[Mpi3-tools] reviewing the document

[Dave Goodell]

On Jan 26, 2011, at 8:09 AM CST, Jeff Squyres wrote:

> On Jan 25, 2011, at 6:58 PM, Dave Goodell wrote:
> 
>>> I'm wondering if there are really two options here:
>>> 
>>> 1. Have a real casting operating (somewhat akin to Martin's initial proposal): have a casting function that returns the OUT value (vs. an int error code).  Then you can nest the output of the casting function as an argument to MPI_Perfvar_handle_allocate(), for example.
>>> 
>>> 2. Have 9 different versions of MPI_Perfvar_handle_allocate() and MPI_Controlvar_handle_allocate() -- one for each MPI handle type.
>>> 
>>> I assume most people will recoil from #2.  But... hmm.  It *is* the safest way to go.  But ugly (because it's lots of functions).  Hmm...
>> 
>> #1 is cute, but it doesn't match MPI error handling conventions, and I'd rather not begin passing the error code back as an OUT arg for just this small set of conversion routines.
> 
> MPI_Wtick, MPI_Wtime, and the f2c / c2f routines return their OUT values.  Indeed, the f2c / c2f routines could be considered "casting-like" operators.

That's a good point, I always forget about f2c/c2f routines because they are just little integer type casting macros in MPICH2.  Maybe it's not quite the departure from convention that I claimed.

Actually, I think I'm in favor of #1 if the implementation is allowed to implement them as macros.  They'll be no-ops for us, but you can have full functions if you like to add some type checking from the compiler.  But if you want to allocate/deallocate memory in the conversion routines in order to create a new generic handle then this system won't work.  Is that what you want?  Or is a "user comment" cast of the pointer value all that you need?

-Dave