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From: troy d straszheim (troy_at_[hidden])
Date: 2007-06-08 12:37:24

On Tue, Jun 05, 2007 at 10:43:48PM +0200, Henrik Sundberg wrote:
> I'm new to svn. And I'm trying to build a good structure for a family
> of systems built on ~200 components with 1-20 subcomponents per
> component.
> Our current (pre-svn) method handles releases on subcomponent level.
> Integration teams selects the subcomponents to build a system from,
> builds it, and releases the resulting binaries/configurations.
> I'm trying to understand what the best svn-structure would be. Boost,
> and KDE, seem to have the same problems as I. I don't understand KDE
> (I did read their tutorial) enough to know how it can be compiled
> without a clear (to me) structure of subreleases.
> I'm trying to understand when to use externals among other things.
> They seemed to be useful for making higher order releases based on
> lower ones. But I got discouraged.

Thanks for your interest.... Since this (is/will become) part of a
proposal for boost I guess this is on-topic. I can give you a
tour/brain-dump of how we do it.

Warning: this is an unedited rambling sprint through a lot of

The jargon we use is 'projects' and 'meta-projects'. Meta-projects
are just collections of projects. I assume the mapping would be
meta-project => component, project => subcomponent.

Our repository (recently outfitted with the slick new Trac browser) is

you'll see projects/ and meta-projects/. Under projects/ there are a
couple hundred projects, many of them have fallen out of use, or are
maintained by people that haven't yet (or never intend to) submitted
them for review.

Each project directory (say, project icetray) looks like this:


And each project is organized in a certain fashion:

The toplevel directory contains a makefile, some cruft, and a public
dir (headers), src dir (src and tests), and resources (misc).

We have essentially three main distributions:
offline-software (core stuff), icerec (core + some algorithms),
simulation (core + other algorithms).

      / \
  icerec simulation

One of the fundamental operations of our enterprise is to have the
simulation group produce data that is used by the icerec group to test
the performance of the components inside icerec. Looking at a release
of the offline-software meta-project:

you can see that the metaproject contains a little bit of boilerplate,
some cruft (that 'mutineeer' thing), and a list of externals, like


which means that when you check out the metaproject, directory ithon/
will be populated with what's on the other end of that URL.

On a regular basis, releases of offline-software come out (this
metaproject ought to be called 'core' or something), and the
simulation and reconstruction groups merge, at their convenicence,
this released code into their metaprojects. For instance this simulation

contains the same externals as offline-software version V01-07-05, as
well as the 'trunks' of a bunch of simulation-specific projects that
may or may not be dependent on offline-software projects.

Similarly for icerec:

As simulation stabilizes, they will tag up their various projects and
when all of their components are 'stable' URLs, they copy off a

Once nice thing about this is that it is easy assemble other
meta-projects. For instance, I put together a visualization tool that
is dependent only on a small subset of offline-software (it only needs
to be able to read data, then it makes pictures) and therefore only
needs to be rereleased when serialization methods change, or there are
new gui features. To achieve this you simply copy off the
offline-software metaproject and tweak the externals:

and people can check this out and build it without having to build the
entire world.

You'll notice that in the meta-projects directory:

there are lots of such compliations of code. I believe about 2/3rds
are in active use.

Another thing that happens very frequently in our world is that
somebody has to do a specific analysis, which involves writing a lot
of customized code and usually hacking everything to bits. Once you
get started making graphs you do *not* want to have your code broken
by somebody's release, and you do *not* want somebody to reject your
changes pending code review. So they simply copy off a metaproject
and make it their PhD. Here's one:

You'll notice that:

* Meta-projects don't nest.

  When the simulation group merges in changes from a new release of
  offline-software, they have to change all of the urls. This is
  dictated by the way svn:externals work. It seems like it isn't
  ideal, but having the dependencies of each metaproject laid out flat
  can be an advantage.

* Branching multiple projects can be tedious.

  If you allow your individual projects to become coupled, you will
  need to branch many at once, and this you have to do by hand (svn
  copy, change external. svn copy, change external...) This can be
  tedious. Nobody has taken the time to develop tools to automate
  this, but SVN has good python bindings, it would probably be just an
  afternoon's work.

Let me stop now. Is that clear? ;)


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