periodic_scheduler

#!/bin/sh

# Copyright (c) 2014 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

# Run tasks periodically.
# Usage: $0  <delay_seconds> <task_name> <task_binary>
#
# Executes task <task_name> by running <task_binary> every <delay_seconds>.

set -e -u

SCRIPT_NAME="$(basename "$0")"
CHECK_DELAY=300  # Check every 5 minutes.
SPOOL_DIR=/var/spool/cron-lite

log() {
  logger -p local3.info -t "${SCRIPT_NAME}" "$@"
}

trap "log 'exiting'" EXIT

check_and_fix_spool_paths() {
  # Avoid weird spool paths if possible.
  test -L /var/spool && unlink /var/spool
  test -L "${SPOOL_DIR}" && unlink "${SPOOL_DIR}"
  mkdir -p "${SPOOL_DIR}"
  if [ ! -O "${SPOOL_DIR}" -o ! -d "${SPOOL_DIR}" ]; then
    log "Spool directory is damaged. Aborting!"
    exit 1
  fi
}

main() {
  local delay="$1"
  local name="$2"
  local spool_file="${SPOOL_DIR}/${name}"
  shift 2

  [ -z "${delay}" ] && exit 1
  [ -z "${name}" ] && exit 1
  [ $# -eq 0 ] && exit 1
  check_and_fix_spool_paths

  while true; do
    # Allow the sleep to be killed manually without terminating the handler.
    sleep "${CHECK_DELAY}" || true

    [ ! -e "${spool_file}" ] && touch "${spool_file}"

    local last_rotation="$(stat -c "%Y" "${spool_file}" 2>/dev/null || echo 0)"
    local now="$(date +%s)"
    local time_diff=$((now - last_rotation))

    if [ ${time_diff} -gt ${delay} ]; then
      rm "${spool_file}" || true
      touch "${spool_file}"
      # Make sure to reclaim status info about background processes.
      # At this point, all background processes should be dead.
      # We don't actually care about the result though.
      wait || true
      log "running $* for ${name}"
      (
        timeout -k ${CHECK_DELAY} sh -c '"$@"' -- "$@" || true
        log "${name} completed"
      ) &
    fi
  done
}

main "$@"