The worker begins by receiving the broadcast from the master:
MPI_Bcast(b, COLS, MPI_INT, host_rank, MPI_COMM_WORLD);Then all workers receive their first batch to work on:
MPI_Recv(int_buffer, COLS, MPI_INT, host_rank, MPI_ANY_TAG,
MPI_COMM_WORLD, &status);
At this stage every worker enters a loop at the top of
which it checks if the tag of the received message is
equal to ROWS. If it is, the worker exits.
If the tag of the message is different from ROWS,
the worker performs the computation:
sum = 0; for (i = 0; i < COLS; i++) sum = sum + int_buffer[i] * b[i];and sends the answer back to the master using the row number as the tag:
int_buffer[0] = sum; MPI_Send (int_buffer, 1, MPI_INT, host_rank, row, MPI_COMM_WORLD);At this stage every worker knows that it should receive either the next job or the termination tag from the master:
MPI_Recv (int_buffer, COLS, MPI_INT, host_rank, MPI_ANY_TAG,
MPI_COMM_WORLD, &status);
When this message is received, the worker goes back to the top
of the loop, where the tag is inspected.