Newsgroups: comp.parallel.mpi
From: Michael Pernice <usimap>
Subject: MPI_PROC_NULL and invalid message tags
Organization: University of Utah Computer Center
Date: 2 Mar 1996 21:06:12 GMT
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Message-ID: <4had84$ha@news.cc.utah.edu>

MPI specifies that valid message tags must be in the range 0 through
MP_TAG_UB.  MPI also provides a predefined constant MPI_PROC_NULL to
identify the "null" process.  The standard says "A communication with
process MPI_PROC_NULL has no effect.  A send to MPI_PROC_NULL succeeds
and returns as soon as possible."  So, I would expect a send to
MPI_PROC_NULL with an invalid message tag to follow this behavior.  I
haven't found anything in the standard to expect otherwise.  However a
send to MPI_PROC_NULL with an invalid message tag on an IBM SP2 using
the MPI-F message-passing library fails with an "invalid message tag"
error message.

My question to the group is:  is the standard ambiguous on this point,
or is the behavior of MPI-F incorrect?

-- 
_______________________________________________________________________________

Michael Pernice                                  Utah Supercomputing Institute 
Phone:  (801) 581-7708                           85 Student Services Building  
Fax:  (801) 585-5366                             University of Utah
Internet:  usimap@sneffels.usi.utah.edu          Salt Lake City, Utah 84112
_______________________________________________________________________________


