Re: converting to subdir-objects

[Bob Friesenhahn]

On Sun, 8 Mar 2015, Harlan Stenn wrote:
> I'm happy to look at that, and each of these Makefiles will need to be
> generated by configure (config.status) because they need to be in the
> build tree.  I figure that's a project to look at once I get
> subdir-objects going.
>
> > Turn convenience libraries into Makefile variables since Makefile
> > variables are vastly more efficient than clunky convenience libraries.
>
> I'm happy to look at that, and it means I'd want a single place to
> define these Makefile variables and then I'd have to update all the
> places they're used.

Put them in an include file where the definitions should logically 
emanate from so they can easily be found.  The Makefile variable is 
just a named list of source files that can be linked in place of the 
similar convenience library.

> If with subdir objects this means a single copy of these files will be
> built and shared that seems great.

Yes.  There would be a single copy of the objects and they would be 
directly applied when the dependent library/application is linked. 
The convenience library requires using 'ar' to store all of the 
objects, and then extracting them later using 'ar' at each point of 
use.

> > And there is the benefit that almost everything (except for linking)
> > can be built simultaneously, using all available CPU cores.
>
> That is great, especially if this approach is no slower for builds folks
> have to do on single-core slow boxes, too.

It would be wrong to claim that non-recursive builds are necessarily 
faster.  They are faster if any library code which was formerly in a 
recursed 'subdir' needs to be rebuilt due to being edited, and faster 
in that a child make did not need to run to decide there is nothing to 
do.  There is no unnecessary work which gets done.  However, the make 
program does take longer to start since it has more to consider at 
once, the dependencies are fully known, and the Makefile file is 
larger.

Builds are no slower for the usual case.

Bob
--
Bob Friesenhahn
address@hidden, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/