Re: Boehm-Demers-Weiser conservative garbage collector and GNAT

[Ludovic Brenta <ludovic.brenta@insalien.org>]

Preben Randhol <randhol+abuse@pvv.org> writes:

> Ludovic Brenta wrote:
> > - Write a thick Ada binding to the C garbage collector, with the same
> >   end result as above, but requiring an additional library at link
> >   time.
> 
> Does this make sense? To rely on C to do the garbage collection of Ada ?

Well, the garbage collector itself is language-independent, so it
would work even on Ada objects.  Indeed, it is already being used for
the Java and Objective C runtimes of GCC.  It supports finalisation of
objects at collection time, so it could even work for Ada's controlled
types.

There would be benefits to this approach: less work (no
reimplementation); and benefit from future updates to the GC.  The
downside, of course, is the increased complexity of the build
configuration for client programs, and the necessity to keep the thick
binding in sync with the GC library.  The latter depends on how stable
the public interface to the library is.

Note that the third approach I mentioned (use the GC that is in GCC
from within libgnat and libgnarl) differs only slightly, and has other
benefits and drawbacks.  For example:

+ the Ada runtime could also use the GC for itself, in addition to
  providing it to clients.

+ Keeping the GC and the Ada runtime in sync would be facilitated by
  the fact that both are in the GCC source tree; besides, the Boehm GC
  in GCC probably changes slowly since so much code already depends on
  it.

+ configuration management simplified to the extreme: to clients, the
  GC would just be part of the runtime provided by the compiler.

- Only available to people using GCC 3.3 as their compiler, as opposed
  to GNAT 3.15p.

I'm still curious to know what Martin's preferred approach is.

-- 
Ludovic Brenta.