D2 weak references

[Leandro Lucarella]

Jason House, el 25 de abril a las 14:19 me escribiste:
> > Is that I guess is very likely that 'tmp' get optimized out. Would
> > declaring it as volatile help? If not, I guess the only way to avoid that
> > race is add a root manually to the GC (or mark the weakref again as no
> > NO_SCAN). But both requires synchronization. =(
> 
> I would use tango.core.atomic that I took from the Tango D2 branch.
> Another option is inline asm, but I'd have to research how to do that.

I don't know how an atomic can help, I don't know much about atomics but
I think they don't have to be pointer sized (different architectures
provide different atomic types). And in any case you don't want tmp to be
atomic, you just don't want it to be optimized out, I think..

I guess asm can never get optimized (right?) so I think that should do.

BTW, that's wrong with volatile? I think it should work too.

> > > You're not considering what can happen if the weak ref dereferencing
> > > thread stops and the rest of the world wreaks havoc on the state of the
> > > world. A collection could run after checking the mark. If one is careful
> > > with that, and a copy of t is kept on the stack, will the optimizer
> > > reuse it? Or will it reread the value? That matters if the finalizer
> > > runs. The mark bit check can fail from reallocation after deletion.
> > > 
> > > I hope that helps...
> > 
> > Yes, thank you.
> 
> It's amazingly difficult to get right for something so "simple"

Indeed.

-- 
Leandro Lucarella (luca) | Blog colectivo: http://www.mazziblog.com.ar/blog/
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