Re: Please Stop It Rebuilding Everything!

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From: Carl Daniel [VC++ MVP] (cpdaniel_remove_this_and_nospam_at_mvps.org.nospam)
Date: 09/23/04 

Date: Thu, 23 Sep 2004 09:17:17 -0700

Andy Capon wrote:
> Hi There,
>
> We have a medium size project about 2000 source files and 700,000
> lines of code, as you can imagine this takes some time to rebuild all.
>
> Now our problem is that we have a code generator we have developed
> that updates some of our classes, as an example lets say I update 50
> files. When we do a build the ide builds nearly all of the source
> files while we swear and then twiddle our thumbs for a couple of
> hours.
>
> Its almost as if it says "well alot of files have changed I will just
> rebuild everything".
>
> Does anyone know why this happens?

Have you analyzed the dependencies in your code to demonstrate that
significantly fewer files should be compiled? When you update classes with
the code generator, are unchanged files given a new timestamp? If so, that
could be a huge source of unnecessary re-work by the compiler.

Are you making proper use of precompiled headers? I'd expect a 700,000 line
program to build in 10 minutes tops, even on a single processor machine if
precompiled headers are used properly and consistently.

> We are useing 2003 but 2002 did it as well.

I know there have been reports of VS always rebuilding everything, but I
don't know any of the details in those cases - hopefully someone else that
does know will reply as well.

> As a side point I have noticed that the upcomeing version can use
> multiple processors to build, will this work within one project as
> then we could at least halve the time.

No, it won't help you. The MP support in Whidbey works at the project
level, so if you have 2000 source files in one project, they'll all be built
sequentially. If you can restructure your code into several projects
(libraries, I'd assume), then you could get some parallel compilation
benefit.

-cd

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