Question

我有以下简单的DelayQueue简单演示。

class DelayedThing implements Delayed {

    private final long waitUntil;
    private final String name;

    public DelayedThing(String name, long wait) {
        this.name = name;
        this.waitUntil = System.currentTimeMillis() + wait;
        System.out.println("DelayedThing(" + name + " wait=" + wait + " until-" + waitUntil);
    }

    @Override
    public long getDelay(TimeUnit unit) {
        System.out.println(name + " getDelay = " + unit.convert(waitUntil - System.currentTimeMillis(), TimeUnit.MILLISECONDS));
        return unit.convert(waitUntil - System.currentTimeMillis(), TimeUnit.MILLISECONDS);
    }

    @Override
    public int compareTo(Delayed o) {
        long diff = this.getDelay(TimeUnit.MILLISECONDS) - o.getDelay(TimeUnit.MILLISECONDS);
        System.out.println(name + ".compareTo(" + o + ") = " + diff);
        return Long.signum(diff);
    }

    @Override
    public String toString() {
        return name;
    }
}

public void test() throws InterruptedException {
    BlockingQueue<Delayed> queue = new DelayQueue<>();
    queue.add(new DelayedThing("one second", 1000));
    queue.add(new DelayedThing("two seconds", 2000));
    queue.add(new DelayedThing("half second", 500));
    for (Delayed d : queue) {
        System.out.println(d);
    }
}

但打印

half second
two seconds
one second

这显然是错误的。

Answer 1

错误是一个微妙的错误。我假设iterator的{{1}}将对每个元素执行一系列DelayQueue次调用。的错！

请参阅iterator() JavaDoc：

返回此队列中所有元素（过期和未过期）的迭代器。

这是非常意外的。

一个正确的解决方案如下：

take

请注意，如果您尝试流式传输队列，也会发生此问题：

while (queue.size() > 0) { System.out.println(queue.take()); }

由于流媒体将在queue.stream().forEach((d) -> { System.out.println(d); });提供的iterator上发生，因此也会产生意外结果。

为什么我的DelayQueue不会以错误的顺序延迟和打印？

1 个答案: