You need to follow the MPI specification and use MPI_THREAD_MULTIPLE. It is not a good idea to make assumptions about what an MPI implementation may do within an MPI function. Otherwise your code may not work with some MPI implementation on some platform. MPI_Test is not read only. Internally it may cause progress to occur on other pending communication operations. Rajeev

On Jun 26, 2018, at 4:26 AM, Florian Lindner <[email protected]> wrote:

Hello,

I have a multi-threaded MPI application. Actually, only two threads. The main thread does all kinds of MPI operations, the secondary thread, launched by std::thread does only MPI_Test, no other MPI operations.

What is the required level of thread safety?

According to https://www.mpich.org/static/docs/v3.1/www3/MPI_Init_thread.html

MPI_THREAD_SINGLE Only one thread will execute.

MPI_THREAD_FUNNELED The process may be multi-threaded, but only the main thread will make MPI calls (all MPI calls are funneled to the main thread).

MPI_THREAD_SERIALIZED The process may be multi-threaded, and multiple threads may make MPI calls, but only one at a time: MPI calls are not made concurrently from two distinct threads (all MPI calls are serialized).

MPI_THREAD_MULTIPLE Multiple threads may call MPI, with no restrictions.

its THREAD_MULTIPLE, since I can not synchronize the main threads MPI calls and MPI_Test from the other thread.

Is that perception correct? I am asking, because I think Test is a relatively small operations and probably read only and therefore maybe a lower thread safety level suffices.

Thanks, Florian _______________________________________________ discuss mailing list [email protected] To manage subscription options or unsubscribe: https://lists.mpich.org/mailman/listinfo/discuss

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