Benjamin Reed commented on ZOOKEEPER-366:

holger you are correct. nanoTime is the way to go. i'll prepare a fix. one 
problem with it is that the fix will be impossible to test.

> Session timeout detection can go wrong if the leader system time changes
> ------------------------------------------------------------------------
>                 Key: ZOOKEEPER-366
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-366
>             Project: Zookeeper
>          Issue Type: Bug
>            Reporter: Benjamin Reed
>            Assignee: Benjamin Reed
>         Attachments: ZOOKEEPER-366.patch
> the leader tracks session expirations by calculating when a session will 
> timeout and then periodically checking to see what needs to be timed out 
> based on the current time. this works great as long as the leaders clock 
> progresses at a steady pace. the problem comes when there are big (session 
> size) changes in clock, by ntp for example. if time gets adjusted forward, 
> all the sessions could timeout immediately. if time goes backward sessions 
> that should timeout may take a lot longer to actually expire.
> this is really just a leader issue. the easiest way to deal with this is to 
> have the leader relinquish leadership if it detects a big jump forward in 
> time. when a new leader gets elected, it will recalculate timeouts of active 
> sessions.

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