On Wednesday, 9 October 2013 at 13:38:12 UTC, Michel Fortin wrote:
On 2013-10-09 11:58:33 +0000, Jacob Carlborg <[email protected]> said:
On 2013-10-09 09:33, Manu wrote:
It sounds pretty easy to reach to me. Compiler generating
inc/dec ref
calls can't possibly be difficult. An optimisation that
simplifies
redundant inc/dec sequences doesn't sound hard either... :/
Is there more to it? Cleaning up circular references I
guess... what
does Apple do?
It's an uncommon edge case, so there's gotta be heaps of room
for
efficient solutions to that (afaik) one edge case. Are there
others?
See my reply to one of your other posts:
http://forum.dlang.org/thread/[email protected]?page=10#post-l33gah:24ero:241:40digitalmars.com
I
don't recall the exact issues but there were several issues
that were brought up in the email conversation.
Here's a quick summary:
Walter's idea was to implement ARC for classes implementing
IUnknown. So if you wanted a ARC'ed class, you implement
IUnknown and you're done. Problems were on the edges of
ARC-controlled pointers and GC-controlled ones (which cannot be
allowed to be mixed), and also with wanting to use the GC to
free cycles for these objects (which would make COM AddRef and
Release unusable when called from non-D code). I think the only
way to make that work sanely is to create another root object
for ref-counted classes.
Another idea was to make *everything* in D ref-counted. ARC
simply becomes another GC implementation. There can be no
confusion between what's ref-counted and what isn't (everything
is). It's much simpler really. But Walter isn't keen on the
idea of having to call a function at every pointer assignment
to keep the reference count up to date (for performance
reasons), so that idea was rejected. This makes some sense,
because unlike Objective-C ARC where only Objective-C object
pointers are ref-counted, in D you'd have to do that with all
pointers, and some will point to external data that does not
need to be ref-counted at all.
It was also pointed out that concurrent GCs require some work
to be done on pointer assignment (and also when moving a
pointer). So it seems to me that advances on the GC front are
going to be limited without that.
And now, things seems to have stalled again. It's a little
disappointing.
I found no summary and stuff seems to get lost,
so I created a page on the wiki.
http://wiki.dlang.org/Versus_the_garbage_collector
