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