In this report we present a fault-tolerant and efficient algorithm for distributed garbage collection and prove its correctness. The algorithm is a generalization of reference counting; it maintains a set of identifiers for processes with references to an object. The set is maintained with pair-wise communication between processes, so no global synchronization is required. The primary cost for maintaining the set is one remote procedure call when an object reference is transferred to a new process for the first time. The distributed collector collaborates with the local collector in detecting garbage; any local collector may be used, so long as it can be extended to provide notification when an object is collected. In fact, the distributed collector could be used without a local collector; in that case, the programmer would insert explicit dispose commands to release an object. The algorithm was designed and implemented as part of the Modula-3 network objects system, but it should be s...

The overall goal of the Emerald garbage collection scheme is to provide an efficient "on-thefly " garbage collection in a distributed object-based system that collects all garbage, and that is robust to partial failures. The first goal is to collect all garbage in the entire distributed system; we say that the collection is comprehensive in contrast to conservative collectors that only collect most garbage. Comprehensiveness is achieved by employing a system-wide mark-and-sweep collection based on concurrently running collectors, one on each node. The second goal of our collector is to be robust to partial failures. When facing node failures the collector will progress in the available parts of the system and, when necessary, wait for temporarily unavailable nodes to become available again. The scheme is being implemented on a network of VAXstations at DIKU. The full scheme employs two concurrent mark-and-sweep collectors on each node in the distributed system, one for comprehensivenes...

This paper describes a multi-threaded and incremental garbage collector operating on shared memory architectures. The technique was developed for parallel implementations of the language LCS, a high level parallel programming language.