[petsc-dev] circular dependencies SLEPc

[Balay, Satish]

Even if SLEPc were merged to PETSc - we would normally avoid circular
dependencies between components - i.e avoid slepc calls from pc/ksp
[this would break --with-single-library=0 build]

Satish

On Wed, 26 Jun 2019, Fande Kong via petsc-dev wrote:

> It would be great if SLEPc can be merged into PETSc. Just like what we did
> for TAO. Then we do not have all these issues at all.
> 
> Any particular reason we can not merge SLEPc into PETSc?
> 
> Fande,
> 
> On Wed, Jun 26, 2019 at 11:22 AM Jed Brown via petsc-dev <
> petsc-dev at mcs.anl.gov> wrote:
> 
> > Matthew Knepley <knepley at gmail.com> writes:
> >
> > > On Wed, Jun 26, 2019 at 1:05 PM Jed Brown <jed at jedbrown.org> wrote:
> > >
> > >> Matthew Knepley <knepley at gmail.com> writes:
> > >>
> > >> > On Wed, Jun 26, 2019 at 12:45 PM Jed Brown <jed at jedbrown.org> wrote:
> > >> >
> > >> >> Matthew Knepley <knepley at gmail.com> writes:
> > >> >>
> > >> >> >> You can implement and register a PC in SLEPc (it would go in
> > >> >> libslepc.so).
> > >> >> >>
> > >> >> >
> > >> >> > I think this is the bad workflow solution. What Barry suggested
> > will
> > >> work
> > >> >> > and be MUCH easier for a developer. Isn't
> > >> >> > the point of our tools to make our lives easier, not to enforce
> > rules
> > >> >> that
> > >> >> > make them harder?
> > >> >>
> > >> >> Circular dependencies with a special build process is an enormous
> > >> >> development and distribution tax.
> > >> >>
> > >> >
> > >> > The difference in the arguments here is that there are very specific
> > >> > problems with the "right" way,
> > >> > namely that I need to deal with two different repos, two testing
> > systems,
> > >> > release schedules, etc.
> > >> > Whereas the taxes above are currently theoretical.
> > >>
> > >> It isn't remotely theoretical.
> > >>
> > >> You could propose merging SLEPc into the PETSc repository (similar to
> > >> what we did with TAO a while back) if you think "PETSc" code will
> > >> frequently need to depend on SLEPc, but creating a circular dependency
> > >> between separate packages is worse than having code in Vec that depends
> > >> on DM.
> > >>
> > >
> > > I think there will be very frequent dependencies. I would say this is
> > > a very convenient stopgap that is preferable to making anyone work in
> > > both places at once.  That is a very real development nightmare.
> >
> > As a concrete issue unrelated from packaging/distribution (which is very
> > important), what happens when a PETSc interface used by SLEPc changes in
> > a branch?  If the repositories are separate and you have this circular
> > dependency, the PETSc build and tests fail until SLEPc updates to the
> > new interface and that lands in 'master' where PETSc can use it.  But
> > the SLEPc updates can't land until the branch with this new change is
> > merged in PETSc, so you have to do custom testing and synchronize these
> > merges.  Stop-the-world disruption is not okay, full stop.
> >
> > I think it's up to Jose whether closer integration is desirable.
> >
>