GNU bug report logs - #28590
Weak tables in 2.2.2 grow indefinitely

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Message #48 received at 28590-done <at> debbugs.gnu.org (full text, mbox):

From: ludo <at> gnu.org (Ludovic Courtès)
To: 28590-done <at> debbugs.gnu.org
Subject: Re: bug#28590: Weak tables in 2.2.2 grow indefinitely
Date: Tue, 07 Nov 2017 11:58:58 +0100

ludo <at> gnu.org (Ludovic Courtès) skribis:

> Consider this program:
>
> (use-modules (ice-9 format))
>
> (define loops 3000000)
>
> (define table
>   (make-weak-key-hash-table))
>
> (let loop ((i loops))
>   (unless #f ;(zero? i)
>     (when (zero? (modulo i 100000))
>       (format #t "heap-size: ~,2h MiB  table: ~s~%"
>               (/ (assoc-ref (gc-stats) 'heap-size) (expt 2. 20))
>               table))
>
>     (hashq-set! table (cons 1 2) #t)
>     (loop (1- i))))
>
> On 2.0.14, the heap size stays at around 24 MiB, and the table size is
> stable at 224,717 buckets (?).
>
> On 2.2.2, the heap grows indefinitely (though logarithmically).  It’s
> not deterministic though: sometimes the heap size stabilizes in the
> 140–300 MiB range, and sometimes it keeps growing endlessly even though
> the table size reaches a maxium at 7,190,537 entries.

This is fixed with Andy’s rewrite of weak tables to bucket-and-chains as
in 2.0:

  https://git.savannah.gnu.org/cgit/guile.git/commit/?h=stable-2.2&id=a053c0510c4a644f9453166b7b385cf30f6d3a21
  https://git.savannah.gnu.org/cgit/guile.git/commit/?h=stable-2.2&id=d01addeb1feba830ddd703e27f89576864a063ff
  https://git.savannah.gnu.org/cgit/guile.git/commit/?h=stable-2.2&id=dc8dda77e0c937abae42a76ea88c6e7995adbd9a
  https://lists.gnu.org/archive/html/guile-devel/2017-10/msg00051.html

\o/

Ludo’.

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