Bugs item #1460493, was opened at 2006-03-29 09:16 Message generated for change (Comment added) made by loewis You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1460493&group_id=5470
Please note that this message will contain a full copy of the comment thread, including the initial issue submission, for this request, not just the latest update. Category: None Group: None >Status: Closed >Resolution: Fixed Priority: 5 Submitted By: HVB bei TUP (hvb_tup) Assigned to: Nobody/Anonymous (nobody) Summary: Why not drop the _active list? Initial Comment: I am using a modified version of subprocess.py, where I have removed the _active list and all references to it. I have tested it (under Windows 2000) and there were no errors. So what is the reason for managing the _active list at all? Why not drop it? ---------------------------------------------------------------------- >Comment By: Martin v. Löwis (loewis) Date: 2006-04-10 17:58 Message: Logged In: YES user_id=21627 This was fixed with said patch. ---------------------------------------------------------------------- Comment By: cheops (atila-cheops) Date: 2006-04-10 16:55 Message: Logged In: YES user_id=1276121 see patch #1467770 ---------------------------------------------------------------------- Comment By: cheops (atila-cheops) Date: 2006-04-05 10:27 Message: Logged In: YES user_id=1276121 the implementation in 2.5 of popen2 seems good if you or astrand could patch subprocess.py accordingly, that would be great. ---------------------------------------------------------------------- Comment By: Martin v. Löwis (loewis) Date: 2006-03-30 18:31 Message: Logged In: YES user_id=21627 attila-cheops, please read the 2.5 version of popen2. popen2 now only adds processes to _active in __del__, not in __init__, so the problem with the application still wanting to wait/poll is solved. Multiple threads simultaneously isn't a problem, since it is (or should be) harmless to invoke poll on a process that has already been waited for. For only one of the poll calls, the wait will actually succeed, and that should be the one that removes it from the _active list. The same strategy should be applied to subprocess. ---------------------------------------------------------------------- Comment By: cheops (atila-cheops) Date: 2006-03-30 10:17 Message: Logged In: YES user_id=1276121 also #1214859 is interesting, has a patch ---------------------------------------------------------------------- Comment By: cheops (atila-cheops) Date: 2006-03-30 10:06 Message: Logged In: YES user_id=1276121 the same problem probably exists in popen2.py there _active is also used so if something is fixed in subprocess.py, it should probably also be fixed in popen2.py ---------------------------------------------------------------------- Comment By: cheops (atila-cheops) Date: 2006-03-30 10:04 Message: Logged In: YES user_id=1276121 what happens if you are doing a _cleanup (iterating over a copy of _active) in multiple threads? can it not happen then that you clean up a process 2 times? thread 1 starts a _cleanup: makes a copy of _active[:] and starts polling thread 2 starts a _cleanup: makes a copy of _active[:] and starts polling thread 1 encounters a finished process and removes it from _active[] thread 2 does not know the process is removed, finds the same process finished and tries to remove it from _active but this fails, because thread 1 removed it already so the action of cleaning up should maybe be serialized if 1 thread is doing it, the other one should block everyone who needs this can of course patch the subprocess.py file, but shouldn't this be fixed in the library? ---------------------------------------------------------------------- Comment By: Neal Norwitz (nnorwitz) Date: 2006-03-30 09:43 Message: Logged In: YES user_id=33168 If you always called wait() the _active list isn't beneficial to you. However, many people do not call wait and the _active list provides a mechanism to cleanup zombied children. This is important for many users. If you need thread safely, you can handle the locking yourself before calling poll()/wait(). ---------------------------------------------------------------------- Comment By: Martin v. Löwis (loewis) Date: 2006-03-29 22:41 Message: Logged In: YES user_id=21627 The purpose of the _active list is to wait(2) for open processes. It needs to stay. ---------------------------------------------------------------------- Comment By: Tristan Faujour (tfaujour) Date: 2006-03-29 15:59 Message: Logged In: YES user_id=1488657 I agree. The use of _active makes subprocess.py thread-UNsafe. See also: Bug #1199282 In order to have a thread-safe subprocess.py, I commented out the call to _cleanup() in Popen.__init__(). As a side effect, _active becomes useless. ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1460493&group_id=5470 _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
