And-or parallel prolog: a recomputation based approach

We argüe that in order to exploit both Independent And- and Or-parallelism in Prolog programs there is advantage in recomputing some of the independent goals, as opposed to all their solutions being reused. We present an abstract model, called the Composition-Tree, for representing and-or parallelism in Prolog Programs. The Composition-tree closely mirrors sequential Prolog execution by recomputing some independent goals rather than fully re-using them. We also outline two environment representation techniques for And-Or parallel execution of full Prolog based on the Composition-tree model abstraction. We argüe that these techniques have advantages over earlier proposals for exploiting and-or parallelism in Prolog

Improving the efficiency of nondeterministic indepemndent and-parallel systems

We present the design and implementation of the and-parallel component of ACE. ACE is a computational model for the full Prolog language that simultaneously exploits both or-parallelism and independent and-parallelism. A high performance implementation of the ACE model has been realized and its performance reported in this paper. We discuss how some of the standard problems which appear when implementing and-parallel systems are solved in ACE. We then propose a number of optimizations aimed at reducing the overheads and the increased memory consumption which occur in such systems when using previously proposed solutions. Finally, we present results from an implementation of ACE which includes the optimizations proposed. The results show that ACE exploits and-parallelism with high efficiency and high speedups. Furthermore, they also show that the proposed optimizations, which are applicable to many other and-parallel systems, significantly decrease memory consumption and increase speedups and absolute performance both in forwards execution and during backtracking

Parallelism in Prolog: concepts and systems

Parallelism is a study area that grows up each day, caused by the cost reduction and popularizing of machines with parallels architecture. In this context, the logical languages, especially PROLOG, show a feasible and practical alternative of parallelism. This exploitation can be accomplished of different ways, and are there several challenges on this task. This survey aims to show the main concepts of parallelism in PROLOG, the faced challenges when aims to do parallelism in this language and the state-of-art of systems development to give parallelism support in logical languages. Systems with basis on implicit parallelism developed in different platforms are presented. At the end, is accomplished a comparison between the presented systems and the implemented models by they.Paralelismo é uma área de estudo que cresce a cada dia, devido à redução do custo e popularização de máquinas com arquiteturas paralelas. Nesse contexto, as linguagens lógicas, sobretudo o PROLOG, apresenta uma alternativa viável e prática de paralelismo. A exploração desse paralelismo pode ser realizada de diferentes formas, e há inúmeros desafios nessa tarefa. Este tutorial visa apresentar os principais conceitos de paralelismo em PROLOG, os desafios enfrentados quando se busca a paralelização nessa linguagem e o estado-da-arte do desenvolvimento de sistemas que dão suporte à paralelização em linguagens lógicas. São apresentados sistemas baseados em paralelismo implícito implementados em diferentes plataformas. Ao final é realizada uma comparação entre os sistemas apresentados e os modelos neles implementados

Paralelismo em Prolog: Conceitos e Sistemas

Paralelismo é uma área de estudo que cresce a cada dia, devido à redução do custo e popularização de máquinas com arquiteturas paralelas. Nesse contexto, as linguagens lógicas, sobretudo o PROLOG, apresenta uma alternativa viável e prática de paralelismo. A exploração desse paralelismo pode ser realizada de diferentes formas, e há inúmeros desafios nessa tarefa. Este tutorial visa apresentar os principais conceitos de paralelismo em PROLOG, os desafios enfrentados quando se busca a paralelização nessa linguagem e o estado-da-arte do desenvolvimento de sistemas que dão suporte à paralelização em linguagens lógicas. São apresentados sistemas baseados em paralelismo implícito implementados em diferentes plataformas. Ao final é realizada uma comparação entre os sistemas apresentados e os modelos neles implementados

Effectiveness of abstract interpretation in automatic parallelization: a case study in logic programming

We report on a detailed study of the application and effectiveness of program analysis based on abstract interpretation to automatic program parallelization. We study the case of parallelizing logic programs using the notion of strict independence. We first propose and prove correct a methodology for the application in the parallelization task of the information inferred by abstract interpretation, using a parametric domain. The methodology is generic in the sense of allowing the use of different analysis domains. A number of well-known approximation domains are then studied and the transformation into the parametric domain defined. The transformation directly illustrates the relevance and applicability of each abstract domain for the application. Both local and global analyzers are then built using these domains and embedded in a complete parallelizing compiler. Then, the performance of the domains in this context is assessed through a number of experiments. A comparatively wide range of aspects is studied, from the resources needed by the analyzers in terms of time and memory to the actual benefits obtained from the information inferred. Such benefits are evaluated both in terms of the characteristics of the parallelized code and of the actual speedups obtained from it. The results show that data flow analysis plays an important role in achieving efficient parallelizations, and that the cost of such analysis can be reasonable even for quite sophisticated abstract domains. Furthermore, the results also offer significant insight into the characteristics of the domains, the demands of the application, and the trade-offs involved

Automatic compile-time parallelization of logic programs for restricted, goal-level, independent and-parallelism.

A framework for the automatic parallelization of (constraint) logic programs is proposed and proved correct. Intuitively, the parallelization process replaces conjunctions of literals with parallel expressions. Such expressions trigger at run-time the exploitation of restricted, goal-level, independent and-parallelism. The parallelization process performs two steps. The first one builds a conditional dependency graph (which can be implified using compile-time analysis information), while the second transforms the resulting graph into linear conditional expressions, the parallel expressions of the &-Prolog language. Several heuristic algorithms for the latter ("annotation") process are proposed and proved correct. Algorithms are also given which determine if there is any loss of parallelism in the linearization process with respect to a proposed notion of maximal parallelism. Finally, a system is presented which implements the proposed approach. The performance of the different annotation algorithms is compared experimentally in this system by studying the time spent in parallelization and the effectiveness of the results in terms of speedups

Cuts and Side-Effects in And-Or Parallel Prolog

Practical Prolog programs usually contain extra-logical features like cuts, side-effects, and database manipulating predicates. In order to exploit implicit parallelism from real applications while preserving sequential Prolog semantics, a parallel logic programming system should necessarily support these features. In this paper we show how Prolog's extra-logical features can be supported in an and-or parallel logic programming system. We show that to support extra-logical features an and-or parallel logic programming system should recompute the solutions to independent goals instead of sharing them. We describe an abstraction called the Composition Tree for representing and-or parallel execution with recomputation. We introduce the notion of "local-leftmostness" in the Composition Tree and use it for deriving complete and efficient methods for supporting extra-logical predicates in and-or parallel logic programming systems based on the Composition Tree abstraction