Synchronisation
C | Fortran-2008 | Fortran-90
MPI_Waitall is a version of MPI_Wait that can be applied to an array of request handlers. This version waits until all the non-blocking routines concerned complete. Other versions are MPI_Wait, MPI_Waitany and MPI_Waitsome.
int MPI_Waitall(int count,
MPI_Request requests[],
MPI_Status statuses[]);Number of request handlers to wait on, as well as the number of statuses contained in the array passed (if MPI_STATUSES_IGNORE is not passed).
The request handlers on the non-blocking routines to wait on.
The array in which write the statuses returned by the non-blocking routines concerned. It can be MPI_STATUSES_IGNORE if statuses are unused.
The error code returned from the waitings.
#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>
/**
* @brief Illustrates how to wait for the completion of multiple non-blocking
* operations.
* @details This program is meant to be run with 3 processes: a sender and two
* receivers.
**/
int main(int argc, char* argv[])
{
MPI_Init(&argc, &argv);
// Get the number of processes and check only 3 processes are used
int size;
MPI_Comm_size(MPI_COMM_WORLD, &size);
if(size != 3)
{
printf("This application is meant to be run with 3 processes.\n");
MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
}
// Get my rank
int my_rank;
MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
if(my_rank == 0)
{
// The "master" MPI process sends the message.
int buffer[2] = {12345, 67890};
MPI_Request requests[2];
printf("MPI process %d sends the values %d & %d.\n", my_rank, buffer[0], buffer[1]);
MPI_Isend(&buffer[0], 1, MPI_INT, 1, 0, MPI_COMM_WORLD, &requests[0]);
MPI_Isend(&buffer[1], 1, MPI_INT, 2, 0, MPI_COMM_WORLD, &requests[1]);
// Wait for both routines to complete
MPI_Waitall(2, requests, MPI_STATUSES_IGNORE);
printf("Process %d: both messages have been sent.\n", my_rank);
}
else
{
// The "slave" MPI processes receive the message.
int received;
MPI_Recv(&received, 1, MPI_INT, 0, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
printf("Process %d received value %d.\n", my_rank, received);
}
MPI_Finalize();
return EXIT_SUCCESS;
}