Re: caching on MPI handles

Eric Salo (salo@mrjones.engr.sgi.com)
Sat, 19 Oct 1996 16:43:39 -0700

> The "etype" and "filetype" are used to specify the logical view of the
> file and are provided in the MPI_Set_view call (pg. 240).
> The user need not provide them again anytime in the program.
> If the user wants to be naughty, he could free etype and
> filetype while the file is still open. But for every I/O operation on
> the file, I need to know what is the current etype and filetype. In
> addition, there is a function MPI_Get_view (pg 242) which is supposed
> to return the current etype and filetype.

Ah. So the issue is really that we would like MPI-2 to be able to support
*layered* implementations of the I/O chapter. Otherwise, MPI could simply bump
the reference counts for the datatypes directly.

It looks like what we need is a routine which does exactly that, then:

MPI_TYPE_DUP(&oldtype, &newtype)

Seems to me that in order for this to be useful, newtype must be set to the
same handle as oldtype. This is different from the semantics of MPI_COMM_DUP,
which returns a new handle, so maybe we want to choose a different name?

-- 
Eric Salo         Silicon Graphics Inc.             "Do you know what the
(415)933-2998     2011 N. Shoreline Blvd, 8U-802     last Xon said, just
salo@sgi.com      Mountain View, CA   94043-1389     before he died?"