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"""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()
zk.start()
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()
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