Re: Automake and deep directory structure

[Bob Friesenhahn]

On Mon, 21 Apr 2014, Zé wrote:

> From what I've gathered, for this case automake offers essentially two 
> approaches: set the project as a shallow directory structure, where 
> ./src/Makefile.am is used to list all files in the project, and convert 
> subdirs into convenience libraries[²].

It is not necessary to use a shallow directory structure if all files 
are listed in one Makefile.am (or the equivalent using Makefile.am 
include fragments).  A bit of extra work is definitely required in 
order to make sure that things like test scripts work properly (e.g. 
the test script may need to change to a sub-directory or know how to 
compute the path to an input file).  The benefit is that 'gmake -j' 
achieves the best build times and unnecessary build actions are 
minimized.  In fact, the primary limiter for compiles becomes the 
linker since it is the only significant serialized step in the build 
process.  If the compile time for any one source file is kept 
reasonable, then parallel compiles fly on modern hardware.  There 
becomes a direct correllation between the number of CPU cores 
available and build time (except for linking!).

The traditional recursive build makes it easy to keep test files/data 
next to each "component" (and suports 'cd component ; make') but it 
can result in quite a lot of time being wasted entering/exiting each 
directory, and quite a lot more time can be spent with linking. 
Configure times can be much longer since there are more files to 
substitute in, and the situation becomes much worse if there are 
subordinate configure scripts. So-called convenience libraries are 
really just containers of objects and these must be extracted to the 
individual .o files at link time, resulting in considerable churn and 
lost time.  Since 'make' does not have a complete view of the build 
dependencies, it is required to do needless actions in order to assure 
a correct build product.

> As there any other options worth mentioning?  And what's the recommended 
> option?

The recommended option seems to be a matter of opinion.

I have used the non-recursive build method for two significant 
projects.  Both of them fit your "deep" project description.

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