This section specifies the interaction between MPI calls and threads. The section lists minimal requirements for thread compliant MPI implementations and defines functions that can be used for initializing the thread environment. MPI may be implemented in environments where threads are not supported or perform poorly. Therefore, MPI implementations are not required to be thread compliant as defined in this section. Regardless of whether or not the MPI implementation is thread compliant, MPI_INITIALIZED, MPI_FINALIZED, MPI_QUERY_THREAD, MPI_IS_THREAD_MAIN, MPI_GET_VERSION and MPI_GET_LIBRARY_VERSION must always be thread-safe. When a thread is executing one of these routines, if another concurrently running thread also makes an MPI call, the outcome will be as if the calls executed in some order.
This section generally assumes a thread package similar to POSIX threads [39], but the syntax and semantics of thread calls are not specified here --- these are beyond the scope of this document.