[petsc-dev] DMGetNamedGlobalVector() implementation?

[Barry Smith]

On Jul 19, 2012, at 1:25 PM, Jed Brown wrote:

> On Thu, Jul 19, 2012 at 1:19 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>   Why not implement it using PetscObjectQuery()/PetscObjectCompose()? and not have to introduce a whole new datatype DMNamedVecLink linked list and other crap?
> 
> The only reason this thing has to exist, and it really has to exist in some form, is that we have a reference loop. For example, the SNES Vec X is obtained from the DM (thus X references the DM), but must be made available to the KSP callback that uses the DM. If we attached X to the DM, then we would have a loop X -> DM -> X. Same for the TS vector needed in SNESComputeFunction.
> 
> The general form of PetscObjectCompose allowing reference loops is terribly dangerous and imprecise (you end up implementing a sort of limited garbage collector that periodically looks for loops, but that is super dangerous in parallel because you need determinism in destruction).

   Is there a way to fix the reference loop problem in PetscObjectCompose()? (Since you have a magic fix for DMGetNamedGlobalVector() can we use that everywhere)

   You have to admit that introducing in a bunch of places separate constructs for containment rather than using a single universal construct is not good software development.

    Barry