Tracking CSP computations

[EN] Tracing is one of the most important techniques for program understanding and debugging. A trace gives the user access to otherwise hidden information about a computation. In the context of concurrent languages, computations are particularly complex due to the non-deterministic execution order of processes and to the restrictions imposed on this order by synchronizations; hence, a tracer is a powerful tool to explore, understand and debug concurrent computations. In CSP, traces are sequences of events that define a particular execution. This notion of trace is completely different to the one used in other paradigms where traces are formed by those source code expressions evaluated during a particular execution. We refer to this second notion of traces as tracks. In this work, we introduce the theoretical basis for tracking concurrent and explicitly synchronized computations in process algebras such as CSP. Tracking computations in this kind of systems is a difficult task due to the subtleties of the underlying operational semantics which combines concurrency, non-determinism and non-termination. We define an instrumented operational semantics that generates as a side-effect an appropriate data structure (a track) which can be used to track computations. The formal definition of a tracking semantics improves the understanding of the tracking process, but also, it allows us to formally prove the correctness of the computed tracks. (C) 2018 Elsevier Inc. All rights reserved.This work has been partially supported by the EU (FEDER) and the Spanish Ministerio de Ciencia, Innovacion y Universidades/AEI under grant TIN2016-76843-C4-1-R and by the Generalitat Valenciana under grant PROMETEO-II/2015/013 (SmartLogic). The authors acknowledge a partial support of European COST Action IC1405 on Reversible Computation - extending horizons of computing. Salvador Tamarit was partially supported by the Conselleria de Educacion, Investigacion, Cultura y Deporte de la Generalitat Valenciana under the grant APOSTD/2016/036.Llorens Agost, ML.; Oliver Villarroya, J.; Silva, J.; Tamarit Muñoz, S. (2019). Tracking CSP computations. Journal of Logical and Algebraic Methods in Programming. 102:138-175. https://doi.org/10.1016/j.jlamp.2018.10.002S13817510

Representation and Implementation of CSP and VCR Traces

Communicating Sequential Processes (CSP) was developed around a formal algebra of processes and a semantics based on traces (and failures and divergences). A trace is a record of the events engaged in by a process. Several programming languages use, or have libraries to use, CSP mechanisms to manage their concurrency. Most of these lack the facility to record the trace of a program. A standard trace is a flat list of events but structured trace models are possible that can provide more information such as the independent or concurrent engagement of the process in some of its events. One such trace model is View-Centric Reasoning (VCR), which offers an additional model of tracing, taking into account the multiple, possibly imperfect views of a concurrent computation. This paper also introduces ''structural'' traces, a new type of trace that reflects the nested parallelism in a CSP system. The paper describes the automated generation of these three trace types in the Communicating Haskell Processes (CHP) library, using techniques which could easily be applied in other libraries such as JCSP and C++CSP2. The ability to present such traces of a concurrent program assists in understanding the behaviour of real CHP programs and for debugging when the trace behaviours are wrong. These ideas and tools promote a deeper understanding of the association between practicalities of real systems software and the underlying CSP formalism