[petsc-dev] "Libraries don't have to suck"

[Karl Rupp]

Hey,

On 12/13/2012 03:46 PM, Jed Brown wrote:
> I'm sure that users would appreciate one release of deprecation. It's
> not hard to implement when deprecating a routine entirely, but it's
> trickier when changing the interface to an existing routine. It can be
> achieved through a "feature test macro" that asks for the old version,
> though this still requires that the user "change their code" (or
> preprocessor definitions) to build with the new version. Some projects
> include the version number in the API, but that looks ugly and confusing
> to the user, especially after the old version has been removed.

I'm also in favor of offering a 'grace period' for the main user 
functions, at least for the most frequently used. I don't have a good 
strategy for dealing with changes to existing functions at hand, though.


> It's technically feasible for PETSc to offer this, but it's still not a
> trivial amount of effort and doesn't fix all the user's complaints.

If it fixes half of the user complaints we would get otherwise, it's 
probably already worth the effort...

Best regards,
Karli


>
> On Sat, Dec 8, 2012 at 6:05 PM, Karl Rupp <rupp at mcs.anl.gov
> <mailto:rupp at mcs.anl.gov>> wrote:
>
>     Hey,
>
>     this thread is sufficiently young such that I add some interesting
>     statement from LLVM rather than opening a new thread:
>
>     "Another major aspect of LLVM remaining nimble (and a controversial
>     topic with clients of the libraries) is our willingness to
>     reconsider previous decisions and make widespread changes to APIs
>     without worrying about backwards compatibility. Invasive changes to
>     LLVM IR itself, for example, require updating all of the
>     optimization passes and cause substantial churn to the C++ APIs.
>     We've done this on several occasions, and though it causes pain for
>     clients, it is the right thing to do to maintain rapid forward
>     progress. To make life easier for external clients (and to support
>     bindings for other languages), we provide C wrappers for many
>     popular APIs (which are intended to be extremely stable) and new
>     versions of LLVM aim to continue reading old .ll and .bc files."
>
>     as well as
>
>     "Despite its success so far, there is still a lot left to be done,
>     as well as the ever-present risk that LLVM will become less nimble
>     and more calcified as it ages. While there is no magic answer to
>     this problem, I hope that the continued exposure to new problem
>     domains, a willingness to reevaluate previous decisions, and to
>     redesign and throw away code will help. After all, the goal isn't to
>     be perfect, it is to keep getting better over time."
>
>     (Page 3 in [1])
>
>     The whole article is a good read. Modularity and reusability don't
>     seem to be something compiler people outside LLVM have really cared
>     about (I haven't checked this claim, though).
>
>     Overall, the take-away is that they also argue in favor of
>     preserving a clean and consistent design even though it requires to
>     sacrifice backwards compatibility. Also, they are aware of the
>     hassle for their users and try to make the transition less painful.
>     A similar model should work with PETSc, e.g. by using pragma
>     messages to point at deprecated functionality for a while. This
>     would allow users to still obtain an executable when moving to a
>     newer version, but at the same time gives them a clear indication
>     that they should migrate to using the new interface soon (and not
>     necessarily *immediately*).
>
>     Best regards,
>     Karli
>
>
>     [1]
>     http://www.drdobbs.com/__architecture-and-design/the-__design-of-llvm/240001128
>     <http://www.drdobbs.com/architecture-and-design/the-design-of-llvm/240001128>
>     [2]
>     http://blog.llvm.org/2011/12/__nvidia-cuda-41-compiler-now-__built-on.html
>     <http://blog.llvm.org/2011/12/nvidia-cuda-41-compiler-now-built-on.html>
>
>
>
>     On 11/26/2012 06:08 PM, Jed Brown wrote:
>
>         Point in favor of evolutionary libraries over the Matryoshka
>         dolls that
>         arise when interfaces are frozen forever.
>
>         http://akkartik.name/blog/__libraries2
>         <http://akkartik.name/blog/libraries2>
>
>
>