[petsc-dev] SNESSetKSP and SNESDestroy

[Stefano Zampini]

I think snes reset should call ksp destroy. I don't see the case for which
this can lead to troubles

Il Gio 30 Mag 2019, 15:43 Matthew Knepley via petsc-dev <
petsc-dev at mcs.anl.gov> ha scritto:

> On Thu, May 30, 2019 at 6:08 AM Pierre Jolivet via petsc-dev <
> petsc-dev at mcs.anl.gov> wrote:
>
>> Hello,
>> I’m doing a continuation loop with something like:
>> KSP ksp;
>> KSPSetUp(ksp);
>> while(cond) {
>>         SNES snes;
>>         SNESCreate(&snes);
>>         SNESSetKSP(snes, &ksp);
>>         SNESSolve(snes);
>>         SNESDestroy(&snes);
>> }
>>
>> For the first iteration, everything is OK.
>> After that, it looks like SNESDestroy is messing up with my outer-defined
>> KSP(*), i.e., for the code to work I need to comment out the SNESDestroy.
>> Is this the expected behavior? (if not, I’ll provide a MWE)
>> How to fix this properly, without having leaks by not destroying the
>> inner-defined SNESes?
>>
>> Thanks in advance,
>> Pierre
>>
>> (*) to the outer-defined KSP is attached a PCFIELDSPLIT, first SNESSolve,
>> everything OK:
>> PC Object: 1 MPI processes
>>   type: fieldsplit
>>     FieldSplit with MULTIPLICATIVE composition: total splits = 2
>>
>> Second SNESSolve:
>> [0]PETSC ERROR: PCFieldSplitSetDefaults() Unhandled case, must have at
>> least two fields, not 1
>
>
> I believe SNESDestroy() calls SNESReset(), which calls KSPReset(), which
> is wiping out your information.
>
> This pattern is in a lot of places. Destroy calls Reset because it is
> natural to reuse the code which tears down
> the internal structures. Reset calls reset on subobjects because we also
> want to tear down their internal structures (usually).
> Reset wouldn't do what we want on resizing if we left subobjects unreset.
> However, this chain is causing subobjects to
> be wiped clean on Destroy, so that we cannot reuse subobjects.
>
> It would not even work if you change the Destroy to Reset in the
> continuation loop. However, I think you can hoist all
> the SNES setup outside the loop. If you are changing sizes, then the KSP
> needs to be wiped out anyway. If not, then
> you do not need to wipe out the SNES.
>
>   Thanks,
>
>      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
>
> https://www.cse.buffalo.edu/~knepley/
> <http://www.cse.buffalo.edu/~knepley/>
>
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