[Scons-users] Scanner / Builder Race Condition?

[William Blevins]

Can we get some small snippets that demonstrate this in practice?

I want to see dependency graphs and other artifacts because this looks
suspicious. You could have found a new bug, but this use case seems common,
so I am surprised others would not have seen it already.

V/R,
William

On Mon, Feb 22, 2016 at 8:22 PM, Brian Cody <brian.j.cody at gmail.com> wrote:

> Hey folks,
>
> We have a command builder that creates a file, let's call it project.prj.
> The project.prj file is a '.prj' file, which we have a scanner for.
>
> create_project_target = env.Command(project_prj, [project_file_sources],
> create_project_function)
>
> Then I have two builds that take it as a source:
>
> version_file = env.GenerateVersionFile(bin_file_name,
> create_project_target)
> binary = env.Compile(bin_file_name, [create_project_target, version_file])
>

Maybe this is a typo, but you have two ways of building bin_file_name ;
SCons should throw an error here.


>
> If the project.prj doesn't already exist, everything works as expected.
> The prj file gets created and then scanned, and then the builds proceed.
>
> The problem is when I change a file in project_file_sources. SCons will
> invoke the scanner on the project.prj file before it runs any build. That's
> OK, it's just a potential waste of time. The problem is that (with multiple
> jobs) it will start running re-building the project.prj file, and before
> waiting for it to be done, it'll start scanning the file again! The scanner
> will now throw an exception.
>
> Simplified log:
> scons: Reading SConscript files ...
> scons: done reading SConscript files.
> scons: Building targets ...
> Start Scanning
> Done Scanning
> scons: rebuilding `project.prj' because `project_prj_source' changed
> create_project_function(["project.prj"], [project_prj_source_list])
> start of create_project_function
> Start Scanning
> PRJ SCANNER EXPLODE!!! <--- helpful try/except block
> end of create_project_function
> scons: *** [bin_file_name] IndexError : list index out of range <--- The
> exact error varies, it's just what happens when the file you're scanning is
> suddenly truncated.
>
> I would rather not disable the multiple jobs, and multiple invocations of
> SCons really isn't acceptable either. Is there any proper way to get SCons
> to wait to scan a file that it has already determined needs to be rebuilt?
>
> Also if we perform an Execute(Delete(project_prj)) at the top of the
> SConstruct it "works", however due to how our version file works it will
> always perform the build of the bin_file_name. This is extremely costly in
> this case! (It's a Xilinx build).
>
> Thank you!
> -Brian
>
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