notEmpty.signal(); // propagate to non-interrupted thread
throw ie;
}
E x = extract();
return x;
} finally {
lock.unlock();
}
}
//获取并移除此队列的头部，在指定的等待时间前等待可用的元素（如果有必要）。
public E poll(long timeout, TimeUnit unit) throws InterruptedException {
long nanos = unit.toNanos(timeout);
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
for (;;) {
if (count != 0) {
E x = extract();
return x;
}
if (nanos <= 0)
return null;
try {
nanos = notEmpty.awaitNanos(nanos);
} catch (InterruptedException ie) {
notEmpty.signal(); // propagate to non-interrupted thread
throw ie;
}
}
} finally {
lock.unlock();
}
}
//获取但不移除此队列的头；如果此队列为空，则返回 null。
public E peek() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return (count == 0) null : items[takeIndex];
} finally {
lock.unlock();
}
}
/**
* 返回此队列中元素的数量。
*/
public int size() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return count;
} finally {
lock.unlock();
}
}
/**
*返回在无阻塞的理想情况下（不存在内存或资源约束）此队列能接受的其他元素数量。
public int remainingCapacity() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return items.length - count;
} finally {
lock.unlock();
}
}
/**
* 从此队列中移除指定元素的单个实例（如果存在）。
*/
public boolean remove(Object o) {
if (o == null) return false;
final E[] items = this.items;
final ReentrantLock lock = this.lock;
lock.lock();
try {
int i = takeIndex;
int k = 0;
for (;;) {
if (k++ >= count)
return false;
if (o.equals(items[i])) {
removeAt(i);
return true;
}
i = inc(i);
}
} finally {
lock.unlock();
}
}
/**
* 如果此队列包含指定的元素，则返回 true。
*/
public boolean contains(Object o) {
if (o == null) return false;
final E[] items = this.items;
final ReentrantLock lock = this.lock;
lock.lock();
try {
int i = takeIndex;
int k = 0;
while (k++ < count) {
if (o.equals(items[i]))
return true;
i = inc(i);
}
return false;
} finally {
lock.unlock();
}
}
}