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MPI Send and Receive
MPI program using MPI_Send and MPI_Recv for communication between processes.
This program will involve two processes: the master process (rank 0) will send a message to a worker process (rank 1), which will then receive the message and print it.
- mpi_send_receive.c
#include <mpi.h> #include <stdio.h> #include <string.h> int main(int argc, char** argv) { // Initialize the MPI environment MPI_Init(&argc, &argv); // Find out rank, size int world_rank; MPI_Comm_rank(MPI_COMM_WORLD, &world_rank); int world_size; MPI_Comm_size(MPI_COMM_WORLD, &world_size); // We are assuming at least 2 processes for this task if (world_size < 2) { fprintf(stderr, "World size must be greater than 1 for %s\n", argv[0]); MPI_Abort(MPI_COMM_WORLD, 1); } int number; if (world_rank == 0) { // If we are rank 0, set the number to 7 and send it to process 1 number = 7; MPI_Send(&number, 1, MPI_INT, 1, 0, MPI_COMM_WORLD); printf("Process 0 sent number %d to process 1\n", number); } else if (world_rank == 1) { // If we are rank 1, receive the number from process 0 MPI_Recv(&number, 1, MPI_INT, 0, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE); printf("Process 1 received number %d from process 0\n", number); } // Finalize the MPI environment MPI_Finalize(); }
MPI Initialization: MPI_Init initializes the MPI environment. This must be called before any other MPI functions.
Rank and Size: MPI_Comm_rank gets the rank of the current process, and MPI_Comm_size gets the total number of processes.
Check Number of Processes: We check if the total number of processes is at least 2, as our example requires two processes.
Sending and Receiving:
Master Process (Rank 0): Sets an integer (number) to 7 and sends it to process 1 using MPI_Send. The parameters of MPI_Send include the data to be sent, the count of elements, the datatype, the destination rank, a tag to identify the message, and the communicator.
Worker Process (Rank 1): Receives the integer from process 0 using MPI_Recv. The parameters of MPI_Recv include the buffer to receive the data, the count of elements, the datatype, the source rank, a tag that matches the sent message, the communicator, and a status object (here we use MPI_STATUS_IGNORE as we do not need the status).
Finalization: MPI_Finalize finalizes the MPI environment and should be called when the MPI operations are complete.