view src/share/vm/gc_implementation/g1/satbQueue.cpp @ 2740:4dfb2df418f2

6484982: G1: process references during evacuation pauses Summary: G1 now uses two reference processors - one is used by concurrent marking and the other is used by STW GCs (both full and incremental evacuation pauses). In an evacuation pause, the reference processor is embedded into the closures used to scan objects. Doing so causes causes reference objects to be 'discovered' by the reference processor. At the end of the evacuation pause, these discovered reference objects are processed - preserving (and copying) referent objects (and their reachable graphs) as appropriate. Reviewed-by: ysr, jwilhelm, brutisso, stefank, tonyp
author johnc
date Thu, 22 Sep 2011 10:57:37 -0700
parents 7e37af9d69ef
children 2ace1c4ee8da
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 * Copyright (c) 2001, 2011, Oracle and/or its affiliates. All rights reserved.
 * 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 if you need additional information or have any
 * questions.

#include "precompiled.hpp"
#include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
#include "gc_implementation/g1/satbQueue.hpp"
#include "memory/allocation.inline.hpp"
#include "memory/sharedHeap.hpp"
#include "runtime/mutexLocker.hpp"
#include "runtime/thread.hpp"
#include "runtime/vmThread.hpp"

// This method removes entries from an SATB buffer that will not be
// useful to the concurrent marking threads. An entry is removed if it
// satisfies one of the following conditions:
// * it points to an object outside the G1 heap (G1's concurrent
//     marking only visits objects inside the G1 heap),
// * it points to an object that has been allocated since marking
//     started (according to SATB those objects do not need to be
//     visited during marking), or
// * it points to an object that has already been marked (no need to
//     process it again).
// The rest of the entries will be retained and are compacted towards
// the top of the buffer. If with this filtering we clear a large
// enough chunk of the buffer we can re-use it (instead of enqueueing
// it) and we can just allow the mutator to carry on executing.

bool ObjPtrQueue::should_enqueue_buffer() {
  assert(_lock == NULL || _lock->owned_by_self(),
         "we should have taken the lock before calling this");

  // A value of 0 means "don't filter SATB buffers".
  if (G1SATBBufferEnqueueingThresholdPercent == 0) {
    return true;

  G1CollectedHeap* g1h = G1CollectedHeap::heap();

  // This method should only be called if there is a non-NULL buffer
  // that is full.
  assert(_index == 0, "pre-condition");
  assert(_buf != NULL, "pre-condition");

  void** buf = _buf;
  size_t sz = _sz;

  // Used for sanity checking at the end of the loop.
  debug_only(size_t entries = 0; size_t retained = 0;)

  size_t i = sz;
  size_t new_index = sz;

  // Given that we are expecting _index == 0, we could have changed
  // the loop condition to (i > 0). But we are using _index for
  // generality.
  while (i > _index) {
    assert(i > 0, "we should have at least one more entry to process");
    i -= oopSize;
    debug_only(entries += 1;)
    oop* p = (oop*) &buf[byte_index_to_index((int) i)];
    oop obj = *p;
    // NULL the entry so that unused parts of the buffer contain NULLs
    // at the end. If we are going to retain it we will copy it to its
    // final place. If we have retained all entries we have visited so
    // far, we'll just end up copying it to the same place.
    *p = NULL;

    bool retain = g1h->is_obj_ill(obj);
    if (retain) {
      assert(new_index > 0, "we should not have already filled up the buffer");
      new_index -= oopSize;
      assert(new_index >= i,
             "new_index should never be below i, as we alwaysr compact 'up'");
      oop* new_p = (oop*) &buf[byte_index_to_index((int) new_index)];
      assert(new_p >= p, "the destination location should never be below "
             "the source as we always compact 'up'");
      assert(*new_p == NULL,
             "we should have already cleared the destination location");
      *new_p = obj;
      debug_only(retained += 1;)
  size_t entries_calc = (sz - _index) / oopSize;
  assert(entries == entries_calc, "the number of entries we counted "
         "should match the number of entries we calculated");
  size_t retained_calc = (sz - new_index) / oopSize;
  assert(retained == retained_calc, "the number of retained entries we counted "
         "should match the number of retained entries we calculated");
  size_t perc = retained_calc * 100 / entries_calc;
  bool should_enqueue = perc > (size_t) G1SATBBufferEnqueueingThresholdPercent;
  _index = new_index;

  return should_enqueue;

void ObjPtrQueue::apply_closure(ObjectClosure* cl) {
  if (_buf != NULL) {
    apply_closure_to_buffer(cl, _buf, _index, _sz);
    _index = _sz;

void ObjPtrQueue::apply_closure_to_buffer(ObjectClosure* cl,
                                          void** buf, size_t index, size_t sz) {
  if (cl == NULL) return;
  for (size_t i = index; i < sz; i += oopSize) {
    oop obj = (oop)buf[byte_index_to_index((int)i)];
    // There can be NULL entries because of destructors.
    if (obj != NULL) {

#ifdef ASSERT
void ObjPtrQueue::verify_oops_in_buffer() {
  if (_buf == NULL) return;
  for (size_t i = _index; i < _sz; i += oopSize) {
    oop obj = (oop)_buf[byte_index_to_index((int)i)];
    assert(obj != NULL && obj->is_oop(true /* ignore mark word */),
           "Not an oop");

#ifdef _MSC_VER // the use of 'this' below gets a warning, make it go away
#pragma warning( disable:4355 ) // 'this' : used in base member initializer list
#endif // _MSC_VER

SATBMarkQueueSet::SATBMarkQueueSet() :
  _closure(NULL), _par_closures(NULL),
  _shared_satb_queue(this, true /*perm*/)

void SATBMarkQueueSet::initialize(Monitor* cbl_mon, Mutex* fl_lock,
                                  int process_completed_threshold,
                                  Mutex* lock) {
  PtrQueueSet::initialize(cbl_mon, fl_lock, process_completed_threshold, -1);
  if (ParallelGCThreads > 0) {
    _par_closures = NEW_C_HEAP_ARRAY(ObjectClosure*, ParallelGCThreads);

void SATBMarkQueueSet::handle_zero_index_for_thread(JavaThread* t) {

#ifdef ASSERT
void SATBMarkQueueSet::dump_active_values(JavaThread* first,
                                          bool expected_active) {
  gclog_or_tty->print_cr("SATB queue active values for Java Threads");
  gclog_or_tty->print_cr(" SATB queue set: active is %s",
                         (is_active()) ? "TRUE" : "FALSE");
  gclog_or_tty->print_cr(" expected_active is %s",
                         (expected_active) ? "TRUE" : "FALSE");
  for (JavaThread* t = first; t; t = t->next()) {
    bool active = t->satb_mark_queue().is_active();
    gclog_or_tty->print_cr("  thread %s, active is %s",
                           t->name(), (active) ? "TRUE" : "FALSE");
#endif // ASSERT

void SATBMarkQueueSet::set_active_all_threads(bool b,
                                              bool expected_active) {
  assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
  JavaThread* first = Threads::first();

#ifdef ASSERT
  if (_all_active != expected_active) {
    dump_active_values(first, expected_active);

    // I leave this here as a guarantee, instead of an assert, so
    // that it will still be compiled in if we choose to uncomment
    // the #ifdef ASSERT in a product build. The whole block is
    // within an #ifdef ASSERT so the guarantee will not be compiled
    // in a product build anyway.
              "SATB queue set has an unexpected active value");
#endif // ASSERT
  _all_active = b;

  for (JavaThread* t = first; t; t = t->next()) {
#ifdef ASSERT
    bool active = t->satb_mark_queue().is_active();
    if (active != expected_active) {
      dump_active_values(first, expected_active);

      // I leave this here as a guarantee, instead of an assert, so
      // that it will still be compiled in if we choose to uncomment
      // the #ifdef ASSERT in a product build. The whole block is
      // within an #ifdef ASSERT so the guarantee will not be compiled
      // in a product build anyway.
                "thread has an unexpected active value in its SATB queue");
#endif // ASSERT

void SATBMarkQueueSet::set_closure(ObjectClosure* closure) {
  _closure = closure;

void SATBMarkQueueSet::set_par_closure(int i, ObjectClosure* par_closure) {
  assert(ParallelGCThreads > 0 && _par_closures != NULL, "Precondition");
  _par_closures[i] = par_closure;

void SATBMarkQueueSet::iterate_closure_all_threads() {
  for(JavaThread* t = Threads::first(); t; t = t->next()) {

void SATBMarkQueueSet::par_iterate_closure_all_threads(int worker) {
  SharedHeap* sh = SharedHeap::heap();
  int parity = sh->strong_roots_parity();

  for(JavaThread* t = Threads::first(); t; t = t->next()) {
    if (t->claim_oops_do(true, parity)) {

  // We also need to claim the VMThread so that its parity is updated
  // otherwise the next call to Thread::possibly_parallel_oops_do inside
  // a StrongRootsScope might skip the VMThread because it has a stale
  // parity that matches the parity set by the StrongRootsScope
  // Whichever worker succeeds in claiming the VMThread gets to do
  // the shared queue.

  VMThread* vmt = VMThread::vm_thread();
  if (vmt->claim_oops_do(true, parity)) {

bool SATBMarkQueueSet::apply_closure_to_completed_buffer_work(bool par,
                                                              int worker) {
  BufferNode* nd = NULL;
    MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
    if (_completed_buffers_head != NULL) {
      nd = _completed_buffers_head;
      _completed_buffers_head = nd->next();
      if (_completed_buffers_head == NULL) _completed_buffers_tail = NULL;
      if (_n_completed_buffers == 0) _process_completed = false;
  ObjectClosure* cl = (par ? _par_closures[worker] : _closure);
  if (nd != NULL) {
    void **buf = BufferNode::make_buffer_from_node(nd);
    ObjPtrQueue::apply_closure_to_buffer(cl, buf, 0, _sz);
    return true;
  } else {
    return false;

void SATBMarkQueueSet::abandon_partial_marking() {
  BufferNode* buffers_to_delete = NULL;
    MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
    while (_completed_buffers_head != NULL) {
      BufferNode* nd = _completed_buffers_head;
      _completed_buffers_head = nd->next();
      buffers_to_delete = nd;
    _completed_buffers_tail = NULL;
    _n_completed_buffers = 0;
  while (buffers_to_delete != NULL) {
    BufferNode* nd = buffers_to_delete;
    buffers_to_delete = nd->next();
  assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
  // So we can safely manipulate these queues.
  for (JavaThread* t = Threads::first(); t; t = t->next()) {