| msg27934 - (view) |
Author: HVB bei TUP (hvb_tup) |
Date: 2006-03-29 07:16 |
| 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? |
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| msg27935 - (view) |
Author: Tristan Faujour (tfaujour) |
Date: 2006-03-29 13:59 |
| 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. |
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| msg27936 - (view) |
Author: Martin v. Löwis (loewis) *  |
Date: 2006-03-29 20:41 |
| Logged In: YES user_id=21627 The purpose of the _active list is to wait(2) for open processes. It needs to stay. |
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| msg27937 - (view) |
Author: Neal Norwitz (nnorwitz) * |
Date: 2006-03-30 07:43 |
| 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(). |
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| msg27938 - (view) |
Author: cheops (atila-cheops) |
Date: 2006-03-30 08:04 |
| 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? |
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| msg27939 - (view) |
Author: cheops (atila-cheops) |
Date: 2006-03-30 08:06 |
| 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 |
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| msg27940 - (view) |
Author: cheops (atila-cheops) |
Date: 2006-03-30 08:17 |
| Logged In: YES user_id=1276121 also #1214859 is interesting, has a patch |
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| msg27941 - (view) |
Author: Martin v. Löwis (loewis) * |
Date: 2006-03-30 16:31 |
| 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. |
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| msg27942 - (view) |
Author: cheops (atila-cheops) |
Date: 2006-04-05 08:27 |
| 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. |
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| msg27943 - (view) |
Author: cheops (atila-cheops) |
Date: 2006-04-10 14:55 |
| Logged In: YES user_id=1276121 see patch #1467770 |
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| msg27944 - (view) |
Author: Martin v. Löwis (loewis) * |
Date: 2006-04-10 15:58 |
| Logged In: YES user_id=21627 This was fixed with said patch. |
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