CODEWITHSUNDEEP
c++mpiopenmpi
Armin
Armin

Reputation: 134

How can I call a (c++)function just for a subset of processes using MPI library?

The question says it all. I have three communicators(Groups are also available). Now I want to call the a function just for one communication subset. That is mask the function for other subsets. Is this possible or should I explicitly right a loop and check for the existence of the current process in the group and then call the function.

Thanks,

Upvotes: 0

Views: 184

Answers (2)

Michael Schlottke-Lakemper
Michael Schlottke-Lakemper

Reputation: 9311

Are you able to modify the code where the three communicators are created? In that case I recommend you add a variable (i.e. my_group as Hristo suggested) that saves the group rank for the rest of the program's runtime. So whenever you need to call a group (or communicator)-specific function, you just check group_rank.

Rationale
Most MPI programs tend to have some sort of global my_rank variable anyways (which stores the process's rank), so adding a my_group would be in line with this programming strategy.

Upvotes: 1

Hristo Iliev
Hristo Iliev

Reputation: 74355

There is no way to call a function over all members of a subcommunicator apart from abusing user-defined reduction operators in MPI_Allreduce(). The cleanest thing to do is:

int group_rank;
// Test if current process belongs to "group"
MPI_Group_rank(group, &group_rank);
if (group_rank != MPI_UNDEFINED)
   call_the_function();

Upvotes: 1

Related Questions