On Feb 15, 2011, at 5:26 PM, Matthew Knepley wrote: > On Tue, Feb 15, 2011 at 4:47 PM, 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? > > Barry > > Two use cases > > 1) error detection when someone tries to reuse a freed object > > We catch this with other error detection. I do not think we would gain much > here.
No really. If I do MatDestroy(mat); MatMult(mat,x,y); then it is possible that MatMutl() will crash while looking around inside where mat points. If MatDestroy(&mat); zeroed mat then MatMult(mat,x,y) could do the safe test of if (!mat) nice error message. Barry > > 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); > > True, but again I do not think the win is large. > > Matt > > -- > 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
