view src/share/vm/gc_implementation/g1/ptrQueue.hpp @ 2034:7e37af9d69ef

7011379: G1: overly long concurrent marking cycles Summary: This changeset introduces filtering of SATB buffers at the point when they are about to be enqueued. If this filtering clears enough entries on each buffer, the buffer can then be re-used and not enqueued. This cuts down the number of SATB buffers that need to be processed by the concurrent marking threads. Reviewed-by: johnc, ysr
author tonyp
date Wed, 19 Jan 2011 09:35:17 -0500
parents f95d63e2154a
children 2ace1c4ee8da
line wrap: on
line source
 * 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 "memory/allocation.hpp"
#include "utilities/sizes.hpp"

// There are various techniques that require threads to be able to log
// addresses.  For example, a generational write barrier might log
// the addresses of modified old-generation objects.  This type supports
// this operation.

// The definition of placement operator new(size_t, void*) in the <new>.
#include <new>

class PtrQueueSet;

  // The ptr queue set to which this queue belongs.
  PtrQueueSet* _qset;

  // Whether updates should be logged.
  bool _active;

  // The buffer.
  void** _buf;
  // The index at which an object was last enqueued.  Starts at "_sz"
  // (indicating an empty buffer) and goes towards zero.
  size_t _index;

  // The size of the buffer.
  size_t _sz;

  // If true, the queue is permanent, and doesn't need to deallocate
  // its buffer in the destructor (since that obtains a lock which may not
  // be legally locked by then.
  bool _perm;

  // If there is a lock associated with this buffer, this is that lock.
  Mutex* _lock;

  PtrQueueSet* qset() { return _qset; }

  // Initialize this queue to contain a null buffer, and be part of the
  // given PtrQueueSet.
  PtrQueue(PtrQueueSet* qset, bool perm = false, bool active = false);
  // Release any contained resources.
  void flush();
  // Calls flush() when destroyed.
  ~PtrQueue() { flush(); }

  // Associate a lock with a ptr queue.
  void set_lock(Mutex* lock) { _lock = lock; }

  void reset() { if (_buf != NULL) _index = _sz; }

  // Enqueues the given "obj".
  void enqueue(void* ptr) {
    if (!_active) return;
    else enqueue_known_active(ptr);

  // This method is called when we're doing the zero index handling
  // and gives a chance to the queues to do any pre-enqueueing
  // processing they might want to do on the buffer. It should return
  // true if the buffer should be enqueued, or false if enough
  // entries were cleared from it so that it can be re-used. It should
  // not return false if the buffer is still full (otherwise we can
  // get into an infinite loop).
  virtual bool should_enqueue_buffer() { return true; }
  void handle_zero_index();
  void locking_enqueue_completed_buffer(void** buf);

  void enqueue_known_active(void* ptr);

  size_t size() {
    assert(_sz >= _index, "Invariant.");
    return _buf == NULL ? 0 : _sz - _index;

  bool is_empty() {
    return _buf == NULL || _sz == _index;

  // Set the "active" property of the queue to "b".  An enqueue to an
  // inactive thread is a no-op.  Setting a queue to inactive resets its
  // log to the empty state.
  void set_active(bool b) {
    _active = b;
    if (!b && _buf != NULL) {
      _index = _sz;
    } else if (b && _buf != NULL) {
      assert(_index == _sz, "invariant: queues are empty when activated.");

  bool is_active() { return _active; }

  static int byte_index_to_index(int ind) {
    assert((ind % oopSize) == 0, "Invariant.");
    return ind / oopSize;

  static int index_to_byte_index(int byte_ind) {
    return byte_ind * oopSize;

  // To support compiler.
  static ByteSize byte_offset_of_index() {
    return byte_offset_of(PtrQueue, _index);
  static ByteSize byte_width_of_index() { return in_ByteSize(sizeof(size_t)); }

  static ByteSize byte_offset_of_buf() {
    return byte_offset_of(PtrQueue, _buf);
  static ByteSize byte_width_of_buf() { return in_ByteSize(sizeof(void*)); }

  static ByteSize byte_offset_of_active() {
    return byte_offset_of(PtrQueue, _active);
  static ByteSize byte_width_of_active() { return in_ByteSize(sizeof(bool)); }


class BufferNode {
  size_t _index;
  BufferNode* _next;
  BufferNode() : _index(0), _next(NULL) { }
  BufferNode* next() const     { return _next;  }
  void set_next(BufferNode* n) { _next = n;     }
  size_t index() const         { return _index; }
  void set_index(size_t i)     { _index = i;    }

  // Align the size of the structure to the size of the pointer
  static size_t aligned_size() {
    static const size_t alignment = round_to(sizeof(BufferNode), sizeof(void*));
    return alignment;

  // BufferNode is allocated before the buffer.
  // The chunk of memory that holds both of them is a block.

  // Produce a new BufferNode given a buffer.
  static BufferNode* new_from_buffer(void** buf) {
    return new (make_block_from_buffer(buf)) BufferNode;

  // The following are the required conversion routines:
  static BufferNode* make_node_from_buffer(void** buf) {
    return (BufferNode*)make_block_from_buffer(buf);
  static void** make_buffer_from_node(BufferNode *node) {
    return make_buffer_from_block(node);
  static void* make_block_from_node(BufferNode *node) {
    return (void*)node;
  static void** make_buffer_from_block(void* p) {
    return (void**)((char*)p + aligned_size());
  static void* make_block_from_buffer(void** p) {
    return (void*)((char*)p - aligned_size());

// A PtrQueueSet represents resources common to a set of pointer queues.
// In particular, the individual queues allocate buffers from this shared
// set, and return completed buffers to the set.
// All these variables are are protected by the TLOQ_CBL_mon. XXX ???
class PtrQueueSet VALUE_OBJ_CLASS_SPEC {
  Monitor* _cbl_mon;  // Protects the fields below.
  BufferNode* _completed_buffers_head;
  BufferNode* _completed_buffers_tail;
  int _n_completed_buffers;
  int _process_completed_threshold;
  volatile bool _process_completed;

  // This (and the interpretation of the first element as a "next"
  // pointer) are protected by the TLOQ_FL_lock.
  Mutex* _fl_lock;
  BufferNode* _buf_free_list;
  size_t _buf_free_list_sz;
  // Queue set can share a freelist. The _fl_owner variable
  // specifies the owner. It is set to "this" by default.
  PtrQueueSet* _fl_owner;

  // The size of all buffers in the set.
  size_t _sz;

  bool _all_active;

  // If true, notify_all on _cbl_mon when the threshold is reached.
  bool _notify_when_complete;

  // Maximum number of elements allowed on completed queue: after that,
  // enqueuer does the work itself.  Zero indicates no maximum.
  int _max_completed_queue;
  int _completed_queue_padding;

  int completed_buffers_list_length();
  void assert_completed_buffer_list_len_correct_locked();
  void assert_completed_buffer_list_len_correct();

  // A mutator thread does the the work of processing a buffer.
  // Returns "true" iff the work is complete (and the buffer may be
  // deallocated).
  virtual bool mut_process_buffer(void** buf) {
    return false;

  // Create an empty ptr queue set.
  PtrQueueSet(bool notify_when_complete = false);

  // Because of init-order concerns, we can't pass these as constructor
  // arguments.
  void initialize(Monitor* cbl_mon, Mutex* fl_lock,
                  int process_completed_threshold,
                  int max_completed_queue,
                  PtrQueueSet *fl_owner = NULL) {
    _max_completed_queue = max_completed_queue;
    _process_completed_threshold = process_completed_threshold;
    _completed_queue_padding = 0;
    assert(cbl_mon != NULL && fl_lock != NULL, "Init order issue?");
    _cbl_mon = cbl_mon;
    _fl_lock = fl_lock;
    _fl_owner = (fl_owner != NULL) ? fl_owner : this;

  // Return an empty oop array of size _sz (required to be non-zero).
  void** allocate_buffer();

  // Return an empty buffer to the free list.  The "buf" argument is
  // required to be a pointer to the head of an array of length "_sz".
  void deallocate_buffer(void** buf);

  // Declares that "buf" is a complete buffer.
  void enqueue_complete_buffer(void** buf, size_t index = 0);

  // To be invoked by the mutator.
  bool process_or_enqueue_complete_buffer(void** buf);

  bool completed_buffers_exist_dirty() {
    return _n_completed_buffers > 0;

  bool process_completed_buffers() { return _process_completed; }
  void set_process_completed(bool x) { _process_completed = x; }

  bool is_active() { return _all_active; }

  // Set the buffer size.  Should be called before any "enqueue" operation
  // can be called.  And should only be called once.
  void set_buffer_size(size_t sz);

  // Get the buffer size.
  size_t buffer_size() { return _sz; }

  // Get/Set the number of completed buffers that triggers log processing.
  void set_process_completed_threshold(int sz) { _process_completed_threshold = sz; }
  int process_completed_threshold() const { return _process_completed_threshold; }

  // Must only be called at a safe point.  Indicates that the buffer free
  // list size may be reduced, if that is deemed desirable.
  void reduce_free_list();

  int completed_buffers_num() { return _n_completed_buffers; }

  void merge_bufferlists(PtrQueueSet* src);

  void set_max_completed_queue(int m) { _max_completed_queue = m; }
  int max_completed_queue() { return _max_completed_queue; }

  void set_completed_queue_padding(int padding) { _completed_queue_padding = padding; }
  int completed_queue_padding() { return _completed_queue_padding; }

  // Notify the consumer if the number of buffers crossed the threshold
  void notify_if_necessary();