JVM PrintGCApplicationConcurrentTime and PrintGCApplicationStoppedTime flags

Question

I'm running a Java program and I need to get how much time each it spent garbage collecting. I found these 2 JVM flags: -XX:+PrintGCApplicationConcurrentTime -XX:+PrintGCApplicationStoppedTime

but I'm not being able to find information about it. I suppose that PrintGCApplicationStoppedTime prints for how long the application time was in a STW, however I am not sure about -XX:+PrintGCApplicationConcurrentTime. Does it print for how long the application was executing concurrently with collection threads?

Thanks in advance.

Answer 1

The names of these flags are not very accurate.

PrintGCApplicationStoppedTime shows how much time the application was stopped at safepoint. Most often safepoints are caused by stop-the-world phases of garbage collection, however, many other reasons exist.

PrintGCApplicationConcurrentTime is how much time the application worked without stopping, i.e. the time between two successive safepoints.