GNU bug report logs - #9900
Using a guardian on a value in a weak hash

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Ian Price <ianprice90 <at> googlemail.com>
To: bug-guile <at> gnu.org
Subject: Using a guardian on a value in a weak hash
Date: Fri, 28 Oct 2011 21:42:45 +0100

Hi guilers,

If I 'guard' a value, and store it in a weak-key hashtable, then it
doesn't appear in the guardian even after it is removed from the
weak-hash by a garbage collection. Note, this only happens in a
_script_, and will work fine in a REPL (you should only need two GCs,
one for the weak hash, and one for the now free value).
e.g.


(define guardian (make-guardian))
(define finalizer-table (make-weak-key-hash-table))

(let ((f (lambda () (display "test\n"))))
  (guardian f)
  (hashq-set! finalizer-table (cons #f #f) f)
  #f)

(write finalizer-table)
(newline)

(gc)(gc)(gc)(gc)(gc)(gc)(gc)(gc)(gc)(gc)(gc)(gc)

(write finalizer-table)
(newline)

(write (guardian))
(newline)


will produce the output


[ian <at> Kagami guile]$ guile -s /tmp/gcbug.scm 
#<weak−key−hash−table 1/31>
#<weak−key−hash−table 0/31>
#f
[ian <at> Kagami guile]$ 

-- 
Ian Price

"Programming is like pinball. The reward for doing it well is
the opportunity to do it again" - from "The Wizardy Compiled"

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