[ python-Bugs-1607041 ] Condition.wait timeout fails when system clock changes

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Bugs item #1607041, was opened at 2006-12-01 13:45
Message generated for change (Comment added) made by kuran
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Category: Python Library
Group: Python 2.4
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: BC (hashstat)
Assigned to: Nobody/Anonymous (nobody)
Summary: Condition.wait timeout fails when system clock changes

Initial Comment:
If the system clock is adjusted after Condition.wait is called with a timeout, the timeout does not expire as expected.  This appears to be due to the threading.Condition class using the system clock to calculate the timeout expiration without taking system clock changes into account.  Let me illustrate this with an example:


   import threading

   c = threading.Condition()
   c.acquire()
   try:
      ...
      c.wait(3600.0)
      ...
   finally:
      c.release()


Let's say the above snippet is executed at 08:00.  Assuming the condition is never notified, the timeout should expire somewhere close to 09:00.  At 08:30 someone notices that the clock is an hour fast and sets it back to 07:30.  The timeout still expire around 09:00 causing a wait of 2 hours instead of the requested 1 hour.

Now let's say instead that the clock was moved ahead to 09:30 at 08:30.  The timeout would expire immediately after only a 30 minute wait.

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Comment By: Jp Calderone (kuran)
Date: 2006-12-01 16:06

Message:
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Why should it work that way?

c.wait(3600) doesn't say "wait until 0900", it says "wait 60 minutes".

If you want c.waitUntil(9 oclock), maybe that would be a good API
addition, but it definitely should be a separate method.


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