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From "Leon Finker"<leon...@gmail.com>
Subject Re: Logging stopped, but Log4j2-AsyncLogger is RUNNABLE and maybe stuck in ThrowableProxy.toExtendedStackTrace
Date Wed, 06 Jul 2016 14:06:06 GMT
Based on google searches, it turns out to be a classic class loading deadlock. I found one
thread that was inside the class' static initializer: <clinit>, which then eventually
ended up logging indirectly and getting blocked on:
	at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:338)
	at com.lmax.disruptor.MultiProducerSequencer.next(MultiProducerSequencer.java:136)
	at com.lmax.disruptor.MultiProducerSequencer.next(MultiProducerSequencer.java:105)
	at com.lmax.disruptor.RingBuffer.publishEvent(RingBuffer.java:450)
	at com.lmax.disruptor.dsl.Disruptor.publishEvent(Disruptor.java:315)
	at org.apache.logging.log4j.core.async.AsyncLoggerDisruptor.enqueueLogMessageInfo(AsyncLoggerDisruptor.java:203)
..

And the AsyncLogger thread is blocked trying to walk the above thread stack and getting deadlocked
on the same class that was in <clinit>.  It's a large codebase, so hard to review all
the libraries and uses. But now we know what to look out for if it happens again. This can
happen with async logging. 

Basically one thread would be in RUNNABLE state, but will say "in Object.wait()" and another
thread would be in <clinit>.

On 2016-07-05 20:10 (-0400), Remko Popma <remko.popma@gmail.com> wrote: 
> The StackOverflow link may still be relevant if the problem is caused by class loading
(by different classloaders?) from different threads. 
> 
> Leon, is there any other thread in the thread dump that is loading a class?
> 
> Sent from my iPhone
> 
> > On 2016/07/06, at 6:31, Ralph Goers <ralph.goers@dslextreme.com> wrote:
> > 
> > The stack overflow reference is using Log4j 1, so that isn’t a match.
> > 
> > Based on the fact that you are in ExtendedThrowablePatternConverter that would imply
that you are logging an exception. But I don’t know why you would be getting stuck in
there. While formatting the exception is slow, it shouldn’t be that slow.
> > 
> > Ralph
> > 
> >> On Jul 5, 2016, at 2:03 PM, Leon Finker <leonfin@gmail.com> wrote:
> >> 
> >> This looks similar:
> >> http://stackoverflow.com/questions/15543521/mixed-usage-of-log4j-and-commons-logging-causes-a-class-loading-deadlock
> >> 
> >> But we don't use any other logging framework besides slf4j, log4j2 and log4j2
bridges.
> >> 
> >>> On 2016-07-05 15:14 (-0400), "Leon Finker"<leonfin@gmail.com> wrote:

> >>> Hi,
> >>> 
> >>> Using log4j2 runtime args with 2.6.1:
> >>> -DAsyncLogger.RingBufferSize=512
> >>> -DLog4jContextSelector=org.apache.logging.log4j.core.async.AsyncLoggerContextSelector
> >>> 
> >>> On CentOS 6.7 and Java 1.8.0_60.
> >>> 
> >>> We noticed that at some point the process has stopped logging to the log
file (during startup). When doing 7 thread dumps over 8 minutes the AsyncLogger thread is
Runnable, but always in the below stack trace. And all the other threads are TIMED_WAITING
to publish new log events RingBuffer.publishEvent. Has anyone seen this before? There was
no log entries for at least 25 minutes till we killed the process and restarted it without
problems. If AsyncLogger was progressing properly, something would appear in the log file
(RollingRandomAccessFile is configured with immediateFlush=true). It's hard to know how big
the stack length was in the ThrowableProxy.toExtendedStackTrace. But the threas is not BLOCKED,
it's RUNNABLE. Also it doesn't look like there is a way to limit the stack depth for the toExtendedStackTrace?
> >>> 
> >>> "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)
> >>>       at java.lang.Class.forName(Class.java:348)
> >>>       at org.apache.logging.log4j.core.util.Loader.initializeClass(Loader.java:241)
> >>>       at org.apache.logging.log4j.core.impl.ThrowableProxy.loadClass(ThrowableProxy.java:487)
> >>>       at org.apache.logging.log4j.core.impl.ThrowableProxy.toExtendedStackTrace(ThrowableProxy.java:617)
> >>>       at org.apache.logging.log4j.core.impl.ThrowableProxy.<init>(ThrowableProxy.java:135)
> >>>       at org.apache.logging.log4j.core.impl.ThrowableProxy.<init>(ThrowableProxy.java:117)
> >>>       at org.apache.logging.log4j.core.async.RingBufferLogEvent.getThrownProxy(RingBufferLogEvent.java:316)
> >>>       at org.apache.logging.log4j.core.pattern.ExtendedThrowablePatternConverter.format(ExtendedThrowablePatternConverter.java:61)
> >>>       at org.apache.logging.log4j.core.pattern.PatternFormatter.format(PatternFormatter.java:38)
> >>>       at org.apache.logging.log4j.core.layout.PatternLayout$PatternSerializer.toSerializable(PatternLayout.java:288)
> >>>       at org.apache.logging.log4j.core.layout.PatternLayout.toText(PatternLayout.java:194)
> >>>       at org.apache.logging.log4j.core.layout.PatternLayout.encode(PatternLayout.java:180)
> >>>       at org.apache.logging.log4j.core.layout.PatternLayout.encode(PatternLayout.java:57)
> >>>       at org.apache.logging.log4j.core.appender.AbstractOutputStreamAppender.directEncodeEvent(AbstractOutputStreamAppender.java:120)
> >>>       at org.apache.logging.log4j.core.appender.AbstractOutputStreamAppender.tryAppend(AbstractOutputStreamAppender.java:113)
> >>>       at org.apache.logging.log4j.core.appender.AbstractOutputStreamAppender.append(AbstractOutputStreamAppender.java:104)
> >>>       at org.apache.logging.log4j.core.appender.RollingRandomAccessFileAppender.append(RollingRandomAccessFileAppender.java:99)
> >>>       at org.apache.logging.log4j.core.config.AppenderControl.tryCallAppender(AppenderControl.java:155)
> >>>       at org.apache.logging.log4j.core.config.AppenderControl.callAppender0(AppenderControl.java:128)
> >>>       at org.apache.logging.log4j.core.config.AppenderControl.callAppenderPreventRecursion(AppenderControl.java:119)
> >>>       at org.apache.logging.log4j.core.config.AppenderControl.callAppender(AppenderControl.java:84)
> >>>       at org.apache.logging.log4j.core.config.LoggerConfig.callAppenders(LoggerConfig.java:390)
> >>>       at org.apache.logging.log4j.core.config.LoggerConfig.processLogEvent(LoggerConfig.java:375)
> >>>       at org.apache.logging.log4j.core.config.LoggerConfig.log(LoggerConfig.java:359)
> >>>       at org.apache.logging.log4j.core.config.LoggerConfig.logParent(LoggerConfig.java:381)
> >>>       at org.apache.logging.log4j.core.config.LoggerConfig.processLogEvent(LoggerConfig.java:376)
> >>>       at org.apache.logging.log4j.core.config.LoggerConfig.log(LoggerConfig.java:359)
> >>>       at org.apache.logging.log4j.core.config.AwaitCompletionReliabilityStrategy.log(AwaitCompletionReliabilityStrategy.java:79)
> >>>       at org.apache.logging.log4j.core.async.AsyncLogger.actualAsyncLog(AsyncLogger.java:310)
> >>>       at org.apache.logging.log4j.core.async.RingBufferLogEvent.execute(RingBufferLogEvent.java:149)
> >>>       at org.apache.logging.log4j.core.async.RingBufferLogEventHandler.onEvent(RingBufferLogEventHandler.java:45)
> >>>       at org.apache.logging.log4j.core.async.RingBufferLogEventHandler.onEvent(RingBufferLogEventHandler.java:29)
> >>>       at com.lmax.disruptor.BatchEventProcessor.run(BatchEventProcessor.java:129)
> >>>       at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
> >>>       at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
> >>>       at java.lang.Thread.run(Thread.java:745)
> >>> 
> >>> 
> >>> Other threads are blocked as in this example stack trace:
> >>> "metrics-logger-reporter-1-thread-1" #20 daemon prio=5 os_prio=0 tid=0x00007ff870e7f800
nid=0x7a0c runnable [0x00007ff838a26000]
> >>>  java.lang.Thread.State: TIMED_WAITING (parking)
> >>>       at sun.misc.Unsafe.park(Native Method)
> >>>       at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:338)
> >>>       at com.lmax.disruptor.MultiProducerSequencer.next(MultiProducerSequencer.java:136)
> >>>       at com.lmax.disruptor.MultiProducerSequencer.next(MultiProducerSequencer.java:105)
> >>>       at com.lmax.disruptor.RingBuffer.publishEvent(RingBuffer.java:450)
> >>>       at com.lmax.disruptor.dsl.Disruptor.publishEvent(Disruptor.java:315)
> >>>       at org.apache.logging.log4j.core.async.AsyncLoggerDisruptor.enqueueLogMessageInfo(AsyncLoggerDisruptor.java:203)
> >>>       at org.apache.logging.log4j.core.async.AsyncLogger.handleRingBufferFull(AsyncLogger.java:170)
> >>>       at org.apache.logging.log4j.core.async.AsyncLogger.publish(AsyncLogger.java:162)
> >>>       at org.apache.logging.log4j.core.async.AsyncLogger.logWithThreadLocalTranslator(AsyncLogger.java:157)
> >>>       at org.apache.logging.log4j.core.async.AsyncLogger.logMessage(AsyncLogger.java:127)
> >>>       at org.apache.logging.log4j.spi.AbstractLogger.logMessage(AbstractLogger.java:2013)
> >>>       at org.apache.logging.log4j.spi.AbstractLogger.logIfEnabled(AbstractLogger.java:1882)
> >>>       at org.apache.logging.slf4j.Log4jLogger.info(Log4jLogger.java:229)
> >>>       at com.codahale.metrics.Slf4jReporter$InfoLoggerProxy.log(Slf4jReporter.java:337)
> >>>       at com.codahale.metrics.Slf4jReporter.logGauge(Slf4jReporter.java:270)
> >>>       at com.codahale.metrics.Slf4jReporter.report(Slf4jReporter.java:187)
> >>>       at com.codahale.metrics.ScheduledReporter.report(ScheduledReporter.java:162)
> >>>       - locked <0x00000006dcadc538> (a com.codahale.metrics.Slf4jReporter)
> >>>       at com.codahale.metrics.ScheduledReporter$1.run(ScheduledReporter.java:117)
> >>>       at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
> >>>       at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
> >>>       at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180)
> >>>       at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294)
> >>>       at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
> >>>       at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
> >>>       at java.lang.Thread.run(Thread.java:745)
> >>> 
> >>> 
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