D2 weak references

[Daniel Keep]

Sean Kelly wrote:
> Jason House wrote:
>> Jason House wrote:
>>
>>> Tango's GC (and therefore
>>> druntime's GC) has an explicit notification mechanism.
>>
>> I guess I shouldn't have assumed that the features of tango became
>> part of druntime.  I don't see any notification mechanism :(
> 
> Same as Tango:
> 
> alias void delegate(Object) DEvent;
> extern (C) void rt_attachDisposeEvent(Object h, DEvent e);
> extern (C) void rt_detachDisposeEvent(Object h, DEvent e);
> 
> I should probably expose these in core.runtime.

How are these events dispatched?  I remember a discussion about race
conditions if these events were fired off after all threads had been
resumed; you could have the event zero out the weak ref AFTER something
else had dereferenced it.

If that's still a possibility, maybe you could add a case where if the
delegate's funcptr is null, it just assumes the context pointer points
to a void*.sizeof word and zeroes it out.  You could do that without
resuming threads.

  -- Daniel