// Author: Wes Kendall
// Copyright 2011 www.mpitutorial.com
// This code is provided freely with the tutorials on mpitutorial.com. Feel
// free to modify it for your own use. Any distribution of the code must
// either provide a link to www.mpitutorial.com or keep this header intact.
//
// Example of using MPI_Probe to dynamically allocated received messages
//
#include <mpi.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

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

 	int world_size;
 	MPI_Comm_size (MPI_COMM_WORLD, &world_size);
	if (world_size != 2)
	{
		fprintf (stderr, "Must use two processes for this example\n");
		MPI_Abort (MPI_COMM_WORLD, 1);
	}
 	int world_rank;
 	MPI_Comm_rank (MPI_COMM_WORLD, &world_rank);

 	int number_amount;
 	if (world_rank == 0)
    {
    	const int MAX_NUMBERS = 100;
    	int numbers[MAX_NUMBERS];
    	// Pick a random amont of integers to send to process one
    	srand (time (NULL));
    	number_amount = (rand () / (float) RAND_MAX) * MAX_NUMBERS;
		// Send the amount of integers to process one
		MPI_Send (numbers, number_amount, MPI_INT, 1, 0, MPI_COMM_WORLD);
		printf ("0 sent %d numbers to 1\n", number_amount);
	}
	else if (world_rank == 1)
	{
		MPI_Status status;
		// Probe for an incoming message from process zero
		MPI_Probe (0, 0, MPI_COMM_WORLD, &status);
		// When probe returns, the status object has the size and other
		// attributes of the incoming message. Get the size of the message.
		MPI_Get_count (&status, MPI_INT, &number_amount);
		// Allocate a buffer just big enough to hold the incoming numbers
		int *number_buf = (int *) malloc (sizeof (int) * number_amount);
		// Now receive the message with the allocated buffer
		MPI_Recv (number_buf, number_amount, MPI_INT, 0, 0, MPI_COMM_WORLD,
		MPI_STATUS_IGNORE);
		printf ("1 dynamically received %d numbers from 0.\n", number_amount);
		free (number_buf);
	}
	MPI_Finalize ();
}