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From "Sean Bridges (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LOG4J2-702) LoggerConfig#waitForCompletion is not thread safe
Date Mon, 14 Jul 2014 03:55:04 GMT

    [ https://issues.apache.org/jira/browse/LOG4J2-702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14060297#comment-14060297
] 

Sean Bridges commented on LOG4J2-702:
-------------------------------------

Sorry, I commented without seeing some of the posts.

Ralph, yes you are right, Remko's solution in his 10/Jul/14 17:05 comment suffers from the
flaw you mention.  I think it is better to loop rather than hardcode a fixed number of iterations.
 Another alternative to looping might be to chain the configs.  Something like,

{code}
//in PrivateConfig
volatile LoggerConfig next;

void log(...) {
   counter.incrementAndGet();
   if(next != null) {
      counter.decrementAndGet();
      next.log(...); 
   } else {
      try {
         ...do stuff
      } finally {
        counter.decrementAndGet();
      }
   }

void stop(LoggerConfig next) {
  this.next = next;
  ...cleanup
}


}

{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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