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https://issues.apache.org/jira/browse/LOG4J2-702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14053946#comment-14053946
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Sean Bridges commented on LOG4J2-702:
-------------------------------------

{quote}
Second, the clearAppenders method is called by stop (and really shouldn't be 
called by anything else). The stop method should only be called after 
updateLoggers has been called to transfer logging to a new configuration, in 
which case calls to all log events would go there, not to the configuration 
being stopped, or during a shutdown, at which point logging shouldn't be 
happening.
{quote}

I think there is still the same problem just pushed up the stack a bit, as you 
can have two threads doing something like,

{code}
Thread B acquire reference to current loggerConfig

Thread A updateLoggers()
Thread A stop()
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}


> LoggerConfig#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
>            Assignee: Matt Sicker
>            Priority: Critical
>             Fix For: 2.0
>
>
> This is in trunk, svn commit 1608156
> LoggerConfig#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 
> LoggerConfig object.  



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