Question

I want to use MPI (MPICH2) on windows. I write this command:

MPI_Barrier(MPI_COMM_WORLD);  

And I expect it blocks all Processors until all group members have called it. But it is not happen. I add a schematic of my code:

int a;  
if(myrank == RootProc)  
   a = 4;  
MPI_Barrier(MPI_COMM_WORLD);  
cout << "My Rank = " << myrank << "\ta = " << a << endl;  

(With 2 processor:) Root processor (0) acts correctly, but processor with rank 1 doesn’t know the a variable, so it display -858993460 instead of 4.

Can any one help me?
Regards

Answer 1

You’re only assigning a in process 0. MPI doesn’t share memory, so if you want the a in process 1 to get the value of 4, you need to call MPI_Send from process 0 and MPI_Recv from process 1.