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How does the distributed garbage collector detect a client that disconnects?

+4 votes
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Is it advisable to use System.exit() for graceful client termination?

posted Sep 29, 2013 by Vinay Shukla

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2 Answers

+1 vote

If you need to use System.exit() to terminate a client VM, to ensure that remote references held in that VM are cleaned up in a more timely fashion, you should make sure that there are no remote references still reachable. Explicitly null any local references to make them unreachable from running threads. It also may help to run a full garbage collection and to run finalizers before exiting:

System.gc();
System.runFinalization();

Go to: http://docs.oracle.com/javase/7/docs/technotes/guides/rmi/faq.html#leases
And search: "D.5 How does the distributed garbage collector detect a client that disconnects? Is it advisable to use System.exit for graceful client termination?"

answer Sep 29, 2013 by Satyabrata Mahapatra
+1 vote

When the Java RMI runtime in a client VM detects that a remote object is no longer referenced locally, it asynchronously notifies the server relatively quickly so that the server can update the object's referenced set accordingly. The distributed garbage collector uses a lease associated with each client-held remote object reference, and renews leases to remote objects while the client still holds such references. The purpose of the lease renewal mechanism is to allow the server to detect the abnormal termination of clients, so that a server does not hold on to a remote object forever because of a client that was not able to send the appropriate "unreferenced" message before it stopped running. In this context, a client invoking System.exit() is considered abnormal termination, because it does not allow the RMI runtime to send the appropriate "unreferenced" messages to the server. Executing System.runFinalizersOnExit in the client before termination is not sufficient, because not all of the necessary processing is handled in a finalizer; i.e. the "unreferenced" message will not get sent to the server. (Using "runFinalizersOnExit" is generally ill-advised and deadlock-prone anyway.)
If you need to use System.exit() to terminate a client VM, to ensure that remote references held in that VM are cleaned up in a more timely fashion, you should make sure that there are no remote references still reachable. Explicitly null any local references to make them unreachable from running threads. It also may help to run a full garbage collection and to run finalizers before exiting:

System.gc();
System.runFinalization();
answer Sep 29, 2013 by Manish Negi
You posted the same answer that i have already given.
Its better to share the link.
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