# Source code for cherrypy.lib.locking

    import datetime

    class NeverExpires(object):

        def expired(self):
            return False

    class Timer(object):
        """A simple timer that will indicate when an expiration time has passed."""
        def __init__(self, expiration):
            'Create a timer that expires at `expiration` (UTC datetime)'
            self.expiration = expiration

        @classmethod
        def after(cls, elapsed):
            """Return a timer that will expire after `elapsed` passes."""
            return cls(
                datetime.datetime.now(datetime.timezone.utc) + elapsed,
            )

        def expired(self):
            return datetime.datetime.now(
                datetime.timezone.utc,
            ) >= self.expiration

    class LockTimeout(Exception):
        'An exception when a lock could not be acquired before a timeout period'

    class LockChecker(object):
        """Keep track of the time and detect if a timeout has expired."""
        def __init__(self, session_id, timeout):
            self.session_id = session_id
            if timeout:
                self.timer = Timer.after(timeout)
            else:
                self.timer = NeverExpires()

        def expired(self):
            if self.timer.expired():
                raise LockTimeout(
                    'Timeout acquiring lock for %(session_id)s' % vars(self))
            return False