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From "Remko Popma (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LOG4J2-702) LoggerConfig#waitForCompletion is not thread safe
Date Sat, 12 Jul 2014 05:19:04 GMT

    [ https://issues.apache.org/jira/browse/LOG4J2-702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14059654#comment-14059654
] 

Remko Popma commented on LOG4J2-702:
------------------------------------

Sean, I believe your analysis is incorrect. The call to {{config.getConfigurationMonitor().checkConfiguration();}}
may cause the Logger's PrivateConfig to be replaced by a fresh one, that is true. This fresh
privateConfig willl contain a new LoggerConfig. The Logger will no longer have a reference
to the old PrivateConfig and new {{logMessage()}} calls will be delegated to the new PrivateConfig
object.

However, the code is currently executing in the old PrivateConfig and will now execute the
next statement ({{loggerConfig.log(event);}} on the old PrivateConfig object, which still
has a reference to the old LoggerConfig.

> 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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