From: Leopold Toetsch <[EMAIL PROTECTED]>
Date: Mon, 18 Jul 2005 17:08:53 +0200
Circular or not isn't really the problem. With generational GC you'll
always have the chance of tenured garbage . . .
Now due to some other pointer store the object C becomes dead. But as
long as we don't scan up to generation j, we don't realize this and
object A stays alive.
That's true, but not my point. I don't understand how the IGP mechanism
permits cycles to be collected at all.
. . .
gen n | gen j
[ A ] -> [ B ] -|-----> [ C ]
^ |
+----------------------+
A circular data structure doesn't really change the picture, except,
when again scanning up to generation j, and we find object C being
alive, we'd have to restart scanning at object A, by following the
backreference.
If non of A, B, or C is referenced from elsewhere, we would still delete
the whole reference loop.
So that means you do not use the IGP pointer to A when collecting any
generation <= j, correct? Otherwise, I imagine you'd always decide that
A is alive, and hence B and C.
But what if A, B, and C are all in the same generation? You'd still
need an IGP entry, even though it's not inter-generational, in order to
handle the backpointer, but how would you then decide that it's invalid?
> ... Is one-pass mark-sweep really a suitable GC algorithm for Parrot?
I still think it's suitable yes. It's only in the above case that we
can't immediately cleanup A, because of the invalidation of the IGP entry.
leo
I am willing to believe that there could be an IGP mechanism that would
perform as described, but I haven't yet heard enough to understand it
myself. Perhaps you should save your (metaphorical) breath, and I'll
wait for a more detailed design.
-- Bob Rogers
