Remko Popma created LOG4J2-669:
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Summary: NPE when combining AsyncLoggerConfig with AsyncLogger
Key: LOG4J2-669
URL: https://issues.apache.org/jira/browse/LOG4J2-669
Project: Log4j 2
Issue Type: Bug
Components: Core
Affects Versions: 2.0-rc1
Reporter: Remko Popma
Assignee: Remko Popma
When all loggers are made asynchronous by setting Log4jContextSelector to
{{org.apache.logging.log4j.core.async.AsyncLoggerContextSelector}}, they
produce {{RingBufferLogEvent}} instances. These RingBufferLogEvents are mutable
by design. They are used as follows:
# Application calls logger.log("msg").
# The AsyncLogger claims a RingBufferLogEvent and populates its fields (level,
timestamp, message, etc).
# The AsyncLogger then "publishes" the RingBufferLogEvent, to pass it to the
event handler thread.
# The event handler thread passes the RingBufferLogEvent to all appenders.
# Finally, the event handler thread calls {{RingBufferLogEvent.clear()}} to
allow the log message to be garbage collected (LOG4J2-304)
This last step causes problems if the log event is still being processed.
To reproduce this issue, configure all loggers to be asynchronous (with the
Log4jContextSelector system property), and in the configuration, have a normal
(non-async) Root logger, and an AsyncLogger.
Be sure not to keep the default additivity="true", to ensure both the Root
logger and the AsyncLogger process the events.
This give the error below:
{code}
2014-06-14 17:57:55,547 ERROR An exception occurred processing Appender File
java.lang.NullPointerException
at java.lang.StringBuilder.<init>(StringBuilder.java:92)
at
org.apache.logging.log4j.core.pattern.NameAbbreviator$PatternAbbreviator.abbreviate(NameAbbreviator.java:286)
at
org.apache.logging.log4j.core.pattern.NamePatternConverter.abbreviate(NamePatternConverter.java:53)
at
org.apache.logging.log4j.core.pattern.LoggerPatternConverter.format(LoggerPatternConverter.java:64)
at
org.apache.logging.log4j.core.pattern.PatternFormatter.format(PatternFormatter.java:36)
at
org.apache.logging.log4j.core.layout.PatternLayout.toSerializable(PatternLayout.java:214)
at
org.apache.logging.log4j.core.layout.PatternLayout.toSerializable(PatternLayout.java:54)
at
org.apache.logging.log4j.core.layout.AbstractStringLayout.toByteArray(AbstractStringLayout.java:46)
at
org.apache.logging.log4j.core.appender.AbstractOutputStreamAppender.append(AbstractOutputStreamAppender.java:104)
at
org.apache.logging.log4j.core.config.AppenderControl.callAppender(AppenderControl.java:97)
at
org.apache.logging.log4j.core.config.LoggerConfig.callAppenders(LoggerConfig.java:426)
at
org.apache.logging.log4j.core.async.AsyncLoggerConfig.asyncCallAppenders(AsyncLoggerConfig.java:118)
at
org.apache.logging.log4j.core.async.AsyncLoggerConfigHelper$Log4jEventWrapperHandler.onEvent(AsyncLoggerConfigHelper.java:222)
at
org.apache.logging.log4j.core.async.AsyncLoggerConfigHelper$Log4jEventWrapperHandler.onEvent(AsyncLoggerConfigHelper.java:207)
at
com.lmax.disruptor.BatchEventProcessor.run(BatchEventProcessor.java:133)
at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
at java.lang.Thread.run(Thread.java:662)
{code}
By the time the {{AsyncLoggerConfigHelper$Log4jEventWrapperHandler}} handles
the event, the original AsyncLogger has already called {{clear()}} on the
event, so the logger name has been set to null, causing the NPE above.
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