[Scons-users] Emitters vs. Scanners

[Plunket, Tom]

No difference, existing targets are scanned right before they are replaced.

From: Scons-users [mailto:scons-users-bounces at scons.org] On Behalf Of Vasily
Sent: Saturday, March 12, 2016 2:11 AM
To: SCons users mailing list <scons-users at scons.org>
Subject: Re: [Scons-users] Emitters vs. Scanners


Hi all,
Cannot you just use target_scanner instead of source one? In my experience target scanner is run only after a builder target is changed and SCons thinks it is ready to be built, but if target_scanner finds more dependencies target would be built only when those new ones are ready.

Thanks,
Vasily
12 марта 2016 г. 7:48 пользователь "Viktor Dick" <viktordick86 at gmail.com<mailto:viktordick86 at gmail.com>> написал:
On 12.03.2016 03:13, Plunket, Tom wrote:
> Print statements in the scanner (“Scanning blahblah.xml”) print
> before the Scene command string (“Exporting blahblah.aep to
> blahblah.xml”).

I guess that's because SCons works in two steps. First, the whole
dependency graph is created (which calls scanners as necessary). Then,
nodes are built. If it is not predictable which sources B will list
additionally until it is created from A, good luck with that. We had a
long discussion on this list a while ago how to create a list of object
files to be linked together in C/C++ projects that follow some
nomenclature for naming of .cpp and .h files. I also tried to create
something like "If you want to create this executable, this intermediate
file is needed. Once the intermediate file is up to date, read it and
you might find further dependencies.", but I was unable to do that with
SCons. My solution was to do the complete first step inside the
SConstruct file, i.e. each time SCons is called I rebuild a database of
"if you want to create this executable, you need to link the object
files from these source files". By using python threads, it is
acceptably fast.

- Viktor


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