1162 lines
39 KiB
Java
1162 lines
39 KiB
Java
/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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/*
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* This file is available under and governed by the GNU General Public
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* License version 2 only, as published by the Free Software Foundation.
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* However, the following notice accompanied the original version of this
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* file:
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*
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* Written by Doug Lea with assistance from members of JCP JSR-166
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* Expert Group and released to the public domain, as explained at
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* http://creativecommons.org/publicdomain/zero/1.0/
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*/
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package java.util.concurrent;
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import java.util.AbstractQueue;
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import java.util.Collection;
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import java.util.Iterator;
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import java.util.NoSuchElementException;
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import java.util.Objects;
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import java.util.Spliterator;
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import java.util.Spliterators;
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import java.util.concurrent.atomic.AtomicInteger;
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import java.util.concurrent.locks.Condition;
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import java.util.concurrent.locks.ReentrantLock;
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import java.util.function.Consumer;
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import java.util.function.Predicate;
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/**
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* An optionally-bounded {@linkplain BlockingQueue blocking queue} based on
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* linked nodes.
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* This queue orders elements FIFO (first-in-first-out).
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* The <em>head</em> of the queue is that element that has been on the
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* queue the longest time.
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* The <em>tail</em> of the queue is that element that has been on the
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* queue the shortest time. New elements
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* are inserted at the tail of the queue, and the queue retrieval
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* operations obtain elements at the head of the queue.
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* Linked queues typically have higher throughput than array-based queues but
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* less predictable performance in most concurrent applications.
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*
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* <p>The optional capacity bound constructor argument serves as a
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* way to prevent excessive queue expansion. The capacity, if unspecified,
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* is equal to {@link Integer#MAX_VALUE}. Linked nodes are
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* dynamically created upon each insertion unless this would bring the
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* queue above capacity.
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*
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* <p>This class and its iterator implement all of the <em>optional</em>
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* methods of the {@link Collection} and {@link Iterator} interfaces.
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*
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* <p>This class is a member of the
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* <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
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* Java Collections Framework</a>.
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*
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* @since 1.5
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* @author Doug Lea
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* @param <E> the type of elements held in this queue
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*/
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public class LinkedBlockingQueue<E> extends AbstractQueue<E>
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implements BlockingQueue<E>, java.io.Serializable {
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private static final long serialVersionUID = -6903933977591709194L;
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/*
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* A variant of the "two lock queue" algorithm. The putLock gates
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* entry to put (and offer), and has an associated condition for
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* waiting puts. Similarly for the takeLock. The "count" field
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* that they both rely on is maintained as an atomic to avoid
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* needing to get both locks in most cases. Also, to minimize need
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* for puts to get takeLock and vice-versa, cascading notifies are
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* used. When a put notices that it has enabled at least one take,
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* it signals taker. That taker in turn signals others if more
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* items have been entered since the signal. And symmetrically for
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* takes signalling puts. Operations such as remove(Object) and
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* iterators acquire both locks.
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*
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* Visibility between writers and readers is provided as follows:
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*
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* Whenever an element is enqueued, the putLock is acquired and
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* count updated. A subsequent reader guarantees visibility to the
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* enqueued Node by either acquiring the putLock (via fullyLock)
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* or by acquiring the takeLock, and then reading n = count.get();
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* this gives visibility to the first n items.
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*
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* To implement weakly consistent iterators, it appears we need to
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* keep all Nodes GC-reachable from a predecessor dequeued Node.
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* That would cause two problems:
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* - allow a rogue Iterator to cause unbounded memory retention
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* - cause cross-generational linking of old Nodes to new Nodes if
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* a Node was tenured while live, which generational GCs have a
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* hard time dealing with, causing repeated major collections.
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* However, only non-deleted Nodes need to be reachable from
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* dequeued Nodes, and reachability does not necessarily have to
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* be of the kind understood by the GC. We use the trick of
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* linking a Node that has just been dequeued to itself. Such a
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* self-link implicitly means to advance to head.next.
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*/
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/**
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* Linked list node class.
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*/
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static class Node<E> {
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E item;
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/**
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* One of:
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* - the real successor Node
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* - this Node, meaning the successor is head.next
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* - null, meaning there is no successor (this is the last node)
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*/
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Node<E> next;
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Node(E x) { item = x; }
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}
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/** The capacity bound, or Integer.MAX_VALUE if none */
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private final int capacity;
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/** Current number of elements */
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private final AtomicInteger count = new AtomicInteger();
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/**
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* Head of linked list.
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* Invariant: head.item == null
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*/
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transient Node<E> head;
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/**
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* Tail of linked list.
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* Invariant: last.next == null
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*/
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private transient Node<E> last;
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/** Lock held by take, poll, etc */
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private final ReentrantLock takeLock = new ReentrantLock();
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/** Wait queue for waiting takes */
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@SuppressWarnings("serial") // Classes implementing Condition may be serializable.
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private final Condition notEmpty = takeLock.newCondition();
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/** Lock held by put, offer, etc */
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private final ReentrantLock putLock = new ReentrantLock();
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/** Wait queue for waiting puts */
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@SuppressWarnings("serial") // Classes implementing Condition may be serializable.
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private final Condition notFull = putLock.newCondition();
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/**
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* Signals a waiting take. Called only from put/offer (which do not
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* otherwise ordinarily lock takeLock.)
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*/
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private void signalNotEmpty() {
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final ReentrantLock takeLock = this.takeLock;
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takeLock.lock();
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try {
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notEmpty.signal();
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} finally {
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takeLock.unlock();
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}
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}
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/**
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* Signals a waiting put. Called only from take/poll.
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*/
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private void signalNotFull() {
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final ReentrantLock putLock = this.putLock;
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putLock.lock();
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try {
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notFull.signal();
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} finally {
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putLock.unlock();
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}
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}
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/**
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* Links node at end of queue.
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*
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* @param node the node
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*/
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private void enqueue(Node<E> node) {
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// assert putLock.isHeldByCurrentThread();
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// assert last.next == null;
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last = last.next = node;
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}
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/**
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* Removes a node from head of queue.
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*
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* @return the node
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*/
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private E dequeue() {
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// assert takeLock.isHeldByCurrentThread();
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// assert head.item == null;
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Node<E> h = head;
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Node<E> first = h.next;
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h.next = h; // help GC
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head = first;
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E x = first.item;
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first.item = null;
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return x;
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}
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/**
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* Locks to prevent both puts and takes.
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*/
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void fullyLock() {
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putLock.lock();
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takeLock.lock();
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}
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/**
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* Unlocks to allow both puts and takes.
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*/
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void fullyUnlock() {
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takeLock.unlock();
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putLock.unlock();
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}
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/**
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* Creates a {@code LinkedBlockingQueue} with a capacity of
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* {@link Integer#MAX_VALUE}.
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*/
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public LinkedBlockingQueue() {
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this(Integer.MAX_VALUE);
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}
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/**
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* Creates a {@code LinkedBlockingQueue} with the given (fixed) capacity.
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*
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* @param capacity the capacity of this queue
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* @throws IllegalArgumentException if {@code capacity} is not greater
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* than zero
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*/
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public LinkedBlockingQueue(int capacity) {
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if (capacity <= 0) throw new IllegalArgumentException();
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this.capacity = capacity;
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last = head = new Node<E>(null);
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}
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/**
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* Creates a {@code LinkedBlockingQueue} with a capacity of
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* {@link Integer#MAX_VALUE}, initially containing the elements of the
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* given collection,
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* added in traversal order of the collection's iterator.
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*
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* @param c the collection of elements to initially contain
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* @throws NullPointerException if the specified collection or any
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* of its elements are null
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*/
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public LinkedBlockingQueue(Collection<? extends E> c) {
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this(Integer.MAX_VALUE);
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final ReentrantLock putLock = this.putLock;
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putLock.lock(); // Never contended, but necessary for visibility
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try {
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int n = 0;
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for (E e : c) {
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if (e == null)
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throw new NullPointerException();
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if (n == capacity)
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throw new IllegalStateException("Queue full");
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enqueue(new Node<E>(e));
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++n;
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}
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count.set(n);
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} finally {
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putLock.unlock();
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}
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}
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// this doc comment is overridden to remove the reference to collections
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// greater in size than Integer.MAX_VALUE
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/**
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* Returns the number of elements in this queue.
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*
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* @return the number of elements in this queue
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*/
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public int size() {
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return count.get();
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}
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// this doc comment is a modified copy of the inherited doc comment,
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// without the reference to unlimited queues.
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/**
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* Returns the number of additional elements that this queue can ideally
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* (in the absence of memory or resource constraints) accept without
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* blocking. This is always equal to the initial capacity of this queue
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* less the current {@code size} of this queue.
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*
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* <p>Note that you <em>cannot</em> always tell if an attempt to insert
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* an element will succeed by inspecting {@code remainingCapacity}
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* because it may be the case that another thread is about to
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* insert or remove an element.
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*/
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public int remainingCapacity() {
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return capacity - count.get();
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}
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/**
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* Inserts the specified element at the tail of this queue, waiting if
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* necessary for space to become available.
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*
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* @throws InterruptedException {@inheritDoc}
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* @throws NullPointerException {@inheritDoc}
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*/
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public void put(E e) throws InterruptedException {
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if (e == null) throw new NullPointerException();
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final int c;
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final Node<E> node = new Node<E>(e);
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final ReentrantLock putLock = this.putLock;
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final AtomicInteger count = this.count;
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putLock.lockInterruptibly();
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try {
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/*
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* Note that count is used in wait guard even though it is
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* not protected by lock. This works because count can
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* only decrease at this point (all other puts are shut
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* out by lock), and we (or some other waiting put) are
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* signalled if it ever changes from capacity. Similarly
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* for all other uses of count in other wait guards.
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*/
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while (count.get() == capacity) {
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notFull.await();
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}
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enqueue(node);
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c = count.getAndIncrement();
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if (c + 1 < capacity)
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notFull.signal();
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} finally {
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putLock.unlock();
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}
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if (c == 0)
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signalNotEmpty();
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}
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/**
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* Inserts the specified element at the tail of this queue, waiting if
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* necessary up to the specified wait time for space to become available.
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*
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* @return {@code true} if successful, or {@code false} if
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* the specified waiting time elapses before space is available
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* @throws InterruptedException {@inheritDoc}
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* @throws NullPointerException {@inheritDoc}
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*/
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public boolean offer(E e, long timeout, TimeUnit unit)
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throws InterruptedException {
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if (e == null) throw new NullPointerException();
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long nanos = unit.toNanos(timeout);
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final int c;
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final ReentrantLock putLock = this.putLock;
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final AtomicInteger count = this.count;
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putLock.lockInterruptibly();
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try {
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while (count.get() == capacity) {
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if (nanos <= 0L)
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return false;
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nanos = notFull.awaitNanos(nanos);
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}
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enqueue(new Node<E>(e));
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c = count.getAndIncrement();
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if (c + 1 < capacity)
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notFull.signal();
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} finally {
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putLock.unlock();
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}
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if (c == 0)
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signalNotEmpty();
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return true;
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}
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/**
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* Inserts the specified element at the tail of this queue if it is
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* possible to do so immediately without exceeding the queue's capacity,
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* returning {@code true} upon success and {@code false} if this queue
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* is full.
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* When using a capacity-restricted queue, this method is generally
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* preferable to method {@link BlockingQueue#add add}, which can fail to
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* insert an element only by throwing an exception.
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*
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* @throws NullPointerException if the specified element is null
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*/
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public boolean offer(E e) {
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if (e == null) throw new NullPointerException();
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final AtomicInteger count = this.count;
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if (count.get() == capacity)
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return false;
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final int c;
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final Node<E> node = new Node<E>(e);
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final ReentrantLock putLock = this.putLock;
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putLock.lock();
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try {
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if (count.get() == capacity)
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return false;
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enqueue(node);
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c = count.getAndIncrement();
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if (c + 1 < capacity)
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notFull.signal();
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} finally {
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putLock.unlock();
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}
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if (c == 0)
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signalNotEmpty();
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return true;
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}
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public E take() throws InterruptedException {
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final E x;
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final int c;
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final AtomicInteger count = this.count;
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final ReentrantLock takeLock = this.takeLock;
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takeLock.lockInterruptibly();
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try {
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while (count.get() == 0) {
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notEmpty.await();
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}
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x = dequeue();
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c = count.getAndDecrement();
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if (c > 1)
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notEmpty.signal();
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} finally {
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takeLock.unlock();
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}
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if (c == capacity)
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signalNotFull();
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return x;
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}
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public E poll(long timeout, TimeUnit unit) throws InterruptedException {
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final E x;
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final int c;
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long nanos = unit.toNanos(timeout);
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final AtomicInteger count = this.count;
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final ReentrantLock takeLock = this.takeLock;
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takeLock.lockInterruptibly();
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try {
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while (count.get() == 0) {
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if (nanos <= 0L)
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return null;
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nanos = notEmpty.awaitNanos(nanos);
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}
|
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x = dequeue();
|
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c = count.getAndDecrement();
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if (c > 1)
|
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notEmpty.signal();
|
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} finally {
|
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takeLock.unlock();
|
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}
|
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if (c == capacity)
|
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signalNotFull();
|
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return x;
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}
|
|
|
|
public E poll() {
|
|
final AtomicInteger count = this.count;
|
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if (count.get() == 0)
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return null;
|
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final E x;
|
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final int c;
|
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final ReentrantLock takeLock = this.takeLock;
|
|
takeLock.lock();
|
|
try {
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if (count.get() == 0)
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return null;
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x = dequeue();
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c = count.getAndDecrement();
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|
if (c > 1)
|
|
notEmpty.signal();
|
|
} finally {
|
|
takeLock.unlock();
|
|
}
|
|
if (c == capacity)
|
|
signalNotFull();
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return x;
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|
}
|
|
|
|
public E peek() {
|
|
final AtomicInteger count = this.count;
|
|
if (count.get() == 0)
|
|
return null;
|
|
final ReentrantLock takeLock = this.takeLock;
|
|
takeLock.lock();
|
|
try {
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|
return (count.get() > 0) ? head.next.item : null;
|
|
} finally {
|
|
takeLock.unlock();
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Unlinks interior Node p with predecessor pred.
|
|
*/
|
|
void unlink(Node<E> p, Node<E> pred) {
|
|
// assert putLock.isHeldByCurrentThread();
|
|
// assert takeLock.isHeldByCurrentThread();
|
|
// p.next is not changed, to allow iterators that are
|
|
// traversing p to maintain their weak-consistency guarantee.
|
|
p.item = null;
|
|
pred.next = p.next;
|
|
if (last == p)
|
|
last = pred;
|
|
if (count.getAndDecrement() == capacity)
|
|
notFull.signal();
|
|
}
|
|
|
|
/**
|
|
* Removes a single instance of the specified element from this queue,
|
|
* if it is present. More formally, removes an element {@code e} such
|
|
* that {@code o.equals(e)}, if this queue contains one or more such
|
|
* elements.
|
|
* Returns {@code true} if this queue contained the specified element
|
|
* (or equivalently, if this queue changed as a result of the call).
|
|
*
|
|
* @param o element to be removed from this queue, if present
|
|
* @return {@code true} if this queue changed as a result of the call
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|
*/
|
|
public boolean remove(Object o) {
|
|
if (o == null) return false;
|
|
fullyLock();
|
|
try {
|
|
for (Node<E> pred = head, p = pred.next;
|
|
p != null;
|
|
pred = p, p = p.next) {
|
|
if (o.equals(p.item)) {
|
|
unlink(p, pred);
|
|
return true;
|
|
}
|
|
}
|
|
return false;
|
|
} finally {
|
|
fullyUnlock();
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Returns {@code true} if this queue contains the specified element.
|
|
* More formally, returns {@code true} if and only if this queue contains
|
|
* at least one element {@code e} such that {@code o.equals(e)}.
|
|
*
|
|
* @param o object to be checked for containment in this queue
|
|
* @return {@code true} if this queue contains the specified element
|
|
*/
|
|
public boolean contains(Object o) {
|
|
if (o == null) return false;
|
|
fullyLock();
|
|
try {
|
|
for (Node<E> p = head.next; p != null; p = p.next)
|
|
if (o.equals(p.item))
|
|
return true;
|
|
return false;
|
|
} finally {
|
|
fullyUnlock();
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Returns an array containing all of the elements in this queue, in
|
|
* proper sequence.
|
|
*
|
|
* <p>The returned array will be "safe" in that no references to it are
|
|
* maintained by this queue. (In other words, this method must allocate
|
|
* a new array). The caller is thus free to modify the returned array.
|
|
*
|
|
* <p>This method acts as bridge between array-based and collection-based
|
|
* APIs.
|
|
*
|
|
* @return an array containing all of the elements in this queue
|
|
*/
|
|
public Object[] toArray() {
|
|
fullyLock();
|
|
try {
|
|
int size = count.get();
|
|
Object[] a = new Object[size];
|
|
int k = 0;
|
|
for (Node<E> p = head.next; p != null; p = p.next)
|
|
a[k++] = p.item;
|
|
return a;
|
|
} finally {
|
|
fullyUnlock();
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Returns an array containing all of the elements in this queue, in
|
|
* proper sequence; the runtime type of the returned array is that of
|
|
* the specified array. If the queue fits in the specified array, it
|
|
* is returned therein. Otherwise, a new array is allocated with the
|
|
* runtime type of the specified array and the size of this queue.
|
|
*
|
|
* <p>If this queue fits in the specified array with room to spare
|
|
* (i.e., the array has more elements than this queue), the element in
|
|
* the array immediately following the end of the queue is set to
|
|
* {@code null}.
|
|
*
|
|
* <p>Like the {@link #toArray()} method, this method acts as bridge between
|
|
* array-based and collection-based APIs. Further, this method allows
|
|
* precise control over the runtime type of the output array, and may,
|
|
* under certain circumstances, be used to save allocation costs.
|
|
*
|
|
* <p>Suppose {@code x} is a queue known to contain only strings.
|
|
* The following code can be used to dump the queue into a newly
|
|
* allocated array of {@code String}:
|
|
*
|
|
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
|
|
*
|
|
* Note that {@code toArray(new Object[0])} is identical in function to
|
|
* {@code toArray()}.
|
|
*
|
|
* @param a the array into which the elements of the queue are to
|
|
* be stored, if it is big enough; otherwise, a new array of the
|
|
* same runtime type is allocated for this purpose
|
|
* @return an array containing all of the elements in this queue
|
|
* @throws ArrayStoreException if the runtime type of the specified array
|
|
* is not a supertype of the runtime type of every element in
|
|
* this queue
|
|
* @throws NullPointerException if the specified array is null
|
|
*/
|
|
@SuppressWarnings("unchecked")
|
|
public <T> T[] toArray(T[] a) {
|
|
fullyLock();
|
|
try {
|
|
int size = count.get();
|
|
if (a.length < size)
|
|
a = (T[])java.lang.reflect.Array.newInstance
|
|
(a.getClass().getComponentType(), size);
|
|
|
|
int k = 0;
|
|
for (Node<E> p = head.next; p != null; p = p.next)
|
|
a[k++] = (T)p.item;
|
|
if (a.length > k)
|
|
a[k] = null;
|
|
return a;
|
|
} finally {
|
|
fullyUnlock();
|
|
}
|
|
}
|
|
|
|
public String toString() {
|
|
return Helpers.collectionToString(this);
|
|
}
|
|
|
|
/**
|
|
* Atomically removes all of the elements from this queue.
|
|
* The queue will be empty after this call returns.
|
|
*/
|
|
public void clear() {
|
|
fullyLock();
|
|
try {
|
|
for (Node<E> p, h = head; (p = h.next) != null; h = p) {
|
|
h.next = h;
|
|
p.item = null;
|
|
}
|
|
head = last;
|
|
// assert head.item == null && head.next == null;
|
|
if (count.getAndSet(0) == capacity)
|
|
notFull.signal();
|
|
} finally {
|
|
fullyUnlock();
|
|
}
|
|
}
|
|
|
|
/**
|
|
* @throws UnsupportedOperationException {@inheritDoc}
|
|
* @throws ClassCastException {@inheritDoc}
|
|
* @throws NullPointerException {@inheritDoc}
|
|
* @throws IllegalArgumentException {@inheritDoc}
|
|
*/
|
|
public int drainTo(Collection<? super E> c) {
|
|
return drainTo(c, Integer.MAX_VALUE);
|
|
}
|
|
|
|
/**
|
|
* @throws UnsupportedOperationException {@inheritDoc}
|
|
* @throws ClassCastException {@inheritDoc}
|
|
* @throws NullPointerException {@inheritDoc}
|
|
* @throws IllegalArgumentException {@inheritDoc}
|
|
*/
|
|
public int drainTo(Collection<? super E> c, int maxElements) {
|
|
Objects.requireNonNull(c);
|
|
if (c == this)
|
|
throw new IllegalArgumentException();
|
|
if (maxElements <= 0)
|
|
return 0;
|
|
boolean signalNotFull = false;
|
|
final ReentrantLock takeLock = this.takeLock;
|
|
takeLock.lock();
|
|
try {
|
|
int n = Math.min(maxElements, count.get());
|
|
// count.get provides visibility to first n Nodes
|
|
Node<E> h = head;
|
|
int i = 0;
|
|
try {
|
|
while (i < n) {
|
|
Node<E> p = h.next;
|
|
c.add(p.item);
|
|
p.item = null;
|
|
h.next = h;
|
|
h = p;
|
|
++i;
|
|
}
|
|
return n;
|
|
} finally {
|
|
// Restore invariants even if c.add() threw
|
|
if (i > 0) {
|
|
// assert h.item == null;
|
|
head = h;
|
|
signalNotFull = (count.getAndAdd(-i) == capacity);
|
|
}
|
|
}
|
|
} finally {
|
|
takeLock.unlock();
|
|
if (signalNotFull)
|
|
signalNotFull();
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Used for any element traversal that is not entirely under lock.
|
|
* Such traversals must handle both:
|
|
* - dequeued nodes (p.next == p)
|
|
* - (possibly multiple) interior removed nodes (p.item == null)
|
|
*/
|
|
Node<E> succ(Node<E> p) {
|
|
if (p == (p = p.next))
|
|
p = head.next;
|
|
return p;
|
|
}
|
|
|
|
/**
|
|
* Returns an iterator over the elements in this queue in proper sequence.
|
|
* The elements will be returned in order from first (head) to last (tail).
|
|
*
|
|
* <p>The returned iterator is
|
|
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
|
|
*
|
|
* @return an iterator over the elements in this queue in proper sequence
|
|
*/
|
|
public Iterator<E> iterator() {
|
|
return new Itr();
|
|
}
|
|
|
|
/**
|
|
* Weakly-consistent iterator.
|
|
*
|
|
* Lazily updated ancestor field provides expected O(1) remove(),
|
|
* but still O(n) in the worst case, whenever the saved ancestor
|
|
* is concurrently deleted.
|
|
*/
|
|
private class Itr implements Iterator<E> {
|
|
private Node<E> next; // Node holding nextItem
|
|
private E nextItem; // next item to hand out
|
|
private Node<E> lastRet;
|
|
private Node<E> ancestor; // Helps unlink lastRet on remove()
|
|
|
|
Itr() {
|
|
fullyLock();
|
|
try {
|
|
if ((next = head.next) != null)
|
|
nextItem = next.item;
|
|
} finally {
|
|
fullyUnlock();
|
|
}
|
|
}
|
|
|
|
public boolean hasNext() {
|
|
return next != null;
|
|
}
|
|
|
|
public E next() {
|
|
Node<E> p;
|
|
if ((p = next) == null)
|
|
throw new NoSuchElementException();
|
|
lastRet = p;
|
|
E x = nextItem;
|
|
fullyLock();
|
|
try {
|
|
E e = null;
|
|
for (p = p.next; p != null && (e = p.item) == null; )
|
|
p = succ(p);
|
|
next = p;
|
|
nextItem = e;
|
|
} finally {
|
|
fullyUnlock();
|
|
}
|
|
return x;
|
|
}
|
|
|
|
public void forEachRemaining(Consumer<? super E> action) {
|
|
// A variant of forEachFrom
|
|
Objects.requireNonNull(action);
|
|
Node<E> p;
|
|
if ((p = next) == null) return;
|
|
lastRet = p;
|
|
next = null;
|
|
final int batchSize = 64;
|
|
Object[] es = null;
|
|
int n, len = 1;
|
|
do {
|
|
fullyLock();
|
|
try {
|
|
if (es == null) {
|
|
p = p.next;
|
|
for (Node<E> q = p; q != null; q = succ(q))
|
|
if (q.item != null && ++len == batchSize)
|
|
break;
|
|
es = new Object[len];
|
|
es[0] = nextItem;
|
|
nextItem = null;
|
|
n = 1;
|
|
} else
|
|
n = 0;
|
|
for (; p != null && n < len; p = succ(p))
|
|
if ((es[n] = p.item) != null) {
|
|
lastRet = p;
|
|
n++;
|
|
}
|
|
} finally {
|
|
fullyUnlock();
|
|
}
|
|
for (int i = 0; i < n; i++) {
|
|
@SuppressWarnings("unchecked") E e = (E) es[i];
|
|
action.accept(e);
|
|
}
|
|
} while (n > 0 && p != null);
|
|
}
|
|
|
|
public void remove() {
|
|
Node<E> p = lastRet;
|
|
if (p == null)
|
|
throw new IllegalStateException();
|
|
lastRet = null;
|
|
fullyLock();
|
|
try {
|
|
if (p.item != null) {
|
|
if (ancestor == null)
|
|
ancestor = head;
|
|
ancestor = findPred(p, ancestor);
|
|
unlink(p, ancestor);
|
|
}
|
|
} finally {
|
|
fullyUnlock();
|
|
}
|
|
}
|
|
}
|
|
|
|
/**
|
|
* A customized variant of Spliterators.IteratorSpliterator.
|
|
* Keep this class in sync with (very similar) LBDSpliterator.
|
|
*/
|
|
private final class LBQSpliterator implements Spliterator<E> {
|
|
static final int MAX_BATCH = 1 << 25; // max batch array size;
|
|
Node<E> current; // current node; null until initialized
|
|
int batch; // batch size for splits
|
|
boolean exhausted; // true when no more nodes
|
|
long est = size(); // size estimate
|
|
|
|
LBQSpliterator() {}
|
|
|
|
public long estimateSize() { return est; }
|
|
|
|
public Spliterator<E> trySplit() {
|
|
Node<E> h;
|
|
if (!exhausted &&
|
|
((h = current) != null || (h = head.next) != null)
|
|
&& h.next != null) {
|
|
int n = batch = Math.min(batch + 1, MAX_BATCH);
|
|
Object[] a = new Object[n];
|
|
int i = 0;
|
|
Node<E> p = current;
|
|
fullyLock();
|
|
try {
|
|
if (p != null || (p = head.next) != null)
|
|
for (; p != null && i < n; p = succ(p))
|
|
if ((a[i] = p.item) != null)
|
|
i++;
|
|
} finally {
|
|
fullyUnlock();
|
|
}
|
|
if ((current = p) == null) {
|
|
est = 0L;
|
|
exhausted = true;
|
|
}
|
|
else if ((est -= i) < 0L)
|
|
est = 0L;
|
|
if (i > 0)
|
|
return Spliterators.spliterator
|
|
(a, 0, i, (Spliterator.ORDERED |
|
|
Spliterator.NONNULL |
|
|
Spliterator.CONCURRENT));
|
|
}
|
|
return null;
|
|
}
|
|
|
|
public boolean tryAdvance(Consumer<? super E> action) {
|
|
Objects.requireNonNull(action);
|
|
if (!exhausted) {
|
|
E e = null;
|
|
fullyLock();
|
|
try {
|
|
Node<E> p;
|
|
if ((p = current) != null || (p = head.next) != null)
|
|
do {
|
|
e = p.item;
|
|
p = succ(p);
|
|
} while (e == null && p != null);
|
|
if ((current = p) == null)
|
|
exhausted = true;
|
|
} finally {
|
|
fullyUnlock();
|
|
}
|
|
if (e != null) {
|
|
action.accept(e);
|
|
return true;
|
|
}
|
|
}
|
|
return false;
|
|
}
|
|
|
|
public void forEachRemaining(Consumer<? super E> action) {
|
|
Objects.requireNonNull(action);
|
|
if (!exhausted) {
|
|
exhausted = true;
|
|
Node<E> p = current;
|
|
current = null;
|
|
forEachFrom(action, p);
|
|
}
|
|
}
|
|
|
|
public int characteristics() {
|
|
return (Spliterator.ORDERED |
|
|
Spliterator.NONNULL |
|
|
Spliterator.CONCURRENT);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Returns a {@link Spliterator} over the elements in this queue.
|
|
*
|
|
* <p>The returned spliterator is
|
|
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
|
|
*
|
|
* <p>The {@code Spliterator} reports {@link Spliterator#CONCURRENT},
|
|
* {@link Spliterator#ORDERED}, and {@link Spliterator#NONNULL}.
|
|
*
|
|
* @implNote
|
|
* The {@code Spliterator} implements {@code trySplit} to permit limited
|
|
* parallelism.
|
|
*
|
|
* @return a {@code Spliterator} over the elements in this queue
|
|
* @since 1.8
|
|
*/
|
|
public Spliterator<E> spliterator() {
|
|
return new LBQSpliterator();
|
|
}
|
|
|
|
/**
|
|
* @throws NullPointerException {@inheritDoc}
|
|
*/
|
|
public void forEach(Consumer<? super E> action) {
|
|
Objects.requireNonNull(action);
|
|
forEachFrom(action, null);
|
|
}
|
|
|
|
/**
|
|
* Runs action on each element found during a traversal starting at p.
|
|
* If p is null, traversal starts at head.
|
|
*/
|
|
void forEachFrom(Consumer<? super E> action, Node<E> p) {
|
|
// Extract batches of elements while holding the lock; then
|
|
// run the action on the elements while not
|
|
final int batchSize = 64; // max number of elements per batch
|
|
Object[] es = null; // container for batch of elements
|
|
int n, len = 0;
|
|
do {
|
|
fullyLock();
|
|
try {
|
|
if (es == null) {
|
|
if (p == null) p = head.next;
|
|
for (Node<E> q = p; q != null; q = succ(q))
|
|
if (q.item != null && ++len == batchSize)
|
|
break;
|
|
es = new Object[len];
|
|
}
|
|
for (n = 0; p != null && n < len; p = succ(p))
|
|
if ((es[n] = p.item) != null)
|
|
n++;
|
|
} finally {
|
|
fullyUnlock();
|
|
}
|
|
for (int i = 0; i < n; i++) {
|
|
@SuppressWarnings("unchecked") E e = (E) es[i];
|
|
action.accept(e);
|
|
}
|
|
} while (n > 0 && p != null);
|
|
}
|
|
|
|
/**
|
|
* @throws NullPointerException {@inheritDoc}
|
|
*/
|
|
public boolean removeIf(Predicate<? super E> filter) {
|
|
Objects.requireNonNull(filter);
|
|
return bulkRemove(filter);
|
|
}
|
|
|
|
/**
|
|
* @throws NullPointerException {@inheritDoc}
|
|
*/
|
|
public boolean removeAll(Collection<?> c) {
|
|
Objects.requireNonNull(c);
|
|
return bulkRemove(e -> c.contains(e));
|
|
}
|
|
|
|
/**
|
|
* @throws NullPointerException {@inheritDoc}
|
|
*/
|
|
public boolean retainAll(Collection<?> c) {
|
|
Objects.requireNonNull(c);
|
|
return bulkRemove(e -> !c.contains(e));
|
|
}
|
|
|
|
/**
|
|
* Returns the predecessor of live node p, given a node that was
|
|
* once a live ancestor of p (or head); allows unlinking of p.
|
|
*/
|
|
Node<E> findPred(Node<E> p, Node<E> ancestor) {
|
|
// assert p.item != null;
|
|
if (ancestor.item == null)
|
|
ancestor = head;
|
|
// Fails with NPE if precondition not satisfied
|
|
for (Node<E> q; (q = ancestor.next) != p; )
|
|
ancestor = q;
|
|
return ancestor;
|
|
}
|
|
|
|
/** Implementation of bulk remove methods. */
|
|
@SuppressWarnings("unchecked")
|
|
private boolean bulkRemove(Predicate<? super E> filter) {
|
|
boolean removed = false;
|
|
Node<E> p = null, ancestor = head;
|
|
Node<E>[] nodes = null;
|
|
int n, len = 0;
|
|
do {
|
|
// 1. Extract batch of up to 64 elements while holding the lock.
|
|
fullyLock();
|
|
try {
|
|
if (nodes == null) { // first batch; initialize
|
|
p = head.next;
|
|
for (Node<E> q = p; q != null; q = succ(q))
|
|
if (q.item != null && ++len == 64)
|
|
break;
|
|
nodes = (Node<E>[]) new Node<?>[len];
|
|
}
|
|
for (n = 0; p != null && n < len; p = succ(p))
|
|
nodes[n++] = p;
|
|
} finally {
|
|
fullyUnlock();
|
|
}
|
|
|
|
// 2. Run the filter on the elements while lock is free.
|
|
long deathRow = 0L; // "bitset" of size 64
|
|
for (int i = 0; i < n; i++) {
|
|
final E e;
|
|
if ((e = nodes[i].item) != null && filter.test(e))
|
|
deathRow |= 1L << i;
|
|
}
|
|
|
|
// 3. Remove any filtered elements while holding the lock.
|
|
if (deathRow != 0) {
|
|
fullyLock();
|
|
try {
|
|
for (int i = 0; i < n; i++) {
|
|
final Node<E> q;
|
|
if ((deathRow & (1L << i)) != 0L
|
|
&& (q = nodes[i]).item != null) {
|
|
ancestor = findPred(q, ancestor);
|
|
unlink(q, ancestor);
|
|
removed = true;
|
|
}
|
|
nodes[i] = null; // help GC
|
|
}
|
|
} finally {
|
|
fullyUnlock();
|
|
}
|
|
}
|
|
} while (n > 0 && p != null);
|
|
return removed;
|
|
}
|
|
|
|
/**
|
|
* Saves this queue to a stream (that is, serializes it).
|
|
*
|
|
* @param s the stream
|
|
* @throws java.io.IOException if an I/O error occurs
|
|
* @serialData The capacity is emitted (int), followed by all of
|
|
* its elements (each an {@code Object}) in the proper order,
|
|
* followed by a null
|
|
*/
|
|
private void writeObject(java.io.ObjectOutputStream s)
|
|
throws java.io.IOException {
|
|
|
|
fullyLock();
|
|
try {
|
|
// Write out any hidden stuff, plus capacity
|
|
s.defaultWriteObject();
|
|
|
|
// Write out all elements in the proper order.
|
|
for (Node<E> p = head.next; p != null; p = p.next)
|
|
s.writeObject(p.item);
|
|
|
|
// Use trailing null as sentinel
|
|
s.writeObject(null);
|
|
} finally {
|
|
fullyUnlock();
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Reconstitutes this queue from a stream (that is, deserializes it).
|
|
* @param s the stream
|
|
* @throws ClassNotFoundException if the class of a serialized object
|
|
* could not be found
|
|
* @throws java.io.IOException if an I/O error occurs
|
|
*/
|
|
private void readObject(java.io.ObjectInputStream s)
|
|
throws java.io.IOException, ClassNotFoundException {
|
|
// Read in capacity, and any hidden stuff
|
|
s.defaultReadObject();
|
|
|
|
count.set(0);
|
|
last = head = new Node<E>(null);
|
|
|
|
// Read in all elements and place in queue
|
|
for (;;) {
|
|
@SuppressWarnings("unchecked")
|
|
E item = (E)s.readObject();
|
|
if (item == null)
|
|
break;
|
|
add(item);
|
|
}
|
|
}
|
|
}
|