Java RMI and Thread Synchronization questions

Question

I actually have two questions about Java RMI and thread synchronization:

1) If I implement my RMI remote methods as synchronized, are they guaranteed to be mutually

Answer 1

You must keep in mind that RMI creates the illusion of a "remote object", but in reality there are no less than three objects: the local stub, the remote skeleton and the actual remote object. As a design trade-off this illusion is not complete and is locking only the local stub. There is no synchronization across the network. Search the internet for RMI+stub+synchronized and you will find plenty of explanations, like for instance this one:

Java RMI and synchronized methods

So you need to implement some kind of non-RMI, purely server-side synchronization yourself. Then you can invoke this pure server-side locks from your remote methods; but you need the additional level of indirection.

To test your code the easiest is to pause your threads under a good debugger like Eclipse. Eclipse will clearly show you which paused thread is holding which lock blocking which other thread(s).