Start the server and check for modified files in a background thread.
        As soon as an update is detected, KeyboardInterrupt is thrown in
        the main thread to exit the server loop. The process exists with status
        code 3 to request a reload by the observer process. If the lockfile
        is not modified in 2*interval second or missing, we assume that the
        observer process died and exit with status code 1 or 2.

def _reloader_child(server, app, interval):
    ''' Start the server and check for modified files in a background thread.
        As soon as an update is detected, KeyboardInterrupt is thrown in
        the main thread to exit the server loop. The process exists with status
        code 3 to request a reload by the observer process. If the lockfile
        is not modified in 2*interval second or missing, we assume that the
        observer process died and exit with status code 1 or 2.
    '''
    lockfile = os.environ.get('BOTTLE_LOCKFILE')
    bgcheck = FileCheckerThread(lockfile, interval)
    try:
        bgcheck.start()
        server.run(app)
    except KeyboardInterrupt:
        pass
    bgcheck.status, status = 5, bgcheck.status
    bgcheck.join() # bgcheck.status == 5 --> silent exit
    if status: sys.exit(status)