| """license: Apache License 2.0, see LICENSE for more details.""" |
| """ZooKeeper Leader Elections |
| |
| :Maintainer: None |
| :Status: Unknown |
| |
| """ |
| from kazoo.exceptions import CancelledError |
| |
| |
| class Election(object): |
| """Kazoo Basic Leader Election |
| |
| Example usage with a :class:`~kazoo.client.KazooClient` instance:: |
| |
| zk = KazooClient() |
| election = zk.Election("/electionpath", "my-identifier") |
| |
| # blocks until the election is won, then calls |
| # my_leader_function() |
| election.run(my_leader_function) |
| |
| """ |
| def __init__(self, client, path, identifier=None): |
| """Create a Kazoo Leader Election |
| |
| :param client: A :class:`~kazoo.client.KazooClient` instance. |
| :param path: The election path to use. |
| :param identifier: Name to use for this lock contender. This |
| can be useful for querying to see who the |
| current lock contenders are. |
| |
| """ |
| self.lock = client.Lock(path, identifier) |
| |
| def run(self, func, *args, **kwargs): |
| """Contend for the leadership |
| |
| This call will block until either this contender is cancelled |
| or this contender wins the election and the provided leadership |
| function subsequently returns or fails. |
| |
| :param func: A function to be called if/when the election is |
| won. |
| :param args: Arguments to leadership function. |
| :param kwargs: Keyword arguments to leadership function. |
| |
| """ |
| if not callable(func): |
| raise ValueError("leader function is not callable") |
| |
| try: |
| with self.lock: |
| func(*args, **kwargs) |
| |
| except CancelledError: |
| pass |
| |
| def cancel(self): |
| """Cancel participation in the election |
| |
| .. note:: |
| |
| If this contender has already been elected leader, this |
| method will not interrupt the leadership function. |
| |
| """ |
| self.lock.cancel() |
| |
| def contenders(self): |
| """Return an ordered list of the current contenders in the |
| election |
| |
| .. note:: |
| |
| If the contenders did not set an identifier, it will appear |
| as a blank string. |
| |
| """ |
| return self.lock.contenders() |
