send_recv_ord_sem.cpp

#include <mpi.h>
#include <iostream>

#define MESSAGE_CAPACITY 1024

int main(int argc, char* argv[])
{
	MPI_Init(&argc, &argv);
	
	int my_rank = -1;
	int process_count = -1;
	
	MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
	MPI_Comm_size(MPI_COMM_WORLD, &process_count);
	
	char hostname[MPI_MAX_PROCESSOR_NAME];
	int hostname_length = -1;
	MPI_Get_processor_name(hostname, &hostname_length);
	
	char ready = 'Y';
	if ( my_rank != 0 )
		MPI_Recv(&ready, /*capacity*/ 1, MPI_CHAR, /*source*/ my_rank - 1, /*tag*/ 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);

	std::cout << "Hello from main thread of process " << my_rank
		<< " of " << process_count << " on " << hostname << std::endl;

	if ( my_rank < process_count - 1 )
		MPI_Send(&ready, /*count*/ 1, MPI_CHAR, /*dest*/ my_rank + 1, /*tag*/ 0, MPI_COMM_WORLD);
	
	MPI_Finalize();
}