On Sunday, 28 April 2013 at 14:44:32 UTC, Steven Schveighoffer
wrote:
On Sat, 27 Apr 2013 07:58:25 -0700, Vladimir Panteleev
<vladi...@thecybershadow.net> wrote:
On Saturday, 27 April 2013 at 06:12:03 UTC, Steven
Schveighoffer wrote:
On Thu, 25 Apr 2013 10:57:13 -0700, Vladimir Panteleev
<vladi...@thecybershadow.net> wrote:
On Thursday, 25 April 2013 at 16:17:57 UTC, Jacob Carlborg
wrote:
You cannot access GC controlled memory in class destructors.
Not true.
Can you be more specific? Maybe the wording was too strong.
Should say "you shouldn't access GC controlled memory in
class destructors."
Or are you thinking of some specific case? Because the
opposite of the above is DEFINITELY not true. I just want to
make that clear.
Last time I checked, destructors were called separately from
deallocation. Thus, referencing memory will not result in
undefined behavior. The order of destruction is
non-deterministic, but otherwise, it's the same as accessing a
clear()'d object, which is perfectly safe (from a memory
safety perspective).
No, destructors are called along with deallocation. At the
moment, the GC mutex is held while the collection is in
progress, so it's not possible that a deallocated block could
be reallocated before a dtor that references that block is
called.
Right, so it makes no difference in practice.
What I meant was that IIRC early versions of the GC used to
rebuild internal free lists, and clobber freed data, in-loop with
calling destructors. Thus, when referencing something in a
destructor, sometimes you'd get the same object (not yet
finalized), and sometimes you'd get garbage. Now you get a
finalized object instead of garbage.
But that is an implementation detail. There is no requirement
for the GC to behave that way.
I don't disagree with you, but do we have a spec for GCs?
I'd think preserving memory safety, even in a destructor, would
be pretty important for a GC design.
In addition, there is no requirement for the GC to run in a
specific thread, so if a destroyed object references a
non-destroyed object, it's possible some thread is using the
non-destroyed object while the dtor is using it in another
thread, even if the object was only ever accessed from one
thread!
Sorry, not following. What's the problem? How is this related?
