New submission from Richard Purdie <richard.pur...@linuxfoundation.org>:
I've been struggling to get signal.pthread_sigmask to do what I expected it to do from the documentation. Having looked at the core python code handling signals I now (think?!) I understand what is happening. It might be possible for python to improve the behaviour, or it might just be something to document, I'm not sure but I though I'd mention it. I'd added pthread_sigmask(SIG_BLOCK, (SIGTERM,)) and pthread_sigmask(SIG_UNBLOCK, (SIGTERM,)) calls around a critical section I wanted to protect from the SIGTERM signal. I was still seeing SIGTERM inside that section. Using SIGMASK to restore the mask instead of SIG_UNBLOCK behaves the same. What I hadn't realised is that firstly python defers signals to a convenient point and secondly that signals are processed in the main thread regardless of the thread they arrived in. This means that I can see SIGTERM arrive in my critical section as one of my other threads created in the background by the core python libs helpfully handles it. This makes SIG_BLOCK rather ineffective in any threaded code. To work around it, I can add my own handlers and have them track whether a signal arrived, then handle any signals after my critical section by re-raising them. It is possible python itself could defer processing signals masked with SIG_BLOCK until they're unblocked. Alternatively, a note in the documentation warning of the pitfalls here might be helpful to save someone else from wondering what is going on! ---------- components: Interpreter Core messages: 416154 nosy: rpurdie priority: normal severity: normal status: open title: pthread_sigmask needs SIG_BLOCK behaviour explaination versions: Python 3.10 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue47139> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
