Parallel and Distributed Programming with Pthreads and Rthreads

This paper describes Rthreads (Remote threads), a soft-ware distributed shared memory system that supports shar-ing of global variables on clusters of computers with phys-ically distributed memory. Other DSM systems either use virtual memory to implement coherence on networks of workstations or require programmers to adopt a special programming model. Rthreads uses primitives to read and write remote data and to synchronize remote accesses sim-ilar to the DSM systems that are based on special pro-gramming models. Unique aspects of Rthreads are: The primitives are syntactically and semantically closely re-lated to the POSIX thread model (Pthreads). A precom-piler automatically transforms Pthread (source) programs into Rthread (source) programs. After the transformation the programmer is still able to alter the Rthread code for optimizing run-time. Moreover, Pthreads and Rthreads can be mixed within a single program. We support heteroge-neous workstation clusters by implementing the Rthreads system on top of PVM, MPI and DCE. We demonstrate that programmer based optimizations may reach a significant performance increase. Our performance results show that the Rthreads system introduces few overhead compared to equivalent programs in the baseline system PVM, and a su-perior performance compared to the DSM systems Adsmith and CVM. 1