[petsc-dev] multiple dispatch code currently in PETSc

[Jed Brown]

On Tue, Jan 15, 2013 at 1:50 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>   Do we really want mallocs for EVERY single multiple-dispatch function
> call in PETSc? I suggest not having MatQueryOp() but calling directly
> PetscOpFListFind() (with the MatOpFList argument) and changing
> PetscOpFListAdd/Find() to use variable args directly.
>
>    Finally do we really want string comparisons at all here? Or do we want
> XXXRegister() (for example, MatRegister()) to compute an integer type id to
> go with each char *type_name and do the search off the integer type id
> instead of strings? Thus making PetscOpFListFind() super light weight?
>

static struct {
  PetscMultiDispatch ptap;
  ...
} MatMultiDispatch;

I would have
PetscMultiDispatchRegister("MatPtAP",2,&MatMultiDispatch.ptap), then

PetscMultiDispatchFind(MatMultiDispatch.ptap,(PetscObject)A,(PetscObject)P,&ptapfunc);

I think passing PetscObject is natural here, in which case using
obj->type_id instead of obj->type_name can be done later. But on that
front, yes, I think making integers for all registered type_names would be
good. Among other things, it would make the PetscObjectTypeCompares fast,
although I think those places should eventually be refactored.


>
>    Barry
>
>
> PetscErrorCode  MatQueryOp(MPI_Comm comm, PetscVoidFunction* function,
> const char op[], PetscInt numArgs, ...)
> {
>   PetscErrorCode ierr;
>   va_list        ap;
>   PetscInt       i;
>   const char     *argType;
>   char           **argTypes = PETSC_NULL;
>
>   PetscFunctionBegin;
>   va_start(ap,numArgs);
>   if (numArgs) {
>     ierr = PetscMalloc(sizeof(char*)*numArgs, &argTypes);CHKERRQ(ierr);
>   }
>   for (i = 0; i < numArgs; ++i) {
>     argType = va_arg(ap,const char*);
>     ierr = PetscStrallocpy(argType, argTypes+i);CHKERRQ(ierr);
>   }
>   va_end(ap);
>   ierr = PetscOpFListFind(comm, MatOpList, function, op, numArgs,
> argTypes);CHKERRQ(ierr);
>   for (i = 0; i < numArgs; ++i) {
>     ierr = PetscFree(argTypes[i]);CHKERRQ(ierr);
>   }
>   ierr = PetscFree(argTypes);CHKERRQ(ierr);
>   PetscFunctionReturn(0);
> }
>
>
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