How to verify log4j2 is logging asynchronously via LMAX disruptor?

Question

I am developing an Eclipse RCP application and have gone to some pains to get log4j2 to work within the app. All seems to work fine now, and as a finishing touch I wanted to make all loggers asynchronously.

I've managed to get the LMAX Disruptor on the classpath, and think I've solved the issue of providing sun.misc as well. Set the VM argument -DLog4jContextSelector=org.apache.logging.log4j.core.async.AsyncLoggerContextSelector in the run config and set up log4j2.xml file correctly as well. I think. And that's where the problem is. I'd like to be able to verify that my application logs asynchronously in the proper fashion, so I can enjoy the benefits latency-wise.

How can I - then - verify that my loggers are working asynchronously, utilising the LMAX Dirsuptor in the process?

Answer 1

There are two types of async logger, handled by different classes.

1. All loggers async: the AsyncLogger class - activated when you use AsyncLoggerContextSelector
2. Mixing sync with async loggers: the AsyncLoggerConfig class - when your configuration file has <AsyncRoot> or <AsyncLogger> elements nested in the configuration for <Loggers>.

In your case you are making all loggers async, so you want to put your breakpoint in AsyncLogger#logMessage(String, Level, Marker, Message, Throwable).

Another way to verify is by setting <Configuration status="trace"> at the top of your configuration file. This will output internal log4j log messages on log4j is configured. You should see something like "Starting AsyncLogger disruptor...". If you see this all loggers are async.

Answer 2

Put a breakpoint in org.apache.logging.log4j.core.async.AsyncLoggerConfig#callAppenders. Then you can watch as the event is put into the disruptor. Likewise org.apache.logging.log4j.core.config.LoggerConfig#callAppenders should be getting hit for synchronous logging OR getting hit from the other side of the disruptor for async logging (at which point everything is synchronous again).