[petsc-dev] XXXDestroy() mistaken design in PETSc

[Barry Smith]

On Feb 19, 2011, at 10:17 PM, Matthew Knepley wrote:

> On Sat, Feb 19, 2011 at 10:08 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> 
>  What about
> 
> extern PetscErrorCode  VecDestroy_(Vec);
> #define VecDestroy(a)  (VecDestroy_(a) || (((a) = 0),0))
> 
>  Not exactly PETSc style, but allows the switch without changing the API.
> 
> Why not let VecDestroy_() take the pointer?

  Could do that. I think it is equivalent.
> 
> Also, what about having a configure mode that goes back to the old interface (on by default),
> but allow the new one to be configured. Might involve putting in #define stuff, or changing
> files a little, but it seems cleaner.

 Won't that configure code also have to change all the calls to Destroy() to pass in the &? 

  My goal was to not change the API (since you feared the universal breakage) hence not add the * to the API. And I hate to have two valid ways of doing the same thing VecFree(Vec*) (for new users) and VecDestroy(Vec) for old users.

  Barry

> 
>    Matt
>  
> 
>   Barry
> 
> On Feb 15, 2011, at 4:47 PM, Barry Smith wrote:
> 
> >
> >  In MPI one calls MPI_Comm_free(&comm) to allow the MPI implementation to set the pointer explicitly to 0 after the object is destroyed.
> >
> >  In Petsc XXXDestroy() does not pass the pointer (because it seemed too unnatural to me in 1994) thus not allowing 0ing the pointer.
> >
> >   Was this a bad design decision? Should it be revisited?
> >
> >   Barry
> >
> >  Two use cases
> >
> > 1) error detection when someone tries to reuse a freed object
> >
> > 2) when removing some objects from a data structure that will be used data one currently needs to do
> >
> >  XXXXDestroy(mystruct->something);CHKERRQ(ierr); mystruct->something = 0;
> >
> > instead of the cleaner XXXDestroy(&mystruct->something);CHKERRQ(ierr);
> 
> 
> 
> 
> -- 
> What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.
> -- Norbert Wiener