JVMTI has a somewhat unique event called DataDumpRequest. One way it is triggered is via the JVMTI.data_dump jcmd, which causes JVMTI to send the DataDumpRequest event to all agents that have registered for the event callback. The agent is free to do pretty much what it wants during the callback, but the normal usage is to dump anything that might be useful for debugging the agent. In the case of the debug agent, it could dump internal data like the list of known threads or the state of each monitor held.