How to programmatically intercept the GC to print information to my log

Question

I am aware that you can use the -verbosegc to print information about the GC to the sysout but I don't want that. I want to intercept whenever GC triggers and print information about it to my custom logger, perhaps save last GC timestamp on a internal variable, etc.

Any hope here?

Answer 1

You can't hook the GC logging mechanism from within a Java program because when the GC thread(s) run the JVM is effectively stopped. Doing so would cause a deadlock so its a good thing we can't. Even using a custom launcher to try and hook via some handle reopen technique and calling up to Java would deadlock. Maybe if a reopen from within a custom launcher was possible (I don't know one way or the other) buffering the data and jumping from Java to native via JNI to retrieve the buffer might work.