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cmpibroadcast
haggisman18
haggisman18

Reputation: 135

Conditional Broadcasting in MPI

I want to write an MPI Program where each process has a boolean value initiate which is initially set to false. Then, rank 0 checks if the value (i,j) of a large 2D Boolean Array is true and if it is then rank 0 sets its value of initiate to true. If rank 0's value of initiate is true then I would like rank 0 to broadcast the new value of initiate to other processes, indirectly telling each of them to kickstart execution of another method.

How could I go about doing this efficiently? Would appreciate to hear any ideas.

-Thanks

PS. I considered sending the 2d boolean array to every process, but that 2d array can be very big under certain circumstances and I am worried that my code would not scale well.

Upvotes: 1

Views: 247

Answers (1)

Mert Hidayetoğlu
Mert Hidayetoğlu

Reputation: 11

I assume you want to make use of the wait time. Elaborating on Gilles Gouaillardet's comment, you can build an "interrupt" kind of structure.

bool initiate = false;

if (rank == 0)
  for(int k = 0; k < I * J; k++)
    if(!bool_arr[k]) {
      initiate = true;
      break;
    }

MPI_Request request;
MPI_Ibcast(&initiate, 1, MPI_C_BOOL, 0, MPI_COMM_WORLD, &request);

for (int iter = 0; iter < numiter; iter++) {

    ; // DO WHATEVER YOU WANT!

    // TEST IF THE BROADCAST COMPLETE ONCE IN A WHILE
    bool complete;
    MPI_Test(&request, &complete, MPI_STATUS_IGNORE);
    if (complete && initiate) {
      function();
      initiate = false; // Avoid calling function() twice
    }
}
// DO NOT MOVE ON WITHOUT WAITING FOR BROADCAST
MPI_Wait(&request, MPI_STATUS_IGNORE);
if (initiate)
  function();

Upvotes: 1

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