Is it safe to call pthread_cancel() on terminated thread?

Question

I\'m wondering if it is safe to call pthread_cancel() on a terminated thread. I couldn\'t find any hints in the manual page. Thanks in advance for any hints.

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Answer 1

I think it needs to be safe, or pthread_cancel would be problematic (next to unusable).

Indeed, if it wouldn't be safe, every call to pthread_cancel would have to be enormously complicated by checking the thread is alive (and ensuring it stays alive until you get to cancel it). A simple "are you still there" wouldn't do.

In conclusion, I believe pthread_cancel must be safe if the thread has terminated. Of course, this might not be the case for a terminated and joined thread.