Yikes! I just wrote:
+---------------
| Joe Marshall  <jrm@ccs.neu.edu> wrote:
| +---------------
| | Suppose that the system has done a full GC.  Now you SETQ *foo* to NIL
| | and perform another full GC.  It seems to me that the storage
| | reclaimed is *exactly* the `size' of *foo*.
| +---------------
| 
| Careful!! Don't forget the builtin "history" variables in the REPL.
| You probably want to do something like this:
| 
| 	> (gc :full t)
| 	> (room)		; size while *foo* still holds a reference
| 	> (setq *foo* nil)	; zap *foo* and * and /
| 	> (setq *foo* nil)	; zap ** and //
| 	> (setq *foo* nil)	; zap *** and ///
| 	> (gc :full t)
| 	> (room)		; size after *foo* is gone
| 
| [I know you know all of this, but CL newbies (such as myself!)
| sometimes overlook it when trying to do GC measurements...]
+---------------

And of course, it just *had* to have a bug, didn't it?!?  ;-}  ;-}
The REPL variables may have had some big junk in them *before* the
first GC, and therefore the first ROOM may print an overly-large
value. I think you may need something like this instead:

  	> (setq *** nil /// nil
		** nil // nil)	; * and / will be taken care of by this, too.
  	> (gc :full t)		; values of GC & ROOM not defined, but
				; probably safe [NIL, T, (values), etc.]).
  	> (room)		; size while *foo* still holds a reference
  	> (setq *foo* nil)	; zap *foo* and * and /
  	> (gc :full t)
  	> (room)		; size after *foo* is gone

If you're manually typing this at the REPL, you can't do much about
+++, ++, +, and -, but at least they're known small constants, given
the above forms. [Well, actually you *can*, if you put of all the above
(and a little more) in a function that clears them out, but...]


-Rob

-----
Rob Warnock, PP-ASEL-IA		<rpw3@rpw3.org>
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