support/scripts/simple_lock

#!/bin/sh
#
# creates a simple semaphore to allow separate concurrent build processes
# to safely write to the same file
#
# Based on this example
# http://unix.stackexchange.com/questions/70/what-unix-commands-can-be-used-as-a-semaphore-lock
#

print_error(){
  echo "Usage: $0 {create|remove} path"
  exit 1
}

if [[ -z "$2" ]]; then
  print_error
fi

path=$2

case "$1" in
  create)
  wait_time="1"
  while true; do
    if mkdir "${path}.lock.d"; then
      break;
    fi
  sleep $wait_time
  done
  ;; 

  remove)
    path="$2"
    rmdir "${path}.lock.d"
  ;;

  *)
    print_error
esac