Java LinkedBlockingQueue 实现

Question

我看着 JDK LinkedBlockingQueue 类，迷路了。

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;
    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(e);
        c = count.getAndIncrement();
        if (c + 1 < capacity)
            notFull.signal();
    } finally {
        putLock.unlock();
    }
    if (c == 0)
        signalNotEmpty();
}

请看最后一个条件(c == 0)，我觉得应该是(c != 0)

谢谢，我明白了。 但我还有另一个关于 LinkedBlockingQueue 实现的问题。 入队和出队功能不得相交。我看到当 put() 被执行时， take() 也可以被执行。 head 和 tail 对象没有同步，入队和出队可以在不同的线程中同时工作。它不是线程安全的，可能会发生故障。

Answer 1

不，目的是仅当队列从 0 变为 1 时(即第一次向空队列中添加内容)发出信号。将项目添加到已经有项目的队列时，您不需要“发出非空信号”。 (您会注意到 notEmpty 条件仅在队列计数 == 0 时才会等待)。