问题描述
LinkedBlockingQueue当消费者在从队列中获取元素之后会这样做时，为什么当前的生产者需要public void put(E e) throws InterruptedException {
if (e == null) throw new NullPointerException();
// Note: convention in all put/take/etc is to preset local var
// holding count negative to indicate failure unless set.
int c = -1;
Node<E> node = new Node<E>(e);
final reentrantlock putLock = this.putLock;
final AtomicInteger count = this.count;
putLock.lockInterruptibly();
try {
/*
* Note that count is used in wait guard even though it is
* not protected by lock. This works because count can
* only decrease at this point (all other puts are shut
* out by lock),and we (or some other waiting put) are
* signalled if it ever changes from capacity. Similarly
* for all other uses of count in other wait guards.
*/
while (count.get() == capacity) {
notFull.await();
}
enqueue(node);
c = count.getAndIncrement();
if (c + 1 < capacity)
notFull.signal(); // Is this necessary?
} finally {
putLock.unlock();
}
if (c == 0)
signalNotEmpty();
}
来唤醒其他生产者？有什么例子可以解释这是必要的吗？
解决方法
我不确定这是否可能。
-
生产者P1，P2（定时）和P3在
notFull.await();处阻塞。 -
消费者C1消费一个元素并唤醒P1。
-
P1将元素放入队列。同时，C2消费另一个元素并唤醒P2。由于P1保持
putLock，因此P2必须等待。不幸的是，P2在等待时超时。 -
P1需要唤醒P3，否则P3会不必要地等待。