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Subject: Re: [OMPI devel] failurewithzero-lengthReduce()andbothsbuf=rbuf=NULL
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2010-02-11 09:29:03

On Feb 11, 2010, at 7:10 AM, Jeff Squyres (jsquyres) wrote:

> I misparsed your reply. Yes, bcast(1) *can* sync if it wants to. I don't have a spec handy to check if bcast(0) is defined or not (similar to reduce). If it is, then sure, it could sync as well.

FWIW, in looking through MPI-2.2, I don't see any language in the description of MPI_BCAST that prevents 0-byte broadcasts. Indeed, for the "count" parameter description, it distinctly says "non-negative integer", which, of course, includes 0. I'm not sure why a zero-count broadcast is useful, but there it is. :-)

That being said, it says "non-negative integer" for the count argument of MPI_REDUCE, too. Hmm. But I don't see getting around REDUCE's qualifying statement later in the text about how each process provides one or a sequence of elements.

Lisandro -- if you feel strongly about this, you might want to bring it up in the context of the Forum and ask about it. I've provided my personal interpretations, but others certainly may disagree.

Jeff Squyres
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