[LOG4J2-669] NPE when combining AsyncLoggerConfig with AsyncLogger

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.0-rc1
• Fix Version/s: 2.0-rc2
• Component/s: Core
• Assignee: Remko Popma
• Reporter: Remko Popma
• Created: 14/Jun/14 09:03
• Updated: 14/Jun/14 12:26
• Resolved: 14/Jun/14 11:35

Description

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:

1. Application calls logger.log("msg").
2. The AsyncLogger claims a RingBufferLogEvent and populates its fields (level, timestamp, message, etc).
3. The AsyncLogger then "publishes" the RingBufferLogEvent, to pass it to the event handler thread.
4. The event handler thread passes the RingBufferLogEvent to all appenders.
5. 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. (There may be other ways to reproduce this, but they all have to do with combining AsyncLogger with AsyncLoggerConfig.)

This give the error below:

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)

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.

Issue Links

• relates to: LOG4J2-668 AsyncAppender ignores RingBufferLogEvents from AsyncLoggers (when all loggers async by setting context selector)