Multiple threads can be used not only as a mechanism for tolerating unpredictable communication latency but also for facilitating dynamic scheduling and load balancing. Multithreaded systems are well suited to highly irregular and dynamic applications, such as tree search problems, and provide a natural way to achieve performance improvement through such new concepts as active messages and remote memory copy. Although already popular in singleprocessor and shared-memory processor systems, multithreading on distributed systems encounters more difficulties and needs to address new issues such as communication, scheduling and migration between threads located in separate addressing spaces. This paper addresses the key issues of multithreaded systems and investigates existing approaches for distributed concurrent computations. Keywords: Multithreaded computation, thread, virtual processor, thread safety, active message, data-driven. This research was supported by Natural Sciences and Eng...

We describe an architecture for the runtime environment for parallel applications as prelude to describing how parallel application might interface to their environment in a portable way. We propose extensions to the Message-Passing Interface (MPI) Standard that provide for dynamic process management, including spawning of new processes by a running application and connection to existing processes to support client/server applications. Such extensions are needed if more of the runtime environment for parallel programs is to be accessible to MPI programs or to be themselves written using MPI.