[petsc-dev] Error checking on input only vectors

[Karl Rupp]

Hey,

>     As an extra error checking on user code we could save the Vec state of read only input Vecs and check it on exit of the routine to insure the user has not changed the Vec. This could be done in PCApply_Shell(), functions provided to SNES and TS etc.

we could do that, but I think this would slow the debug build down by 
quite a substantial amount (VecGetArrayRead() is used quite a lot 
internally as well), resulting in users to go with optimized builds 
during the development phase more often. Also, since VecGetArrayRead() 
returns a pointer to const, a user needs to cast away the const in order 
to manipulate entries, which already serves as an indication of doing 
something evil.

What about a second debug level instead, something like 
'PETSC_DEBUG_EXTRA', which enables additional, more expensive checks 
like the one you suggested? We could do similar valgrind-like checks for 
matrices, etc. there.

Best regards,
Karli


>
> On Jul 16, 2013, at 8:08 AM, Rémi Lacroix <remi.lacroix at inria.fr> wrote:
>
>> Hello,
>>
>> I'm currently developing a preconditioner using PETSc. I have a small question about the PCApply function.
>>
>> Is it safe to destroy the content of the input vector x while applying the preconditioner or should I make a copy of it and work on that?
>>
>> Best regards,
>>
>> --
>> Rémi Lacroix
>> Équipe ALPINES
>> Inria Paris-Rocquencourt / Laboratoire Jacques Louis Lions, UPMC
>>
>