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Created on 2014-12-02 10:09 by Radosław.Szkodziński, last changed 2022-04-11 14:58 by admin. This issue is now closed.
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| File name | Uploaded | Description | Edit | |
| testmp.py | Radosław.Szkodziński, 2014-12-02 10:09 | Testcase - hangs | ||
| Messages (2) | |||
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| msg231984 - (view) | Author: Radosław Szkodziński (Radosław.Szkodziński) | Date: 2014-12-02 10:09 | |
multiprocessing.Queue.empty() uses pipe polling on Windows. Unfortunately, pipe semantics on windows are different from POSIX. The result is either: - Hang when one process tries to get() and another checks for empty() - Falsely returning empty() == False despite nothing being possible to get - because the other process is actually trying to read from the queue. The attached testcase demonstrates the first case, with main process hard hanging on my Python 2.7.8 (anaconda), 32-bit on Windows 7 64-bit. Whether 1 or 2 happens depends on specific program flow. Both can cause deadlocks in code that should be valid. Note that get(block=False) actually works correctly. It is possible that the problem is also present in Python 3. |
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| msg232056 - (view) | Author: Eryk Sun (eryksun) *  |
Date: 2014-12-02 22:53 | |
This also hangs for me in 2.7.8 64-bit, Windows 7. To poll the pipe, the parent process calls PeekNamedPipe, which blocks because the child has already called ReadFile. > It is possible that the problem is also present in Python 3. multiprocessing switched to overlapped I/O in 3.3, which avoids this problem. |
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| History | |||
|---|---|---|---|
| Date | User | Action | Args |
| 2022-04-11 14:58:10 | admin | set | github: 67165 |
| 2021-02-23 11:30:24 | eryksun | set | status: open -> closed resolution: out of date stage: resolved |
| 2014-12-02 22:53:07 | eryksun | set | nosy:
+ eryksun messages: + msg232056 |
| 2014-12-02 15:40:56 | r.david.murray | set | nosy:
+ sbt |
| 2014-12-02 10:09:33 | Radosław.Szkodziński | create | |