ArrayBlockingQueue源码分析

ArrayBlockingQueue是一个有界的阻塞队列，底层维护的是一个数组。遵循先进先出FIFO，从尾部插入，从头部取出。如果队列已满，插入操作将阻塞，如果队列是空的，从队列里面取出元素也会阻塞。

构造方法

/* * fair 当多线程同时访问时，采用公平锁，还是非公平锁，默认 false 非公平锁 * * 公平锁：先发出请求的线程将先执行 * 非公平锁：哪个线程的请求先执行的顺序不确定 */ public ArrayBlockingQueue(int capacity, boolean fair) { if (capacity <= 0) throw new IllegalArgumentException(); this.items = new Object[capacity]; lock = new ReentrantLock(fair); notEmpty = lock.newCondition(); notFull = lock.newCondition(); }

put添加元素：如果队列已满将阻塞

public void put(E e) throws InterruptedException { checkNotNull(e); final ReentrantLock lock = this.lock; lock.lockInterruptibly(); try { // 如果队列已满，插入操作将阻塞 while (count == items.length) notFull.await(); enqueue(e); } finally { lock.unlock(); } }

add添加元素：如果队列已满将抛出异常

public boolean add(E e) { return super.add(e); }

offer添加元素：如果队列已满直接返回false, 不会抛出异常

public boolean offer(E e) { checkNotNull(e); final ReentrantLock lock = this.lock; lock.lock(); try { //如果队列已满直接返回false if (count == items.length) return false; else { enqueue(e); return true; } } finally { lock.unlock(); } }

offer添加元素：如果队列已满将先等待给定的时间间隔，如果在等待了给定的时间间隔之后还是满的，则返回false, 不会抛出异常

public boolean offer(E e, long timeout, TimeUnit unit) throws InterruptedException { checkNotNull(e); long nanos = unit.toNanos(timeout); final ReentrantLock lock = this.lock; lock.lockInterruptibly(); try { // 如果队列已满将先等待给定的时间间隔 while (count == items.length) { if (nanos <= 0) return false; nanos = notFull.awaitNanos(nanos); } enqueue(e); return true; } finally { lock.unlock(); } }

take取出对应位置的元素，并将该位置的值设置为null, 如果队列为空，取出元素操作将阻塞

public E take() throws InterruptedException { final ReentrantLock lock = this.lock; lock.lockInterruptibly(); try { //如果队列为空，取出元素操作将阻塞 while (count == 0) notEmpty.await(); return dequeue(); } finally { lock.unlock(); } }

poll取出元素，并将该位置的值设置为null, 如果队列为空，立刻直接返回null

public E poll() { final ReentrantLock lock = this.lock; lock.lock(); try { return (count == 0) ? null : dequeue(); } finally { lock.unlock(); } }

poll取出元素，并将该位置的值设置为null, 如果队列为空，将先等待给定的时间间隔，如果在等待了给定的时间间隔之后还是空的,则返回null

public E poll(long timeout, TimeUnit unit) throws InterruptedException { long nanos = unit.toNanos(timeout); final ReentrantLock lock = this.lock; lock.lockInterruptibly(); try { while (count == 0) { if (nanos <= 0) return null; nanos = notEmpty.awaitNanos(nanos); } return dequeue(); } finally { lock.unlock(); } }

peek取出当前位置的元素，不会将其设置为null 与take不同，如果队列为空将返回null

public E peek() { final ReentrantLock lock = this.lock; lock.lock(); try { return itemAt(takeIndex); // null when queue is empty } finally { lock.unlock(); } }

toArray转换成数组

public Object[] toArray() { Object[] a; final ReentrantLock lock = this.lock; lock.lock(); try { final int count = this.count; a = new Object[count]; int n = items.length - takeIndex; if (count <= n)// 说明putIndex一定在takeIndex与items.length之间 System.arraycopy(items, takeIndex, a, 0, count); else { System.arraycopy(items, takeIndex, a, 0, n); System.arraycopy(items, 0, a, n, count - n); } } finally { lock.unlock(); } return a; } 相关资源：python入门教程(PDF版)