[mpi3-coll] Nonblocking collectives standard draft

[Torsten Hoefler]

On Mon, Dec 01, 2008 at 07:36:10PM -0600, Rajeev Thakur wrote:
> > However, if we do need to provide the above semantics for 
> > MPI_Cancel, we will have to deal with a funny non-locality of 
> > behavior. Suppose we have an MPI_Ibcast and one of the 
> > receivers calls MPI_Cancel. What happens to the other 
> > participants? Do they all have to call MPI_Cancel to not 
> > participate or is any one calling it sufficient? 
> > What about things like MPI_Gather and MPI_AlltoAll? We 
> > certainly don't want to force non-all-to-all operations to 
> > have to do an all-reduce at the end to check for cancellation.
> 
> Yup, those are the issues that come up. One could say that MPI_Cancel is not
> allowed for nonblocking collectives.
That has already been said for exactly such reasons :). I guess Greg
missed some of our discussions about this. The quintessence was that we
should not allow MPI_Cancel for collective requests. This is also
documented in the current standard proposal.

Best,
  Torsten

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Torsten Hoefler       | Postdoctoral Researcher
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