[jboss-jira] [JBoss JIRA] (WFCORE-40) Deadlock while logging

[David Lloyd (JIRA)]

    [ https://issues.jboss.org/browse/WFCORE-40?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12997892#comment-12997892 ] 

David Lloyd commented on WFCORE-40:
-----------------------------------

It seems extremely unlikely that the JVM is stuck in this method.  I think it's more likely that the log handler in question is writing to a target (either console or disk) and the write is failing.  Because filling in the stack trace is such a time-intensive operation, it has a very high chance of appearing on the stack trace, giving the appearance of no forward progress when actually there is simply a loop of exception throws.

Anyway, now we've confused the issue a bit.  I guess the underlying problem is that one thread is writing a bunch of stuff in a loop, monopolizing the lock, while other threads sit and wait for the lock.  It's possible that the failure in the one thread is in turn being logged, causing the loop to be infinite, though I would find this surprising as there are safeguards to prevent this behavior.

> Deadlock while logging
> ----------------------
>
>                 Key: WFCORE-40
>                 URL: https://issues.jboss.org/browse/WFCORE-40
>             Project: WildFly Core
>          Issue Type: Bug
>      Security Level: Public(Everyone can see) 
>          Components: Logging
>         Environment: CentOS 6.5 64bit, java7u45 64bit (and 32 bit, the same behavior)
>            Reporter: Stefan Schueffler
>            Assignee: James Perkins
>            Priority: Critical
>         Attachments: stack_140901_2254
>
>
> We hit really often a deadlock? in org.jboss.stdio.StdioContext$DelegatingPrintStream.println(StdioContext.java:474)
> Even if the "StdioContext" belongs to Jboss-Logging, the problem occurs in our production wildfly installation twice to 4 times a day - all threads are deadlocking while trying to log.debug, log.error, or (sometimes) System.out.println from our application code, and wildfly does not respond anymore...
> The partial stacktrace always is similar to this one:
> {code}
>  "default task-64" prio=10 tid=0x4c539c00 nid=0x5ef9 waiting for monitor entry [0x495e0000]
>    java.lang.Thread.State: BLOCKED (on object monitor)
>         at java.io.PrintStream.println(PrintStream.java:806)
>         - waiting to lock <0x5ee0adf8> (a java.io.PrintStream)
>         at org.jboss.stdio.StdioContext$DelegatingPrintStream.println(StdioContext.java:474)
>         at jsp.communications.statuschange.selectStatus_jsp._jspService(selectStatus_jsp.java:413)
>         at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:69)
>         at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
>         at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:85)
>         at io.undertow.servlet.handlers.FilterHandler.handleRequest(FilterHandler.java:82)
> {code}
> While investigating the StdioContext - class, i really wondered whether the used "locking/checking by using a threadlocal" could have worked in a multi-threaded environment (it should have the very same problems as every "double checking" algorithm without proper synchronization).
> If all threads are hanging in this particular lock, only a full wildfly-restart recovers in our case.
> My preferred solution would be a rework of the used org.jboss.stdio. classes, as the used idioms of ThreadLocals for reentrant-checks are at least highly unusual?



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