+/* A simple example pingpong pogram to test MPI_Send and MPI_Recv */
+
+
+
+#include <stdio.h>
+#include <mpi.h>
+
+main(int argc, char *argv[])
+{
+ const int tag1 = 42, tag2= 43; /* Message tag */
+ int rank;
+ int size;
+ int msg=99;
+ int err;
+ int pivot;
+ MPI_Status status;
+
+ err = MPI_Init(&argc, &argv); /* Initialize MPI */
+ if (err != MPI_SUCCESS) {
+ printf("MPI initialization failed!\n");
+ exit(1);
+ }
+ err = MPI_Comm_size(MPI_COMM_WORLD, &size); /* Get nr of tasks */
+ err = MPI_Comm_rank(MPI_COMM_WORLD, &rank); /* Get id of this process */
+ if ( size < 2 ) {
+ printf("run this program with exactly 2 processes (-np 2)\n");
+ MPI_Finalize();
+ exit(0);
+ }
+ if (0 == rank) {
+ printf("\n *** Ping-pong test (MPI_Send/MPI_Recv) ***\n\n");
+ }
+
+ /* start pingpong tests between several pairs */
+ for (pivot=0; pivot<size-1; pivot++) {
+
+ if (pivot == rank) {
+ printf("\n== pivot=%d : pingpong [%d] <--> [%d]\n",pivot,pivot,pivot+1);
+
+ int dst= rank + 1;
+ printf("[%d] About to send 1st message '%d' to process [%d] \n", rank,msg, dst);
+ err = MPI_Send(&msg, 1, MPI_INT, dst, tag1, MPI_COMM_WORLD);
+
+ err = MPI_Recv(&msg, 1, MPI_INT, dst, tag2, MPI_COMM_WORLD, &status); /* Receive a message */
+ printf("[%d] Received relpy message '%d' from process [%d] \n", rank,msg, dst);
+
+ }
+ if ((pivot+1) == rank) {
+ int src= rank - 1;
+ err = MPI_Recv(&msg, 1, MPI_INT, src, tag1, MPI_COMM_WORLD, &status); /* Receive a message */
+ printf("[%d] Received 1st message '%d' from process [%d] \n", rank,msg, src);
+ msg++;
+ printf("[%d] increment message's value to '%d'\n", rank,msg);
+ printf("[%d] About to send back message '%d' to process [%d] \n", rank,msg, src);
+ err = MPI_Send(&msg, 1, MPI_INT, src, tag2, MPI_COMM_WORLD);
+ }
+ }
+ err = MPI_Finalize(); /* Terminate MPI */
+ return 0;
+}