ArrayBlockingQueue是concurrent包提供的一个
线程安全的
队列,由一个数组来保存队列元素.通过
takeIndex和
putIndex来分别记录出队列和入队列的下标,以保证在出队列时
不进行元素移动.
class="java" name="code">
//在出队列或者入队列的时候对takeIndex或者putIndex进行累加,如果已经到了数组末尾就又从0开始,保证数组的循环使用.
final int inc(int i) {
return (++i == items.length) ? 0 : i;
}
//入队列操作
private void insert(E x) {
items[putIndex] = x;
putIndex = inc(putIndex);
++count;
notEmpty.signal();//唤醒等待的出队线程
}
//使用offer入队列,如果队列已满就立即返回false
public boolean offer(E e) {
checkNotNull(e);
final ReentrantLock lock = this.lock;
lock.lock();
try {
if (count == items.length)
return false;
else {
insert(e);
return true;
}
} finally {
lock.unlock();
}
}
//使用put入队列的话,如果队列已满当前线程就等待然后释放锁,直到被notFull唤醒,再重新检查,直到成功插入队列
public void put(E e) throws InterruptedException {
checkNotNull(e);
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
while (count == items.length)
notFull.await();
insert(e);
} finally {
lock.unlock();
}
}
//出队列操作
private E extract() {
final Object[] items = this.items;
E x = this.<E>cast(items[takeIndex]);
items[takeIndex] = null;
takeIndex = inc(takeIndex);
--count;
notFull.signal();//唤醒等待入队的线程
return x;
}
//poll出队是不需要等待的,如果当前队列是空就直接返回null
public E poll() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return (count == 0) ? null : extract();
} finally {
lock.unlock();
}
}
//take就跟put一样,如果队列是空的就等待直到被notEmpty唤醒
public E take() throws InterruptedException {
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
while (count == 0)
notEmpty.await();
return extract();
} finally {
lock.unlock();
}
}
最后需要注意的就是带
超时唤醒的是
offer和
poll而不是put和take