New submission from Sean Murphy:
Python fails to pass a Queue when calling Process with
multiprocessing.set_start_method set to "spawn" or "forkserver".
Traceback (most recent call last):
File "<string>", line 1, in <module>
File "/usr/lib/python3.5/multiprocessing/spawn.py", line 106, in spawn_main
exitcode = _main(fd)
File "/usr/lib/python3.5/multiprocessing/spawn.py", line 116, in _main
self = pickle.load(from_parent)
File "/usr/lib/python3.5/multiprocessing/synchronize.py", line 111, in
__setstate__
self._semlock = _multiprocessing.SemLock._rebuild(*state)
FileNotFoundError: [Errno 2] No such file or directory
Here is a minimized example:
```
#!/usr/bin/env python3
import multiprocessing
def check_child(q):
print("Queue", q)
if __name__ == '__main__':
multiprocessing.set_start_method('spawn')
# multiprocessing.set_start_method('fork')
# multiprocessing.set_start_method('forkserver')
q = multiprocessing.Queue(-1)
print("q", q)
proc = multiprocessing.Process(target=check_child, args=(q,))
proc.start()
```
Also, this fails when the Queue is implicitly passed to the child.
```
class Blerg():
def __init__(self):
self.q = multiprocessing.Queue(-1)
def print_queue(self):
print("Queue", self.q)
if __name__ == '__main__':
multiprocessing.set_start_method('spawn')
blerg = Blerg()
blerg.print_queue()
proc = multiprocessing.Process(target=blerg.print_queue)
proc.start()
```
$ python3 --version
Python 3.5.2
Windows (which defaults to "spawn" style multiprocessing) does not seem to have
this issue (at least in 2.7.12).
----------
components: Library (Lib)
messages: 283150
nosy: Sean Murphy
priority: normal
severity: normal
status: open
title: Multiprocessing spawn/forkserver fails to pass Queues
type: crash
versions: Python 3.5
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue28965>
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