ArrayBlockingQueue 源码分析

本文主要是介绍ArrayBlockingQueue 源码分析，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

ArrayBlockingQueue 实际实现是一个环形数组,并且保护了线程安全,那么是如何保证线程安全的?

环形数组怎么实现的?

先看下里面的几个参数是干嘛的

    /** The queued items */数据,存数据的 final Object[] items;/** items index for next take, poll, peek or remove */取出的引索int takeIndex;/** items index for next put, offer, or add */放置的引索int putIndex;/** Number of elements in the queue */实际上有几个数据,为什么会有这个东西,因为实际实现是环形数组,但是这只是个概念int count;/** Concurrency control uses the classic two-condition algorithm* found in any textbook.*//** Main lock guarding all access */默认的非公平锁,支持公平锁final ReentrantLock lock;/** Condition for waiting takes */空锁private final Condition notEmpty;/** Condition for waiting puts */满锁private final Condition notFull;

ArrayBlockingQueue 实际实现是一个环形数组先看下它咋实现的

    private void enqueue(E x) {// assert lock.getHoldCount() == 1;// assert items[putIndex] == null;拿到局部变量防止并发final Object[] items = this.items;将数据放入数组items[putIndex] = x;如果到头了反回到尾节点if (++putIndex == items.length) putIndex = 0;真实数量++count++;非空锁解锁,take方法此时可以继续执行了notEmpty.signal();}

/*** Inserts the specified element at the tail of this queue, waiting* for space to become available if the queue is full.** @throws InterruptedException {@inheritDoc}* @throws NullPointerException {@inheritDoc}*/public void put(E e) throws InterruptedException {Objects.requireNonNull(e);final ReentrantLock lock = this.lock;lock.lockInterruptibly();try {如果数据相等证明满了,锁住不放while (count == items.length)notFull.await();enqueue(e);} finally {lock.unlock();}}

offer如果队列满了会抛弃掉,offer方法如果满了会锁住挂起等到加入为止

 public E take() throws InterruptedException {final ReentrantLock lock = this.lock;lock.lockInterruptibly();try {while (count == 0)如果 == 0 证明没数据了,等有数据再解开循环notEmpty.await();return dequeue();} finally {lock.unlock();}}

    /*** Extracts element at current take position, advances, and signals.* Call only when holding lock.*/private E dequeue() {// assert lock.getHoldCount() == 1;// assert items[takeIndex] != null;final Object[] items = this.items;@SuppressWarnings("unchecked")取出数据E x = (E) items[takeIndex];把当前节点置空items[takeIndex] = null;走向下一个节点if (++takeIndex == items.length) takeIndex = 0;数据量-1count--;if (itrs != null)itrs.elementDequeued();解锁notFull.signal();return x;}

环形数组示例图片嘛,大概这样