[issue24283] Print not safe in signal handlers
New submission from Devin Jeanpierre: The code attached runs a while loop that prints, and has a signal handler that also prints. There is a thread that constantly fires off signals, but this is just to ensure the condition for the bug happens -- this is a bug with signal handling, not threads -- I can trigger a RuntimeError (... with a missing message?) by commenting out the threading lines and instead running a separate process while true; do kill -s SIGUSR1 4687; done. Traceback: $ python3 threading_print_test.py hello world Traceback (most recent call last): File /usr/local/google/home/devinj/Downloads/threading_print_test.py, line 36, in module main() File /usr/local/google/home/devinj/Downloads/threading_print_test.py, line 30, in main print(world) File /usr/local/google/home/devinj/Downloads/threading_print_test.py, line 13, in print_hello print(hello) RuntimeError: reentrant call inside _io.BufferedWriter name='stdout' -- files: threading_print_test.py messages: 244020 nosy: Devin Jeanpierre, haypo priority: normal severity: normal status: open title: Print not safe in signal handlers Added file: http://bugs.python.org/file39491/threading_print_test.py ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue24283 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue24283] Print not safe in signal handlers
Changes by R. David Murray rdmur...@bitdance.com: -- nosy: +pitrou ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue24283 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue24283] Print not safe in signal handlers
Antoine Pitrou added the comment: RuntimeError: reentrant call inside _io.BufferedWriter name='stdout' As the exception message suggests: the IO stack is not reentrant. If an ongoing IO call is interrupted by a signal, and the signal handler calls again into the IO stack, this situation is detected and an error is raised. If instead we allowed the IO call to continue, all sorts of problems could ensue (data loss, crashes...). So, indeed, print() is not safe in signal handlers. Though the fact that it raises an exception, rather than crashes, makes things easier for the developer ;) -- resolution: - wont fix stage: - resolved status: open - closed ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue24283 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue24283] Print not safe in signal handlers
Devin Jeanpierre added the comment: It doesn't do any of those things in Python 2, to my knowledge. Why aren't we willing to make this work? -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue24283 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue24283] Print not safe in signal handlers
STINNER Victor added the comment: It doesn't do any of those things in Python 2, to my knowledge. Well, even if Python 2 doesn't warn you, threading_print_test.py is also wrong on Python 2. Python 3 is better because it warns you :-) Why aren't we willing to make this work? It would be very complex to support reentrant calls in the io stack. It's much easier to redesign your application to defer the work of the signal handler outside the signal handler. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue24283 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
