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I am trying to probe for messages in order to communicate between MPI processes (8 processes). The first process to reach a certain part of the code will signal all the other processes, and the others will terminate upon reaching there.

Here is what I've implemented: (any simpler solutions are welcome)

if(depth == size){
    endTime = MPI_Wtime();
    MPI_Iprobe(MPI_ANY_SOURCE, 0, MPI_COMM_WORLD, &stat, MPI_STATUS_IGNORE);
    if(!stat){
        printf("Execution completed in %.5f seconds.\n", endTime - beginTime);
        for (ctr = 0; ctr < mpi_processors; ctr++) {
            if(ctr == mpi_my_pid) continue;
            MPI_Isend(&stat, 1, MPI_INT, ctr, 0, MPI_COMM_WORLD, &req);
            printf("sent to %d from %d\n",ctr,mpi_my_pid);

        }
    }
    return 1;
}

The code is self-explanatory. stat is a dummy variable just for "send"ing a message, and also used as the flag for the Iprobe. The problem is, stat is always zero in all processes, meaning that probing doesn't return any waiting messages to be received. But I can confirm that MPI_Isend runs correctly and sends the message.

Am I doing something fundamentally wrong, or is there a simple bug somewhere that I can't see?

Thanks,

Can.

Can Poyrazoğlu
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    Your code is fundamentally wrong because you do not complete the `MPI_Isend` operation. It might work in your case (e.g. given your MPI implementation) because the message is very small and is likely sent using the eager protocol, but the standard requires that you wait/test the `req` handle. – Hristo Iliev Dec 30 '12 at 21:21
  • how do I do that? I couldn't find any examples involving test/wait. the ones I've found don't have anything related to test/wait. – Can Poyrazoğlu Dec 30 '12 at 21:31

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