[Haskell-cafe] ForeignPtrs with liveness dependencies

Einar Karttunen ekarttun at cs.helsinki.fi
Tue Jul 26 11:48:31 EDT 2005

"Simon Marlow" <simonmar at microsoft.com> writes:
> No, unfortunately not.  You have foo's finalizer which refers to bar via
> a touchForeignPtr.  If both foo and bar are unreachable (references from
> finalizers don't count), then both foo and bar's finalizers will be
> started together, and may run in any order.

I didn't realize the "references from finalizers don't count" rule.
What would happen if the finalizer of foo would resurrect bar after 
bar's finalizer has been run?

> So touchForeignPtr does only one thing: it expresses the precise
> relationship "bar is alive if foo is alive".  If both are not alive,
> then both finalizers can run, in any order.

So reference counting the objects is the solution?

> I realise this is very subtle.  By all means suggest improvements to the
> docs.

Mentioning that references from finalizers don't count could help
someone not to repeat my mistakes.

- Einar Karttunen

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