Parallel execution of prolog programs

Abstract

Since the early days of logic programming, researchers in the field realized the potential for exploitation of parallelism present in the execution of logic programs. Their high-level nature, the presence of non-determinism, and their referential transparency, among other characteristics, make logic programs interesting candidates for obtaining speedups through parallel execution. At the same time, the fact that the typical applications of logic programming frequently involve irregular computations, make heavy use of dynamic data structures with logical variables, and involve search and speculation, makes the techniques used in the corresponding parallelizing compilers and run-time systems potentially interesting even outside the field. The objective of this paper is to provide a comprehensive survey of the issues arising in parallel execution of logic programming languages along with the most relevant approaches explored to date in the field. Focus is mostly given to the challenges emerging from the parallel execution of Prolog programs. The paper describes the major techniques used for shared memory implementation of Or-parallelism, Andparallelism, and combinations of the two. We also explore some related issues, such as memory management, compile-time analysis, and execution visualization.

High Level Thread-Based Competitive Or-Parallelism in Logtalk

“…When one of the subgoals generates an exception, the competitive or-parallelism call terminates with the same exception. 1 When two or more subgoals generate exceptions, the competitive or-parallelism call terminates with one of the generated exceptions.…”

“…A number of approaches have been proposed to tackle this problem (see e.g [1]). Arguably, the two most successful ones are environment copying, as implemented in the Muse [7] and YapOr [8] systems, and binding arrays, as implemented in the Aurora system [9].…”

“…Or-parallelism is a simple form of parallelism in logic programs [1], where the bodies of alternative clauses for the same goal are executed concurrently. Orparallelism is often explored implicitly, possibly with hints from the programmer to guide the system.…”

“…The ISO Prolog multi-threading standardization proposal [5] is currently implemented in several systems including SWI-Prolog, Yap and XSB, providing a highly portable solution given the number of operating systems supported by these Prolog systems. In contrast, most or-parallelism systems described in the literature [1] are no longer available, due to the complexity of maintaining and porting their implementations.…”

Multivariant Non-failure Analysis via Standard Abstract Interpretation

“…It is essential for determining lower bounds on the computational cost of goals since without such information a lower bound of almost zero (corresponding to an early failure) must often be assumed [9]. Detecting non-failure is also very useful in the context of parallelism because it allows avoiding unnecessary speculative parallelism and ensuring no-slowdown properties for the parallelized programs (in addition to using the lower bounds mentioned previously to perform granularity control) [10]. Non-failure information is also instrumental in partial evaluation and other program transformations, such as reordering of calls, and has also been used in query optimization in deductive databases [7].…”