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Race condition determining value of $? variable
From: |
Марк Коренберг |
Subject: |
Race condition determining value of $? variable |
Date: |
Mon, 26 Feb 2007 16:49:16 +0500 |
Configuration Information [Automatically generated, do not change]:
Machine: i386
OS: linux-gnu
Compiler: i386-redhat-linux-gcc
Compilation CFLAGS: -DPROGRAM='bash' -DCONF_HOSTTYPE='i386'
-DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='i386-redhat-linux-gnu'
-DCONF_VENDOR='redhat' -DSHELL -DHAVE_CONFIG_H -I. -I. -I./include
-I./lib -D_GNU_SOURCE -O2 -march=i386 -mcpu=i686 -g
uname output: Linux server-testvpn 2.4.24 #33 SMP юФЧ жЕЧ 22 10:05:53
MSK 2007 i686 i686 i386 GNU/Linux
Machine Type: i386-redhat-linux-gnu
Bash Version: 2.05b
Patch Level: 0
Release Status: release
Description:
Race condition, appeared when background job completed in moment
between ending of foregroung program and calculating value of $? variable
Repeat-By:
set -m
exec 4>/dev/null
while true; do
usleep $((RANDOM*30)) >&4 2>&1 &
output=$( /bin/false )
#when sigchild appear here, become race condition ;-)
# and return value of usleep is placed to $?
# what was also tested:
# 1. manually written usleep which always return code 22 after sleeping
# tmp=$?; [ "$tmp" = 0 ] || continue ; echo $tmp => show 22
in the output
# 2. output=$( exec /bin/false ) - triggers race condition
# 3. output=`/bin/false` - trigger rage condition
# 4. /bin/false - NOT TRIGGERS
# 5. ( /bin/false ) - NOT TRIGGERS
[ "$?" = 0 ] || continue
echo "YEP! race condition catched!"
break;
done
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