simonmar at microsoft.com
Tue Oct 15 05:44:39 EDT 2002
> I dont have cvs write access but you should mention something about
> expressing gc dependencies between ForeignPtr's. the only two
> ways to do
> this in the current haskell systems are
> * weak pointers
> * touchForeignPtr from the finalizer of another ForeignPtr
Actually I have a feeling that in GHC it doesn't work to use
touchForeignPtr from the finalizer of one ForeignPtr in order to keep
another alive. According to our semantics for weak pointers, I think
the two finalizers can still be run together, because pointers from a
finalizer are not followed when calculating reachability.
Hmm. I'm not sure what to do about this.
> if the second one is not allowed by restricting us to C only
> then the first needs to be added into the FFI, (or some other
> invented). I consider this functionality vital for any non-trivial use
> of ForeignPtr, and it becomes more important as we move more
> stuff to C
> land, as C structures become more common.
Yes, this is a good point. I'll add it to the document.
> for more info on the use of this, see the FFI touchForeignPtr
> documentation and the paper describing Weak pointers in ghc. the fact
> that multiple people saw the need for this and came up with solutions
> probably says something about its usefulness.
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