Garbage collection notification?

Question

I\'d like to register a callback with the JVM so I know when garbage collection is happening. Is there any way to do this?

EDIT: I want to do this so I can log out

Answer 1

Another use case for getting impending GC notifications: if your app is load balanced then you can then notify the load balancer to take your node out of the pool when a GC is about to start to that it does not receive requests that would have to wait for a full GC to get dealt with.

That doesn't help in-flight requests that arrived just before the GC kicked in but, in my case at least, most requests are subsecond and major GCs are 5-10s, every few minutes. We can tweak the NewGen ratios etc but the general point still applies: major GC may be much longer than typical response times so you may want to premptively stop a node starting a major GC from receiving requests.

When GC is over, a thread in the JVM can send a notification to the load balancer to let it know its back in business or the LB can rely on its usual keepalive.