Candidate: Cristian Ungureanu
Advisor: Benjamin Goldberg

Abstract Models of Distributed Memory Management

10:00 a.m., Wednesday, January 14, 1998
12th floor conference room, 719 Broadway


In this dissertation, we are presenting a model suitable for reasoning about memory management in concurrent and distributed systems. The model provides a suitable level of abstraction: it is low-level enough so that we can express communication, allocation and garbage collection, but otherwise hides many of the lower-level details of an actual implementation. Using it, we can give compact, and provably correct, characterizations of garbage collection algorithms in distributed systems.

The models are rewriting systems whose terms are programs in which the ``code'' and the ``store'' are syntactically apparent. Evaluation is expressed as conditional rewriting and includes store and communication operations. Using techniques developed for communicating and concurrent systems we give a semantics suitable for proving equivalence of such programs. Garbage collection becomes a rewriting relation that removes part of the store without affecting the behavior of the program.

We introduce and prove correct a very general garbage collection rule based on reachability; any actual implementation which is capable of providing the transitions (including their atomicity constraints) specified by the strategy is therefore correct. We give examples of such specific implementations, and show how their correctness follows from the correctness of the general relation.