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

No, it isn't safe to call pthread_cancel() on a thread that has been terminated.

The reason is that the implementation may reuse the thread ID of the terminated thread for another thread and calling "pthread_cancel()" on that TID may trigger the termination on threads that shouldn't be terminated or undefined behaviour.