Abstract

This paper describes the distributed memory implementation of a shared memory parallel functional language. The language is Id, an implicitly parallel, mostly functional language that is currently evolving into a dialect of Haskell. The target is a distributed memory machine, because we expect these to be the most widely available parallel platforms in the future. The difficult problem is to bridge the gap between the shared memory language model and the distributed memory machine model. The language model assumes that all data is uniformly accessible, whereas the machine has a severe memory hierarchy: a processor's access to remote memory (using explicit communication) is orders of magnitude slower than its access to local memory. Thus, avoiding communication is crucial for good performance. The Id language, and its general dataflow-inspired compilation to multithreaded code are described elsewhere. In this paper, we focus on our new parallel runtime system and its features for avoiding communication and for tolerating its latency when necessary: multithreading, scheduling and load balancing; the distributed heap model and distributed coherent cacheing, and parallel garbage collection. We have completed the first implementation, and we present some preliminary performance measurements.

Citations