Deriving distributed garbage collectors from distributed termination algorithms

This thesis concentrates on the derivation of a modularised version of the DMOS distributed garbage collection algorithm and the implementation of this algorithm in a distributed computational environment. DMOS appears to exhibit a unique combination of attractive characteristics for a distributed garbage collector but the original algorithm is known to contain a bug and, previous to this work, lacks a satisfactory, understandable implementation. The relationship between distributed termination detection algorithms and distributed garbage collectors is central to this thesis. A modularised DMOS algorithm is developed using a previously published distributed garbage collector derivation methodology that centres on mapping centralised collection schemes to distributed termination detection algorithms. In examining the utility and suitability of the derivation methodology, a family of six distributed collectors is developed and an extension to the methodology is presented. The research work described in this thesis incorporates the definition and implementation of a distributed computational environment based on the ProcessBase language and a generic definition of a previously unimplemented distributed termination detection algorithm called Task Balancing. The role of distributed termination detection in the DMOS collection mechanisms is defined through a process of step-wise refinement. The implementation of the collector is achieved in two stages; the first stage defines the implementation of two distributed termination mappings with the Task Balancing algorithm; the second stage defines the DMOS collection mechanisms

Lazy Cyclic Reference Counting

Reference counting is a widely employed memory management technique, in which garbage collection operations are interleaved with computation. Standard reference counting has the major drawback of being unable to handle cyclic structures. This paper presents an important optimisation to a recently published algorithm for cyclic reference counting. Proofs of the correctness of the original and lazy algorithms are provided, together with performance figures

A New Architecture for Concurrent Lazy Cyclic Reference Counting on Multi-Processor Systems

Multi-processor systems have become the standard in current computer architectures. Software developers have the possibility to take advantage of the additional computing power available to concurrent programs. This paper presents a way to automatically use additional processors, by performing memory management concurrently. A new architecture with little explicit synchronization for concurrent lazy cyclic reference counting is described. This architecture was implemented and preliminary performance tests point at significant efficiency improvements over the sequential counterpart