Hi,
your program hangs because rank 0 does not call MPI_Bcast()
generally speaking, when using collective operations (such as MPI_Bcast),
all tasks of the communicators must invoke the collective operation, and
with "matching" arguments.
in the case of MPI_Bcast(), the root value must be the same on all tasks,
and all tasks must transfer
the same amount of data :
if all tasks use the same datatype, then the count must be the same on
all tasks,
otherwise, the datatype size * count must be the same on all tasks
/* for the sake of completion, there are known issues specific to Open
MPI when you mix
large and small datatypes */
Cheers,
Gilles
----- Original Message -----
> Greetings!
>
> I include a static header file utils.h with a function linspace. My
main.cpp file is as follows:
>
> #include <iostream>
> #include <utils.h>
> #include <mpi.h>
>
> using namespace std;
>
> int main(int argc, const char * argv[]) {
>
> float start = 0., end = 1.;
> unsigned long int num = 100;
>
> double *linspaced;
>
> float delta = (end - start) / num;
> int size, rank;
>
>
> MPI_Init(NULL, NULL);
>
> MPI_Comm_size(MPI_COMM_WORLD, &size);
> MPI_Comm_rank(MPI_COMM_WORLD, &rank);
> MPI_Status status;
>
> // These have to be converted into unsigned long ints
> int casesPerNode = num / size;
> int remainderCases = num % size;
>
>
> if(rank==0){
> linspaced = new double[num];
>
> if(remainderCases!=0){
> linspace(&linspaced[(size-1)*casesPerNode], end - delta*
remainderCases, end, remainderCases);
>
> } else {
> linspace(&linspaced[(size-1)*casesPerNode], end - delta*
casesPerNode, end, casesPerNode);
>
> }
>
> } else {
>
> MPI_Bcast(&linspaced, num, MPI_DOUBLE, 0, MPI_COMM_WORLD);
>
>
> // Sending job to master node.
> // The node is already overloaded with coordinating.
> // Additional task now is also to take on remainder cases.
>
>
> // cout << "Rank " << rank << endl;
> float start_in = start + casesPerNode*delta*(rank-1);
> float end_in = start + casesPerNode*delta*(rank) - delta;
>
> linspace(&linspaced[(rank-1)*casesPerNode], start_in, end_in,
casesPerNode);
>
>
> }
>
> MPI_Barrier(MPI_COMM_WORLD);
> // cout << "Print Here Rank " << rank << endl ;
>
>
> MPI_Finalize();
>
> /*
> for(int i=0; i< num; i++){
> cout << *(linspaced + i) << endl;
> }
> */
>
> return 0;
>
> }
> and my utils.h file is:
>
> void linspace(double *ret, double start_in, double end_in, unsigned
long int num_in)
> {
> /* This function generates equally spaced elements and returns
> an array with the results */
>
>
> assert(num_in!=0);
>
>
> cout << "\tReceived start :" << start_in << "\tEnd :" << end_in <
< "\tNum_in :" << num_in << endl;
>
> double delta_in = (end_in - start_in) / (num_in - 1);
>
> if(num_in == 1){
> *(ret) = start_in;
> }
>
> *(ret) = start_in;
> for(int i=1; i < num_in-1; i++) {
> *(ret + i) = *(ret + i - 1) + delta_in;
> }
> *(ret + (num_in - 1)) = end_in;
>
> /*
> cout << "Finished executing linspace " << endl;
> for(int i = 0; i<num_in; i++){
> cout << "Address : " << &ret << "\tElement " << i << " : " << *(
ret + i) << endl;
> }
> */
> }
> I am unable to diagnose why my code gets stuck at MPI_Bcast. What
could I do to fix it?
>
> Thanks
>
>
> PS: I’m new to OpenMPI and may have a lot of these doubts initially.
Thanks for patience and support.
> _______________________________________________
> users mailing list
> users@lists.open-mpi.org
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