Re: Crosspost: Help wanted from comp.compilers

["Robert I. Eachus" <rieachus@attbi.com>]

John R. Strohm wrote:

> Now, it was EASY to build systems that had horrendous recompilation
> problems.  Usually, in order to build such a system, you had to screw up
> some fairly basic software engineering things.  For example, if you build a
> system-wide "types" package, then every time you touch that package, you get
> to recompile the world.  If you build a system-wide "magic numbers" package,
> same problem.  Observe that the exact same problems arise in C/C++.  The
> answer is, of course, DON'T DO THAT.

This resulted in one of the few "official" MITRE inputs to the Ada 9X 
requirements process, and the one that meant we felt it was important to 
submit as a MITRE position not just representing the group making the 
recomendations.  Every time MITRE got called in by the government to 
resolve Ada compiler problems that were ususally described as 
"recompiles with this compiler are much too slow," it turned out that 
the real solution was to fix some software engineering issues. (John 
Strohm gave a good selection of some of them.  Another favorite was 
rapidly changing interfaces during the coding phase.  In one case, I 
found a package specification that had changed 17 times in one month. 
During that time, the package body had been changed twice!)

Of course, given the usual contracting environment, the sooner MITRE got 
called in to resolve the problem, the more money (and schedule time 
which was often more valuable) the government saved.  So even if someone 
did figure out an elegant way to recompile the world quickly, we (on 
behalf of the US government) did not want it.

Oh and of course, not all government programs are written in Ada.  For 
programs in C, this problem usually showed up as a configuration 
management problem when trying to link all the code together.  On at 
least one project where I was on the "Red Team" to resolve that, the 
recommendation was to cancel the project.  (They had fallen into the 
trap of having more than one version of the truth by having different 
software repositories for different software groups on a large project. 
  When they finally tried to do an "all up" system build, it turned out 
that there were over 1000 files with multiple versions.  After studying 
a significant sample of the differences, we estimated the time to merge 
the differences with some chance of getting a working version at over 
two years!)

-- 

                                                Robert I. Eachus

�In an ally, considerations of house, clan, planet, race are 
insignificant beside two prime questions, which are: 1. Can he shoot? 2. 
Will he aim at your enemy?� -- from the Laiden novels by Sharon Lee and 
Steve Miller.