Antoine Pitrou <solip...@pitrou.net> added the comment:
I can reproduce on Ubuntu 18.04 with git master. Here is a better example which clearly shows the issue: https://gist.github.com/pitrou/d9784d5ec679059cd02fce4b38ea2fa6 After a few runs, you'll see that the child Process hangs when trying to flush the standard streams: Timeout (0:00:01)! Thread 0x00007efbff6c0080 (most recent call first): File "/home/antoine/cpython/default/Lib/multiprocessing/util.py", line 435 in _flush_std_streams File "/home/antoine/cpython/default/Lib/multiprocessing/process.py", line 335 in _bootstrap File "/home/antoine/cpython/default/Lib/multiprocessing/popen_fork.py", line 71 in _launch File "/home/antoine/cpython/default/Lib/multiprocessing/popen_fork.py", line 19 in __init__ File "/home/antoine/cpython/default/Lib/multiprocessing/context.py", line 276 in _Popen File "/home/antoine/cpython/default/Lib/multiprocessing/context.py", line 224 in _Popen File "/home/antoine/cpython/default/Lib/multiprocessing/process.py", line 121 in start File "/home/antoine/cpython/default/bpo40399.py", line 25 in <module> Child process failed! @Delgan, mixing processes and threads is problematic with the default settings. See here: https://docs.python.org/3/library/multiprocessing.html#contexts-and-start-methods """Note that safely forking a multithreaded process is problematic.""" If you call `multiprocessing.set_start_method("forkserver")` at the start of your program, the problem will disappear. ---------- nosy: +pitrou, vstinner title: Program hangs if process created right after adding object to a Queue -> IO streams locking can be broken after fork() with threads versions: +Python 3.9 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue40399> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
