[issue38904] "signal only works in main thread" in main thread
New submission from Richard Warfield : I have an application (https://github.com/litxio/ptghci) using embedded Python, which needs to set a signal handler (and use the prompt-toolkit library which itself sets signal handlers). My call to signal.signal is guarded by a check that we're running in the main thread: if threading.current_thread() is threading.main_thread(): print (threading.current_thread().name) signal.signal(signal.SIGINT, int_handler) And the above indeed prints "MainThread". But this raises an exception: File "app.py", line 45, in __init__ signal.signal(signal.SIGINT, int_handler) File "/usr/lib/python3.8/signal.py", line 47, in signal handler = _signal.signal(_enum_to_int(signalnum), _enum_to_int(handler)) ValueError: signal only works in main thread This seems like something that should not happen. Now, I tried to generate a simple replicating example but thus far haven't been able to do so -- simply calling signal.signal from PyRun_SimpleString doesn't do the trick, even within a pthreads thread. -- messages: 357390 nosy: Richard Warfield priority: normal severity: normal status: open title: "signal only works in main thread" in main thread type: behavior versions: Python 3.8 ___ Python tracker <https://bugs.python.org/issue38904> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue38904] "signal only works in main thread" in main thread
Richard Warfield added the comment: I should mention, this behavior is new in 3.8.0. It did not occur in 3.7.x. -- ___ Python tracker <https://bugs.python.org/issue38904> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue38904] "signal only works in main thread" in main thread
Richard Warfield added the comment: Thanks for looking into this. Changing the behavior of the "threading" module to be consistent with the runtime and "signal" module would be sufficient, at least for my particular case. If the "if threading.current_thread() is threading.main_thread()" guard worked as expected it would be clear how to resolve the problem. On Sat, Dec 14, 2019 at 6:25 AM Eric Snow wrote: > > Eric Snow added the comment: > > Before 3.8, the "signal" module checked against the thread in which the > module was initially loaded, treating that thread as the "main" thread. > That same was true (and still is) for the "threading" module. The problem > for both modules is that the Python runtime may have actually been > initialized in a different thread, which is the actual "main" thread. > > Since Python 3.8 we store the ID of the thread where the runtime is > initialized and use that in the check the "signal" module does. However, > the "threading" module still uses the ID of the thread where it is first > imported. So your check against "threading.main_thread()" must be in code > that isn't running in the same thread where you ran Py_Initialize(). It > probably used to work because you imported "signal" and "threading" for the > first time in the same thread. > > So what next? > > First, I've created issue39042 to address the current different meanings > of "main thread". That should resolve the discrepancy between the signal > and threading modules. > > Second, what can we do to help embedders make sure they are running their > code in the main thread (e.g. when setting signals)? Is there any C-API we > could add which would have helped you here? > > -- > nosy: +eric.snow, vstinner > > ___ > Python tracker > <https://bugs.python.org/issue38904> > ___ > -- ___ Python tracker <https://bugs.python.org/issue38904> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue38904] "signal only works in main thread" in main thread
Richard Warfield added the comment: I think so, yes. On Wed, Dec 18, 2019 at 1:10 AM Eric Snow wrote: > > Eric Snow added the comment: > > So resolving issue39042 would be enough, particularly if we backported > the change to 3.8? > > -- > > ___ > Python tracker > <https://bugs.python.org/issue38904> > ___ > -- ___ Python tracker <https://bugs.python.org/issue38904> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
