The Profiling Approach

The Profiling Approach

The program has two major components. There is a small C++ jvmti agent which writes out a log file describing a profile of the application it has been attached to. Then a Java application can render/display a profile based on this log. Generating a log means that profile can be analysed retrospective/offline. It should be possible to do online profiling by writing the log file into a memory mapped file which can then be concurrently read by the Java application.

Honest profiler takes the same approach outlined by Jeremy Manson where calls are made to the AsyncGetCallTrace jvm method which avoids the need for threads to reach a safe point in order to read their call trace. Consequently it avoids a number of profiler accuracy issues that other sampling profilers suffer from.

The downside of using this method is that the code in your async callback has horrific restrictions on it. What honest profiler does is copy the current stack trace into a non-blocking, allocation free, circular MPSC queue. These stack traces are then read by another thread which writes out the log file and looks up information about useful things like methods names.

Based upon code originally open sourced by Jeremy Manson/Google: http://jeremymanson.blogspot.co.uk/2013/07/lightweight-asynchronous-sampling.html