[C++-sig] Py++ and caching

[Roman Yakovenko]

On 9/27/06, Kirill Lapshin <kir at lapshin.net> wrote:
>
> > This is not a new idea. It has been raised few times on pygccxml development
> > mailing list. I don't actually understand how it should work
>
> I think it is hard to make bulletproof, but relatively easy to get 99%
> there. The hard part is already done -- you already cache gccxml
> results. If we hit the cache, then chances are the generated code
> already exists and there is no need to update it. There are only two
> reasons why that may be not the case: there are no generated files (user
> have deleted them), or python code describing what has to be exported
> has changed. Arguably first option is quite rare -- if there is cache,
> but no generated files then user should've deleted them manually. If we
> disregard this case then all we have to check is whether python code
> have been changed since last run of Py++. So we basically have to know
> the name(s) of python driver script(s) and record somewhere when last
> time Py++ has been run.
> Accounting for the possibility of tampering with generated files is much
> more complicated and arguably is not possible to do reliably for the
> case of split files, since without loading gccxml output we can't tell
> what are the names of generated files. We can cover one common case of
> all generated files being deleted by checking whether main generated
> .cpp file is present. Not a bulletproof solution but certainly better
> then nothing.

This is what I thought. I don't like to have "holes" in the solution,
when we talk
about source code. It is too dangerous.

> For example I was struggling with plugging Py++ into MSVC
> project/solution build. I've tried quite a few options, and finally
> settled on dummy project for code generation that runs Py++ in post
> build step. As a result code generation is started every time I run
> build, even if I haven't touched anything. Not nice, but other options
> were even uglier. No you may see why I would like to save the 15 sec.

At work we had similar problem with "gettext" utility *.pi and *.mo files.
I will take a look how we solved it and let you know.

> > I understand that it is not possible to implement such functionality without
> > some help from Py++. I think you need a function that will check whether
> > header files are different from those Py++ has in cache.
>
> That should be really simple, no? When I instantiate cache, but before
> instantiating module_builder, I can ask cache whether it is stale or
> not. Right?

The functionality does not exists, but it should be simple to add it.

> > Py++ has goodies package. This package contains few utilities\convenience
> > function that were contributed by other users.  Can you create an
> > initial version
> > of the script and define missing functionality, than we will work
> > together to improve it and to add it to the goodies package?
> >
>
> Sounds like a good idea. Will give it a try. Though I am bit tied up
> with other stuff, and it is not a high priority thing on my todo list.
> So don't expect anything soon, but hopefully I will dig into this
> eventually.

When you have time, let me know, we will work together on it.

-- 
Roman Yakovenko
C++ Python language binding
http://www.language-binding.net/