Re: Dependence based on whether files has been changed

[Philip Guenther]

On Mon, May 16, 2011 at 9:17 AM, Peng Yu <address@hidden> wrote:
> Scons has the support for updating target only if the dependent file
> contents are changed.
> http://www.scons.org/doc/0.98.5/HTML/scons-user/c779.html
>
> I know that it may not always easy and possible to duplicate feature
> of other tools. But GNU make is still faster than scons and sometime
> much faster than scons (especially if there are many dependences in a
> Makefile). Considering this I'd still rather use make than scons.
>
> Therefore, I'm wondering if there is any plan to add the features
> based on file contents in GNU make in the future.

Maybe part of the reason that GNU make is faster than scons is that
scons is actually checking the contents of all the source files to see
whether they changed while GNU make only has to compare the timestamps
on the files.  If so, then putting the "check contents of the files"
feature into GNU make will make it just as slow.

I'll note that it's possible to write makefile rules to do content
comparison of files.  I know I've posted at least one version of
example rules to do that to the list, though I don't use them myself
and make no claims about performance.  Check the archive for details.


Philip Guenther