Question
It's too clear just run the program and answer these question Why does half the processes send before receiving and vice versa? What would happen
It's too clear just run the program and answer these question Why does half the processes send before receiving and vice versa? What would happen if all send before receiving?
------------------------------------------------------------------------------------------------------------------------ #include "mpi.h" #include #include #define MASTER 0
int main (int argc, char *argv[]) { int numtasks, taskid, len, partner, message; char hostname[MPI_MAX_PROCESSOR_NAME]; MPI_Status status;
MPI_Init(&argc, &argv); MPI_Comm_rank(MPI_COMM_WORLD, &taskid); MPI_Comm_size(MPI_COMM_WORLD, &numtasks);
/* need an even number of tasks */ if (numtasks % 2 != 0) { if (taskid == MASTER) printf("Quitting. Need an even number of tasks: numtasks=%d ", numtasks); } else { if (taskid == MASTER) printf("MASTER: Number of MPI tasks is: %d ",numtasks);
MPI_Get_processor_name(hostname, &len); printf ("Hello from task %d on %s! ", taskid, hostname);
/* determine partner and then send/receive with partner */ if (taskid < numtasks/2) { partner = numtasks/2 + taskid; MPI_Send(&taskid, 1, MPI_INT, partner, 1, MPI_COMM_WORLD); MPI_Recv(&message, 1, MPI_INT, partner, 1, MPI_COMM_WORLD, &status); } else if (taskid >= numtasks/2) { partner = taskid - numtasks/2; MPI_Recv(&message, 1, MPI_INT, partner, 1, MPI_COMM_WORLD, &status); MPI_Send(&taskid, 1, MPI_INT, partner, 1, MPI_COMM_WORLD); }
/* print partner info and exit*/ printf("Task %d is partner with %d ",taskid,message); }
MPI_Finalize(); }
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