jdk8-mips64-public/hotspot: src/share/vm/gc_implementation/parNew/parNewGeneration.cpp@bca17e38de00 (annotated)

src/share/vm/gc_implementation/parNew/parNewGeneration.cpp@bca17e38de00 (annotated)

src/share/vm/gc_implementation/parNew/parNewGeneration.cpp

Tue, 09 Aug 2011 10:16:01 -0700

author: jmasa
date: Tue, 09 Aug 2011 10:16:01 -0700
changeset 3294: bca17e38de00
parent 2651: 92da084fefc9
child 3357: 441e946dc1af
permissions: -rw-r--r--

6593758: RFE: Enhance GC ergonomics to dynamically choose ParallelGCThreads
Summary: Select number of GC threads dynamically based on heap usage and number of Java threads
Reviewed-by: johnc, ysr, jcoomes

 /*
  * 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(int active_workers, 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;
  public:
   bool is_valid(int id) const { return id < length(); }
   ParallelTaskTerminator* terminator() { return &_term; }
 };
 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(int active_threads, bool promotion_failed)
 {
   _term.reset_for_reuse(active_threads);
   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)
   {}
 // Reset the terminator for the given number of
 // active threads.
 void ParNewGenTask::set_for_termination(int active_workers) {
   _state_set->reset(active_workers, _gen->promotion_failed());
   // Should the heap be passed in?  There's only 1 for now so
   // grab it instead.
   GenCollectedHeap* gch = GenCollectedHeap::heap();
   gch->set_n_termination(active_workers);
 }
 // The "i" passed to this method is the part of the work for
 // this thread.  It is not the worker ID.  The "i" is derived
 // from _started_workers which is incremented in internal_note_start()
 // called in GangWorker loop() and which is called under the
 // which is  called under the protection of the gang monitor and is
 // called after a task is started.  So "i" is based on
 // first-come-first-served.
 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);
   assert(_state_set->is_valid(i), "Should not have been called");
   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);
   virtual void set_for_termination(int active_workers) {
     _state_set.terminator()->reset_for_reuse(active_workers);
   }
 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");
   FlexibleWorkGang* workers = gch->workers();
   assert(workers != NULL, "Need parallel worker threads.");
   _state_set.reset(workers->active_workers(), _generation.promotion_failed());
   ParNewRefProcTaskProxy rp_task(task, _generation, *_generation.next_gen(),
                                  _generation.reserved().end(), _state_set);
   workers->run_task(&rp_task);
   _state_set.reset(0 /* bad value in debug if not reset */,
                    _generation.promotion_failed());
 }
 void ParNewRefProcTaskExecutor::execute(EnqueueTask& task)
 {
   GenCollectedHeap* gch = GenCollectedHeap::heap();
   FlexibleWorkGang* 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();
   FlexibleWorkGang* workers = gch->workers();
   assert(workers != NULL, "Need workgang for parallel work");
   int active_workers =
       AdaptiveSizePolicy::calc_active_workers(workers->total_workers(),
                                    workers->active_workers(),
                                    Threads::number_of_non_daemon_threads());
   workers->set_active_workers(active_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.");
   int n_workers = active_workers;
   // Set the correct parallelism (number of queues) in the reference processor
   ref_processor()->set_active_mt_degree(n_workers);
   // Always set the terminator for the active number of workers
   // because only those workers go through the termination protocol.
   ParallelTaskTerminator _term(n_workers, task_queues());
   ParScanThreadStateSet thread_state_set(workers->active_workers(),
                                          *to(), *this, *_next_gen, *task_queues(),
                                          _overflow_stacks, desired_plab_sz(), _term);
   ParNewGenTask tsk(this, _next_gen, reserved().end(), &thread_state_set);
   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(0 /* Bad value in debug if not 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);
   // Can  the mt_degree be set later (at run_task() time would be best)?
   rp->set_active_mt_degree(active_workers);
   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;
 }

Mercurial > jdk8-mips64-public > hotspot / annotate

src/share/vm/gc_implementation/parNew/parNewGeneration.cpp@bca17e38de00 (annotated)

src/share/vm/gc_implementation/parNew/parNewGeneration.cpp