'Create a Double Barrier
:param client: A :class:`~kazoo.client.KazooClient` instance.
:param path: The barrier path to use.
:param num_clients: How many clients must enter the barrier to
proceed.
:type num_clients: int
:param identifier: An identifier to use for this member of the
barrier when participating. Defaults to the
hostname + process id.'

def __init__(self, client, path, num_clients, identifier=None):

    self.client = client
    self.path = path
    self.num_clients = num_clients
    self._identifier = (identifier or ('%s-%s' % (socket.getfqdn(), os.getpid())))
    self.participating = False
    self.assured_path = False
    self.node_name = uuid.uuid4().hex
    self.create_path = ((self.path + '/') + self.node_name)
