mirror of
https://github.com/autc04/Retro68.git
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52 lines
1.5 KiB
Bash
52 lines
1.5 KiB
Bash
#! /bin/sh
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# Shell-based mutex using mkdir. This script is used in make to prefer
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# serialized execution to avoid consuming too much RAM. If reusing it,
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# bear in mind that the lock-breaking logic is not race-free, so disable
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# it in err() if concurrent execution could cause more serious problems.
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self=`basename $0`
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lockdir="$1" prog="$2"; shift 2 || exit 1
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# Remember when we started trying to acquire the lock.
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count=0
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err () {
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if test -f $lockdir/lock-$1.$$; then
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rm -rf $lockdir
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echo "$self: *** (PID $$) removed stale $lockdir" >&2
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# Possible variant for uses where races are more problematic:
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#echo "$self: *** (PID $$) giving up, maybe rm -r $lockdir" >&2
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#exit 42
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else
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touch $lockdir/lock-$1.$$
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fi
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}
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until mkdir "$lockdir" 2>/dev/null; do
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# Say something periodically so the user knows what's up.
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if [ `expr $count % 30` = 0 ]; then
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# Check for valid lock.
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if pid=`cat $lockdir/pid 2>/dev/null` && kill -0 $pid 2>/dev/null; then
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echo "$self: (PID $$) waiting $count sec to acquire $lockdir from PID $pid" >&2
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elif test -z "$pid"; then
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echo "$self: (PID $$) cannot read $lockdir/pid" >&2
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err nopid
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else
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echo "$self: (PID $$) cannot signal $lockdir owner PID $pid" >&2
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err dead
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fi
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fi
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sleep 1
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count=`expr $count + 1`
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done
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trap 'rm -rf "$lockdir"' 0
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echo $$ > $lockdir/pidT && mv $lockdir/pidT $lockdir/pid
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echo "$self: (PID $$) acquired $lockdir after $count seconds" >&2
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echo $prog "$@"
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$prog "$@"
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# The trap runs on exit.
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