[mpiwg-p2p] Get/Set Info Update

[Jim Dinan]

Hi All,

I made a first attempt at updating the get/set info text with the feedback
from the December meeting.  For starters, I'm working with just the
communicator get/set info text, so please ignore RMA and I/O for now.  For
the previous draft of the proposal, please refer to the PDF posted under
"references" on the issue page (
https://github.com/mpi-forum/mpi-issues/issues/63) or the existing PR.

I pushed the changes to a work-in-progress branch, in case anyone would
like to see the history (
https://github.com/mpiwg-p2p/mpi-standard/tree/wip/get-info).  You can also
compare with the main spec:
https://github.com/mpi-forum/mpi-standard/compare/mpi-3.x...mpiwg-p2p:wip/get-info?expand=1

Here's the to-do list I captured from the last meeting:

 1. Remove info key deletion by omission in calls to set_info (breaks
existing semantic)
 2. Allow get_info to return keys not set by the user (e.g. "filename" info
key)
 3. Should get_info return all info keys supported by the implementation?

I took a whack at #1 and #2.  I'm still thinking about how to handle info
keys that don't have good defaults (e.g. "filename") and whether #3 is a
good idea.  Anyway, without further ado, here is the updated text:

MPI_COMM_SET_INFO:

\mpifunc{MPI\_COMM\_SET\_INFO} updates the hints of the
communicator associated with
\mpiarg{comm} using the hints provided in \mpiarg{info}.

\mpifunc{MPI\_COMM\_SET\_INFO} is a collective

routine. The info object may be different on each process, but any

info entries that an implementation requires to be the same on all

processes must appear with the same value in each process's info
object.

\begin{users}
Some info items that an implementation can use when it creates a

communicator cannot easily be changed once the communicator has been
created. Thus, an implementation may ignore hints issued in this call
that it would have accepted in a creation call.

%
An implementation may also be unable to update certain info hints once set.

%
\mpifunc{MPI\_COMM\_GET\_INFO} can be used to determine whether updates
to existing info hints were ignored by the implementation.

\end{users}

MPI_COMM_GET_INFO:

\mpifunc{MPI\_COMM\_GET\_INFO} returns a new info object containing
the hints of the communicator associated with \mpiarg{comm}.
%
The current setting of all hints related to this communicator is returned in
\mpiarg{info\_used}, including any user-supplied hints that were not ignored
by the \MPI/ implementation.
%
If no such hints
exist, a handle to a newly created info object is returned that
contains no key/value pair. The user is responsible for freeing
\mpiarg{info\_used} via \mpifunc{MPI\_INFO\_FREE}.

\begin{users}
The info object returned in \mpiarg{info\_used} will contain all hints
currently active for this communicator. This set of hints may differ
from the set of hints specified during communicator creation or in a call
to \mpifunc{MPI\_COMM\_SET\_INFO}, as some hints and info updates specified
by the user may be ignored by \MPI/ implementation.  Additional info hints
that are set by \MPI/ implementation may also be present.
\end{users}

Please send feedback!
 ~Jim.
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