Description

fdirosa4188

opened on May 15, 2023

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It is clear looking at the source code that the Queue class uses time() and other non-monotonic timing sources. So if a queue get function is called with a timeout value and the system time is changed during that get it could end up waiting in the get for potentially days. The easiest way to reproduce is to set the timeout in the get to 5 minutes and which it is waiting on the queue to get an entry set the system clock back a few years. You will notice it will not exit the get.

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1. fdirosa4188

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on May 15, 2023
2. arhadthedev

   added

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   3.11only security fixesonly security fixes

   3.12only security fixesonly security fixes

   on May 15, 2023
3. arhadthedev commented on May 15, 2023

   

   arhadthedev

   on May 15, 2023

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   @rhettinger (as a queue module expert)
4. Agent-Hellboy commented on May 16, 2023

   

   Agent-Hellboy

   on May 16, 2023

   Contributor

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   do you have a reproducible code?
   it's monotonic
   

   cpython/Lib/queue.py

   Line 7 in 0bb61dd

   from time import monotonic as time

   As the issue template suggests you should share the reproducible code and the execution environment as well
5. fdirosa4188 commented on May 17, 2023

   

   fdirosa4188

   on May 17, 2023

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   I am using Python 3.8.6 on Linux.
   Attached is python code that reproduces this problem. I set a specific date/time before the queue.get blocking call with a 10 second timeout and then change the date/time to a different date/time during the queue.get and it does not return after 10 seconds.

   There is a variable in the attached script called Make_It_Fail that is set to True. You can set it to False to see how the script works without date/time changes then set it to True to see how queue.get does not return after 10 seconds has elapsed.
   queue_timeout_test.py.txt
6. aludwig98 commented on May 19, 2023

   

   aludwig98

   on May 19, 2023

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   This seems to have been resolved in Python 3.9, 3.10.

   See here: #85876
7. fdirosa4188 commented on Jun 1, 2023

   

   fdirosa4188

   on Jun 1, 2023

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   I tried my queue_timeout.test.py script on Python 3.11 and it still does not timeout after 10 seconds. The queue.get() function blocks and seems to still be effected by changes to the system time on Linux.

   Reacted by Berk Orbay
8. duaneg commented on May 24, 2025

   

   duaneg

   on May 24, 2025

   Contributor

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   I can't reproduce the bug on current HEAD (v3.15-alpha), but then I can't reproduce it on v3.11.0 either. In both cases it produces the correct, expected output:

   Date/Time before queue.get(): 05/18/2024 23:34:43
   Calling queue get with blocking and 10 seconds timeout
   Date/Time during queue.get(): 05/18/2023 18:34:43
   10.00 seconds has elapsed and it is not blocked
   

   As @Agent-Hellboy says, the queue code itself uses a monotonic clock, and after #28662 so does the underlying lock the condition variable waits on.

   @fdirosa4188 please re-test and close if confirmed.
9. picnixz

   added

   pendingThe issue will be closed if no feedback is providedThe issue will be closed if no feedback is provided

   on May 24, 2025
10. picnixz

    closed this as completedon Jun 29, 2025
11. picnixz

    reopened this on Jun 29, 2025
12. picnixz

    closed this as completedon Jun 29, 2025

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