SUMMARYThreads exhibit a simply expressed and powerful form of concurrency, easily exploitable in applications that run on both uni-and multi-processors, shared-and distributed-memory systems. This paper presents the design and implementation of Ariadne: a layered, C-based software architecture for multi-threaded distributed computing on a variety of platforms. Ariadne is a portable user-space threads system that runs on shared-and distributed-memory multiprocessors. Thread-migration is supported at the application level in homogeneous environments (e.g., networks of SPARCs and Sequent Symmetrys, Intel hypercubes). Threads may migrate between processes to access remote data, preserving locality of reference for computations with a dynamic data space. Ariadne can be tuned to specific applications through a customization layer. Support is provided for scheduling via a built-in or application-specific scheduler, and interfacing with any communications library. Ariadne currently runs on the SPARC (SunOS 4.x and SunOS 5.x), Sequent Symmetry, Intel 2360, Silicon Graphics workstation (IRIX), and IBM RS/6000 environments. We present simple performance benchmarks comparing Ariadne to threads libraries in the SunOS 4.x and SunOS 5.x systems.

ParaSol is a novel multithreaded system for sharedand distributed-memor y par allel simulation, designed to support a variety of domain-specific Simulation Object Libraries. We report on the design of the ParaSol kernel, which drives executions based on optimistic and adaptive synchronization protocols. The active-transaction flow methodology we advocate is enabled by an underlying, efficient lightweight process system. Though this process-and object-interaction view is known to both simplify and speed transition from model design to simulation implementation, migratable threads and objects pose many serious challenges to efficient kernel operation. Good solutions to these challenging problems are key to good simulator performance. We present techniques for the support of optimistic parallel simulations, addressing synchronization, state-saving, rollback, inter-process communication, and process scheduling.

We present results on the experimental design and development of a Connectionless, Lightweight, and Multiway (CLAM) communications environment. The system provides efficient and scalable multiprotocol support for distributed applications that use multimodal data. We present motivation behind design decisions for the CLAM system, and describe two simple, but effective scheduling algorithms for the simultaneous support of multiple, threads-based user-space protocols. One algorithm is readily portable to shared-memory multiprocessors, and enables two or more protocols to coexist within an OS-level process. We present experimental results on the performance of both algorithms.

We present a novel and portable threads‐based system for concurrent applications on shared‐ and distributed‐memory environments. The Ariadne system provides stateful user‐space threads that can be very effective in medium to coarse grained applications. The interface is the same for uniprocessors and multiprocessors. Sequential programs are readily converted into parallel programs for shared or distributed memory, with low development effort. Ariadne supports the development of customized schedulers, and offers a thread migration capability in distributed environments. Scheduling of computations at the threads level enables both task‐ and data‐driven executions. Thread migration is a useful feature which turns remote memory accesses into local accesses, enables load‐balancing and simplifies program development. Ariadne employs a unique runtime stack rewriting mechanism to migrate threads between homogeneous processors. Ariadne currently runs on the SPARC (SunOS 4.x, SunOS 5.x), Sequent Symmetry, Intel Paragon, Silicon Graphics IRIX and IBM RS/6000 environments. We present some examples of Ariadne programs, along with performance measurements. © 1998 John Wiley & Sons, Ltd.

Our focus is on the novel use of a proeess-oriented methodology in distributed-memory simulation systems. To the best of our knowledge, the few existing systems which adopt a process-view strictly use message-passing to effect process-interaction in distributed-memory settings. As a result, these systems avoid scenarios in which processes access passive but shared components.This can restrict the manner in which a system is modelled and hinder the phase of distributed model construction. In this paper, we propose an approach which utilizes mobile processes in distributed-memory simulation systems. Mobile processes can move around the system at will, with easy access toremote system components. The approach basically entails the migration of a requesting process with its timestamp to the remote site hosting the requested passive object. Major advantages of this approach include one-time transmission, fixed communication topology, and increased locality of reference. Early results based on lightweight processes show that the mobile process paradigm can be as efficient as the message-passing paradigm.