[CMake] Parallel make & custom command

[Marcel Loose]

On Wed, 2011-06-29 at 20:46 +0200, Michael Wild wrote:
> On 06/29/2011 05:22 PM, Marcel Loose wrote:
> > Hi all,
> > 
> > I'm having a problem with a parallel 'make' where one or more
sources
> > are generated by a custom command.
> > 
> > The situation is as follows. There are a couple of targets
(executables)
> > that depend on the same source file being generated by a custom
> > command. 
> > 
> > I notice that, when doing a parallel build, the custom command is
> > executed multiple times, thereby potentially overwriting or
corrupting
> > the same file that's generated in different threads.
> > 
> > My feeling is that this is caused by the fact that CMake generates a
> > build.cmake file for each target separately. Hence, when doing a
> > parallel build, these build.cmake files are also processed in
parallel. 
> > 
> > Am I correct in this assumption? And if so, what's the proper
solution
> > for this problem?
> > 
> > Best regards,
> > Marcel Loose.
> > 
> 
> Yes, I've seen this issue too. The only way I can think of fixing this
> is by having a single custom target which depends on the generated
> files, and then have the executables using the generated sources
depend
> on that custom target. This way you force the custom target to be run
> first before the other targets, thus avoiding the custom commands
> generating the sources from running multiple times.
> 
> Michael
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Seems my webmail client completely screwed up the topic threading :-(
Here's my reply again, hopefully now placed properly. Sorry for the
noise.

After I had posted my question I realized that this issue has come up
quite recently on the mailing list in a thread that I started -- see
http://www.mail-archive.com/cmake@cmake.org/msg36362.html. Although the
original question was related to building mulitple targets in parallel,
Michael Hertling showed that CMake inherently has problems with parallel
builds when custom targets/commands come into play.

So maybe I should open an isse for this?

Best regards,
Marcel Loose.