bearophile wrote:
<snip>
Time ago I have suggested to split the D pointers in two types, the
GC-managed ones and the ones that work on the C heap, that the GC
never touches. The type system can assure they never get mixed by
mistake.
I can imagine this making interfacing external APIs a pain in the rear
end....
Now I think (just an idea) the type of GC-managed pointers
can be split in two types: the ones that are fully managed by a
moving GC (see below) and the ones managed by a conservative GC, such
memory is pinned, and the GC doesn't move it around. The type system
will assure such three groups doesn't mix unless the programmer is
really determined to mix them :-)
<snip>
I'm not sure that having two separate, independent GCs will work. But
having two GC heaps along these lines might.
One way I can see is having an "immovable" type modifier in line with
const and invariant. Anything that isn't allocated as immovable, the GC
may move around if it's clever enough. But an immovable reference could
just as well be implicitly convertible to a non-immovable reference -
the GC'll know which heap it points into.
Immovable might be useful for interfacing external APIs. We could also
spec that only immovable pointer/reference types may be used in a union.
BTW even D1 needs some work in the area of moving GC:
http://d.puremagic.com/issues/show_bug.cgi?id=679
Stewart.
