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#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>
int main(int argc, char *argv[])
{
int i, myid, ntasks;
int size = 10000000;
int *message;
int *receiveBuffer;
MPI_Status statuses[2];
MPI_Request requests[2];
double t0, t1;
int source, destination;
int count;
MPI_Init(&argc, &argv);
MPI_Comm_size(MPI_COMM_WORLD, &ntasks);
MPI_Comm_rank(MPI_COMM_WORLD, &myid);
/* Allocate message buffers */
message = malloc(sizeof(int) * size);
receiveBuffer = malloc(sizeof(int) * size);
/* Initialize message */
for (i = 0; i < size; i++) {
message[i] = myid;
}
/* Set source and destination ranks */
if (myid < ntasks - 1) {
destination = myid + 1;
} else {
destination = MPI_PROC_NULL;
}
if (myid > 0) {
source = myid - 1;
} else {
source = MPI_PROC_NULL;
}
/* Start measuring the time spend in communication */
MPI_Barrier(MPI_COMM_WORLD);
t0 = MPI_Wtime();
/* Describe the receiving requests */
MPI_Recv_init(receiveBuffer, size, MPI_INT, source, MPI_ANY_TAG,
MPI_COMM_WORLD, &requests[0]);
/* Describe the sending requests */
MPI_Send_init(message, size, MPI_INT, destination, myid + 1,
MPI_COMM_WORLD, &requests[1]);
/* Start communication */
MPI_Startall(2, requests);
/* Blocking wait for messages */
MPI_Waitall(2, requests, statuses);
/* Finalize measuring the time and print it out */
t1 = MPI_Wtime();
/* Use status parameter to find out the no. of elements received */
MPI_Get_count(&statuses[0], MPI_INT, &count);
printf("Sender: %d. Sent elements: %d. Tag: %d. Receiver: %d\n",
myid, size, myid + 1, destination);
printf("Receiver: %d. Received elements: %d. Tag %d. Sender: %d.\n",
myid, count, statuses[0].MPI_TAG, statuses[0].MPI_SOURCE);
MPI_Barrier(MPI_COMM_WORLD);
fflush(stdout);
if (myid == 0) {
printf("\n");
printf("Timings:\n");
printf("Time elapsed in rank %2d: %6.3f\n", myid, t1 - t0);
}
MPI_Barrier(MPI_COMM_WORLD);
fflush(stdout);
if (myid == ntasks - 1) {
printf("Time elapsed in rank %2d: %6.3f\n", myid, t1 - t0);
}
free(message);
free(receiveBuffer);
MPI_Finalize();
return 0;
}