http://hdl.handle.net/1880/45313 Thu, 23 May 2013 04:51:02 GMT 2013-05-23T04:51:02Z http://hdl.handle.net/1880/46623 Title: LIMITATIONS AND CAPABILITIES OF WEAK MEMORY CONSISTENCY SYSTEMS Authors: KAWASH, JALAL Abstract: This dissertation develops and exploits a formalism for specifying memory consistency models. This formalism lays down the foundations for describing memory consistency models at various levels, and develops techniques to prove the equivalence between models defined at different levels. Two levels, called non-operational and operational, are addressed in this dissertation. The non-operational level describes these models in terms of program instructions or procedures, while the operational level describes them in terms of implementation events. Formal techniques are developed to prove the equivalence of rigorous specifications at both levels. This formalism is then exploited to define the memory consistency models of two state-of-the-art multiprocess systems: the SPARC version 8 architecture and the Java Virtual Machine. These models are defined at both operational and non-operational levels. These operational and non-operational descriptions are proved equivalent. The SPARC models provide "reasonably" weak memory consistency models that are capable of avoiding the use of explicit synchronization primitives for certain problems. However, Java provides a consistency model that is completely dependent on synchronization primitives, without which no form of coordination between different threads is possible. Fundamental process coordination problems have been extensively studied for traditional systems with strong memory consistency. This dissertation revisits the critical section and the producer/consumer problems in the context of weak memory consistency models. It establishes that the majority of known weak memory consistency models are incapable of supporting a solution to the critical section problem without the use of explicit synchronization primitives. Surprisingly, most of these models are capable of supporting solutions to versions of the producer/consumer problem without the use of these primitives. Wed, 22 Mar 2000 00:00:00 GMT http://hdl.handle.net/1880/46623 2000-03-22T00:00:00Z http://hdl.handle.net/1880/46030 Title: CRITICAL SECTIONS AND PRODUCER/CONSUMER QUEUES IN WEAK MEMORY SYSTEMS Authors: Higham, Lisa; Kawash, Jalal Abstract: In machines with a weak memory consistency model, the ordering constraints on memory accesses are few. In order to properly program these machines, certain powerful or explicit synchronization instructions are additionally provided in their architecture. We show that although a solution to the critical section problem (also referred to as the mutual exclusion problem) is impossible without such powerful synchronization, certain versions of the producer/consumer problem can be solved even in the weakest systems without the need for any such powerful instructions. These instructions are expensive, and avoiding their use is desirable for better performance. Sun, 01 Jun 1997 00:00:00 GMT http://hdl.handle.net/1880/46030 1997-06-01T00:00:00Z http://hdl.handle.net/1880/45997 Title: BOUNDS FOR MUTUAL EXCLUSION WITH ONLY PROCESSOR CONSISTENCY Authors: Higham, Lisa; Kawash, Jalal Abstract: Most weak memory consistency models are incapable of supporting a solution to mutual exclusion using only read and write operations. Processor Consistency-Goodman's version is an exception. Ahamad et al.[1] showed that Peterson's mutual exclusion algorithm is correct for PC-G, but Lamport's bakery algorithm is not. In this paper, we derive a lower bound on the number and type (single- or multi-writer) of variables that a mutual exclusion algorithm must use in order to be correct for PC-G. We show that any such solution for n processes must use at least one multi-writer and n single-writers. This lower bound is tight when n = 2, and is tight when n >_2 for solutions that do not provide fairness. We show that Burn's algorithm is an unfair solution for mutual exclusion in PC-G that achieves our bound. However, five other known algorithms that use the same number and type of variables are incorrect for PC-G. A corollary of this investigation is that, in contrast to Sequential Consistency, multi-writers cannot be implemented from single-writers in PC-G. Wed, 15 Dec 1999 00:00:00 GMT http://hdl.handle.net/1880/45997 1999-12-15T00:00:00Z http://hdl.handle.net/1880/45995 Title: JAVA: MEMORY CONSISTENCY AND PROCESS COORDINATION Authors: Higham, Lisa; Kawash, Jalal Abstract: In Java, some memory updates are necessarily visible to some threads but never to others. A definition of Java memory consistency must take this fact into consideration to capture the semantics of non-terminating systems, such as a Java operating system. This paper presents a programmer-centered formal definition of Java memory behavior that captures those semantics. Our definition is employed to prove that it is impossible to provide fundamental process coordination in Java, such as critical sections and producer/consumer coordination, without the use of the synchronized and volatile constructs. However, we show that a weaker form of synchronization suffices to solve some of these problems in Java. Wed, 01 Apr 1998 00:00:00 GMT http://hdl.handle.net/1880/45995 1998-04-01T00:00:00Z