A thread taxonomy for MPI

In 1994, we presented extensions to MPI and offered an early paper on potential thread extensions to MPI as well as non-blocking collective extensions to MPI. The present paper is a thorough review of thread issues in MPI, including alternative models, their computational uses, and the impact on implementations. A number of issues are addressed: barriers to thread safety in MPI implementations with MPICH as an example and changes of the semantics of non-thread-safe MPI calls, different thread models, their uses, and possible integration. Minimal portable thread management and synchronization mechanisms API extensions for MPI are considered. A tentative design for multi-threaded thread-safe ADI and Channel Device for MPICH is proposed. We consider threads as both an implementation device for MPI and as a user-level mechanism to achieve fine-grain concurrency. The reduction of the process to a simple resource container (as considered by Mach), with the thread as the main named computational unit is suggested. Specific results thus far with Windows NT version of MPICH are mentioned.