How does the Distributed Garbage Collection algorithm work?

Govind Seshadri

The RMI subsystem implements a reference counting-based distributed garbage collection (DGC) algorithm to provide automatic memory management facilities for remote server objects.

Basically, DGC works by having the remote server keep track of all external client references to it at any given time. When a client obtains a remote reference, it is addded to the remote object's referenced set. The DGC then marks the remote object as dirty and increases its reference count by one. When a client drops a reference, the DGC decreases its reference count by one, and marks the object as clean. When the reference count reaches zero, the remote object is free of any live client references. It is then placed on the weak reference list and subject to periodic garbage collection.