[jira] [Commented] (LOG4J2-702) LoggerContext#waitForCompletion is not thread safe

["Matt Sicker (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LOG4J2-702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14053370#comment-14053370 ] 

Matt Sicker commented on LOG4J2-702:
------------------------------------

Oh man, good catch on a neat threading issue! Taking a look at what's going on here, I think a slightly more complex locking mechanism will be needed for the counter. Before this change, the whole method {{waitForCompletion}} was synchronized. It seems like this could be doable.

> LoggerContext#waitForCompletion is not thread safe
> --------------------------------------------------
>
>                 Key: LOG4J2-702
>                 URL: https://issues.apache.org/jira/browse/LOG4J2-702
>             Project: Log4j 2
>          Issue Type: Bug
>          Components: Core
>    Affects Versions: 2.0-rc2
>            Reporter: Sean Bridges
>            Priority: Critical
>
> This is in trunk, svn commit 1608156
> LoggerContext#waitForCompletion uses an AtomicInteger counter to try to detect if there are any calls currently executing the log(Event) method, but it does not do so in a thread safe manner.  Consider two threads A and B, where Thread A is calling clearAppenders(), and Thread B is calling log(Event),
> {code}
> Thread A  loggerConfig.clearAppenders()
> Thread A  loggerConfig.waitForCompletion()
> Thread A  counter.get() //returns 0
> Thread A  //loggerConfig.waitForCompletion() returns
> Thread B  loggerConfig.log(Event)
> Thread B  counter.increment()
> Thread A  proceeds assuming no log calls are onging, but thread B is in the log method
> {code}
> I'm not sure what the requirements are, but if the requirement is to not lose logging events, I think you need some sort of synchronization outside of the LoggerContext object.  



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