可重入锁ReentrantLock

23 Mar 2012 in java on lock, 锁 - Hits()

今天学习一下可重入锁ReentrantLock：

先来借别人的例子来看它怎么用：

这是java DelayQueue的take方法：

public E take() throws InterruptedException { final ReentrantLock lock = this.lock; lock.lockInterruptibly(); try { for (;;) { E first = q.peek(); if (first == null) { available.await(); //此时已经释放锁了,因为是等待状态，也不存在同步问题

//到这一步又获得了锁，可能是被signalAll方法唤醒的 } else { long delay = first.getDelay(TimeUnit.NANOSECONDS); if (delay > 0) { long tl = available.awaitNanos(delay);//释放锁到一定时间
//再次获得锁 } else { E x = q.poll(); assert x != null; if (q.size() != 0) available.signalAll(); //唤醒 return x; } } } } finally { lock.unlock(); } }

这是offer方法:

public boolean offer(E e) {

                final ReentrantLock lock = this.lock;

                lock.lock();

                try {

                    E first = q.peek();

                    q.offer(e);

                    if (first == null || e.compareTo(first) < 0)

                        available.signalAll();

//这里判断之前是空的，现在有元素了，应该唤醒，但是此时此方法还在保持锁

return true;

} finally {

lock.unlock();

}

参见:http://tenyears.iteye.com/blog/48750

详见java.concurrency.in.practice一书第十三章