GNU bug report logs - #17466
unexpected bytevector contents with get-bytevector-n

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: J Kalbhenn <jkal <at> posteo.eu>
Subject: bug#17466: closed (Re: bug#17466: unexpected bytevector contents
 with get-bytevector-n)
Date: Wed, 28 May 2014 17:33:03 +0000

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Your bug report

#17466: unexpected bytevector contents with get-bytevector-n

which was filed against the guile package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 17466 <at> debbugs.gnu.org.

-- 
17466: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=17466
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: ludo <at> gnu.org (Ludovic Courtès)
To: J Kalbhenn <jkal <at> posteo.eu>
Cc: 17466-done <at> debbugs.gnu.org
Subject: Re: bug#17466: unexpected bytevector contents with get-bytevector-n
Date: Wed, 28 May 2014 19:32:22 +0200

This is fixed by commit 1baa215, which will be in Guile 2.0.12.

It turns out that when shrinking a bytevector, as happens before
‘get-bytevector-n’ returns, the pointer to the bytevector’s contents
would not be left pointing to the old bytevector.  When that old
bytevector was eventually reclaimed, anything could happen.

Thanks!

Ludo’.

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From: J Kalbhenn <jkal <at> posteo.eu>
To: bug-guile <at> gnu.org
Subject: unexpected bytevector contents with get-bytevector-n
Date: Sun, 11 May 2014 13:00:23 +0200

concerning the following code example
--
(import (rnrs io ports) (ice-9 pretty-print))
(define (problem-part port) (pretty-print (get-bytevector-n port 4096)))

(let loop ((count 100))
  (if (> count 0)
    (begin (call-with-input-string "22222222222222222222" problem-part)
(loop (- count 1)))))
__

when i run it i get output with portions like this
--
#vu8(50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50)
#vu8(0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0)
#vu8(50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50)
#vu8(50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50)
#vu8(50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50)
#vu8(50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50)
#vu8(50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50)
#vu8(50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50)
#vu8(0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0)
#vu8(50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50)
#vu8(50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50)
#vu8(50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50)
#vu8(50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50)
#vu8(50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50)
#vu8(50 50 50 50 50 50 50 50 16 224 240 0 0 0 0 0 50 50 50 50)
#vu8(50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50)
--

and i would expect the bytevector to always be the same.

this first occurred to me in a more complicated scenario where:
  - the input port is a file-port
  - pretty-print was used at first and then display instead, but the
problem persisted with a much lower frequency

system info
  guile 2.0.11
  linux 3.14.2-1-ARCH x86_64

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