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From: drc@cs.brown.edu (David R. Chase)
Newsgroups: comp.lang.c++
Subject: Re: distinguishing stack/heap, garbage collection
Message-ID: <32545@brunix.UUCP>
Date: 13 Mar 90 08:52:39 GMT
References: <9084@shlump.nac.dec.com> <25fc5b7b.4abf@polyslo.CalPoly.EDU>
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Reply-To: drc@cs.brown.edu (David R. Chase)
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In article <25fc5b7b.4abf@polyslo.CalPoly.EDU> ttwang@polyslo.CalPoly.EDU (Thomas Wang) writes:
>
>There is such a GC package.  It is called MM.  Version 1.0 is available
...
>Version 2.0 will support exception handling, 

I hope this isn't a rude question, but is there an easy possibility
(with your system) of adding smarts to the compiler to get help in
efficient implementation of your GC and exception handling?  (That is,
does your exception handling follow
Tiemann/Cedar/Modula-2+/Modula-3/Ada, or does it follow Stroustrop's
proposal (has that been published?)).  Static declaration of the
exceptions handled, as in (invented syntax)

  try <stmt> except {
    case e1 : ...
    case e2 : ...
    case e3 : ...
  }

with the intention that e1, e2, e3 are constants, allows a pretty
nifty implementation that imposes no run-time overhead for not taking
the exception (except for the optimizations missed, but that's another
issue and note that at least the scope in which the optimizer must be
throttled is smaller than it would be for setjmp/longjmp).  An
additional extension (annotation) is to tag procedures (and procedure
types) with the exceptions that they may raise.  This permits static
checking for posible uncaught exceptions, and informs programmers
about the possible errors.

For garbage collection, of course, I'd hope that the compiler would
automatically handle the dirty work for me if I declare that a class
has supertype "collectable" ("dirty work" means generating a method to
do the collection for me so I don't have to go to any additional
trouble).  Down the road, of course, the compiler should even figure
out when stack storage is adequate for the allocation of one of these
objects and do the obvious optimization.

Please understand that I'm not asking if it does these things yet -- I
just want to know if the hooks exist to permit a streamlined
implementation at some time in the future.

Just curious -- I'm not exactly in a position to go FTP the bits just
yet.  (Any garbage collector aficionados care to comment on this
package?)

David