Implementing a wave algorithm in MPI involves creating a pattern where each process communicates with its neighbors in a specific sequence.
This can be used to model wave-like propagation of information across the processes.
In this example, let's consider a simple scenario where each process sends a message to its next neighbor, waits to receive a message from its previous neighbor, and then sends a confirmation back.
This pattern creates a “wave” of communication that passes through the processes from start to end and then back. It's a basic representation of wave algorithms commonly used in parallel computing for synchronization and data propagation.
#include <mpi.h> #include <stdio.h> #include <stdlib.h> int main(int argc, char** argv) { MPI_Init(&argc, &argv); int world_rank, world_size; MPI_Comm_rank(MPI_COMM_WORLD, &world_rank); MPI_Comm_size(MPI_COMM_WORLD, &world_size); int token; // Create a wave of communication from the first to the last process if (world_rank != 0) { MPI_Recv(&token, 1, MPI_INT, world_rank - 1, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE); printf("Process %d received token %d from process %d\n", world_rank, token, world_rank - 1); } else { // Start the wave token = -1; } MPI_Barrier(MPI_COMM_WORLD); if (world_rank != world_size - 1) { token++; MPI_Send(&token, 1, MPI_INT, world_rank + 1, 0, MPI_COMM_WORLD); printf("Process %d sent token %d to process %d\n", world_rank, token, world_rank + 1); } // Create a wave of confirmation back from the last to the first process if (world_rank != world_size - 1) { MPI_Recv(&token, 1, MPI_INT, world_rank + 1, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE); printf("Process %d received confirmation %d from process %d\n", world_rank, token, world_rank + 1); } MPI_Barrier(MPI_COMM_WORLD); if (world_rank != 0) { MPI_Send(&token, 1, MPI_INT, world_rank - 1, 0, MPI_COMM_WORLD); printf("Process %d sent confirmation %d to process %d\n", world_rank, token, world_rank - 1); } MPI_Finalize(); return 0; }
The program starts with the first process initializing the wave by sending a token to the next process.
Each process waits to receive the token from its previous neighbor, prints a message, and then sends the token to its next neighbor.
After reaching the last process, a confirmation wave is sent back in the reverse order.
Each process in the reverse wave receives a confirmation token from its next neighbor and sends it to its previous neighbor.
MPI_Barrier is used to synchronize processes between the forward and reverse waves.
This implementation demonstrates a basic wave algorithm where communication flows from the first to the last process and then back. The output will show the flow of tokens and confirmations through the processes.