Parallelism and recursion in message passing libraries: an efficient methodology

Nested parallelism appears naturally in many applications. It is required whenever a function performing parallel statements needs to call a subroutine using parallelism. A particular case occurs when the function is recursive. Nested parallelism is to parallel programming as basic as nested loops to sequential programming. Despite this, most existing parallel languages do not provide this feature. This paper presents a new methodology to expand message passing libraries (MPL) with nested parallelism. The tool to support the methodology has processor virtualization, load balancing, pipeline parallelism and collective operations, among other features. The computational results prove that the performance obtained is comparable to that obtained using classical message passing programs. Since the methodology does not force the programmer to leave the MPL environment, all the efficiency and portability of the MPL model is preserved. Copyright 1999 John Wiley & Sons, Ltd.