RE: Accessing ForeignObj contents from Haskell

[Simon Marlow]

> [EMAIL PROTECTED] (Marcin 'Qrczak' Kowalczyk) wrote,
> 
> > Wed, 16 Aug 2000 07:32:48 -0700, Simon Marlow 
> <[EMAIL PROTECTED]> pisze:
> > 
> > > I'm not sure I understand; how does autoPtrToBytes work if it
> > > doesn't use a ForeignObj?
> > 
> > autoPtrToBytes:: Int -> IO (Ptr a)
> > autoPtrToBytes size = do
> >     ptr <- mallocBytes size
> >     addFinalizer ptr (free ptr)
> >     return ptr
> 
> This looks very nice.  My only concern is that
> `addFinalizer' is a weak pointer operation, and thus, not
> part of the core FFI (which only provides ForeignObj and
> StablePtr).

We shouldn't mandate addFinalizer as part of the FFI at least until we have
a solution to the identity problem.  The only safe addFinalizers are those
on primitive heap-resident objects (i.e. addForeignFinalizer, mkWeakIORef).

[ eg. our last thoughts on this were something like this:
        
        barrier :: a -> IO a

        as in   fo <- newForeignObj a
                  fo' <- barrier fo
                  addFinalizer fo' (...)
                  ... only use fo' ...

        barrier is another null primop.  But this is fairly ugly and 
        prevents some legitimate optimisations.

]

Cheers,
        Simon