Re: Garbage collection?

[eachus@mitre-bedford.arpa (Robert I. Eachus)]

In article <1992Apr21.160955.2523@titan.ksc.nasa.gov> mcroberts@titan.ksc.nasa.
gov writes:

  > I'm curious as to the state of the art in automated garbage
  > collection.

   No Ada compiler I know of does complete garbage collection.  This
is not because it is too hard, but because the interaction of tasking
and garbage collection leads to unacceptable compromises.  Since in
good Ada compilers the only way to create garbage that needs
collection is with access types, the general wisdom in Ada currently
is that garbage collection is the resposibility of the application.
I'm not happy with that, but that is the way the culture has evolved.

   Is this something one needs to worry about when using solid
   production quality Ada compilers...

   Yes.

                                   ...and is there any negative
   performance impact if you don't clean up your own garbage.

   Very definitely.  An application which doesn't create much garbage
and doesn't need to run for long periods of time can ignore the
problem, but most real-time applications cannot.  Fortunately, the
type of garbage collection needed for most real-time applications is
easy to program in Ada.  However, the structures needed by many AI
applications are not easy to clean up after.  I've thought about
writing a more-or-less portable garbage collector which would only
need a few low-level routines rewritten to move it to a new
environment.  But it would be a lot of work, and the usual "solution"
to the problem in safety critical systems instead is to just forbid
access types.
--

					Robert I. Eachus

with STANDARD_DISCLAIMER;
use  STANDARD_DISCLAIMER;
function MESSAGE (TEXT: in CLEVER_IDEAS) return BETTER_IDEAS is...