New submission from Andre Merzky:
- create a class which is a subclass of multiprocessing.Process ('A')
- in its __init__ create new thread ('B') and share a queue with it
- in A's run() method, run 'C=subprocess.Popen(args="/bin/false")'
- push 'C' though the queue to 'B'
- call 'C.pull()' --> returns 0
Apart from returning 0, the pull will also return immediately, even if the task
is long running. The task does not die -- 'ps' shows it is well alive.
I assume that the underlying reason is that 'C' is moved sideways in the
process tree, and the wait is happening in a thread which is not the parent of
C. I assume (or rather guess, really) that the system level waitpid call
raises a 'ECHILD' (see wait(2)), but maybe that is misinterpreted as 'process
gone'?
I append a test script which shows different combinations of process spawner
and watcher classes. All of them should report an exit code of '1' (as all run
/bin/false), or should raise an error. None should report an exit code of 0 --
but some do.
PS.: I implore you not to argue if the above setup makes sense -- it probably
does not. However, it took significant work to condense a real problem into
that small excerpt, and it is not a full representation of our application
stack. I am not interested in discussing alternative approaches: we have
those, and I can live with the error not being fixed.
#!/usr/bin/env python
from subprocess import Popen
from threading import Thread as T
from multiprocessing import Process as P
import multiprocessing as mp
class A(P):
def __init__(self):
P.__init__(self)
self.q = mp.Queue()
def b(q):
C = q.get()
exit_code = C.poll()
print "exit code: %s" % exit_code
B = T(target = b, args=[self.q])
B.start ()
def run(self):
C = Popen(args = '/bin/false')
self.q.put(C)
a = A()
a.start()
a.join()
----------
components: Library (Lib)
files: test_mp.py
messages: 248553
nosy: Andre Merzky
priority: normal
severity: normal
status: open
title: subprocess.Popen behaves incorrect when moved in process tree
type: behavior
versions: Python 2.7
Added file: http://bugs.python.org/file40177/test_mp.py
_______________________________________
Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue24862>
_______________________________________
_______________________________________________
Python-bugs-list mailing list
Unsubscribe:
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
