[mpas-developers] Restructuring high-level MPAS driver

[Jones, Philip W]

Michael,

The use...only approach is ok and I think CAM/CCSM uses this a lot, but in my experience it often results in cluttered code and can confuse automated dependency generators.

In POP, we always used the private statement at the top of every module to enforce encapsulation and that worked pretty well.  That also helped in making, say, generic routine interfaces public, while the specific instantiations remained private.  And we had to add the POP_ prefix when CCSM went from a multiple executable model to a subroutinized coupler, so I've been through that before.

I guess I'm not a huge fan of the renaming/aliasing on the use...only line, again because it often causes confusion when you're trying to track something down.

However, I'm not a hard-core advocate of any particular approach and there are always exceptions to every rule.  If we can come up with good design practices or guidelines for these issues, I think we're fine.  Just pointing out that we will encounter some of these in the not-so-distant future and it might be good to come up with some of these guidelines now so that we can implement as we go rather than coming into a coupler and having to rewrite it all in a painful, tedious transition later.

Phil

On 10/29/10 12:08 PM, "Michael Duda" <duda at ucar.edu> wrote:

On the issue of naming conflicts, I can certainly see the
advantage of longer routine names. Another way we might consider
to address this issue, too, would be to make use of the 'only'
clause in Fortran use statements to limit the symbols imported by
a module to just what is needed; in cases of unavoidable conflict,
there is always the option to do something like

   use subdriver, only : mpas_model_init => init, mpas_model_run => run

Another language feature that I've not used much to date, but that
I've noticed others have begun using, is the 'private' clause;
this seems like good practice to me, too.

Cheers,
Michael


On Fri, Oct 29, 2010 at 11:40:55AM -0600, Jones, Philip W wrote:
>
> Folks,
>
> A couple of quick comments.
>
> The structure:
>    call init()
>     call run()
>     call finalize()
>
> Is certainly consistent with all other component and coupling frameworks, so should ease compatibility.  At some point, you'll probably need to specify arguments for input state, output state, some sort of time interval (for the run method) and returned error codes.
>
> Another comment, that I think I've brought up previously, is that the generic names init, run, finalize (and probably others throughout mpas) are at risk for creating namespace conflicts in other components.  It'll be safer in the long run if mpas modules, public variables and public routine names add an mpas_ prefix or other string to reduce the possibility of conflict.  Similarly, there will be cases even within the framework where we will need to distinguish between component models, like MPAS_OcnInit  and MPAS_AtmInit, or something similar.
>
> Finally, now that I've recommended making all the names longer with prefixes, I have run into compilers already (Absoft) that are having trouble with some of the long routine names (esp. Xylar's ;^) ).  We will probably need to deal with this at some point for portability.
>
> Phil, engaging in drive-by software engineering...
>
>
> ---
> Correspondence/TSPA/DUSA EARTH
> ------------------------------------------------------------
> Philip Jones                                pwjones at lanl.gov
> Climate, Ocean and Sea Ice Modeling
> Los Alamos National Laboratory
> T-3 MS B216                                 Ph: 505-500-2699
> PO Box 1663                                Fax: 505-665-5926
> Los Alamos, NM 87545-1663
>
>
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Thanks,

Phil

---
Correspondence/TSPA/DUSA EARTH
------------------------------------------------------------
Philip Jones                                pwjones at lanl.gov
Climate, Ocean and Sea Ice Modeling
Los Alamos National Laboratory
T-3 MS B216                                 Ph: 505-500-2699
PO Box 1663                                Fax: 505-665-5926
Los Alamos, NM 87545-1663