/* 
* The proc 0 and proc 1 send to proc 2 separately,
* proc 2 call MPI_PROBE to know whether the messages come,
* if so, it calls MPI_RECV to receive the messages
* Compile: mpicc mpi_probe01.c -o mpi_probe01
* Run: mpirun -np 3 mpi_probe01
*/

#include<stdio.h>	//for input/output
#include<mpi.h>		//for mpi routines

main( int argc, char** argv)
{
	int rank;			//the rank of this process
	int tag=0;			//not important here
	int n, i[1];
	float x[1];
	MPI_Status status;	//not important here

	MPI_Init(&argc, &argv);						//Initializing mpi
	MPI_Comm_rank(MPI_COMM_WORLD, &rank);	//Getting my rank

	if( rank == 0 )
	{
		printf("Proc 0: Sleep for 5 sec before send...\n");
		sleep(5);
		printf("Proc 0: Sending message...\n");
		MPI_Send(i, 1, MPI_INT, 2, tag, MPI_COMM_WORLD);
	}
	else if( rank == 1)
	{
		printf("Proc 1: Sleep for 3 sec before send...\n");
		sleep(3);
		printf("Proc 1: Sending message...\n");
		MPI_Send(x, 1, MPI_FLOAT, 2, tag, MPI_COMM_WORLD);
	}
	else //rank == 2
	{
		for (n = 1; n <= 2; n ++)
		{
			printf("Proc 2: Wait for message comes...\n");
			MPI_Probe(MPI_ANY_SOURCE, tag, MPI_COMM_WORLD, &status);
			printf("Proc 2: New message...\n");
			if (status.MPI_SOURCE == 0)
			{
				MPI_Recv(i, 1, MPI_INT, 0, tag, MPI_COMM_WORLD, &status);
			}
			else
			{
				MPI_Recv(x, 1, MPI_FLOAT, 1, tag, MPI_COMM_WORLD, &status);
			}
			printf("Proc 2: Received message from Proc %d successfully!!\n", status.MPI_SOURCE);
		}
	}

	MPI_Finalize();		//Finalize MPI
	return 0;
}