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

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Message #8 received at 9900 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Israelsson Tampe <stefan.itampe <at> gmail.com>
To: 9900 <at> debbugs.gnu.org
Subject: Re: bug#9900: Using a guardian on a value in a weak hash
Date: Sat, 29 Oct 2011 19:42:13 +0200

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f below in the code is referencing a direct function and not a closure that
is not gc:able it seams
although there is no references to it. It looks like the loaded file
references that code and it will not be
gc:ed until the same file is loaded again (make sure to save the old
guardian so that one can inspect)
The weak key hastable is wrongly used and swaping key and value gives
correct behavior

Regards
Stefan

On Fri, Oct 28, 2011 at 10:42 PM, Ian Price <ianprice90 <at> googlemail.com>wrote:

>
> 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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