Newsgroups: comp.parallel.mpi
From: maniattb@cs.rpi.edu (Bill Maniatty)
Subject: Parameters of MPI_Pack/MPI_Unpack
Organization: Rensselaer Computer Science Dept.
Date: 15 Dec 1995 21:01:25 GMT
Message-ID: <4asnn5$3f3@usenet.rpi.edu>

Hi Everyone:

Sorry if this is a stupid question, but I didn't see an answer in the FAQ.
It is my impression that MPI_Pack/MPI_Unpack do a data type conversion
on the input buffer, initializing the data structure specified by the
output buffer, but does no communication or I/O.  This being the case
why do these calls have the communication handles in them.
For example our MPI library uses the following calling convention:

int MPI_Pack(void* inbuf, int incount, MPI_Datatype datatype, void *outbuf,
             int outsize, int *position,  MPI_Comm comm);
int MPI_Unpack(void* inbuf, int insize, int *position, void *outbuf,
               int outcount, MPI_Datatype datatype, MPI_Comm comm);

I'm just curious why the last parameter in both calls (comm) is present.
On first inspection it seems that the underlying implementation would
never require access to that additional information, is there something
that I'm missing?

Thanks:

Bill


-- 
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|	maniattb@cs.rpi.edu - in real life Bill Maniatty
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