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Deadlocks, in which threads wait on each other in a cyclic fashion and can't make progress, have plagued parallel programs for decades. In recent years, as the parallel programming mechanism known as futures has gained popularity, interest in preventing deadlocks in programs with futures has increased as well. Various static and dynamic algorithms exist to detect and prevent deadlock in programs with futures, generally by constructing some approximation of the dependency graph of the program but, as far as we are aware, all are specialized to a particular programming language. A recent paper introduced graph types, by which one can statically approximate the dependency graphs of a program in a language-independent fashion. By analyzing the graph type directly instead of the source code, a graph-based program analysis, such as one to detect deadlock, can be made language-independent. Indeed, the paper that proposed graph types also proposed a deadlock detection algorithm. Unfortunately, the algorithm was based on an unproven conjecture which we show to be false. In this paper, we present, and prove sound, a type system for finding possible deadlocks in programs that operates over graph types and can therefore be applied to many different languages. As a proof of concept, we have implemented the algorithm over a subset of the OCaml language extended with built-in futures.
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Static prediction of parallel computation graphs
Many algorithms for analyzing parallel programs, for example to detect deadlocks or data races or to calculate the execution cost, are based on a model variously known as a cost graph, computation graph or dependency graph, which captures the parallel structure of threads in a program. In modern parallel programs, computation graphs are highly dynamic and depend greatly on the program inputs and execution details. As such, most analyses that use these graphs are either dynamic analyses or are specialized static analyses that gather a subset of dependency information for a specific purpose. This paper introduces graph types, which compactly represent all of the graphs that could arise from program execution. Graph types are inferred from a parallel program using a graph type system and inference algorithm, which we present drawing on ideas from Hindley-Milner type inference, affine logic and region type systems. We have implemented the inference algorithm over a subset of OCaml, extended with parallelism primitives, and we demonstrate how graph types can be used to accelerate the development of new graph-based static analyses by presenting proof-of-concept analyses for deadlock detection and cost analysis.
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- PAR ID:
- 10602088
- Publisher / Repository:
- Association for Computing Machinery (ACM)
- Date Published:
- Journal Name:
- Proceedings of the ACM on Programming Languages
- Volume:
- 6
- Issue:
- POPL
- ISSN:
- 2475-1421
- Format(s):
- Medium: X Size: p. 1-31
- Size(s):
- p. 1-31
- Sponsoring Org:
- National Science Foundation
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