Garbage Collecting the Grid: A Complete DGC for Activities

Grids are becoming more and more dynamic, running parallel applications on large scale and heterogeneous resources. Explicitly stopping a whole distributed application is becoming increasingly difficult. In that context, there is a strong need to free resources a soon as they become useless, leading to automatic termination, using distributed garbage collecting techniques. We propose in this paper a new distributed garbage collector for active objects taking into account cycles but with a complexity similar to the distributed garbage collector of Java/RMI. The algorithm is based on a different approach to collect acyclic and cyclic garbage. On one hand, acyclic garbage is collected by knowing the immediate referencers of an active object and detecting the lack of these referencers. This behavior with respect to acyclic garbage is common to the distributed garbage collector of RMI. On the other hand, cyclic garbage is detected by considering the recursive closure of all the referencers of an active object and finding cycles of active objects waiting for requests. These cycles are found by letting idle active objects make a consensus on a common final activity. The algorithm is fully distributed and has been implemented with no modifications to the local garbage collector. Benchmarks have shown the scalability of the algorithm in a