1#! /bin/sh
2# Shell-based mutex using mkdir.
3
4lockdir="$1" prog="$2"; shift 2 || exit 1
5
6# Remember when we started trying to acquire the lock.
7count=0
8touch lock-stamp.$$
9
10trap 'rm -r "$lockdir" lock-stamp.$$' 0
11
12until mkdir "$lockdir" 2>/dev/null; do
13    # Say something periodically so the user knows what's up.
14    if [ `expr $count % 30` = 0 ]; then
15	# Reset if the lock has been renewed.
16	if [ -n "`find \"$lockdir\" -newer lock-stamp.$$`" ]; then
17	    touch lock-stamp.$$
18	    count=1
19	# Steal the lock after 5 minutes.
20	elif [ $count = 300 ]; then
21	    echo removing stale $lockdir >&2
22	    rm -r "$lockdir"
23	else
24	    echo waiting to acquire $lockdir >&2
25	fi
26    fi
27    sleep 1
28    count=`expr $count + 1`
29done
30
31echo $prog "$@"
32$prog "$@"
33
34# The trap runs on exit.
35