An Evaluation of Thread-Safe and Contexts-Domains Features in Cray SHMEM

There is increasing use of multithreading in High Performance Computing (HPC) programs in order to maximize the use of hardware resources of multi-core compute nodes. The latest version of the OpenSHMEM API Specification does not standardize the interaction between threads and OpenSHMEM routines in multithreaded applications. In this paper, we evaluate two proposals that have been put forward to try to address this deficiency: “Thread-Safe” and “Contexts-Domains”. Both of these proposals have been implemented, at least in part, in Cray SHMEM, a vendor-specific OpenSHMEM implementation from Cray Inc. We provide a design overview of the two proposals and give some experimental results showing significant performance benefits of each. To the best of our knowledge, this is the first paper to compare and contrast these two proposals.