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

Lisandro Dalcin dalcinl at gmail.com
Tue Feb 15 19:19:01 CST 2011

On 15 February 2011 19:47, Barry Smith <bsmith at mcs.anl.gov> 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?

This is what I needed in petsc4py, so I had to write my own wrapper
routines: http://code.google.com/p/petsc4py/source/browse/src/PETSc/petscobj.pxi#35

>   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);

I think (2) is the more compelling use case...

Lisandro Dalcin
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