The Revenge of Finalizers

[Simon Marlow]

> > Indeed, I very nearly implemented such a thing as part of the patch
> > I sent out.  However, it didn't look trivial enough to implement so
> > I backed off.  The "blocked" state needs to be saved & restored at
> > various points: when starting a finalizer, when invoking a
> > foreign-exported function, and when invoking an exception handler.
> 
> I think it's fairly easy.  A sketch is something like:
>   
>   // primitive called from Haskell
>   void blockFinalizer(Cell m, State world) {
>     blocked += 1;
>     eval(ap(m,world));
>     blocked -= 1;
>     runFinalizers();
>   }

Does this run into problems with exceptions?

Also, this is a nested call to eval(), in a primitive, which can invoke
an IO action and therefore re-enter Haskell without going through
unsafePerformIO.  Is that safe?

Cheers,
	Simon