locking for munin

git-svn-id: file:///svn/unbound/trunk@1253 be551aaa-1e26-0410-a405-d3ace91eadb9

diff --git a/contrib/unbound_munin_ b/contrib/unbound_munin_
index 4d7df61753a77aa6aec75e72c77c77d0d63359d5..a9c084a55d4a85552cd64c81375cffcdd1a1a529 100755 (executable)
--- a/contrib/unbound_munin_
+++ b/contrib/unbound_munin_
@@ -98,6 +98,7 @@ conf=${unbound_conf:-/usr/local/etc/unbound/unbound.conf}
 ctrl=${unbound_control:-/usr/local/sbin/unbound-control}
 warn=${spoof_warn:-1000}
 crit=${spoof_crit:-100000}
+lock=$state.lock
 
 # number of seconds between polling attempts.
 # makes the statefile hang around for at least this many seconds,
@@ -117,20 +118,39 @@ get_value ( ) {
 
 # download the state from the unbound server.
 get_state ( ) {
+       # obtain lock for fetching the state
+       # because there is a race condition in fetching and writing to file
+       i=0
+       while test ! -f $lock || test "`cat $lock`" != $$; do
+               while test -f $lock; do
+                       # wait
+                       i=`expr $i + 1`
+                       if test $i -gt 100000; then
+                               echo "error locking $lock" "=" `cat $lock`
+                               rm -f $lock
+                               exit 1
+                       fi
+               done
+               # try to get it
+               echo $$ >$lock
+       done
        # do not refetch if the file exists and only LEE seconds old
        if test -f $state; then
                now=`date +%s`
                get_value "time.now"
                value="`echo $value | sed -e 's/\..*$//'`"
                if test $now -lt `expr $value + $lee`; then
+                       rm -f $lock
                        return
                fi
        fi
        $ctrl -c $conf stats > $state
        if test $? -ne 0; then
                echo "error retrieving data from unbound server"
+               rm -f $lock
                exit 1
        fi
+       rm -f $lock
 }
 
 if test "$1" = "autoconf" ; then