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From "Leon Finker (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LOG4J2-1457) Class loader deadlock when using async logging
Date Mon, 11 Jul 2016 20:24:11 GMT

    [ https://issues.apache.org/jira/browse/LOG4J2-1457?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15371540#comment-15371540
] 

Leon Finker commented on LOG4J2-1457:
-------------------------------------

Loader.loadClass() could call Class.forName(className), which is equivalent to Class.forName(className,
true, currentLoader). 

Or Loader.loadClass could call getThreadContextClassLoader().loadClass(className), which ends
up in ClassLoader:
{noformat}
 protected Class<?> loadClass(String name, boolean resolve)
        throws ClassNotFoundException
    {
        synchronized (getClassLoadingLock(name)) {
{noformat}

That should also deadlock the same since it wants to acquire the class loader+name lock.

> Class loader deadlock when using async logging
> ----------------------------------------------
>
>                 Key: LOG4J2-1457
>                 URL: https://issues.apache.org/jira/browse/LOG4J2-1457
>             Project: Log4j 2
>          Issue Type: Bug
>    Affects Versions: 2.6.1
>         Environment: On CentOS 6.7 and Java 1.8.0_60.
>            Reporter: Leon Finker
>            Priority: Critical
>         Attachments: threaddump.txt
>
>
> We've encountered a class loading deadlock. Please review attached thread dump. Is it
possible to have an option of pre-initializing the exception's thread stack on the caller's
thread? It's hard to predict what libraries are doing in their classes' static initializers
and may eventually end up logging and causing deadlock.
> In the attached thread dump here are the threads of interest:
> "Log4j2-AsyncLogger[AsyncContext@18b4aac2]1" #16 daemon prio=5 os_prio=0 tid=0x00007ff870c7b000
nid=0x79f3 in Object.wait() [0x00007ff839142000]
>    java.lang.Thread.State: RUNNABLE
>         at java.lang.Class.forName0(Native Method)
> ...
> and
> "1A03340:Company:japan" #568 prio=5 os_prio=0 tid=0x00007ff871677000 nid=0x725 runnable
[0x00007ff74bd27000]
> ...<clinit>...



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