This stack trace is not from Log4j 2.13.2. The line numbers don’t match. This
error indicates that one of the parameters being passed on the logging method
is a Collection. The Layout is iterating over the Collection in an attempt to
format it. However, some other thread is modifying the Collection while the
Async Logger thread is trying to iterate through it. Log4j has no way to
prevent this as it is an object owned by the application.
1. See above.
2. It would be expected that the stack trace would be coming from the
StatusLogger, which appears to be the case. I don’t see any reason logging
would continue to fail. The AppenderControl should catch the error. However, if
you have configured the Appender to not ignore exceptions then it is possible
that that AsyncLoggerConfig is not handling the error. We will have to look
further to see if that is the case.
Ralph
> On May 23, 2020, at 3:46 PM, Mitchell Rathbun (BLOOMBERG/ 731 LEX)
> <mrathb...@bloomberg.net> wrote:
>
> We recently started occasionally getting the following error:
>
> 2020-05-22 05:54:07,995 INFO STDERR [Thread-2] {} 2020-05-22 05:54:07,994
> Log4j2-TF-2-AsyncLoggerConfig-1 ERROR An exception occurred processing
> Appender WINGMAN java.util.ConcurrentModificationException
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> java.util.HashMap$HashIterator.nextNode(HashMap.java:1442)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> java.util.HashMap$KeyIterator.next(HashMap.java:1466)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.message.ParameterFormatter.appendCollection(ParameterFormatter.java:599)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.message.ParameterFormatter.appendPotentiallyRecursiveValue(ParameterFormatter.java:507)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.message.ParameterFormatter.recursiveDeepToString(ParameterFormatter.java:432)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.message.ParameterFormatter.formatMessage2(ParameterFormatter.java:189)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.message.ParameterizedMessage.formatTo(ParameterizedMessage.java:225)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.core.pattern.MessagePatternConverter.format(MessagePatternConverter.java:119)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.core.pattern.PatternFormatter.format(PatternFormatter.java:38)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.core.layout.PatternLayout$PatternSerializer.toSerializable(PatternLayout.java:333)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.core.layout.PatternLayout.toText(PatternLayout.java:232)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.core.layout.PatternLayout.encode(PatternLayout.java:217)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.core.layout.PatternLayout.encode(PatternLayout.java:57)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.core.appender.AbstractOutputStreamAppender.directEncodeEvent(AbstractOutputStreamAppender.java:177)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.core.appender.AbstractOutputStreamAppender.tryAppend(AbstractOutputStreamAppender.java:170)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.core.appender.AbstractOutputStreamAppender.append(AbstractOutputStreamAppender.java:161)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.core.appender.RollingRandomAccessFileAppender.append(RollingRandomAccessFileAppender.java:218)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.core.config.AppenderControl.tryCallAppender(AppenderControl.java:156)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.core.config.AppenderControl.callAppender0(AppenderControl.java:129)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.core.config.AppenderControl.callAppenderPreventRecursion(AppenderControl.java:120)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.core.config.AppenderControl.callAppender(AppenderControl.java:84)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.core.config.LoggerConfig.callAppenders(LoggerConfig.java:448)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.core.async.AsyncLoggerConfig.asyncCallAppenders(AsyncLoggerConfig.java:115)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.core.async.AsyncLoggerConfigDisruptor$Log4jEventWrapperHandler.onEvent(AsyncLoggerConfigDisruptor.java:112)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> org.apache.logging.log4j.core.async.AsyncLoggerConfigDisruptor$Log4jEventWrapperHandler.onEvent(AsyncLoggerConfigDisruptor.java:98)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> com.lmax.disruptor.BatchEventProcessor.processEvents(BatchEventProcessor.java:169)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> com.lmax.disruptor.BatchEventProcessor.run(BatchEventProcessor.java:126)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {} at
> java.lang.Thread.run(Thread.java:748)
> 2020-05-22 05:54:07,996 INFO STDERR [Thread-2] {}
>
> We are using a RollingRandomAccessFileAppeneder with an AsyncLogger, and
> recently upgraded our log4j2 version to 2.13.2. The system property
> Log4jContextSelector is set to
> org.apache.logging.log4j.core.selector.BasicContextSelector. It seems from
> the few posts I have seen online that this shouldn't happen if async logging
> is being used. So I have two questions:
>
> 1. Why are we seeing this/what generally could cause this?
>
> 2. When this error occurs, the file that logs were being written to gets
> overwritten completely with the stack trace posted above. The process
> continues to run after this but no new logs ever get written to the file.
> This makes this a critical error and also makes it very difficult to debug
> why this error is happening to begin with. Is there a way to prevent this
> from happening so that the error just gets appended to the file instead of
> overwriting everything that is there?
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