Java RMI and synchronized methods

Question

I\'m studying the book \"Distributed Systems\" (by Tanenbaum & Van Steen) and they say something that seems to conflict to what seems to be instead thought by many on Java R

Answer 1

What your first reference is saying is that within a single VM instance, invocations on an RMI Stub (client to an RMI server) will be internally synchronized. That is, the stub (or proxy, as the text seems to call it) itself will prevent multiple threads from concurrently invoking a method on the remote server. It clarifies, however, that two VMs each with stubs for a remote server will not be blocked from concurrently invoking the remote server (which is obvious, because they cannot share a lock, and RMI itself does not prevent concurrency at the server). If this is undesirable, the RMI server will have to implement a locking mechanism to prevent multiple concurrent invocations.

The second reference does not in anyway contradict the first. The second merely clarifies that if you try to synchronize on a stub, it will only be locked locally, and will not impact the concurrency of the remote server.

Combining the two texts, we can read that synchronizing on a stub will prevent the multiple threads in the same VM from concurrently accessing the remote, but will not prevent threads in distinct VMs from concurrent access.