Hi all,
I have a question on the "Semantics of Point-to-Point Communication" in
a multithreaded context.
For me the situation for the code below is not clear, especially with
respect to the paragraph in MPI-3.1 p.41, l.10-17 :
void test(int rank) {
int msg = 0;
if (rank == 0) {
#pragma omp parallel num_threads(2)
#pragma omp critical
{
MPI_Send(&msg, 1, MPI_INT, 1, 42, MPI_COMM_WORLD);
msg++;
}
} else if (rank == 1) {
MPI_Recv(&msg, 1, MPI_INT, 0, 42, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
printf("Received %i\n", msg);
MPI_Recv(&msg, 1, MPI_INT, 0, 42, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
printf("Received %i\n", msg);
}
}
Two threads on the first process send a message, the first thread sends
0, the second thread send 1. From OpenMP semantics, the first send
happens before the second send.
Is there a guarantee, that the other process receives the 0 first?
Thanks,
Joachim
--
Dipl.-Inf. Joachim Protze
IT Center
Group: High Performance Computing
Division: Computational Science and Engineering
RWTH Aachen University
Seffenter Weg 23
D 52074 Aachen (Germany)
Tel: +49 241 80- 24765
Fax: +49 241 80-624765
protze(a)itc.rwth-aachen.de
www.itc.rwth-aachen.de
