transferred?

 }

 void ParScanThreadState::push_on_overflow_stack(oop p) {

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

   overflow_stack()->push(p);

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

 }

 HeapWord* ParScanThreadState::alloc_in_to_space_slow(size_t word_sz) {

   // Otherwise, if the object is small enough, try to reallocate the

   // buffer.

   HeapWord* obj = NULL;

   if (!_to_space_full) {

     ParGCAllocBuffer* const plab = to_space_alloc_buffer();

     Space*            const sp   = to_space();

     if (word_sz * 100 <

         ParallelGCBufferWastePct * plab->word_sz()) {

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

       plab->retire(false, false);

       size_t buf_size = plab->word_sz();

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

       if (buf_space == NULL) {

         const size_t min_bytes =

           ParGCAllocBuffer::min_size() << LogHeapWordSize;

         size_t free_bytes = sp->free();

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

           buf_size = free_bytes >> LogHeapWordSize;

           assert(buf_size == (size_t)align_object_size(buf_size),

                  "Invariant");

           buf_space  = sp->par_allocate(buf_size);

           free_bytes = sp->free();

         }

       }

       if (buf_space != NULL) {

         plab->set_word_size(buf_size);

         plab->set_buf(buf_space);

         record_survivor_plab(buf_space, buf_size);

         obj = plab->allocate(word_sz);

         // Note that we cannot compare buf_size < word_sz below

         // because of AlignmentReserve (see ParGCAllocBuffer::allocate()).

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

                "Else should have been able to allocate");

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

         // buffer we just grabbed for subsequent small requests

         // even if not for this one.

       } else {

         // We're used up.

         _to_space_full = true;

       }

     } else {

       // Too large; allocate the object individually.

       obj = sp->par_allocate(word_sz);

     }

   }

   return obj;

 }

 void ParScanThreadState::undo_alloc_in_to_space(HeapWord* obj,

                                                 size_t word_sz) {

   // Is the alloc in the current alloc buffer?

   if (to_space_alloc_buffer()->contains(obj)) {

     assert(to_space_alloc_buffer()->contains(obj + word_sz - 1),

            "Should contain whole object.");

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

   } else {

     CollectedHeap::fill_with_object(obj, word_sz);

   }

 }

 void ParScanThreadState::print_and_clear_promotion_failure_size() {

   if (_promotion_failure_size != 0) {

     if (PrintPromotionFailure) {

       gclog_or_tty->print(" (%d: promotion failure size = " SIZE_FORMAT ") ",

         _thread_num, _promotion_failure_size);

     }

     _promotion_failure_size = 0;

   }

 }

 class ParScanThreadStateSet: private ResourceArray {

 public:

   // Initializes states for the specified number of threads;

   ParScanThreadStateSet(int                     num_threads,

                         Space&                  to_space,

                         ParNewGeneration&       gen,

                         Generation&             old_gen,

                         ObjToScanQueueSet&      queue_set,

                         Stack<oop>*             overflow_stacks_,

                         size_t                  desired_plab_sz,

                         ParallelTaskTerminator& term);

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

   inline ParScanThreadState& thread_state(int i);

   void reset(bool promotion_failed);

   void flush();

   #if TASKQUEUE_STATS

   static void

     print_termination_stats_hdr(outputStream* const st = gclog_or_tty);

   void print_termination_stats(outputStream* const st = gclog_or_tty);

   static void

     print_taskqueue_stats_hdr(outputStream* const st = gclog_or_tty);

   void print_taskqueue_stats(outputStream* const st = gclog_or_tty);

   void reset_stats();

   #endif // TASKQUEUE_STATS

 private:

   ParallelTaskTerminator& _term;

   ParNewGeneration&       _gen;

   Generation&             _next_gen;

 };

 ParScanThreadStateSet::ParScanThreadStateSet(

   int num_threads, Space& to_space, ParNewGeneration& gen,

   Generation& old_gen, ObjToScanQueueSet& queue_set,

   Stack<oop>* overflow_stacks,

   size_t desired_plab_sz, ParallelTaskTerminator& term)

   : ResourceArray(sizeof(ParScanThreadState), num_threads),

     _gen(gen), _next_gen(old_gen), _term(term)

 {

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

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

          "overflow_stack allocation mismatch");

   // Initialize states.

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

     new ((ParScanThreadState*)_data + i)

         ParScanThreadState(&to_space, &gen, &old_gen, i, &queue_set,

                            overflow_stacks, desired_plab_sz, term);

   }

 }

 inline ParScanThreadState& ParScanThreadStateSet::thread_state(int i)

 {

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

   return ((ParScanThreadState*)_data)[i];

 }

 void ParScanThreadStateSet::reset(bool promotion_failed)

 {

   _term.reset_for_reuse();

   if (promotion_failed) {

     for (int i = 0; i < length(); ++i) {

       thread_state(i).print_and_clear_promotion_failure_size();

     }

   }

 }

 #if TASKQUEUE_STATS

 void

 ParScanThreadState::reset_stats()

 {

   taskqueue_stats().reset();

   _term_attempts = 0;

   _overflow_refills = 0;

   _overflow_refill_objs = 0;

 }

 void ParScanThreadStateSet::reset_stats()

 {

   for (int i = 0; i < length(); ++i) {

     thread_state(i).reset_stats();

   }

 }

 void

 ParScanThreadStateSet::print_termination_stats_hdr(outputStream* const st)

 {

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

   st->print_raw_cr("     elapsed  --strong roots-- "

                    "-------termination-------");

   st->print_raw_cr("thr     ms        ms       %   "

                    "    ms       %   attempts");

   st->print_raw_cr("--- --------- --------- ------ "

                    "--------- ------ --------");

 }

 void ParScanThreadStateSet::print_termination_stats(outputStream* const st)

 {

   print_termination_stats_hdr(st);

   for (int i = 0; i < length(); ++i) {

     const ParScanThreadState & pss = thread_state(i);

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

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

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

     st->print_cr("%3d %9.2f %9.2f %6.2f "

                  "%9.2f %6.2f " SIZE_FORMAT_W(8),

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

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

   }

 }

 // Print stats related to work queue activity.

 void ParScanThreadStateSet::print_taskqueue_stats_hdr(outputStream* const st)

 {

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

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

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

 }

 void ParScanThreadStateSet::print_taskqueue_stats(outputStream* const st)

 {

   print_taskqueue_stats_hdr(st);

   TaskQueueStats totals;

   for (int i = 0; i < length(); ++i) {

     const ParScanThreadState & pss = thread_state(i);

     const TaskQueueStats & stats = pss.taskqueue_stats();

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

     totals += stats;

     if (pss.overflow_refills() > 0) {

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

                    SIZE_FORMAT_W(10) " overflow objects",

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

     }

   }

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

   DEBUG_ONLY(totals.verify());

 }

 #endif // TASKQUEUE_STATS

 void ParScanThreadStateSet::flush()

 {

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

   // possible since this might otherwise become a bottleneck

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

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

   for (int i = 0; i < length(); ++i) {

     ParScanThreadState& par_scan_state = thread_state(i);

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

     // retire the last buffer.

     par_scan_state.to_space_alloc_buffer()->

       flush_stats_and_retire(_gen.plab_stats(),

                              false /* !retain */);

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

     // them all into one.

     ageTable *local_table = par_scan_state.age_table();

     _gen.age_table()->merge(local_table);

     // Inform old gen that we're done.

     _next_gen.par_promote_alloc_done(i);

     _next_gen.par_oop_since_save_marks_iterate_done(i);

   }

   if (UseConcMarkSweepGC && ParallelGCThreads > 0) {

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

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

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

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

     // performance.

     CFLS_LAB::compute_desired_plab_size();

   }

 }

 ParScanClosure::ParScanClosure(ParNewGeneration* g,

                                ParScanThreadState* par_scan_state) :

   OopsInGenClosure(g), _par_scan_state(par_scan_state), _g(g)

 {

   assert(_g->level() == 0, "Optimized for youngest generation");

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

 }

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

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

 void ParScanWithoutBarrierClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, false, false); }

 void ParScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, false); }

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

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

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

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

 ParScanWeakRefClosure::ParScanWeakRefClosure(ParNewGeneration* g,

                                              ParScanThreadState* par_scan_state)

   : ScanWeakRefClosure(g), _par_scan_state(par_scan_state)

 {}

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

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

 #ifdef WIN32

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

 #endif

 ParEvacuateFollowersClosure::ParEvacuateFollowersClosure(

     ParScanThreadState* par_scan_state_,

     ParScanWithoutBarrierClosure* to_space_closure_,

     ParScanWithBarrierClosure* old_gen_closure_,

     ParRootScanWithoutBarrierClosure* to_space_root_closure_,

     ParNewGeneration* par_gen_,

     ParRootScanWithBarrierTwoGensClosure* old_gen_root_closure_,

     ObjToScanQueueSet* task_queues_,

     ParallelTaskTerminator* terminator_) :

     _par_scan_state(par_scan_state_),

     _to_space_closure(to_space_closure_),

     _old_gen_closure(old_gen_closure_),

     _to_space_root_closure(to_space_root_closure_),

     _old_gen_root_closure(old_gen_root_closure_),

     _par_gen(par_gen_),

     _task_queues(task_queues_),

     _terminator(terminator_)

 {}

 void ParEvacuateFollowersClosure::do_void() {

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

   while (true) {

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

     oop obj_to_scan;

     par_scan_state()->trim_queues(0);

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

     // attempt to steal work from promoted.

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

                              par_scan_state()->hash_seed(),

                              obj_to_scan)) {

       bool res = work_q->push(obj_to_scan);

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

       //   if successful, goto Start.

       continue;

       // try global overflow list.

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

       continue;

     }

     // Otherwise, offer termination.

     par_scan_state()->start_term_time();

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

     par_scan_state()->end_term_time();

   }

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

          "Broken overflow list?");

   // Finish the last termination pause.

   par_scan_state()->end_term_time();

 }

 ParNewGenTask::ParNewGenTask(ParNewGeneration* gen, Generation* next_gen,

                 HeapWord* young_old_boundary, ParScanThreadStateSet* state_set) :

     AbstractGangTask("ParNewGeneration collection"),

     _gen(gen), _next_gen(next_gen),

     _young_old_boundary(young_old_boundary),

     _state_set(state_set)

   {}

 void ParNewGenTask::work(int i) {

   GenCollectedHeap* gch = GenCollectedHeap::heap();

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

   // and handle marks.

   ResourceMark rm;

   HandleMark hm;

   // We would need multiple old-gen queues otherwise.

   assert(gch->n_gens() == 2, "Par young collection currently only works with one older gen.");

   Generation* old_gen = gch->next_gen(_gen);

   ParScanThreadState& par_scan_state = _state_set->thread_state(i);

   par_scan_state.set_young_old_boundary(_young_old_boundary);

   par_scan_state.start_strong_roots();

   gch->gen_process_strong_roots(_gen->level(),

                                 true,  // Process younger gens, if any,

                                        // as strong roots.

                                 false, // no scope; this is parallel code

                                 false, // not collecting perm generation.

                                 SharedHeap::SO_AllClasses,

                                 &par_scan_state.to_space_root_closure(),

                                 true,   // walk *all* scavengable nmethods

                                 &par_scan_state.older_gen_closure());

   par_scan_state.end_strong_roots();

   // "evacuate followers".

   par_scan_state.evacuate_followers_closure().do_void();

 }

 #ifdef _MSC_VER

 #pragma warning( push )

 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list

 #endif

 ParNewGeneration::

 ParNewGeneration(ReservedSpace rs, size_t initial_byte_size, int level)

   : DefNewGeneration(rs, initial_byte_size, level, "PCopy"),

   _overflow_list(NULL),

   _is_alive_closure(this),

   _plab_stats(YoungPLABSize, PLABWeight)

 {

   NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;)

   NOT_PRODUCT(_num_par_pushes = 0;)

   _task_queues = new ObjToScanQueueSet(ParallelGCThreads);

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

   for (uint i1 = 0; i1 < ParallelGCThreads; i1++) {

     ObjToScanQueue *q = new ObjToScanQueue();

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

     _task_queues->register_queue(i1, q);

   }

   for (uint i2 = 0; i2 < ParallelGCThreads; i2++)

     _task_queues->queue(i2)->initialize();

   _overflow_stacks = NULL;

   if (ParGCUseLocalOverflow) {

     _overflow_stacks = NEW_C_HEAP_ARRAY(Stack<oop>, ParallelGCThreads);

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

       new (_overflow_stacks + i) Stack<oop>();

     }

   }

   if (UsePerfData) {

     EXCEPTION_MARK;

     ResourceMark rm;

     const char* cname =

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

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

                                      ParallelGCThreads, CHECK);

   }

 }

 #ifdef _MSC_VER

 #pragma warning( pop )

 #endif

 // ParNewGeneration::

 ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) :

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

 template <class T>

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

 #ifdef ASSERT

   {

     assert(!oopDesc::is_null(*p), "expected non-null ref");

     oop obj = oopDesc::load_decode_heap_oop_not_null(p);

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

     // as a weak reference.

     assert(obj->is_oop(), "expected an oop while scanning weak refs");

   }

 #endif // ASSERT

   _par_cl->do_oop_nv(p);

   if (Universe::heap()->is_in_reserved(p)) {

     oop obj = oopDesc::load_decode_heap_oop_not_null(p);

     _rs->write_ref_field_gc_par(p, obj);

   }

 }

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

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

 // ParNewGeneration::

 KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) :

   DefNewGeneration::KeepAliveClosure(cl) {}

 template <class T>

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

 #ifdef ASSERT

   {

     assert(!oopDesc::is_null(*p), "expected non-null ref");

     oop obj = oopDesc::load_decode_heap_oop_not_null(p);

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

     // as a weak reference.

     assert(obj->is_oop(), "expected an oop while scanning weak refs");

   }

 #endif // ASSERT

   _cl->do_oop_nv(p);

   if (Universe::heap()->is_in_reserved(p)) {

     oop obj = oopDesc::load_decode_heap_oop_not_null(p);

     _rs->write_ref_field_gc_par(p, obj);

   }

 }

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

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

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

   T heap_oop = oopDesc::load_heap_oop(p);

   if (!oopDesc::is_null(heap_oop)) {

     oop obj = oopDesc::decode_heap_oop_not_null(heap_oop);

     if ((HeapWord*)obj < _boundary) {

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

       oop new_obj = obj->is_forwarded()

                       ? obj->forwardee()

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

       oopDesc::encode_store_heap_oop_not_null(p, new_obj);

     }

     if (_gc_barrier) {

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

       if ((HeapWord*)obj < _gen_boundary) {

         _rs->write_ref_field_gc_par(p, obj);

       }

     }

   }

 }

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

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

 class ParNewRefProcTaskProxy: public AbstractGangTask {

   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;

 public:

   ParNewRefProcTaskProxy(ProcessTask& task, ParNewGeneration& gen,

                          Generation& next_gen,

                          HeapWord* young_old_boundary,

                          ParScanThreadStateSet& state_set);

 private:

   virtual void work(int i);

 private:

   ParNewGeneration&      _gen;

   ProcessTask&           _task;

   Generation&            _next_gen;

   HeapWord*              _young_old_boundary;

   ParScanThreadStateSet& _state_set;

 };

 ParNewRefProcTaskProxy::ParNewRefProcTaskProxy(

     ProcessTask& task, ParNewGeneration& gen,

     Generation& next_gen,

     HeapWord* young_old_boundary,

     ParScanThreadStateSet& state_set)

   : AbstractGangTask("ParNewGeneration parallel reference processing"),

     _gen(gen),

     _task(task),

     _next_gen(next_gen),

     _young_old_boundary(young_old_boundary),

     _state_set(state_set)

 {

 }

 void ParNewRefProcTaskProxy::work(int i)

 {

   ResourceMark rm;

   HandleMark hm;

   ParScanThreadState& par_scan_state = _state_set.thread_state(i);

   par_scan_state.set_young_old_boundary(_young_old_boundary);

   _task.work(i, par_scan_state.is_alive_closure(),

              par_scan_state.keep_alive_closure(),

              par_scan_state.evacuate_followers_closure());

 }

 class ParNewRefEnqueueTaskProxy: public AbstractGangTask {

   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;

   EnqueueTask& _task;

 public:

   ParNewRefEnqueueTaskProxy(EnqueueTask& task)

     : AbstractGangTask("ParNewGeneration parallel reference enqueue"),

       _task(task)

   { }

   virtual void work(int i)

   {

     _task.work(i);

   }

 };

 void ParNewRefProcTaskExecutor::execute(ProcessTask& task)

 {

   GenCollectedHeap* gch = GenCollectedHeap::heap();

   assert(gch->kind() == CollectedHeap::GenCollectedHeap,

          "not a generational heap");

   WorkGang* workers = gch->workers();

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

   ParNewRefProcTaskProxy rp_task(task, _generation, *_generation.next_gen(),

                                  _generation.reserved().end(), _state_set);

   workers->run_task(&rp_task);

   _state_set.reset(_generation.promotion_failed());

 }

 void ParNewRefProcTaskExecutor::execute(EnqueueTask& task)

 {

   GenCollectedHeap* gch = GenCollectedHeap::heap();

   WorkGang* workers = gch->workers();

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

   ParNewRefEnqueueTaskProxy enq_task(task);

   workers->run_task(&enq_task);

 }

 void ParNewRefProcTaskExecutor::set_single_threaded_mode()

 {

   _state_set.flush();

   GenCollectedHeap* gch = GenCollectedHeap::heap();

   gch->set_par_threads(0);  // 0 ==> non-parallel.

   gch->save_marks();

 }

 ScanClosureWithParBarrier::

 ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) :

   ScanClosure(g, gc_barrier) {}

 EvacuateFollowersClosureGeneral::

 EvacuateFollowersClosureGeneral(GenCollectedHeap* gch, int level,

                                 OopsInGenClosure* cur,

                                 OopsInGenClosure* older) :

   _gch(gch), _level(level),

   _scan_cur_or_nonheap(cur), _scan_older(older)

 {}

 void EvacuateFollowersClosureGeneral::do_void() {

   do {

     // Beware: this call will lead to closure applications via virtual

     // calls.

     _gch->oop_since_save_marks_iterate(_level,

                                        _scan_cur_or_nonheap,

                                        _scan_older);

   } while (!_gch->no_allocs_since_save_marks(_level));

 }

 bool ParNewGeneration::_avoid_promotion_undo = false;

 void ParNewGeneration::adjust_desired_tenuring_threshold() {

   // Set the desired survivor size to half the real survivor space

   _tenuring_threshold =

     age_table()->compute_tenuring_threshold(to()->capacity()/HeapWordSize);

 }

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

 void ParNewGeneration::collect(bool   full,

                                bool   clear_all_soft_refs,

                                size_t size,

                                bool   is_tlab) {

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

   GenCollectedHeap* gch = GenCollectedHeap::heap();

   assert(gch->kind() == CollectedHeap::GenCollectedHeap,

     "not a CMS generational heap");

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

   WorkGang* workers = gch->workers();

   _next_gen = gch->next_gen(this);

   assert(_next_gen != NULL,

     "This must be the youngest gen, and not the only gen");

   assert(gch->n_gens() == 2,

          "Par collection currently only works with single older gen.");

   // Do we have to avoid promotion_undo?

   if (gch->collector_policy()->is_concurrent_mark_sweep_policy()) {

     set_avoid_promotion_undo(true);

   }

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

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

   // do it.

   if (!collection_attempt_is_safe()) {

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

     return;

   }

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

   init_assuming_no_promotion_failure();

   if (UseAdaptiveSizePolicy) {

     set_survivor_overflow(false);

     size_policy->minor_collection_begin();

   }

   TraceTime t1("GC", PrintGC && !PrintGCDetails, true, gclog_or_tty);

   // Capture heap used before collection (for printing).

   size_t gch_prev_used = gch->used();

   SpecializationStats::clear();

   age_table()->clear();

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

   gch->save_marks();

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

   ParallelTaskTerminator _term(workers->total_workers(), task_queues());

   ParScanThreadStateSet thread_state_set(workers->total_workers(),

                                          *to(), *this, *_next_gen, *task_queues(),

                                          _overflow_stacks, desired_plab_sz(), _term);

   ParNewGenTask tsk(this, _next_gen, reserved().end(), &thread_state_set);

   int n_workers = workers->total_workers();

   gch->set_par_threads(n_workers);

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

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

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

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

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

   if (n_workers > 1) {

     GenCollectedHeap::StrongRootsScope srs(gch);

     workers->run_task(&tsk);

   } else {

     GenCollectedHeap::StrongRootsScope srs(gch);

     tsk.work(0);

   }

   thread_state_set.reset(promotion_failed());

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

   ReferenceProcessor* rp = ref_processor();

   IsAliveClosure is_alive(this);

   ScanWeakRefClosure scan_weak_ref(this);

   KeepAliveClosure keep_alive(&scan_weak_ref);

   ScanClosure               scan_without_gc_barrier(this, false);

   ScanClosureWithParBarrier scan_with_gc_barrier(this, true);

   set_promo_failure_scan_stack_closure(&scan_without_gc_barrier);

   EvacuateFollowersClosureGeneral evacuate_followers(gch, _level,

     &scan_without_gc_barrier, &scan_with_gc_barrier);

   rp->setup_policy(clear_all_soft_refs);

   if (rp->processing_is_mt()) {

     ParNewRefProcTaskExecutor task_executor(*this, thread_state_set);

     rp->process_discovered_references(&is_alive, &keep_alive,

                                       &evacuate_followers, &task_executor);

   } else {

     thread_state_set.flush();

     gch->set_par_threads(0);  // 0 ==> non-parallel.

     gch->save_marks();

     rp->process_discovered_references(&is_alive, &keep_alive,

                                       &evacuate_followers, NULL);

   }

   if (!promotion_failed()) {

     // Swap the survivor spaces.

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

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

     if (ZapUnusedHeapArea) {

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

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

       // collection(s).  When a minor collection fails to collect

       // sufficient space resizing of the young generation can occur

       // an redistribute the spaces in the young generation.  Mangle

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

       // other spaces.

       to()->mangle_unused_area();

     }

     swap_spaces();

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

     // for full GC's.

     size_policy->reset_gc_overhead_limit_count();

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

   } else {

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

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

     remove_forwarding_pointers();

     if (PrintGCDetails) {

       gclog_or_tty->print(" (promotion failed)");

     }

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

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

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

     gch->set_incremental_collection_failed();

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

     _next_gen->promotion_failure_occurred();

     // Reset the PromotionFailureALot counters.

     NOT_PRODUCT(Universe::heap()->reset_promotion_should_fail();)

   }

   // set new iteration safe limit for the survivor spaces

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

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

   adjust_desired_tenuring_threshold();

   if (ResizePLAB) {

     plab_stats()->adjust_desired_plab_sz();

   }

   if (PrintGC && !PrintGCDetails) {

     gch->print_heap_change(gch_prev_used);

   }

   if (PrintGCDetails && ParallelGCVerbose) {

     TASKQUEUE_STATS_ONLY(thread_state_set.print_termination_stats());

     TASKQUEUE_STATS_ONLY(thread_state_set.print_taskqueue_stats());

   }

   if (UseAdaptiveSizePolicy) {

     size_policy->minor_collection_end(gch->gc_cause());

     size_policy->avg_survived()->sample(from()->used());

   }

   update_time_of_last_gc(os::javaTimeMillis());

   SpecializationStats::print();

   rp->set_enqueuing_is_done(true);

   if (rp->processing_is_mt()) {

     ParNewRefProcTaskExecutor task_executor(*this, thread_state_set);

     rp->enqueue_discovered_references(&task_executor);

   } else {

     rp->enqueue_discovered_references(NULL);

   }

   rp->verify_no_references_recorded();

 }

 static int sum;

 void ParNewGeneration::waste_some_time() {

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

     sum += i;

   }

 }

 static const oop ClaimedForwardPtr = oop(0x4);

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

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

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

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

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

 oop ParNewGeneration::real_forwardee(oop obj) {

   oop forward_ptr = obj->forwardee();

   if (forward_ptr != ClaimedForwardPtr) {

     return forward_ptr;

   } else {

     return real_forwardee_slow(obj);

   }

 }

 oop ParNewGeneration::real_forwardee_slow(oop obj) {

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

   oop forward_ptr = obj->forwardee();

   while (forward_ptr == ClaimedForwardPtr) {

     waste_some_time();

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

     forward_ptr = obj->forwardee();

   }

   return forward_ptr;

 }

 #ifdef ASSERT

 bool ParNewGeneration::is_legal_forward_ptr(oop p) {

   return

     (_avoid_promotion_undo && p == ClaimedForwardPtr)

     || Universe::heap()->is_in_reserved(p);

 }

 #endif

 void ParNewGeneration::preserve_mark_if_necessary(oop obj, markOop m) {

   if (m->must_be_preserved_for_promotion_failure(obj)) {

     // We should really have separate per-worker stacks, rather

     // than use locking of a common pair of stacks.

     MutexLocker ml(ParGCRareEvent_lock);

     preserve_mark(obj, m);

   }

 }

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

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

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

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

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

 // copy_to_survivor_space_avoiding_with_undo.

 oop ParNewGeneration::copy_to_survivor_space_avoiding_promotion_undo(

         ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) {

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

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

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

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

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

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

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

   // word in a local and then analyze it.

   oopDesc dummyOld;

   dummyOld.set_mark(m);

   assert(!dummyOld.is_forwarded(),

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

   oop new_obj = NULL;

   oop forward_ptr;

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

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

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

     if (new_obj == NULL) {

       set_survivor_overflow(true);

     }

   }

   if (new_obj == NULL) {

     // Either to-space is full or we decided to promote

     // try allocating obj tenured

     // Attempt to install a null forwarding pointer (atomically),

     // to claim the right to install the real forwarding pointer.

     forward_ptr = old->forward_to_atomic(ClaimedForwardPtr);

     if (forward_ptr != NULL) {

       // someone else beat us to it.

         return real_forwardee(old);

     }

     new_obj = _next_gen->par_promote(par_scan_state->thread_num(),

                                        old, m, sz);

     if (new_obj == NULL) {

       // promotion failed, forward to self

       _promotion_failed = true;

       new_obj = old;

       preserve_mark_if_necessary(old, m);

       // Log the size of the maiden promotion failure

       par_scan_state->log_promotion_failure(sz);

     }

     old->forward_to(new_obj);

     forward_ptr = NULL;

   } else {

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

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

     forward_ptr = old->forward_to_atomic(new_obj);

     // Restore the mark word copied above.

     new_obj->set_mark(m);

     // Increment age if obj still in new generation

     new_obj->incr_age();

     par_scan_state->age_table()->add(new_obj, sz);

   }

   assert(new_obj != NULL, "just checking");

   if (forward_ptr == NULL) {

     oop obj_to_push = new_obj;

     if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) {

       // Length field used as index of next element to be scanned.

       // Real length can be obtained from real_forwardee()

       arrayOop(old)->set_length(0);

       obj_to_push = old;

       assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push,

              "push forwarded object");

     }

     // Push it on one of the queues of to-be-scanned objects.

     bool simulate_overflow = false;

     NOT_PRODUCT(

       if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) {

         // simulate a stack overflow

         simulate_overflow = true;

       }

     )

     if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) {

       // Add stats for overflow pushes.

       if (Verbose && PrintGCDetails) {

         gclog_or_tty->print("queue overflow!\n");

       }

       push_on_overflow_list(old, par_scan_state);

       TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0));

     }

     return new_obj;

   }

   // Oops.  Someone beat us to it.  Undo the allocation.  Where did we

   // allocate it?

   if (is_in_reserved(new_obj)) {

     // Must be in to_space.

     assert(to()->is_in_reserved(new_obj), "Checking");

     if (forward_ptr == ClaimedForwardPtr) {

       // Wait to get the real forwarding pointer value.

       forward_ptr = real_forwardee(old);

     }

     par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz);

   }

   return forward_ptr;

 }

 // Multiple GC threads may try to promote the same object.  If two

 // or more GC threads copy the object, only one wins the race to install

 // the forwarding pointer.  The other threads have to undo their copy.

 oop ParNewGeneration::copy_to_survivor_space_with_undo(

         ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) {

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

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

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

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

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

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

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

   // word here, install it in a local oopDesc, and then analyze it.

   oopDesc dummyOld;

   dummyOld.set_mark(m);

   assert(!dummyOld.is_forwarded(),

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

   bool failed_to_promote = false;

   oop new_obj = NULL;

   oop forward_ptr;

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

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

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

     if (new_obj == NULL) {

       set_survivor_overflow(true);

     }

   }

   if (new_obj == NULL) {

     // Either to-space is full or we decided to promote

     // try allocating obj tenured

     new_obj = _next_gen->par_promote(par_scan_state->thread_num(),

                                        old, m, sz);

     if (new_obj == NULL) {

       // promotion failed, forward to self

       forward_ptr = old->forward_to_atomic(old);

       new_obj = old;

       if (forward_ptr != NULL) {

         return forward_ptr;   // someone else succeeded

       }

       _promotion_failed = true;

       failed_to_promote = true;

       preserve_mark_if_necessary(old, m);

       // Log the size of the maiden promotion failure

       par_scan_state->log_promotion_failure(sz);

     }

   } else {

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

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

     // Restore the mark word copied above.

     new_obj->set_mark(m);

     // Increment age if new_obj still in new generation

     new_obj->incr_age();

     par_scan_state->age_table()->add(new_obj, sz);

   }

   assert(new_obj != NULL, "just checking");

   // Now attempt to install the forwarding pointer (atomically).

   // We have to copy the mark word before overwriting with forwarding

   // ptr, so we can restore it below in the copy.

   if (!failed_to_promote) {

     forward_ptr = old->forward_to_atomic(new_obj);

   }

   if (forward_ptr == NULL) {

     oop obj_to_push = new_obj;

     if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) {

       // Length field used as index of next element to be scanned.

       // Real length can be obtained from real_forwardee()

       arrayOop(old)->set_length(0);

       obj_to_push = old;

       assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push,

              "push forwarded object");

     }

     // Push it on one of the queues of to-be-scanned objects.

     bool simulate_overflow = false;

     NOT_PRODUCT(

       if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) {

         // simulate a stack overflow

         simulate_overflow = true;

       }

     )

     if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) {

       // Add stats for overflow pushes.

       push_on_overflow_list(old, par_scan_state);

       TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0));

     }

     return new_obj;

   }

   // Oops.  Someone beat us to it.  Undo the allocation.  Where did we

   // allocate it?

   if (is_in_reserved(new_obj)) {

     // Must be in to_space.

     assert(to()->is_in_reserved(new_obj), "Checking");

     par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz);

   } else {

     assert(!_avoid_promotion_undo, "Should not be here if avoiding.");

     _next_gen->par_promote_alloc_undo(par_scan_state->thread_num(),

                                       (HeapWord*)new_obj, sz);

   }

   return forward_ptr;

 }

 #ifndef PRODUCT

 // It's OK to call this multi-threaded;  the worst thing

 // that can happen is that we'll get a bunch of closely

 // spaced simulated oveflows, but that's OK, in fact

 // probably good as it would exercise the overflow code

 // under contention.

 bool ParNewGeneration::should_simulate_overflow() {

   if (_overflow_counter-- <= 0) { // just being defensive

     _overflow_counter = ParGCWorkQueueOverflowInterval;

     return true;

   } else {

     return false;

   }

 }

 #endif

 // In case we are using compressed oops, we need to be careful.

 // If the object being pushed is an object array, then its length

 // field keeps track of the "grey boundary" at which the next

 // incremental scan will be done (see ParGCArrayScanChunk).

 // When using compressed oops, this length field is kept in the

 // lower 32 bits of the erstwhile klass word and cannot be used

 // for the overflow chaining pointer (OCP below). As such the OCP

 // would itself need to be compressed into the top 32-bits in this

 // case. Unfortunately, see below, in the event that we have a

 // promotion failure, the node to be pushed on the list can be

 // outside of the Java heap, so the heap-based pointer compression

 // would not work (we would have potential aliasing between C-heap

 // and Java-heap pointers). For this reason, when using compressed

 // oops, we simply use a worker-thread-local, non-shared overflow

 // list in the form of a growable array, with a slightly different

 // overflow stack draining strategy. If/when we start using fat

 // stacks here, we can go back to using (fat) pointer chains

 // (although some performance comparisons would be useful since

 // single global lists have their own performance disadvantages

 // as we were made painfully aware not long ago, see 6786503).

 #define BUSY (oop(0x1aff1aff))

 void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) {

   assert(is_in_reserved(from_space_obj), "Should be from this generation");

   if (ParGCUseLocalOverflow) {

     // In the case of compressed oops, we use a private, not-shared

     // overflow stack.

     par_scan_state->push_on_overflow_stack(from_space_obj);

   } else {

     assert(!UseCompressedOops, "Error");

     // if the object has been forwarded to itself, then we cannot

     // use the klass pointer for the linked list.  Instead we have

     // to allocate an oopDesc in the C-Heap and use that for the linked list.

     // XXX This is horribly inefficient when a promotion failure occurs

     // and should be fixed. XXX FIX ME !!!

 #ifndef PRODUCT

     Atomic::inc_ptr(&_num_par_pushes);

     assert(_num_par_pushes > 0, "Tautology");

 #endif

     if (from_space_obj->forwardee() == from_space_obj) {

       oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1);

       listhead->forward_to(from_space_obj);

       from_space_obj = listhead;

     }

     oop observed_overflow_list = _overflow_list;

     oop cur_overflow_list;

     do {

       cur_overflow_list = observed_overflow_list;

       if (cur_overflow_list != BUSY) {

         from_space_obj->set_klass_to_list_ptr(cur_overflow_list);

       } else {

         from_space_obj->set_klass_to_list_ptr(NULL);

       }

       observed_overflow_list =

         (oop)Atomic::cmpxchg_ptr(from_space_obj, &_overflow_list, cur_overflow_list);

     } while (cur_overflow_list != observed_overflow_list);

   }

 }

 bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) {

   bool res;

   if (ParGCUseLocalOverflow) {

     res = par_scan_state->take_from_overflow_stack();

   } else {

     assert(!UseCompressedOops, "Error");

     res = take_from_overflow_list_work(par_scan_state);

   }

   return res;

 }

 // *NOTE*: The overflow list manipulation code here and

 // in CMSCollector:: are very similar in shape,

 // except that in the CMS case we thread the objects

 // directly into the list via their mark word, and do

 // not need to deal with special cases below related

 // to chunking of object arrays and promotion failure

 // handling.

 // CR 6797058 has been filed to attempt consolidation of

 // the common code.

 // Because of the common code, if you make any changes in

 // the code below, please check the CMS version to see if

 // similar changes might be needed.

 // See CMSCollector::par_take_from_overflow_list() for

 // more extensive documentation comments.

 bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) {

   ObjToScanQueue* work_q = par_scan_state->work_queue();

   // How many to take?

   size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,

                                  (size_t)ParGCDesiredObjsFromOverflowList);

   assert(!UseCompressedOops, "Error");

   assert(par_scan_state->overflow_stack() == NULL, "Error");

   if (_overflow_list == NULL) return false;

   // Otherwise, there was something there; try claiming the list.

   oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);

   // Trim off a prefix of at most objsFromOverflow items

   Thread* tid = Thread::current();

   size_t spin_count = (size_t)ParallelGCThreads;

   size_t sleep_time_millis = MAX2((size_t)1, objsFromOverflow/100);

   for (size_t spin = 0; prefix == BUSY && spin < spin_count; spin++) {

     // someone grabbed it before we did ...

     // ... we spin for a short while...

     os::sleep(tid, sleep_time_millis, false);

     if (_overflow_list == NULL) {

       // nothing left to take

       return false;

     } else if (_overflow_list != BUSY) {

      // try and grab the prefix

      prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);

     }

   }

   if (prefix == NULL || prefix == BUSY) {

      // Nothing to take or waited long enough

      if (prefix == NULL) {

        // Write back the NULL in case we overwrote it with BUSY above

        // and it is still the same value.

        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);

      }

      return false;

   }

   assert(prefix != NULL && prefix != BUSY, "Error");

   size_t i = 1;

   oop cur = prefix;

   while (i < objsFromOverflow && cur->klass_or_null() != NULL) {

     i++; cur = oop(cur->klass());

   }

   // Reattach remaining (suffix) to overflow list

   if (cur->klass_or_null() == NULL) {

     // Write back the NULL in lieu of the BUSY we wrote

     // above and it is still the same value.

     if (_overflow_list == BUSY) {

       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);

     }

   } else {

     assert(cur->klass_or_null() != BUSY, "Error");

     oop suffix = oop(cur->klass());       // suffix will be put back on global list

     cur->set_klass_to_list_ptr(NULL);     // break off suffix

     // It's possible that the list is still in the empty(busy) state

     // we left it in a short while ago; in that case we may be

     // able to place back the suffix.

     oop observed_overflow_list = _overflow_list;

     oop cur_overflow_list = observed_overflow_list;

     bool attached = false;

     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {

       observed_overflow_list =

         (oop) Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);

       if (cur_overflow_list == observed_overflow_list) {

         attached = true;

         break;

       } else cur_overflow_list = observed_overflow_list;

     }

     if (!attached) {

       // Too bad, someone else got in in between; we'll need to do a splice.

       // Find the last item of suffix list

       oop last = suffix;

       while (last->klass_or_null() != NULL) {

         last = oop(last->klass());

       }

       // Atomically prepend suffix to current overflow list

       observed_overflow_list = _overflow_list;

       do {

         cur_overflow_list = observed_overflow_list;

         if (cur_overflow_list != BUSY) {

           // Do the splice ...

           last->set_klass_to_list_ptr(cur_overflow_list);

         } else { // cur_overflow_list == BUSY

           last->set_klass_to_list_ptr(NULL);

         }

         observed_overflow_list =

           (oop)Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);

       } while (cur_overflow_list != observed_overflow_list);

     }

   }

   // Push objects on prefix list onto this thread's work queue

   assert(prefix != NULL && prefix != BUSY, "program logic");

   cur = prefix;

   ssize_t n = 0;

   while (cur != NULL) {

     oop obj_to_push = cur->forwardee();

     oop next        = oop(cur->klass_or_null());

     cur->set_klass(obj_to_push->klass());

     // This may be an array object that is self-forwarded. In that case, the list pointer

     // space, cur, is not in the Java heap, but rather in the C-heap and should be freed.

     if (!is_in_reserved(cur)) {

       // This can become a scaling bottleneck when there is work queue overflow coincident

       // with promotion failure.

       oopDesc* f = cur;

       FREE_C_HEAP_ARRAY(oopDesc, f);

     } else if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) {

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

       obj_to_push = cur;

     }

     bool ok = work_q->push(obj_to_push);

     assert(ok, "Should have succeeded");

     cur = next;

     n++;

   }

   TASKQUEUE_STATS_ONLY(par_scan_state->note_overflow_refill(n));

 #ifndef PRODUCT

   assert(_num_par_pushes >= n, "Too many pops?");

   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);

 #endif

   return true;

 }

 #undef BUSY

 void ParNewGeneration::ref_processor_init()

 {

   if (_ref_processor == NULL) {

     // Allocate and initialize a reference processor

     _ref_processor =

       new ReferenceProcessor(_reserved,                  // span

                              ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing

                              (int) ParallelGCThreads,    // mt processing degree

                              refs_discovery_is_mt(),     // mt discovery

                              (int) ParallelGCThreads,    // mt discovery degree

                              refs_discovery_is_atomic(), // atomic_discovery

                              NULL,                       // is_alive_non_header

                              false);                     // write barrier for next field updates

   }

 }

 const char* ParNewGeneration::name() const {

   return "par new generation";

 }

 bool ParNewGeneration::in_use() {

   return UseParNewGC && ParallelGCThreads > 0;

 }