Java LinkedBlockingQueue 分析

最新推荐文章于 2025-07-06 09:47:42 发布

最新推荐文章于 2025-07-06 09:47:42 发布 · 163 阅读

文章标签：

本文介绍Java并发包中LinkedBlockingQueue的实现原理与使用方法。它是一个线程安全的链式阻塞队列，支持FIFO操作，可用于多线程间的任务传递。文章详细解释了其构造函数、内部数据结构及主要方法。

package java.util.concurrent
public class LinkedBlockingQueue<E> extends AbstractQueue<E> implements BlockingQueue<E>, java.io.Serializable

线程安全的链式阻塞队列

内部有个static class Node<E> 实现链式结构

构造函数

    /**
     * Creates a {@code LinkedBlockingQueue} with a capacity of
     * {@link Integer#MAX_VALUE}.
     */
    public LinkedBlockingQueue() {
        this(Integer.MAX_VALUE);
    }

    /**
     * Creates a {@code LinkedBlockingQueue} with the given (fixed) capacity.
     *
     * @param capacity the capacity of this queue
     * @throws IllegalArgumentException if {@code capacity} is not greater
     *         than zero
     */
    public LinkedBlockingQueue(int capacity) {
        if (capacity <= 0) throw new IllegalArgumentException();
        this.capacity = capacity;
        last = head = new Node<E>(null);
    }

    /**
     * Creates a {@code LinkedBlockingQueue} with a capacity of
     * {@link Integer#MAX_VALUE}, initially containing the elements of the
     * given collection,
     * added in traversal order of the collection's iterator.
     *
     * @param c the collection of elements to initially contain
     * @throws NullPointerException if the specified collection or any
     *         of its elements are null
     */
    public LinkedBlockingQueue(Collection<? extends E> c) {
        this(Integer.MAX_VALUE);
        final ReentrantLock putLock = this.putLock;
        putLock.lock(); // Never contended, but necessary for visibility
        try {
            int n = 0;
            for (E e : c) {
                if (e == null)
                    throw new NullPointerException();
                if (n == capacity)
                    throw new IllegalStateException("Queue full");
                enqueue(new Node<E>(e));
                ++n;
            }
            count.set(n);
        } finally {
            putLock.unlock();
        }
    }

可以设置队列的长度，默认为Integer.MAX_VALUE

或从一个Collection，创建LinkedBlockingQueue

内部的锁和相关条件

 /** Lock held by take, poll, etc */
    private final ReentrantLock takeLock = new ReentrantLock();

    /** Wait queue for waiting takes */
    private final Condition notEmpty = takeLock.newCondition();

    /** Lock held by put, offer, etc */
    private final ReentrantLock putLock = new ReentrantLock();

    /** Wait queue for waiting puts */
    private final Condition notFull = putLock.newCondition();

数据元素操作

add、remove

add会调用offer()；

add：添加元素，返回是否操作成功的boolean标识。链表未满才可添加

remove：删除元素，返回是否操作成功的boolean标识。链表未空才可删除

offer、poll

offer：添加元素，返回是否操作成功的boolean标识。链表未满才可添加

poll：删除元素，返回被删除的元素。若无元素被删除，返回null

put、take

put：阻塞式添加元素，当链表满了，阻塞线程。

take：阻塞式删除元素，当链表空了，阻塞线程。返回移除的元素。

LinkedBlockingQueue 是一个先进先出(FIFO)的阻塞式队列