Robert Collins <robe...@robertcollins.net> added the comment: I'm not sure it is sensibly implementable in pure python: the semantics of signal handling (AIUI) are that the vm is interrupted, sets a flag to say 'when the GIL is released or the next bytecode interpretation happens, please process signal X' [the former for C extensions, the latter for regular code], and then the OS level signal handler returns. The current C or bytecode execution completes and then we dispatch to the python signal handler.
Now, what we would want here is that attempts to acquire/release the RLock in a signal handler would behave as though the RLock.acquire/release methods were atomic. The general way to enforce such atomicity is via a lock or mutex. Now, because the call stack looks like this: <signal>thread.acquire() <non-signal-code>thread.acquire() The other acquire, if it already holds this supposed mutex, would block the python signal handler acquire call from obtaining it; The inner acquire would have to error *whether or not a timeout was passed*, because the non-signal-code won't progress and complete until the python signal handler code returns. One could, in principle, use stack inspection to determine how far through a nested acquire/release the outer code is, but that seems, uhm, pathological to me :). The crux of the problem is detecting whether the non-reentrant thread.lock is held because (a) another thread holds it or (b) this thread holds it. If we can inspect its internals, we could determine that this thread holds it - and thus we must be reentered into the acquire/release methods. With that tricky thing established, we could look at the remaining logic to make sure that each line is either atomic or conditional on reentrancy. Simpler I think to require CRLocks always, and provide a portable C implementation which will always complete before returning to execution in the calling thread, avoiding this issue entirely. ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue13697> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
