An approach to formalization and analysis of message passing libraries

  • Authors:

  • Robert Palmer;Michael DeLisi;Ganesh Gopalakrishnan;Robert M. Kirby

  • Affiliations:

  • School of Computing, University of Utah;School of Computing, University of Utah;School of Computing, University of Utah;School of Computing, University of Utah

  • Venue:
  • FMICS'07 Proceedings of the 12th international conference on Formal methods for industrial critical systems
  • Year:
  • 2007

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Abstract

Message passing using libraries implementing the MessagePassing Interface (MPI) standard is the dominant communication mechanismin high performance computing (HPC) applications. Yet, the lackof an implementation independent formal semantics for MPI is a hugevoid that must be filled, especially given the fact that MPI will be implementedon novel hardware platforms in the near future. To help reasonabout programs that use MPI for communication, we have developed aformal TLA+ semantic definition of the point to point communicationoperations to augment the existing standard. The proposed semantics includes42 MPI functions, including all 35 point to point operations, manyof which have not been formally modeled previously. We also present aframework to extract models from SPMD-style C programs, so that designersmay understand the semantics of MPI by exercising short, yetpithy, communication scenarios written in C/MPI. In this paper, wedescribe (i) the TLA+ MPI model features, such as handling the explicitmemory for each process to facilitate the modeling of C pointers,and some of the widely used MPI operations, (ii) the model extractionframework and the simplifications made to the model that help facilitateexplicit-state model checking of formal semantic definitions, (iii) a customizedmodel checker for MPI that performs much faster model checking,and features a dynamic partial-order reduction algorithm whose correctnessis directly based on the formal semantics, and (iv) an error trailreplay facility in the Visual Studio environment. Our effort has helpedidentify a few omissions in the MPI reference standard document. Thesebenefits suggest that a formal semantic definition and exploration approachas described here must accompany every future effort in creatingparallel and distributed programming libraries.