Why do condition variables sometimes erroneously wake up?

Posted by aspo on Stack Overflow See other posts from Stack Overflow or by aspo
Published on 2010-04-28T06:24:18Z Indexed on 2010/04/28 6:33 UTC
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concurrency

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condition-variables

I've known for eons that the way you use a condition variable is

lock
while not task_done
  wait on condition variable
unlock

Because sometimes condition variables will spontaneously wake. But I've never understood why that's the case. In the past I've read it's expensive to make a condition variable that doesn't have that behavior, but nothing more than that.

So... why do you need to worry about falsely being woken up when waiting on a condition variable?

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