Java中的虚假唤醒真的发生了吗？ [英] Do spurious wakeups in Java actually happen?

问题描述

看到各种与锁相关的问题，并且（几乎）总是找到'因为虚假的唤醒而导致的循环'术语 ¹ 我想，有没有人经历过这样的唤醒（假设一个像样的硬件/软件环境）例如）？

Seeing various locking related question and (almost) always finding the 'loop because of spurious wakeups' terms¹ I wonder, has anyone experienced such kind of a wakeup (assuming a decent hardware/software environment for example)?

我知道虚假一词意味着没有明显的理由，但这种事件可能是什么原因？

I know the term 'spurious' means no apparent reason but what can be the reasons for such kind of an event?

（ ¹ 注意：我不是在质疑循环练习。）

(¹ Note: I'm not questioning the looping practice.)

编辑：一个帮助问题（对于那些喜欢代码示例的人）：

A helper question (for those who like code samples):

如果我有以下程序，我运行它：

If I have the following program, and I run it:

public class Spurious {
    public static void main(String[] args) {
        Lock lock = new ReentrantLock();
        Condition cond = lock.newCondition();
        lock.lock();
        try {
            try {
                cond.await();
                System.out.println("Spurious wakeup!");
            } catch (InterruptedException ex) {
                System.out.println("Just a regular interrupt.");
            }
        } finally {
            lock.unlock();
        }
    }
}

我该怎么做才能唤醒这个等待虚假而不等待永远的随机事件？

What can I do to wake this await up spuriously without waiting forever for a random event?

推荐答案

维基百科关于虚假唤醒的文章有这样的消息：

The Wikipedia article on spurious wakeups has this tidbit:

Linux中的 pthread_cond_wait（）函数是使用 futex 系统实现的呼叫。当进程收到信号时，Linux上的每个阻塞系统调用都会突然返回 EINTR 。 ... pthread_cond_wait（）无法重启等待，因为它可能会在 futex 系统调用。只有呼叫者检查不变量才能避免这种竞争条件。因此，POSIX信号将产生虚假唤醒。

The pthread_cond_wait() function in Linux is implemented using the futex system call. Each blocking system call on Linux returns abruptly with EINTR when the process receives a signal. ... pthread_cond_wait() can't restart the waiting because it may miss a real wakeup in the little time it was outside the futex system call. This race condition can only be avoided by the caller checking for an invariant. A POSIX signal will therefore generate a spurious wakeup.

摘要：如果Linux进程发出信号则表示等待线程将各自享受一个漂亮的，热的虚假的唤醒。

Summary: If a Linux process is signaled its waiting threads will each enjoy a nice, hot spurious wakeup.

我买它。这是一个比通常模糊的性能原因更容易吞下的药丸。

I buy it. That's an easier pill to swallow than the typically vague "it's for performance" reason often given.

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