Optimistic Synchronization in Distributed Shared Memory

This paper introduces optimistic lock synchronization using the group write consistency model (GWC). GWC guarantees strict ordering of all shared writes in a processor group. In optimistic synchronization, if a lock-requesting processor can assume that the lock is free, execution of mutually exclusive code starts immediately. Wrong assumption results in rollback. Shared variable updates remain in the group until the lock manager grants the lock to the requesting processor. By evaluating the time needed for three processors to execute mutually exclusive code, GWC can outperform weak, release, and even entry consistency. Simulations of task management using exclusive access to a shared queue, also show much faster mutual exclusion with GWC. Optimistic mutual exclusion may further halve total delays in accessing shared resources. 1 Introduction Distributed shared memory(DSM) systems are networks of computers that transparently share variable values among processors. They are message pass..