gistfile1.sh

#!/bin/bash

if [ $# -gt 1 ]; then
CLIENT=$1
HOSTNAME=$2
else
  echo fail
  exit 1
fi


SCRIPT='
local client = KEYS[1]
local host = ARGV[1]

-- Decrement the count, if back to 0 release the munin-update
if redis.call("DECR", client .. "_hostcount") == 0 then
  redis.call("DEL", client)
  return 1
end
return 0
'

ret=`redis-cli EVAL "${SCRIPT}" 1 $CLIENT $HOSTNAME`
if [ $ret -eq 1 ]; then
  redis-cli "PUBLISH" "${CLIENT}hosts-finished" "munin-update go!"
fi
root@blackfish:/usr/local/bin# cat rsync_lock.sh
#!/bin/bash

if [ $# -gt 1 ]; then
CLIENT=$1
HOSTNAME=$2
else
  echo fail
  exit 1
fi


SCRIPT='
local client = KEYS[1]
local host = ARGV[1]
redis.call("SET", client .. "_hostcount", 0, "NX")
--  lock the client in the name of host if not exists, expires 120 seconds
if redis.call("SET", client, host, "EX", 120, "NX") == "OK" then
  return redis.call("INCR", client .. "_hostcount")
else
  if redis.call("get", client) ~= "munin-update" then
    -- another host is also sync set timeout back to 120 for us
    redis.call("EXPIRE", client, 120)
    return redis.call("INCR", client .. "_hostcount")
  end
  --  need to wait
  return -1
end
return 0
'

# ensure a value exists
redis-cli "SET" "${CLIENT}_hostcount" 0  "NX"
channel=${CLIENT}munin-update-finished

attempts=5
while [ `redis-cli EVAL "${SCRIPT}" 1 $CLIENT $HOSTNAME` -eq -1 ]; do
  if [ $attempts -eq 0 ]; then
    echo "failed to set ${CLIENT} to ${HOST} after 5 attempts"
    exit 2
  fi
  attempts=$(( $attempts - 1 )) 
  if [ -z "${sub_PID}" ]; then
    coproc sub { redis-cli --raw "SUBSCRIBE" "${channel}" ; }
    # read 3 lines that say we where subscribed
    read -ru ${sub[0]}; read -ru ${sub[0]};read -ru ${sub[0]};
  fi
  read -ru ${sub[0]};
  if [ "$REPLY" != 'message' ]; then
    kill $sub_PID
    exit 3
  fi
  read -ru ${sub[0]};
  if [ "$REPLY" != "${channel}" ]; then
    kill $sub_PID
    exit 4
  fi
  read -ru ${sub[0]};
  #echo "channel ${channel} message $REPLY"
done
[ ! -z "${sub_PID}" ] && kill $sub_PID
exit 0