The concurrent graph: basic technology for irregular problems

This paper describes basic programming technology to support irregular applications on scalable concurrent hardware and shows how the technology has been applied to a variety of large-scale industrial application problems. The technology is based on the concept of a concurrent graph library that provides an adaptive collection of lightweight threads that may relocate between computers dynamically. The graph is portable to a wide range of high-performance multicomputers, shared-memory multiprocessors, and networked workstations. For each machine it is optimized to take advantage of the best available underlying communication and synchronization mechanisms. The graph provides a framework for adaptive reenement of computations, automatic load balancing, and interactive, on-they visualization. It has been applied to a variety of large scale irregular applications to provide portable, scalable implementations with substantial code reuse. The applications described in this article typify a broad category of problems in continuum and non-continuum ow simulations. Over the last ten years there has been a constant evolution of high-performance parallel architectures with new machines appearing on a yearly basis. These architec-tures increasingly leverage low-cost workstation and shared-memory technology on a small scale (less than 256 computers) with distributed memory multicomputer technology to provide scalability. These hybrid architectures, such as the Intel Paragon, Cray T3D, and SGI Power Challenge, provide a combination of shared-address space and message-passing programming models. As the performance gap between these models continues to diminish, there is a gradual evolution toward architectures that support a global address space implemented through a memory hierarchy. This paper describes basic programming techniques and technology to support large-scale irregular applications on hybrid architectures. This support maintains applications investments by providing portability, scalability, and maintainability. An