keyway_lib.sh

# dP
# 88
# 88  .dP  .d8888b. dP    dP dP  dP  dP .d8888b. dP    dP
# 88888"   88ooood8 88    88 88  88  88 88'  `88 88    88
# 88  `8b. 88.  ... 88.  .88 88.88b.88' 88.  .88 88.  .88
# dP   `YP `88888P' `8888P88 8888P Y8P  `88888P8 `8888P88
#                        .88                          .88
#                    d8888P                       d8888P
#
# A simple lock file library.
# Version 0.0.1
#
# Return Code Explanation:
# 1: Your application was not able to acquire lock.
# 2: There was some other problem:
#    a: Keyway could not create the lock directory.
#    b: Keyway could not create or remove a lock.
#
# Example Usage:
#
# #!/bin/bash
# source keyway_lib.sh
#
# acquire_lock_for "maintenance"
# echo "execute critical section"
# release_lock_for "maintenance"

# Customize the location of your lock files for this application.
LOCK_DIR="locks"

acquire_lock_for() {
  if not_locked $1; then
    lock_log "Creating $1 lock."
    touch "$LOCK_DIR/$1".lock
    check_execution "acquire lock"
  fi
}

release_lock_for() {
  lock_log "Releasing $1 lock."
  rm "$LOCK_DIR/$1".lock
  check_execution "release lock"
}

not_locked() {
  check_lock_dir
  for lock in "$LOCK_DIR"/*.lock
  do
    if [ -f $lock ]; then
      lock_log "Cannot run $1 -- application locked by $lock."
      exit 1
    fi
  done
}

check_lock_dir() {
  if [ ! -d $LOCK_DIR ]; then
    lock_log "Creating lock directory: $LOCK_DIR"
    mkdir -p $LOCK_DIR
    check_execution "create lock directory"
  fi
}

check_execution() {
  if [ $? -ne 0 ]; then
    lock_log "Could not $1, exiting."
    exit 2
  fi
}

lock_log() {
  datetime=`date +"%Y-%m-%d %H:%M:%S"`
  printf "$datetime - Keyway: $1\n"
}