[mpich-discuss] Non-blocking collectives

[Jed Brown]

Rajeev Thakur <thakur at mcs.anl.gov> writes:

> It doesn't have to be a matching Wait. The implementation is required
> to make progress on other pending communication while it is blocked in
> a Wait.

Or blocked in any of a number of other places, if non-blocking
collective requests have the same completion semantics as point-to-point
requests.  E.g., this shouldn't deadlock:

  MPI_Iallreduce(...,COMM_WORLD,&req);
  if (!rank) MPI_Wait(&req);
  MPI_Allgather(...,COMM_WORLD);
  if (rank) MPI_Wait(&req);
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