Mine

#!/bin/bash

SIG=-TERM   # default signal sent to the process when the timer expires
timeout=4  # default timeout
interval=1  # default interval between checks if the process is still alive
delay=2     # default delay between posting the given signal and
            # destroying the process (kill -KILL)
case $# in
  0) echo "$prog: $usage" >&2 ; exit 2 ;;
esac

(
  for t in $timeout $delay
  do
    while (( $t > $interval ))
    do
      sleep $interval
      kill -0 $$ || exit
      t=$(( $t - $interval ))
    done
    sleep $t
    kill $SIG $$ && kill -0 $$ || exit
    SIG=-KILL
  done
) 2> /dev/null &

trap "exit 0" SIGKILL SIGTERM

echo $$
exec "$@"