[CMake] ExternalProject and redundant update/configure/compile actions.

[Alan W. Irwin]

On 2013-09-16 17:24-0000 Williams, Norman K wrote:

> OK, yeah, I know about disabling updates.  I don't remember who or when I
> got the advice NOT to disable updates.
>
> And all of the projects in our Super-Duper-build do get set to specific
> SVN/GIT/CVS tags.  This is the only way
> to get predictable behavior.
>
> And my reasoning was 'if you always request a specific tag, you never need
> to have an update command.' But then I was told to leave that be.
>
> The only rationale for always updating is that if you change the tag to
> download, it will re-download the source, and rebuild with the new source.
> If you disable update then you'll have to delete the files down in
> <PRJ>-prefix/src/<PRJ>-stamp to retrigger a download.
>
> Or do what I generally do and delete the source, build, AND prefix
> directories.
>
> All of this starts out as 'expert-level CMAKE hacking' and gets
> progressively more abstruse as I go along. I keep trying to think of how
> to simplify it for people who want to build and use applications using the
> SuperBuild. Not sure who they are, or if I really should try and bend over
> backwards to make things easy for them.

I suggest you try 2.8.12.  The reason I say that is for CMake versions
before 2.8.12, the cmake -E touch command (used a lot within the
ExternalProject module) has only one-second time resolution, i.e., the
time for the file that is touched is rounded down to the nearest
second.  Anyhow, I worked around the problem by replacing cmake -E
touch everywhere by the system touch command within a local version of
the ExternalProject module, and a lot of annoying dependency issues
disappeared as a result.  (I could use that workaround because Linux
and MSYS are the only platforms where I currently use ExternalProject,
and a system touch command is available for both those cases.)

Apparently this time resolution issue for the cmake -E touch command
has now been fixed for CMake-2.8.12 (for platforms that support
setting file update times to better than one second).  I don't know
whether your particular dependency issue will be fixed by that, but it
should certainly be worth trying CMake-2.8.12 as a first step whenever
annoying dependency issues are discovered for the ExternalProject
module for prior CMake versions.

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); the Time
Ephemerides project (timeephem.sf.net); PLplot scientific plotting
software package (plplot.sf.net); the libLASi project
(unifont.org/lasi); the Loads of Linux Links project (loll.sf.net);
and the Linux Brochure Project (lbproject.sf.net).
__________________________

Linux-powered Science
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