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111
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1 #! /bin/sh
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145
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2 # Shell-based mutex using mkdir. This script is used in make to prefer
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3 # serialized execution to avoid consuming too much RAM. If reusing it,
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4 # bear in mind that the lock-breaking logic is not race-free, so disable
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5 # it in err() if concurrent execution could cause more serious problems.
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111
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6
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145
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7 self=`basename $0`
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111
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8 lockdir="$1" prog="$2"; shift 2 || exit 1
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9
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10 # Remember when we started trying to acquire the lock.
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11 count=0
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145
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12
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13 err () {
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14 if test -f $lockdir/lock-$1.$$; then
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15 rm -rf $lockdir
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16 echo "$self: *** (PID $$) removed stale $lockdir" >&2
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111
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17
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145
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18 # Possible variant for uses where races are more problematic:
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19 #echo "$self: *** (PID $$) giving up, maybe rm -r $lockdir" >&2
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20 #exit 42
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21 else
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22 touch $lockdir/lock-$1.$$
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23 fi
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24 }
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111
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25
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26 until mkdir "$lockdir" 2>/dev/null; do
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27 # Say something periodically so the user knows what's up.
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28 if [ `expr $count % 30` = 0 ]; then
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145
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29 # Check for valid lock.
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30 if pid=`cat $lockdir/pid 2>/dev/null` && kill -0 $pid 2>/dev/null; then
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31 echo "$self: (PID $$) waiting $count sec to acquire $lockdir from PID $pid" >&2
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32 elif test -z "$pid"; then
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33 echo "$self: (PID $$) cannot read $lockdir/pid" >&2
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34 err nopid
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111
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35 else
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145
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36 echo "$self: (PID $$) cannot signal $lockdir owner PID $pid" >&2
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37 err dead
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111
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38 fi
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39 fi
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40 sleep 1
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41 count=`expr $count + 1`
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42 done
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43
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145
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44 trap 'rm -rf "$lockdir"' 0
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45 echo $$ > $lockdir/pidT && mv $lockdir/pidT $lockdir/pid
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46 echo "$self: (PID $$) acquired $lockdir after $count seconds" >&2
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47
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111
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48 echo $prog "$@"
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49 $prog "$@"
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50
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51 # The trap runs on exit.
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