Thread-safety in an MPI implementation: Requirements and analysis

13 years 4 months ago

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The MPI-2 Standard has carefully speciﬁed the interaction between MPI and usercreated threads. The goal of this speciﬁcation is to allow users to write multithreaded MPI programs while also allowing MPI implementations to deliver high performance. However, a simple reading of the thread-safety speciﬁcation does not reveal what its implications are for an implementation and what implementers must be aware (and careful) of. In this paper, we describe and analyze what the MPI Standard says about thread safety and what it implies for an implementation. We classify the MPI functions based on their thread-safety requirements and discuss several issues to consider when implementing thread safety in MPI. We use the example of generating new context ids (required for creating new communicators) to demonstrate how a simple solution for the single-threaded case does not naturally extend to the multithreaded case and how a na¨ıve thread-safe algorithm can be expensive. We then present an ...

William Gropp, Rajeev Thakur

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