[Mpi-forum] Request introspection

[Fab Tillier]

Jeff Squyres wrote on Mon, 1 Aug 2011 at 16:50:30

> MPI now has 3 different types of requests that I can think of, with pending
> proposals for (at least) 2 more:
> 
> - point-to-point
> - collective
> - generalized
> - timers (proposed)
> - file (proposed)
> 
> Would it be worthwhile to have a simple introspection routine that can
> return an enum telling you the type of a request handle?  E.g.,
> MPI_REQUEST_GET_TYPE that has an OUT parameter that will be set to
> MPI_REQUEST_PT2PT, MPI_REQUEST_COLLECTIVE,
> MPI_REQUEST_GENERALIZED, etc.
> 
> I can generally see how this might be useful to applications, but I can't think
> of a "must have" kind of use case.

The only place I can see this being useful is for logging type of stuff, by an intermediate entity that did not create the request.  Otherwise, the entity that created the request implicitly knows what type it is, and shouldn't ever need to query the type.

Having an introspection routine like you propose would add extra burden on implementations that use, for example, generalized requests for non-blocking I/O.  I could also see timer requests implemented using generalized requests.

> Does anyone else think that this would be valuable / useful?

Without a lot of thought (I'm on vacation after all), I don't.

Cheers,
-Fab