Garbage Collection on an Open Network

We present a distributed garbage collection algorithm that eventually collects all cycles in an open network. As with recent reference counting algorithms, it explicitly maintain the distributed inverse reference graph (i.e., each object maintains a list of sites known to have references to it). We show that a modiied depth-rst traversal of this inverse graph is suucient to locate any garbage it contains. We also provide a heuristic to control the frequency of distributed collections. The inverse graph has other uses, such as maintaining distributed consistency, which makes it particularly useful in a network where cooperation is not assured.