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#! /bin/sh
# Shell-based mutex using mkdir.
lockdir="$1" prog="$2"; shift 2 || exit 1
# Remember when we started trying to acquire the lock.
count=0
touch lock-stamp.$$
trap 'rm -r "$lockdir" lock-stamp.$$' 0
until mkdir "$lockdir" 2>/dev/null; do
# Say something periodically so the user knows what's up.
if [ `expr $count % 30` = 0 ]; then
# Reset if the lock has been renewed.
if [ -n "`find \"$lockdir\" -newer lock-stamp.$$`" ]; then
touch lock-stamp.$$
count=1
# Steal the lock after 5 minutes.
elif [ $count = 300 ]; then
echo removing stale $lockdir >&2
rm -r "$lockdir"
else
echo waiting to acquire $lockdir >&2
fi
fi
sleep 1
count=`expr $count + 1`
done
echo $prog "$@"
$prog "$@"
# The trap runs on exit.
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