New submission from Sanchit <sanc...@cs.wisc.edu>:
While spawning, if a process having code built on top of Python's multiprocessing module calls multiprocessing.reduction.DupFd() (in /Lib/multiprocessing/reduction.py) multiple times on the same File descriptor by mistake, then it ends up invoking duplicate_for_child(fd)) of the class Popen, which, in turn, adds a duplicate FD to a list. This list is then used in spawnv_passfds() in /Lib/multiprocessing/util.py, which uses that list as an argument in a call of _posixsubprocess.fork_exec(). In Modules/_posixsubprocess.c, checks exist to ensure that all the FDs in the list are unique, positive, and in a sorted order. If duplicate entries are found, a ValueError: bad value(s) in fds_to_keep exception is raised, and the execution is terminated. Even if this exception were somehow handled, a developer can't change the aforementioned FD list in Python without breaking modularity. It's better to let developers get away with calling multiprocessing.reduction.DupFd() (in /Lib/multiprocessing/reduction.py) on by not accepting duplicate entries in the first place, so that spawning a process can be successful. ---------- components: Library (Lib) messages: 386546 nosy: sanchit priority: normal severity: normal status: open title: Do not add duplicate FDs to list in duplicate_for_child() type: behavior versions: Python 3.10, Python 3.6, Python 3.7, Python 3.8, Python 3.9 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue43142> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
