Efficient evaluation strategies for structured concurrency constructs in parallel Scheme systems

Abstract

In Scheme-based parallel Lisp systems there are proposed a number of structured concurrency constructs like pcall, par, par- and, par-or and plet, etc. A standard evaluation strategy for these structured constructs has been the eager task creation (ETC) that creates child processes to execute their argument expressions whenever these structured constructs are encountered. But the ETC strategy for structured concurrency constructs is known to be inefficient because of overhead caused by excessive process creation. In this paper we propose an efficient evaluation strategy for structured concurrency constructs, called the steal-based evaluation (SBE) strategy, which suppresses excessive process creation. SBE is based on an extended use of two basic actions steal and inlining of lazy task creation used in an efficient implementation of future. The idea of SBE is extended to give a parallel implementation of the delay construct and stream computation expressed with delay yielding the steal-based lazy evaluation (SLE). In Concluding Remarks there are discussed the following issues: a programming style called structural parallel symbolic programming which is based on a functional core of Scheme and the SBE strategy, Restricted Eager Task Creation to suppress excessive process creation under ETC, and a simple constraint-based automatic parallelization of functional programs.