Scalable Reader-Writer Synchronization for Shared-Memory Multiprocessors

Reader-writer synchronization relaxes the constraints of mutual exclusion to permit more than one process to inspect a shared object concurrently, as long as none of them changes its value. On uniprocessors, mutual exclusion and readerwriter locks are typically designed to de-schedule blocked processes; however, on shared-memory multiprocessors it is often advantageous to have processes busy wait. Unfortunately, implementations of busy-wait locks on sharedmemory multiprocessors typically cause memory and network contention that degrades performance. Several researchers have shown how to implement scalable mutual exclusion locks that exploit locality in the memory hierarchies of shared-memory multiprocessors to eliminate contention for memory and for the processor-memory interconnect. In this paper we present reader-writer locks that similarly exploit locality to achieve scalability, with variants for reader preference, writer preference, and reader-writer fairness. Performance results on a BBN TC2000 multiprocessor demonstrate that our algorithms provide low latency and excellent scalability.