为什么wait（）总是在循环内调用 [英] Why should wait() always be called inside a loop

问题描述

我已经读过我们应该总是在循环中调用 wait（）：

I have read that we should always call a wait() from within a loop:

while (!condition) { obj.wait(); }

没有循环就可以正常工作，为什么会这样？

It works fine without a loop so why is that?

推荐答案

您不仅需要循环它，还要检查循环中的条件。 Java不保证您的线程只能通过notify（）/ notifyAll（）调用或正确的notify（）/ notifyAll（）调用来唤醒。由于此属性，无环版本可能适用于您的开发环境，并且意外地在生产环境中失败。

You need not only to loop it but check your condition in the loop. Java does not guarantee that your thread will be woken up only by a notify()/notifyAll() call or the right notify()/notifyAll() call at all. Because of this property the loop-less version might work on your development environment and fail on the production environment unexpectedly.

例如，您正在等待某些事情：

For example, you are waiting for something:

synchronized (theObjectYouAreWaitingOn) {
   while (!carryOn) {
      theObjectYouAreWaitingOn.wait();
   }
}

一个邪恶的线程出现了：

An evil thread comes along and:

theObjectYouAreWaitingOn.notifyAll();

如果邪恶的线程没有/不能搞乱 carryOn 您只需继续等待合适的客户。

If the evil thread does not/can not mess with the carryOn you just continue to wait for the proper client.

编辑：添加了更多样本。
等待可以中断。它抛出InterruptedException，你可能需要在try-catch中包装wait。根据您的业务需求，您可以退出或取消异常并继续等待。

Added some more samples. The wait can be interrupted. It throws InterruptedException and you might need to wrap the wait in a try-catch. Depending on your business needs, you can exit or suppress the exception and continue waiting.

这篇关于为什么wait（）总是在循环内调用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！