Log4j: Events appear in the wrong logfile
- by Markus
Hi there!
To be able to log and trace some events I've added a LoggingHandler class to my java project. Inside this class I'm using two different log4j logger instances - one for logging an event and one for tracing an event into different files. The initialization block of the class looks like this:
public void initialize()
{
System.out.print("starting logging server ...");
// create logger instances
logLogger = Logger.getLogger("log");
traceLogger = Logger.getLogger("trace");
// create pattern layout
String conversionPattern = "%c{2} %d{ABSOLUTE} %r %p %m%n";
try
{
patternLayout = new PatternLayout();
patternLayout.setConversionPattern(conversionPattern);
}
catch (Exception e)
{
System.out.println("error: could not create logger layout pattern");
System.out.println(e);
System.exit(1);
}
// add pattern to file appender
try
{
logFileAppender = new FileAppender(patternLayout, logFilename, false);
traceFileAppender = new FileAppender(patternLayout, traceFilename, false);
}
catch (IOException e)
{
System.out.println("error: could not add logger layout pattern to corresponding appender");
System.out.println(e);
System.exit(1);
}
// add appenders to loggers
logLogger.addAppender(logFileAppender);
traceLogger.addAppender(traceFileAppender);
// set logger level
logLogger.setLevel(Level.INFO);
traceLogger.setLevel(Level.INFO);
// start logging server
loggingServer = new LoggingServer(logLogger, traceLogger, serverPort, this);
loggingServer.start();
System.out.println(" done");
}
To make sure that only only thread is using the functionality of a logger instance at the same time each logging / tracing method calls the logging method .info() inside a synchronized-block. One example looks like this:
public void logMessage(String message)
{
synchronized (logLogger)
{
if (logLogger.isInfoEnabled() && logFileAppender != null)
{
logLogger.info(instanceName + ": " + message);
}
}
}
If I look at the log files, I see that sometimes a event appears in the wrong file. One example:
trace 10:41:30,773 11080 INFO masterControl(192.168.2.21): string broadcast message was pushed from 1267093 to vehicle 1055293 (slaveControl 1)
trace 10:41:30,784 11091 INFO masterControl(192.168.2.21): string broadcast message was pushed from 1156513 to vehicle 1105792 (slaveControl 1)
trace 10:41:30,796 11103 INFO masterControl(192.168.2.21): string broadcast message was pushed from 1104306 to vehicle 1055293 (slaveControl 1)
trace 10:41:30,808 11115 INFO masterControl(192.168.2.21): vehicle 1327879 was pushed to slave control 1
10:41:30,808 11115 INFO masterControl(192.168.2.21): string broadcast message was pushed from 1101572 to vehicle 106741 (slaveControl 1)
trace 10:41:30,820 11127 INFO masterControl(192.168.2.21): string broadcast message was pushed from 1055293 to vehicle 1104306 (slaveControl 1)
I think that the problem occures everytime two event happen at the same time (here: 10:41:30,808). Does anybody has an idea how to solve my problem? I already tried to add a sleep() after the method call, but that doesn't helped ...
BR,
Markus
Edit:
logtrace 11:16:07,75511:16:07,755 1129711297 INFOINFO masterControl(192.168.2.21): string broadcast message was pushed from 1291400 to vehicle 1138272 (slaveControl 1)masterControl(192.168.2.21): vehicle 1333770 was added to slave control 1
or
log 11:16:08,562 12104 INFO 11:16:08,562 masterControl(192.168.2.21): string broadcast message was pushed from 117772 to vehicle 1217744 (slaveControl 1)
12104 INFO masterControl(192.168.2.21): vehicle 1169775 was pushed to slave control 1
Edit 2:
It seems like the problem only occurs if logging methods are called from inside a RMI thread (my client / server exchange information using RMI connections). ...
Edit 3:
I solved the problem by myself: It seems like log4j is NOT completely thread-save. After synchronizing all log / trace methods using a separate object everything is working fine. Maybe the lib is writing the messages to a thread-unsafe buffer before writing them to file?
