Meaning of message "operations coalesced during safepoint"

Question

A java app runs with the following flag: -XX:+PrintSafepointStatistics, and then produces the following line on the standard output console:

2 VM operations coalesced during safepoint

Anyone cares to explain what this mean ?

More generally - is there a Java reference manual somewhere detailling all JVM flags, their use and, most importantly, the expected output, with relevant explanations ?

Answer 1

Here is a list of the possible VM operations.

This counter is incremented for each subsequent vm operation dealt with while the VM is at a safepoint, i.e. if 1 vm op is processed than it is not incremented, if 2 vm ops are processed it is incremented once, if 3 vm ops are processed it is incremented twice (etc etc).

Answer 2

I don't have a specific answer about that message, but can point to safepoint.cpp in Java 6 source code containing that message.

A collection of JVM options for various versions has been compiled by Joseph D. Mocker