[petsc-dev] multiple dispatch code currently in PETSc

[Dmitry Karpeev]

On Tue, Jan 15, 2013 at 2:14 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> 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.
>
Some of the arguments aren't PetscObjects (e.g., PODs).
Each dispatcher (e.g., MatMultMult) can have static integer typeids for all
of its arguments that are registered
or retrieved only on the first invocation and reused from then on.

Dmitry.

>
>
>>
>>    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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