The Revenge of Finalizers
ross at soi.city.ac.uk
Wed Oct 16 20:28:14 EDT 2002
> [...] Can we easily identify which are the unsafe places and fix them?
> Look at all prims with types in IO. Look at what data structures they
> touch. Check if there are accesses to that data structure 'both
> sides' of a call to eval (there may be a few functions which invoke
> eval so watch for them). Check if any such accesses break data
> structure invariants.
> Since this can affect Hugs as it stands (when you use unsafePerformIO),
> would you mind taking a look?
There are over 200 calls to eval() in Hugs. Almost all of them look OK
on a cursory scan. As Alastair said, most are at the start of primitives,
and Hugs uses its stack and local variables a lot. But there's an unsafe
use in evalName(), and I don't understand the mutual recursion between
eval() and run().
There's another problem with Simon's patch I haven't been able to pin
down: if you run the example, interrupt it at the right point and type
another expression, the finalizers run, but the expression is lost.
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