On Feb 15, 2011, at 8:03 PM, Matthew Knepley wrote: > On Tue, Feb 15, 2011 at 7:58 PM, Barry Smith <bsmith at mcs.anl.gov> wrote: > > 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. > > I agree, but the immediate type test at the start of MatMult() has caught > most things for me. I do not consider > double-free a recoverable error, so a SEGV is alright here as well.
If I am sitting in front of a Matlab or Python scripting session I would much prefer an error that returns to my Matlab or Python prompt so I can keep on doing stuff versus a crash that requires restarting Matlab or Python. Barry > > Matt > > > 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 > > > > > -- > 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
