On Jan 9, 2015, at 7:46 AM, Jeff Squyres (jsquyres) <jsquy...@cisco.com> wrote:
> Yes, I know examples 3.8/3.9 are blocking examples. > > But it's morally the same as: > > MPI_WAITALL(send_requests...) > MPI_WAITALL(recv_requests...) > > Strictly speaking, that can deadlock, too. > > It reality, it has far less chance of deadlocking than examples 3.8 and 3.9 > (because you're likely within the general progression engine, and the > implementation will progress both the send and receive requests while in the > first WAITALL). > > But still, it would be valid for an implementation to *only* progress the > send requests -- and NOT the receive requests -- while in the first WAITALL. > Which makes it functionally equivalent to examples 3.8/3.9. That's not true. The implementation is required to make progress on all outstanding requests (assuming they can be progressed). The following should not deadlock: ----✂---- for (...) MPI_Isend(...) for (...) MPI_Irecv(...) MPI_Waitall(send_requests...) MPI_Waitall(recv_requests...) ----✂---- -Dave
