gather.cpp

#include "mpi.h"
#include <unistd.h>
#include <vector>

int main(int argc, char **argv) {
	MPI_Init(&argc, &argv);

	int rank, size;
	MPI_Comm_rank(MPI_COMM_WORLD, &rank);
	MPI_Comm_size(MPI_COMM_WORLD, &size);

	std::vector<int> data = { rank };
	if (rank == 0) {
		data.resize(size);
		for (int i = 1; i < size; ++i) {
			MPI_Recv(data.data() + i, 1, MPI_DOUBLE, i, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
		}
	} else {
		if (rank == 1) {
			usleep(1000000);
		}
		MPI_Ssend(data.data(), 1, MPI_INT, 0, 0, MPI_COMM_WORLD);
		if (rank != 1) {
			usleep(1000000);
		}
	}

	if (rank == 0) {
		for (int i = 0; i < size; ++i) {
			printf("%d ", data[i]);
		}
		printf("\n");
	}

	MPI_Finalize();
	return 0;
}