JDK14/Java14源码在线阅读

/*
 * Copyright (c) 2001, 2019, 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/g1/g1BufferNodeList.hpp"
#include "gc/g1/g1CardTableEntryClosure.hpp"
#include "gc/g1/g1CollectedHeap.inline.hpp"
#include "gc/g1/g1DirtyCardQueue.hpp"
#include "gc/g1/g1FreeIdSet.hpp"
#include "gc/g1/g1RedirtyCardsQueue.hpp"
#include "gc/g1/g1RemSet.hpp"
#include "gc/g1/g1ThreadLocalData.hpp"
#include "gc/g1/heapRegionRemSet.hpp"
#include "gc/shared/suspendibleThreadSet.hpp"
#include "gc/shared/workgroup.hpp"
#include "memory/iterator.hpp"
#include "runtime/flags/flagSetting.hpp"
#include "runtime/mutexLocker.hpp"
#include "runtime/orderAccess.hpp"
#include "runtime/os.hpp"
#include "runtime/safepoint.hpp"
#include "runtime/thread.inline.hpp"
#include "runtime/threadSMR.hpp"
#include "utilities/quickSort.hpp"

G1DirtyCardQueue::G1DirtyCardQueue(G1DirtyCardQueueSet* qset) :
  // Dirty card queues are always active, so we create them with their
  // active field set to true.
  PtrQueue(qset, true /* active */)
{ }

G1DirtyCardQueue::~G1DirtyCardQueue() {
  flush();
}

void G1DirtyCardQueue::handle_completed_buffer() {
  assert(_buf != NULL, "precondition");
  BufferNode* node = BufferNode::make_node_from_buffer(_buf, index());
  G1DirtyCardQueueSet* dcqs = dirty_card_qset();
  if (dcqs->process_or_enqueue_completed_buffer(node)) {
    reset();                    // Buffer fully processed, reset index.
  } else {
    allocate_buffer();          // Buffer enqueued, get a new one.
  }
}

// Assumed to be zero by concurrent threads.
static uint par_ids_start() { return 0; }

G1DirtyCardQueueSet::G1DirtyCardQueueSet(Monitor* cbl_mon,
                                         BufferNode::Allocator* allocator) :
  PtrQueueSet(allocator),
  _cbl_mon(cbl_mon),
  _completed_buffers_head(NULL),
  _completed_buffers_tail(NULL),
  _num_cards(0),
  _process_cards_threshold(ProcessCardsThresholdNever),
  _process_completed_buffers(false),
  _max_cards(MaxCardsUnlimited),
  _max_cards_padding(0),
  _free_ids(par_ids_start(), num_par_ids()),
  _mutator_refined_cards_counters(NEW_C_HEAP_ARRAY(size_t, num_par_ids(), mtGC))
{
  ::memset(_mutator_refined_cards_counters, 0, num_par_ids() * sizeof(size_t));
  _all_active = true;
}

G1DirtyCardQueueSet::~G1DirtyCardQueueSet() {
  abandon_completed_buffers();
  FREE_C_HEAP_ARRAY(size_t, _mutator_refined_cards_counters);
}

// Determines how many mutator threads can process the buffers in parallel.
uint G1DirtyCardQueueSet::num_par_ids() {
  return (uint)os::initial_active_processor_count();
}

size_t G1DirtyCardQueueSet::total_mutator_refined_cards() const {
  size_t sum = 0;
  for (uint i = 0; i < num_par_ids(); ++i) {
    sum += _mutator_refined_cards_counters[i];
  }
  return sum;
}

void G1DirtyCardQueueSet::handle_zero_index_for_thread(Thread* t) {
  G1ThreadLocalData::dirty_card_queue(t).handle_zero_index();
}

void G1DirtyCardQueueSet::enqueue_completed_buffer(BufferNode* cbn) {
  MonitorLocker ml(_cbl_mon, Mutex::_no_safepoint_check_flag);
  cbn->set_next(NULL);
  if (_completed_buffers_tail == NULL) {
    assert(_completed_buffers_head == NULL, "Well-formedness");
    _completed_buffers_head = cbn;
    _completed_buffers_tail = cbn;
  } else {
    _completed_buffers_tail->set_next(cbn);
    _completed_buffers_tail = cbn;
  }
  _num_cards += buffer_size() - cbn->index();

  if (!process_completed_buffers() &&
      (num_cards() > process_cards_threshold())) {
    set_process_completed_buffers(true);
    ml.notify_all();
  }
  verify_num_cards();
}

BufferNode* G1DirtyCardQueueSet::get_completed_buffer(size_t stop_at) {
  MutexLocker x(_cbl_mon, Mutex::_no_safepoint_check_flag);

  if (num_cards() <= stop_at) {
    return NULL;
  }

  assert(num_cards() > 0, "invariant");
  assert(_completed_buffers_head != NULL, "invariant");
  assert(_completed_buffers_tail != NULL, "invariant");

  BufferNode* bn = _completed_buffers_head;
  _num_cards -= buffer_size() - bn->index();
  _completed_buffers_head = bn->next();
  if (_completed_buffers_head == NULL) {
    assert(num_cards() == 0, "invariant");
    _completed_buffers_tail = NULL;
    set_process_completed_buffers(false);
  }
  verify_num_cards();
  bn->set_next(NULL);
  return bn;
}

#ifdef ASSERT
void G1DirtyCardQueueSet::verify_num_cards() const {
  size_t actual = 0;
  BufferNode* cur = _completed_buffers_head;
  while (cur != NULL) {
    actual += buffer_size() - cur->index();
    cur = cur->next();
  }
  assert(actual == _num_cards,
         "Num entries in completed buffers should be " SIZE_FORMAT " but are " SIZE_FORMAT,
         _num_cards, actual);
}
#endif

void G1DirtyCardQueueSet::abandon_completed_buffers() {
  BufferNode* buffers_to_delete = NULL;
  {
    MutexLocker x(_cbl_mon, Mutex::_no_safepoint_check_flag);
    buffers_to_delete = _completed_buffers_head;
    _completed_buffers_head = NULL;
    _completed_buffers_tail = NULL;
    _num_cards = 0;
    set_process_completed_buffers(false);
  }
  while (buffers_to_delete != NULL) {
    BufferNode* bn = buffers_to_delete;
    buffers_to_delete = bn->next();
    bn->set_next(NULL);
    deallocate_buffer(bn);
  }
}

void G1DirtyCardQueueSet::notify_if_necessary() {
  MonitorLocker ml(_cbl_mon, Mutex::_no_safepoint_check_flag);
  if (num_cards() > process_cards_threshold()) {
    set_process_completed_buffers(true);
    ml.notify_all();
  }
}

// Merge lists of buffers. Notify the processing threads.
// The source queue is emptied as a result. The queues
// must share the monitor.
void G1DirtyCardQueueSet::merge_bufferlists(G1RedirtyCardsQueueSet* src) {
  assert(allocator() == src->allocator(), "precondition");
  const G1BufferNodeList from = src->take_all_completed_buffers();
  if (from._head == NULL) return;

  MutexLocker x(_cbl_mon, Mutex::_no_safepoint_check_flag);
  if (_completed_buffers_tail == NULL) {
    assert(_completed_buffers_head == NULL, "Well-formedness");
    _completed_buffers_head = from._head;
    _completed_buffers_tail = from._tail;
  } else {
    assert(_completed_buffers_head != NULL, "Well formedness");
    _completed_buffers_tail->set_next(from._head);
    _completed_buffers_tail = from._tail;
  }
  _num_cards += from._entry_count;

  assert(_completed_buffers_head == NULL && _completed_buffers_tail == NULL ||
         _completed_buffers_head != NULL && _completed_buffers_tail != NULL,
         "Sanity");
  verify_num_cards();
}

G1BufferNodeList G1DirtyCardQueueSet::take_all_completed_buffers() {
  MutexLocker x(_cbl_mon, Mutex::_no_safepoint_check_flag);
  G1BufferNodeList result(_completed_buffers_head, _completed_buffers_tail, _num_cards);
  _completed_buffers_head = NULL;
  _completed_buffers_tail = NULL;
  _num_cards = 0;
  return result;
}

class G1RefineBufferedCards : public StackObj {
  BufferNode* const _node;
  CardTable::CardValue** const _node_buffer;
  const size_t _node_buffer_size;
  const uint _worker_id;
  size_t* _total_refined_cards;
  G1RemSet* const _g1rs;

  static inline int compare_card(const CardTable::CardValue* p1,
                                 const CardTable::CardValue* p2) {
    return p2 - p1;
  }

  // Sorts the cards from start_index to _node_buffer_size in *decreasing*
  // address order. Tests showed that this order is preferable to not sorting
  // or increasing address order.
  void sort_cards(size_t start_index) {
    QuickSort::sort(&_node_buffer[start_index],
                    _node_buffer_size - start_index,
                    compare_card,
                    false);
  }

  // Returns the index to the first clean card in the buffer.
  size_t clean_cards() {
    const size_t start = _node->index();
    assert(start <= _node_buffer_size, "invariant");

    // Two-fingered compaction algorithm similar to the filtering mechanism in
    // SATBMarkQueue. The main difference is that clean_card_before_refine()
    // could change the buffer element in-place.
    // We don't check for SuspendibleThreadSet::should_yield(), because
    // cleaning and redirtying the cards is fast.
    CardTable::CardValue** src = &_node_buffer[start];
    CardTable::CardValue** dst = &_node_buffer[_node_buffer_size];
    assert(src <= dst, "invariant");
    for ( ; src < dst; ++src) {
      // Search low to high for a card to keep.
      if (_g1rs->clean_card_before_refine(src)) {
        // Found keeper.  Search high to low for a card to discard.
        while (src < --dst) {
          if (!_g1rs->clean_card_before_refine(dst)) {
            *dst = *src;         // Replace discard with keeper.
            break;
          }
        }
        // If discard search failed (src == dst), the outer loop will also end.
      }
    }

    // dst points to the first retained clean card, or the end of the buffer
    // if all the cards were discarded.
    const size_t first_clean = dst - _node_buffer;
    assert(first_clean >= start && first_clean <= _node_buffer_size, "invariant");
    // Discarded cards are considered as refined.
    *_total_refined_cards += first_clean - start;
    return first_clean;
  }

  bool refine_cleaned_cards(size_t start_index) {
    bool result = true;
    size_t i = start_index;
    for ( ; i < _node_buffer_size; ++i) {
      if (SuspendibleThreadSet::should_yield()) {
        redirty_unrefined_cards(i);
        result = false;
        break;
      }
      _g1rs->refine_card_concurrently(_node_buffer[i], _worker_id);
    }
    _node->set_index(i);
    *_total_refined_cards += i - start_index;
    return result;
  }

  void redirty_unrefined_cards(size_t start) {
    for ( ; start < _node_buffer_size; ++start) {
      *_node_buffer[start] = G1CardTable::dirty_card_val();
    }
  }

public:
  G1RefineBufferedCards(BufferNode* node,
                        size_t node_buffer_size,
                        uint worker_id,
                        size_t* total_refined_cards) :
    _node(node),
    _node_buffer(reinterpret_cast<CardTable::CardValue**>(BufferNode::make_buffer_from_node(node))),
    _node_buffer_size(node_buffer_size),
    _worker_id(worker_id),
    _total_refined_cards(total_refined_cards),
    _g1rs(G1CollectedHeap::heap()->rem_set()) {}

  bool refine() {
    size_t first_clean_index = clean_cards();
    if (first_clean_index == _node_buffer_size) {
      _node->set_index(first_clean_index);
      return true;
    }
    // This fence serves two purposes. First, the cards must be cleaned
    // before processing the contents. Second, we can't proceed with
    // processing a region until after the read of the region's top in
    // collect_and_clean_cards(), for synchronization with possibly concurrent
    // humongous object allocation (see comment at the StoreStore fence before
    // setting the regions' tops in humongous allocation path).
    // It's okay that reading region's top and reading region's type were racy
    // wrto each other. We need both set, in any order, to proceed.
    OrderAccess::fence();
    sort_cards(first_clean_index);
    return refine_cleaned_cards(first_clean_index);
  }
};

bool G1DirtyCardQueueSet::refine_buffer(BufferNode* node,
                                        uint worker_id,
                                        size_t* total_refined_cards) {
  G1RefineBufferedCards buffered_cards(node,
                                       buffer_size(),
                                       worker_id,
                                       total_refined_cards);
  return buffered_cards.refine();
}

#ifndef ASSERT
#define assert_fully_consumed(node, buffer_size)
#else
#define assert_fully_consumed(node, buffer_size)                \
  do {                                                          \
    size_t _afc_index = (node)->index();                        \
    size_t _afc_size = (buffer_size);                           \
    assert(_afc_index == _afc_size,                             \
           "Buffer was not fully consumed as claimed: index: "  \
           SIZE_FORMAT ", size: " SIZE_FORMAT,                  \
            _afc_index, _afc_size);                             \
  } while (0)
#endif // ASSERT

bool G1DirtyCardQueueSet::process_or_enqueue_completed_buffer(BufferNode* node) {
  if (Thread::current()->is_Java_thread()) {
    // If the number of buffers exceeds the limit, make this Java
    // thread do the processing itself.  We don't lock to access
    // buffer count or padding; it is fine to be imprecise here.  The
    // add of padding could overflow, which is treated as unlimited.
    size_t limit = max_cards() + max_cards_padding();
    if ((num_cards() > limit) && (limit >= max_cards())) {
      if (mut_process_buffer(node)) {
        return true;
      }
    }
  }
  enqueue_completed_buffer(node);
  return false;
}

bool G1DirtyCardQueueSet::mut_process_buffer(BufferNode* node) {
  uint worker_id = _free_ids.claim_par_id(); // temporarily claim an id
  uint counter_index = worker_id - par_ids_start();
  size_t* counter = &_mutator_refined_cards_counters[counter_index];
  bool result = refine_buffer(node, worker_id, counter);
  _free_ids.release_par_id(worker_id); // release the id

  if (result) {
    assert_fully_consumed(node, buffer_size());
  }
  return result;
}

bool G1DirtyCardQueueSet::refine_completed_buffer_concurrently(uint worker_id,
                                                               size_t stop_at,
                                                               size_t* total_refined_cards) {

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