[email protected] writes:

I apologize for creating a new thread, I have accidentally deleted the original message.

Not to split hairs, can you please clarify the following:

After doing a non-blocking collective:

The MPI_Wait would be satisfied as soon as the other ranks in the communicator have called the non-blocking collective (and may not yet have called MPI_Wait), right?

Yes.

Or do they wait until all of them have called MPI_Wait?

No, that would make the MPI_Wait synchronizing, mostly defeating any potential benefit of non-blocking collectives. Note that the non-blocking request can complete in other ways, e.g., via MPI_Test.

On the contrary, if one of the ranks calls MPI_Wait (without calling the non-blocking collective, which is an incorrect program), will the MPI_Wait be satisfied?

This doesn't even make sense. Where would you be getting an MPI_Request on which to call MPI_Wait?