docker-mailserver/target/scripts/helpers/lock.sh

#! /bin/bash

# This becomes the sourcing script name
# (example: check-for-changes.sh)
SCRIPT_NAME="$(basename "$0")"
# Used inside of lock files to identify them and
# prevent removal by other instances of docker-mailserver
LOCK_ID="$(uuid)"

function _create_lock
{
  LOCK_FILE="/tmp/docker-mailserver/${SCRIPT_NAME}.lock"
  while [[ -e "${LOCK_FILE}" ]]
  do
    _log 'warn' "Lock file '${LOCK_FILE}' exists - another execution of '${SCRIPT_NAME}' is happening - trying again shortly"
    # Handle stale lock files left behind on crashes
    # or premature/non-graceful exits of containers while they're making changes
    if [[ -n "$(find "${LOCK_FILE}" -mmin +1 2>/dev/null)" ]]
    then
      _log 'warn' 'Lock file older than 1 minute - removing stale lock file'
      rm -f "${LOCK_FILE}"
    fi
    sleep 5
  done
  trap _remove_lock EXIT

  _log 'trace' "Creating lock ${LOCK_FILE}"
  echo "${LOCK_ID}" >"${LOCK_FILE}"
}

function _remove_lock
{
  LOCK_FILE="${LOCK_FILE:-"/tmp/docker-mailserver/${SCRIPT_NAME}.lock"}"
  [[ -z "${LOCK_ID}" ]] && _exit_with_error "Cannot remove ${LOCK_FILE} as there is no LOCK_ID set"
  if [[ -e "${LOCK_FILE}" ]] && grep -q "${LOCK_ID}" "${LOCK_FILE}" # Ensure we don't delete a lock that's not ours
  then
    rm -f "${LOCK_FILE}"
    _log 'trace' "Removed lock ${LOCK_FILE}"
  fi
}