* bug#10668: FFI: ‘set-pointer-finalizer!’ overrides the previous finalizer
@ 2012-01-30 22:31 Ludovic Courtès
2012-07-06 18:26 ` Andy Wingo
0 siblings, 1 reply; 2+ messages in thread
From: Ludovic Courtès @ 2012-01-30 22:31 UTC (permalink / raw)
To: 10668
Hi,
The ‘set-pointer-finalizer!’ procedure is harmful because it erases any
previously set finalizer.
Said finalizer could come from a guardian:
(define ptr (make-pointer 123))
(define g (make-guardian))
(g ptr)
(set-pointer-finalizer! ptr (dynamic-func "scm_is_pair" (dynamic-link)))
(set! ptr #f)
(gc)
(g) ;; Should return PTR.
=> #f
or from a weak hash table:
(define ptr (make-pointer 123))
(define t (make-weak-value-hash-table))
(hashq-set! t ptr #t)
(set-pointer-finalizer! ptr (dynamic-func "scm_is_pair" (dynamic-link)))
(set! ptr #f)
(gc)
(gc)
(hash-fold alist-cons '() t)
=> ((#<pointer 0x7b> . #t)) ;; Should be the empty list.
There are several ways to fix this:
1. Deprecate ‘set-pointer-finalizer!’ in favor of guardians, with the
problem that it would be up to the user to actually call the
guardians.
2. Implement ‘set-pointer-finalizer!’ in terms of guardians, with a
gc-hook to automatically call the guardians and invoke any
finalizers.
3. Fix ‘set-pointer-finalizer!’ to honor the previously-set finalizer,
if any. This means (a) finding a way to keep previous-finalizer
info around, and (b) duplicating part of the (hairy) code from
guardians.c to honor the previous finalizer.
None of these solutions is really pleasant.
Thoughts?
Thanks,
Ludo’.
^ permalink raw reply [flat|nested] 2+ messages in thread
* bug#10668: FFI: ‘set-pointer-finalizer!’ overrides the previous finalizer
2012-01-30 22:31 bug#10668: FFI: ‘set-pointer-finalizer!’ overrides the previous finalizer Ludovic Courtès
@ 2012-07-06 18:26 ` Andy Wingo
0 siblings, 0 replies; 2+ messages in thread
From: Andy Wingo @ 2012-07-06 18:26 UTC (permalink / raw)
To: Ludovic Courtès; +Cc: 10668-done
On Mon 30 Jan 2012 23:31, ludo@gnu.org (Ludovic Courtès) writes:
> The ‘set-pointer-finalizer!’ procedure is harmful because it erases any
> previously set finalizer.
>
> Said finalizer could come from a guardian:
>
> (define ptr (make-pointer 123))
> (define g (make-guardian))
> (g ptr)
> (set-pointer-finalizer! ptr (dynamic-func "scm_is_pair" (dynamic-link)))
> (set! ptr #f)
> (gc)
>
> (g) ;; Should return PTR.
> => #f
This has worked since 75ba64d6797f5857cc9885eb753126119a8c8b68.
Andy
--
http://wingolog.org/
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2012-01-30 22:31 bug#10668: FFI: ‘set-pointer-finalizer!’ overrides the previous finalizer Ludovic Courtès
2012-07-06 18:26 ` Andy Wingo
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