[petsc-dev] CMake: make, install, find_package ?

[Matthew Knepley]

On Mon, Nov 6, 2017 at 12:49 PM, Franck Houssen <franck.houssen at inria.fr>
wrote:

> ----- Mail original -----
> > De: "Satish Balay" <balay at mcs.anl.gov>
> > À: "Franck Houssen" <franck.houssen at inria.fr>
> > Cc: "petsc-dev" <petsc-dev at mcs.anl.gov>
> > Envoyé: Lundi 6 Novembre 2017 16:08:55
> > Objet: Re: [petsc-dev] CMake: make, install, find_package ?
> >
> > On Mon, 6 Nov 2017, Franck Houssen wrote:
> >
> > >
> > > Yes ! Your friend let you the keys of his car. The car has no wheel.
> Why
> > > did he gave you his keys ?!... :D (joking)
> >
> > Actually - its more akin to - friend gives you a car - and leaves the
> > keys in the console, with instructions there.
>
> :D
>
> > However you look arround in the trunk and find something that looks like
> a key - and assume hay
> > - it must start this car - and retool it and start the car with it :)
> >
> > Anyhow - Barry wants to get rid of the cmake related code from petsc..
> >
>
> Yeah, that's your decision ! But know that, if you impose a full global
> ordering of all packages of all possible dependencies (to be done once =
> associating a unique number to each package), then:
> 1. "your" configure (python) will probably also benefit of it (less "bugs"
> when reconfiguring for instance, ...).
> 2. cmake and find_package will work (with commits in the bundle I sent):
> this could be nice to lots of people too...
>
> Dependencies order seems to have been the base line systematic problem you
> had: neither cmake, nor autotools are meant to deal with the graph of
> dependencies (no way they can do that), this must be guaranteed by the dev
> (no choice).
> Who was first ? Chicken or Egg ? How to know ? :D CMake/autotools can not
> know if blas needs lapack or if it is the other way !
>
> Dependencies order must be imposed : in configure, that's already what you
> do already (but only locally - scalapack knows it needs mpi and lapack).
> If you do that globally, you solve everything at once (in likely 15 to 30
> mins !) and avoid cmake to deal with problems (order) he has no way to
> solve.
>

That is a terrible model. You have a closed world assumption, which is the
opposite of what we want for configure. You would end up renumbering all the
time. Instead we use topological sort to impose a total order on the fly.
This is why we have mathematics, to figure out the right thing to do without
enumerating everything ahead of time.

   Matt


> > Satish
> >
>



-- 
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.caam.rice.edu/~mk51/>
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