/*
 * Copyright (c) 2013, 2015, Red Hat, Inc. and/or its affiliates.
 *
 * 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 "classfile/stringTable.hpp"
#include "gc/shared/gcTimer.hpp"
#include "gc/shared/isGCActiveMark.hpp"
#include "gc/shared/strongRootsScope.hpp"
#include "gc/shenandoah/shenandoahBarrierSet.hpp"
#include "gc/shenandoah/shenandoahConcurrentMark.inline.hpp"
#include "gc/shenandoah/shenandoahHeap.inline.hpp"
#include "gc/shenandoah/shenandoahRootProcessor.hpp"
#include "gc/shenandoah/brooksPointer.hpp"
#include "gc/shared/referenceProcessor.hpp"
#include "code/codeCache.hpp"
#include "classfile/symbolTable.hpp"
#include "classfile/systemDictionary.hpp"
#include "memory/iterator.inline.hpp"
#include "oops/oop.inline.hpp"
#include "gc/shared/taskqueue.inline.hpp"

// Mark the object and add it to the queue to be scanned
ShenandoahMarkObjsClosure::ShenandoahMarkObjsClosure(SCMObjToScanQueue* q, bool update_refs) :
  _heap((ShenandoahHeap*)(Universe::heap())),
  _mark_refs(ShenandoahMarkRefsClosure(q, update_refs)),
  _live_data(NEW_C_HEAP_ARRAY(size_t, _heap->max_regions(), mtGC))
{
  Copy::zero_to_bytes(_live_data, _heap->max_regions() * sizeof(size_t));
}

ShenandoahMarkObjsClosure::~ShenandoahMarkObjsClosure() {
  // Merge liveness data back into actual regions.

  // We need to lock the heap here, to avoid race with growing of heap.
  MutexLockerEx ml(ShenandoahHeap_lock, true);
  ShenandoahHeapRegion** regions = _heap->heap_regions();
  for (uint i = 0; i < _heap->num_regions(); i++) {
    regions[i]->increase_live_data(_live_data[i]);
  }
  FREE_C_HEAP_ARRAY(size_t, _live_data);
}

ShenandoahMarkRefsClosure::ShenandoahMarkRefsClosure(SCMObjToScanQueue* q, bool update_refs) :
  MetadataAwareOopClosure(((ShenandoahHeap *) Universe::heap())->ref_processor()),
  _queue(q),
  _heap((ShenandoahHeap*) Universe::heap()),
  _scm(_heap->concurrentMark()),
  _update_refs(update_refs)
{
}

void ShenandoahMarkRefsClosure::do_oop(narrowOop* p) {
  Unimplemented();
}


// Walks over all the objects in the generation updating any
// references to from space.

class CLDMarkAliveClosure : public CLDClosure {
private:
  CLDClosure* _cl;
public:
  CLDMarkAliveClosure(CLDClosure* cl) : _cl(cl) {
  }
  void do_cld(ClassLoaderData* cld) {
    ShenandoahIsAliveClosure is_alive;
    if (cld->is_alive(&is_alive)) {
      _cl->do_cld(cld);
    }
  }
};

class ShenandoahMarkRootsTask : public AbstractGangTask {
private:
  ShenandoahRootProcessor* _rp;
  bool _update_refs;
public:
  ShenandoahMarkRootsTask(ShenandoahRootProcessor* rp, bool update_refs) :
    AbstractGangTask("Shenandoah update roots task"), _update_refs(update_refs),
    _rp(rp) {
  }

  void work(uint worker_id) {
    // tty->print_cr("start mark roots worker: "INT32_FORMAT, worker_id);
    ShenandoahHeap* heap = ShenandoahHeap::heap();
    SCMObjToScanQueue* q = heap->concurrentMark()->get_queue(worker_id);
    ShenandoahMarkRefsClosure cl(q, _update_refs);

    CodeBlobToOopClosure blobsCl(&cl, true);
    CLDToOopClosure cldCl(&cl);

    ResourceMark m;
    if (ShenandoahProcessReferences && ClassUnloadingWithConcurrentMark) {
      _rp->process_strong_roots(&cl, &cldCl, &blobsCl);
    } else {
      _rp->process_all_roots(&cl, &cldCl, &blobsCl);
    }
    // tty->print_cr("finish mark roots worker: "INT32_FORMAT, worker_id);
  }
};

class SCMConcurrentMarkingTask : public AbstractGangTask {
private:
  ShenandoahConcurrentMark* _cm;
  ParallelTaskTerminator* _terminator;
  int _seed;
  bool _update_refs;

public:
  SCMConcurrentMarkingTask(ShenandoahConcurrentMark* cm, ParallelTaskTerminator* terminator, bool update_refs) :
    AbstractGangTask("Root Region Scan"), _cm(cm), _terminator(terminator), _update_refs(update_refs), _seed(17) {
  }

      
  void work(uint worker_id) {

    SCMObjToScanQueue* q = _cm->get_queue(worker_id);
    ShenandoahMarkObjsClosure cl(q, _update_refs);
    ShenandoahHeap* heap = ShenandoahHeap::heap();
    while (true) {
      if (heap->cancelled_concgc() ||
	  (!_cm->try_queue(q, &cl) &&
	   !_cm->try_draining_an_satb_buffer(worker_id) &&
	   !_cm->try_to_steal(worker_id, &cl, &_seed))
	  ) {
	if (_terminator->offer_termination()) break;
      }
    }
    if (ShenandoahTracePhases && heap->cancelled_concgc()) {
      tty->print_cr("Cancelled concurrent marking");
    }
  }
};

void ShenandoahConcurrentMark::prepare_unmarked_root_objs() {

  ShenandoahHeap* heap = ShenandoahHeap::heap();
  bool update_refs = heap->need_update_refs();

  if (update_refs) {
    COMPILER2_PRESENT(DerivedPointerTable::clear());
  }

  prepare_unmarked_root_objs_no_derived_ptrs(update_refs);

  if (update_refs) {
    COMPILER2_PRESENT(DerivedPointerTable::update_pointers());
  }

}

void ShenandoahConcurrentMark::prepare_unmarked_root_objs_no_derived_ptrs(bool update_refs) {
  assert(Thread::current()->is_VM_thread(), "can only do this in VMThread");

  ShenandoahHeap* heap = ShenandoahHeap::heap();
  if (ShenandoahParallelRootScan) {

    ClassLoaderDataGraph::clear_claimed_marks();
    heap->conc_workers()->set_active_workers(_max_conc_worker_id);
    ShenandoahRootProcessor root_proc(heap, _max_conc_worker_id);
    TASKQUEUE_STATS_ONLY(reset_taskqueue_stats());
    ShenandoahMarkRootsTask mark_roots(&root_proc, update_refs);
    heap->conc_workers()->run_task(&mark_roots);

    // Mark through any class loaders that have been found alive.
    ShenandoahMarkRefsClosure cl(get_queue(0), update_refs);
    CLDToOopClosure cldCl(&cl);
    CLDMarkAliveClosure cld_keep_alive(&cldCl);
    ClassLoaderDataGraph::roots_cld_do(NULL, &cld_keep_alive);

  } else {
    ShenandoahMarkRefsClosure cl(get_queue(0), update_refs);
    heap->roots_iterate(&cl);
  }

  if (!(ShenandoahProcessReferences && ClassUnloadingWithConcurrentMark)) {
    ShenandoahMarkRefsClosure cl(get_queue(0), update_refs);
    heap->weak_roots_iterate(&cl);
  }

  // tty->print_cr("all root marker threads done");
}


void ShenandoahConcurrentMark::initialize() {
  _max_conc_worker_id = MAX2((uint) ConcGCThreads, 1U);
  _task_queues = new SCMObjToScanQueueSet((int) _max_conc_worker_id);

  for (uint i = 0; i < _max_conc_worker_id; ++i) {
    SCMObjToScanQueue* task_queue = new SCMObjToScanQueue();
    task_queue->initialize();
    _task_queues->register_queue(i, task_queue);
  }
  JavaThread::satb_mark_queue_set().set_buffer_size(1014 /* G1SATBBufferSize */);
}

void ShenandoahConcurrentMark::mark_from_roots() {
  if (ShenandoahGCVerbose) {
    tty->print_cr("STOPPING THE WORLD: before marking");
    tty->print_cr("Starting markFromRoots");
  }

  ShenandoahHeap* sh = (ShenandoahHeap *) Universe::heap();

  bool update_refs = sh->need_update_refs();

  sh->shenandoahPolicy()->record_phase_start(ShenandoahCollectorPolicy::conc_mark);
  ParallelTaskTerminator terminator(_max_conc_worker_id, _task_queues);

  if (ShenandoahProcessReferences) {
    ReferenceProcessor* rp = sh->ref_processor();
    // enable ("weak") refs discovery
    rp->enable_discovery(true /*verify_no_refs*/);
    rp->setup_policy(false); // snapshot the soft ref policy to be used in this cycle
  }
  
  SCMConcurrentMarkingTask markingTask = SCMConcurrentMarkingTask(this, &terminator, update_refs);
  sh->conc_workers()->set_active_workers(_max_conc_worker_id);
  sh->conc_workers()->run_task(&markingTask);

  if (ShenandoahGCVerbose) {
    tty->print("total workers = %u active workers = %u\n", 
	       sh->conc_workers()->total_workers(), 
	       sh->conc_workers()->active_workers());
    TASKQUEUE_STATS_ONLY(print_taskqueue_stats());
    TASKQUEUE_STATS_ONLY(reset_taskqueue_stats());
  }

  if (ShenandoahGCVerbose) {
    tty->print_cr("Finishing markFromRoots");
    tty->print_cr("RESUMING THE WORLD: after marking");
  }

  sh->shenandoahPolicy()->record_phase_end(ShenandoahCollectorPolicy::conc_mark);
}

class FinishDrainSATBBuffersTask : public AbstractGangTask {
private:
  ShenandoahConcurrentMark* _cm;
  ParallelTaskTerminator* _terminator;
public:
  FinishDrainSATBBuffersTask(ShenandoahConcurrentMark* cm, ParallelTaskTerminator* terminator) :
    AbstractGangTask("Finish draining SATB buffers"), _cm(cm), _terminator(terminator) {
  }

  void work(uint worker_id) {
    _cm->drain_satb_buffers(worker_id, true);
  }
};

class ShenandoahUpdateAliveRefs : public OopClosure {
private:
  ShenandoahHeap* _heap;
public:
  ShenandoahUpdateAliveRefs() : _heap(ShenandoahHeap::heap()) {
  }
  virtual void do_oop(oop* p) {
    _heap->maybe_update_oop_ref(p);
  }

  virtual void do_oop(narrowOop* p) {
    Unimplemented();
  }
};

void ShenandoahConcurrentMark::finish_mark_from_roots() {
  if (ShenandoahGCVerbose) {
    tty->print_cr("Starting finishMarkFromRoots");
  }

  IsGCActiveMark is_active;

  ShenandoahHeap* sh = (ShenandoahHeap *) Universe::heap();

  // Trace any (new) unmarked root references.
  sh->shenandoahPolicy()->record_phase_start(ShenandoahCollectorPolicy::rescan_roots);
  prepare_unmarked_root_objs();
  sh->shenandoahPolicy()->record_phase_end(ShenandoahCollectorPolicy::rescan_roots);
  sh->shenandoahPolicy()->record_phase_start(ShenandoahCollectorPolicy::drain_satb);
  {
    StrongRootsScope scope(_max_conc_worker_id);
    ParallelTaskTerminator terminator(_max_conc_worker_id, _task_queues);
    // drain_satb_buffers(0, true);
    FinishDrainSATBBuffersTask drain_satb_buffers(this, &terminator);
    sh->conc_workers()->set_active_workers(_max_conc_worker_id);
    sh->conc_workers()->run_task(&drain_satb_buffers);
    sh->shenandoahPolicy()->record_phase_end(ShenandoahCollectorPolicy::drain_satb);
  }
  
  // Finally mark everything else we've got in our queues during the previous steps.
  {
    sh->shenandoahPolicy()->record_phase_start(ShenandoahCollectorPolicy::drain_queues);
    ParallelTaskTerminator terminator(_max_conc_worker_id, _task_queues);
    SCMConcurrentMarkingTask markingTask = SCMConcurrentMarkingTask(this, &terminator, sh->need_update_refs());
    sh->conc_workers()->set_active_workers(_max_conc_worker_id);
    sh->conc_workers()->run_task(&markingTask);
    sh->shenandoahPolicy()->record_phase_end(ShenandoahCollectorPolicy::drain_queues);
  }

#ifdef ASSERT
  for (int i = 0; i < (int) _max_conc_worker_id; i++) {
    assert(_task_queues->queue(i)->is_empty(), "Should be empty");
  }
#endif

  // When we're done marking everything, we process weak references.
  if (ShenandoahProcessReferences) {
    sh->shenandoahPolicy()->record_phase_start(ShenandoahCollectorPolicy::weakrefs);
    weak_refs_work();
    sh->shenandoahPolicy()->record_phase_end(ShenandoahCollectorPolicy::weakrefs);
  }

#ifdef ASSERT
  for (int i = 0; i < (int) _max_conc_worker_id; i++) {
    assert(_task_queues->queue(i)->is_empty(), "Should be empty");
  }
#endif

  if (ShenandoahGCVerbose) {
    tty->print_cr("Finishing finishMarkFromRoots");
#ifdef SLOWDEBUG
    for (int i = 0; i <(int)_max_conc_worker_id; i++) {
      tty->print("Queue: "INT32_FORMAT":", i);
      _task_queues->queue(i)->stats.print(tty, 10);
      tty->cr();
      _task_queues->queue(i)->stats.verify();
    }
#endif
  }

  // We still need to update (without marking) alive refs in JNI handles.
  if (ShenandoahProcessReferences && ClassUnloadingWithConcurrentMark) {
    ShenandoahUpdateAliveRefs cl;
    ShenandoahIsAliveClosure is_alive;
    JNIHandles::weak_oops_do(&is_alive, &cl);
  }

#ifdef ASSERT
  verify_roots();

  if (ShenandoahDumpHeapAfterConcurrentMark) {
    sh->ensure_parsability(false);
    sh->print_all_refs("post-mark");
  }
#endif
}

#ifdef ASSERT
void ShenandoahVerifyRootsClosure1::do_oop(oop* p) {
  oop obj = oopDesc::load_heap_oop(p);
  if (! oopDesc::is_null(obj)) {
    guarantee(ShenandoahHeap::heap()->is_marked_current(obj), "oop must be marked");
    guarantee(obj == ShenandoahBarrierSet::resolve_oop_static_not_null(obj), "oop must not be forwarded");
  }
}

void ShenandoahConcurrentMark::verify_roots() {
  ShenandoahVerifyRootsClosure1 cl;
  CodeBlobToOopClosure blobsCl(&cl, true);
  CLDToOopClosure cldCl(&cl);
  ClassLoaderDataGraph::clear_claimed_marks();
  ShenandoahRootProcessor rp(ShenandoahHeap::heap(), 1);
  rp.process_roots(&cl, &cl, &cldCl, &cldCl, &cldCl, &blobsCl);
}
#endif

class ShenandoahSATBBufferClosure : public SATBBufferClosure {
private:
  SCMObjToScanQueue* _queue;

public:
  ShenandoahSATBBufferClosure(SCMObjToScanQueue* q) :
    _queue(q)
  {
  }

  void do_buffer(void** buffer, size_t size) {
    // tty->print_cr("draining one satb buffer");
    for (size_t i = 0; i < size; ++i) {
      void* entry = buffer[i];
      oop obj = oop(entry);
      // tty->print_cr("satb buffer entry: "PTR_FORMAT, p2i((HeapWord*) obj));
      if (!oopDesc::is_null(obj)) {
	obj = ShenandoahBarrierSet::resolve_oop_static_not_null(obj);
	bool pushed = _queue->push(obj);
	assert(pushed, "overflow queue should always succeed pushing");
      }
    }
  }
};

class ShenandoahSATBThreadsClosure : public ThreadClosure {
  ShenandoahSATBBufferClosure* _satb_cl;
  int _thread_parity;

 public:
  ShenandoahSATBThreadsClosure(ShenandoahSATBBufferClosure* satb_cl) :
    _satb_cl(satb_cl),
    _thread_parity(Threads::thread_claim_parity()) {}

  void do_thread(Thread* thread) {
    if (thread->is_Java_thread()) {
      if (thread->claim_oops_do(true, _thread_parity)) {
        JavaThread* jt = (JavaThread*)thread;
        jt->satb_mark_queue().apply_closure_and_empty(_satb_cl);
      }
    } else if (thread->is_VM_thread()) {
      if (thread->claim_oops_do(true, _thread_parity)) {
        JavaThread::satb_mark_queue_set().shared_satb_queue()->apply_closure_and_empty(_satb_cl);
      }
    }
  }
};

void ShenandoahConcurrentMark::drain_satb_buffers(uint worker_id, bool remark) {

  // tty->print_cr("start draining SATB buffers");

  ShenandoahHeap* sh = (ShenandoahHeap*) Universe::heap();
  SCMObjToScanQueue* q = get_queue(worker_id);
  ShenandoahSATBBufferClosure cl(q);

  SATBMarkQueueSet& satb_mq_set = JavaThread::satb_mark_queue_set();
  while (satb_mq_set.apply_closure_to_completed_buffer(&cl));

  if (remark) {
    ShenandoahSATBThreadsClosure tc(&cl);
    Threads::threads_do(&tc);
  }

  // tty->print_cr("end draining SATB buffers");

}

bool ShenandoahConcurrentMark::drain_one_satb_buffer(uint worker_id) {

  ShenandoahHeap* sh = (ShenandoahHeap*) Universe::heap();
  SCMObjToScanQueue* q = get_queue(worker_id);
  ShenandoahSATBBufferClosure cl(q);

  SATBMarkQueueSet& satb_mq_set = JavaThread::satb_mark_queue_set();
  bool result = satb_mq_set.apply_closure_to_completed_buffer(&cl);
  return result;
}

#if TASKQUEUE_STATS
void ShenandoahConcurrentMark::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 ShenandoahConcurrentMark::print_taskqueue_stats(outputStream* const st) const {
  print_taskqueue_stats_hdr(st);
  ShenandoahHeap* sh = (ShenandoahHeap*) Universe::heap();
  TaskQueueStats totals;
  const int n = sh->max_conc_workers();
  for (int i = 0; i < n; ++i) {
    st->print(INT32_FORMAT_W(3), i); 
    _task_queues->queue(i)->stats.print(st);
    st->print("\n");
    totals += _task_queues->queue(i)->stats;
  }
  st->print_raw("tot "); totals.print(st); st->cr();
  DEBUG_ONLY(totals.verify());

}

void ShenandoahConcurrentMark::print_push_only_taskqueue_stats(outputStream* const st) const {
  print_taskqueue_stats_hdr(st);
  ShenandoahHeap* sh = (ShenandoahHeap*) Universe::heap();
  TaskQueueStats totals;
  const int n = sh->max_conc_workers();
  for (int i = 0; i < n; ++i) {
    st->print(INT32_FORMAT_W(3), i); 
    _task_queues->queue(i)->stats.print(st);
    st->print("\n");
    totals += _task_queues->queue(i)->stats;
  }
  st->print_raw("tot "); totals.print(st); st->cr();

  DEBUG_ONLY(totals.verify_only_pushes());
}

void ShenandoahConcurrentMark::reset_taskqueue_stats() {
  ShenandoahHeap* sh = (ShenandoahHeap*) Universe::heap();
  const int n = sh->max_conc_workers();
  for (int i = 0; i < n; ++i) {
    _task_queues->queue(i)->stats.reset();
  }
}
#endif // TASKQUEUE_STATS

// Weak Reference Closures
class ShenandoahCMDrainMarkingStackClosure: public VoidClosure {
  ShenandoahHeap* _sh;
  ShenandoahConcurrentMark* _scm;
  uint _worker_id;
  int _seed;

public:
  ShenandoahCMDrainMarkingStackClosure(uint worker_id): _worker_id(worker_id), _seed(17) {
    _sh = (ShenandoahHeap*) Universe::heap();
    _scm = _sh->concurrentMark();
  }

      
  void do_void() {

    SCMObjToScanQueue* q = _scm->get_queue(_worker_id);
    ShenandoahMarkObjsClosure cl(q, _sh->need_update_refs());
    while (true) {
      if (!_scm->try_queue(q, &cl) &&
	  !_scm->try_draining_an_satb_buffer(_worker_id) &&
	  !_scm->try_to_steal(_worker_id, &cl, &_seed)) {
	break;
      }
    }
  }
};


class ShenandoahCMKeepAliveAndDrainClosure: public OopClosure {
  SCMObjToScanQueue* _queue;
  ShenandoahHeap* _sh;
  ShenandoahConcurrentMark* _scm;

  size_t _ref_count;

public:
  ShenandoahCMKeepAliveAndDrainClosure(SCMObjToScanQueue* q) :
    _queue(q) {
    _sh = (ShenandoahHeap*) Universe::heap();
    _scm = _sh->concurrentMark();
    _ref_count = 0;
  }

  virtual void do_oop(oop* p){ do_oop_work(p);}
  virtual void do_oop(narrowOop* p) {  
    assert(false, "narrowOops Aren't implemented");
  }


  void do_oop_work(oop* p) {  

    oop obj;
    if (_sh->need_update_refs()) {
      obj = _sh->maybe_update_oop_ref(p);
    } else {
      obj = oopDesc::load_heap_oop(p);
    }

    assert(obj == oopDesc::bs()->resolve_oop(obj), "only get updated oops in weak ref processing");

    if (obj != NULL) {
      if (Verbose && ShenandoahTraceWeakReferences) {
	gclog_or_tty->print_cr("\twe're looking at location "
			       "*"PTR_FORMAT" = "PTR_FORMAT,
			       p2i(p), p2i((void*) obj));
	obj->print();
      }
      bool pushed = _queue->push(obj);
      assert(pushed, "overflow queue should always succeed pushing");

      _ref_count++;
    }    
  }

  size_t ref_count() { return _ref_count; }

};

class ShenandoahRefProcTaskProxy : public AbstractGangTask {

private:
  AbstractRefProcTaskExecutor::ProcessTask& _proc_task;

public:

  ShenandoahRefProcTaskProxy(AbstractRefProcTaskExecutor::ProcessTask& proc_task) :
    AbstractGangTask("Process reference objects in parallel"),
    _proc_task(proc_task) {
  }

  void work(uint worker_id) {
    ShenandoahHeap* heap = ShenandoahHeap::heap();
    ShenandoahIsAliveClosure is_alive;
    ShenandoahCMKeepAliveAndDrainClosure keep_alive(heap->concurrentMark()->get_queue(worker_id));
    ShenandoahCMDrainMarkingStackClosure complete_gc(worker_id);
    _proc_task.work(worker_id, is_alive, keep_alive, complete_gc);
  }
};

class ShenandoahRefEnqueueTaskProxy : public AbstractGangTask {

private:
  AbstractRefProcTaskExecutor::EnqueueTask& _enqueue_task;

public:

  ShenandoahRefEnqueueTaskProxy(AbstractRefProcTaskExecutor::EnqueueTask& enqueue_task) :
    AbstractGangTask("Enqueue reference objects in parallel"),
    _enqueue_task(enqueue_task) {
  }

  void work(uint worker_id) {
    _enqueue_task.work(worker_id);
  }
};

class ShenandoahRefProcTaskExecutor : public AbstractRefProcTaskExecutor {

private:
  WorkGang* _workers;

public:

  ShenandoahRefProcTaskExecutor() : _workers(ShenandoahHeap::heap()->conc_workers()) {
  }

  // Executes a task using worker threads.
  void execute(ProcessTask& task) {
    ShenandoahRefProcTaskProxy proc_task_proxy(task);
    _workers->run_task(&proc_task_proxy);
  }

  void execute(EnqueueTask& task) {
    ShenandoahRefEnqueueTaskProxy enqueue_task_proxy(task);
    _workers->run_task(&enqueue_task_proxy);
  }
};


void ShenandoahConcurrentMark::weak_refs_work() {
   ShenandoahHeap* sh = (ShenandoahHeap*) Universe::heap();
   ReferenceProcessor* rp = sh->ref_processor();

   // Setup collector policy for softref cleaning.
   bool clear_soft_refs = sh->collector_policy()->use_should_clear_all_soft_refs(true /* bogus arg*/);
   if (ShenandoahTraceWeakReferences) {
     tty->print_cr("clearing soft refs: %s", BOOL_TO_STR(clear_soft_refs));
   }
   rp->setup_policy(clear_soft_refs);

   uint serial_worker_id = 0;
   ShenandoahIsAliveClosure is_alive;
   ShenandoahCMKeepAliveAndDrainClosure keep_alive(get_queue(serial_worker_id));
   ShenandoahCMDrainMarkingStackClosure complete_gc(serial_worker_id);
   ShenandoahRefProcTaskExecutor par_task_executor;
   bool processing_is_mt = true;
   AbstractRefProcTaskExecutor* executor = (processing_is_mt ? &par_task_executor : NULL);

   if (ShenandoahTraceWeakReferences) {
     gclog_or_tty->print_cr("start processing references");
   }

   rp->process_discovered_references(&is_alive, &keep_alive, 
				     &complete_gc, &par_task_executor, 
				     NULL,
                                     ShenandoahHeap::heap()->tracer()->gc_id());
   
   if (ShenandoahTraceWeakReferences) {
     gclog_or_tty->print_cr("finished processing references, processed "SIZE_FORMAT" refs", keep_alive.ref_count());
     gclog_or_tty->print_cr("start enqueuing references");
   }

   rp->enqueue_discovered_references(executor);

   if (ShenandoahTraceWeakReferences) {
     gclog_or_tty->print_cr("finished enqueueing references");
   }

   rp->verify_no_references_recorded();
   assert(!rp->discovery_enabled(), "Post condition");

   if (ClassUnloadingWithConcurrentMark) {
     // Unload classes and purge SystemDictionary.
     bool purged_class = SystemDictionary::do_unloading(&is_alive);
     // Unload nmethods.
     CodeCache::do_unloading(&is_alive, purged_class);
     // Prune dead klasses from subklass/sibling/implementor lists.
     Klass::clean_weak_klass_links(&is_alive);
     // Delete entries from dead interned strings.
     StringTable::unlink(&is_alive);
     // Clean up unreferenced symbols in symbol table.
     SymbolTable::unlink();

     ClassLoaderDataGraph::purge();
   }
}

void ShenandoahConcurrentMark::cancel() {
  ShenandoahHeap* sh = ShenandoahHeap::heap();

  // Cancel weak-ref discovery.
  if (ShenandoahProcessReferences) {
    ReferenceProcessor* rp = sh->ref_processor();
    rp->abandon_partial_discovery();
    rp->disable_discovery();
  }

  // Clean up marking stacks.
  SCMObjToScanQueueSet* queues = task_queues();
  for (uint i = 0; i < _max_conc_worker_id; ++i) {
    SCMObjToScanQueue* task_queue = queues->queue(i);
    task_queue->set_empty();
    task_queue->overflow_stack()->clear();
  }

  // Cancel SATB buffers.
  JavaThread::satb_mark_queue_set().abandon_partial_marking();
}

SCMObjToScanQueue* ShenandoahConcurrentMark::get_queue(uint worker_id) {
  worker_id = worker_id % _max_conc_worker_id;
  return _task_queues->queue(worker_id);
}