This post talks about a MPI Broadcast function – MPI_Bcast. Broadcast operation is used to send data from one process to all other processes within a communicator. Every process receives the same data.
Syntax for MPI_Bcast
int MPI_Bcast(void *buffer, int count, MPI_Datatype datatype, int root, MPI_Comm comm)
Input Parameters
- count : number of elements/values to be Broadcasted (for example : 0)
- datatype : data type of elements/values to be sent (for example : 10)
- root : rank of root process (for example : 0)
- comm : communicator (for example : MPI_COMM_WORLD)
Input/Output Parameters
- buffer : Pointer to the data/array to be sent/received (for example : int *myarr)
Example code –
#include"stdio.h"
#include"mpi.h"
int main(int argc, char **argv)
{
int myid, size;
int data;
//Initialize MPI environment
MPI_Init(&argc,&argv);
//Get total number of processes
MPI_Comm_size(MPI_COMM_WORLD, &size);
//Get my unique identification among all processes
MPI_Comm_rank(MPI_COMM_WORLD, &myid);
//Initialize data to some value
data = 20;
//If root
if(myid==0)
{
data = 10;
}
//Bradcast the data
MPI_Bcast(&data, 1, MPI_INT, 0, MPI_COMM_WORLD);
//Every process prints the value of data
printf("myid:%d \t data = %d\n",myid, data);
//End MPI environment
MPI_Finalize();
}
To compile this code, use following command –
mpicc mpi_broadcast.c
To execute this code, run following command –
mpiexec -n 4 ./a.out
Output of this code will be something similar to the following –
myid:0 data = 10
myid:1 data = 10
myid:2 data = 10
myid:3 data = 10To know more about MPI, visit our dedicated page for MPI here.
If you are new to Parallel Programming / HPC, visit our dedicated page for beginners.