CMake (was More about x-packages)

[Alan W. Irwin]

On 2007-12-20 13:23-0200 Paulo Cesar Pereira de Andrade wrote:

>  :-) Well, I expect that people that generate binaries from sources will
> care to install autotools, but I see the point of having the generated
> files, as it may take significant time to regenerate them, due to the
> extensive tests. For example, monolithic X Free86 would build everything
> in less than 20 minutes on an average P4, while modular Xorg will take
> a few hours, and most of the time is spent on autotools scripts.

You will get some substantial speed improvements if you move to a different
build system.  At least that is what KDE experienced when they moved from
autotools to CMake, and that was the PLplot developer's experience as as
well when we moved PLplot from autotools to CMake.  The configuration speed
improvements are because cmake is a fast executable that takes the place of
the relatively slow configure script.  There are also build speed
improvements which I ascribe to the cmake executable setting up
straightforward Makefile rules to do compiling and linking while autotools
uses libtool, a ~220K (!) script that must be run for every compile or link
step.

Another advantage of CMake is it is quite easy to understand so that
build-system support tends to be more widespread within a software project
rather than relying on one or two gurus to actually understand autotools.
That was a big deal for me because in the past I did spend a lot of time
implementing autotools support for new PLplot features or attempting to
debug autotools build problems for PLplot. I was tired of that effort.

I am well aware that X changed to the autotools build system not that long
in the past, and most X developers are probably not immediately ready for
yet another such transition.  In fact, if the PLplot experience can be
generalized there will be a tremendous amount of initial nay-saying with
virtually all of it based on no experience with CMake! However, if just one
forward-thinking X developer is concerned enough about the slow autotools
configure and build speeds or the amount of autotools "magic" that is
required to support new X features, then I suggest they try developing a
CMake-based build system for just part of X (at first) to see how they like
it for their own builds.  From such a start it is relatively easy to go the
rest of the way to a full-blown CMake-based build system that everybody can
use.

CMake-based build systems can be developed in parallel with autotools
because there are no filename name clashes between the two build systems.
When we tried that approach for PLplot there was only one downside; our team
of developers (despite the initial nay-saying) caught on so fast to using
CMake that all our new features over the last year have only been
implemented in our CMake-based build system. That was the death knell of our
autotools-based build system, and we have just now completely removed it as
a result.

The PLplot developers have collected links at
http://www.miscdebris.net/plplot_wiki/index.php?title=General_CMake_documentation_links
which we have found useful during the development of our new CMake-based
build system.

Alan
__________________________
Alan W. Irwin

Astronomical research affiliation with Department of Physics and Astronomy,
University of Victoria (astrowww.phys.uvic.ca).

Programming affiliations with the FreeEOS equation-of-state implementation
for stellar interiors (freeeos.sf.net); PLplot scientific plotting software
package (plplot.org); the libLASi project (unifont.org/lasi); the Loads of
Linux Links project (loll.sf.net); and the Linux Brochure Project
(lbproject.sf.net).
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Linux-powered Science
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