Source code for kazoo.recipe.barrier

"""Zookeeper Barriers

:Maintainer: None
:Status: Unknown

import os
import socket
import uuid

from kazoo.exceptions import KazooException, NoNodeError, NodeExistsError
from kazoo.protocol.states import EventType

[docs]class Barrier(object): """Kazoo Barrier Implements a barrier to block processing of a set of nodes until a condition is met at which point the nodes will be allowed to proceed. The barrier is in place if its node exists. .. warning:: The :meth:`wait` function does not handle connection loss and may raise :exc:`~kazoo.exceptions.ConnectionLossException` if the connection is lost while waiting. """
[docs] def __init__(self, client, path): """Create a Kazoo Barrier :param client: A :class:`~kazoo.client.KazooClient` instance. :param path: The barrier path to use. """ self.client = client self.path = path
[docs] def create(self): """Establish the barrier if it doesn't exist already""" self.client.retry(self.client.ensure_path, self.path)
[docs] def remove(self): """Remove the barrier :returns: Whether the barrier actually needed to be removed. :rtype: bool """ try: self.client.retry(self.client.delete, self.path) return True except NoNodeError: return False
[docs] def wait(self, timeout=None): """Wait on the barrier to be cleared :returns: True if the barrier has been cleared, otherwise False. :rtype: bool """ cleared = self.client.handler.event_object() def wait_for_clear(event): if event.type == EventType.DELETED: cleared.set() exists = self.client.exists(self.path, watch=wait_for_clear) if not exists: return True cleared.wait(timeout) return cleared.is_set()
[docs]class DoubleBarrier(object): """Kazoo Double Barrier Double barriers are used to synchronize the beginning and end of a distributed task. The barrier blocks when entering it until all the members have joined, and blocks when leaving until all the members have left. .. note:: You should register a listener for session loss as the process will no longer be part of the barrier once the session is gone. Connection losses will be retried with the default retry policy. """
[docs] def __init__(self, client, path, num_clients, identifier=None): """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. """ 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
[docs] def enter(self): """Enter the barrier, blocks until all nodes have entered""" try: self.client.retry(self._inner_enter) self.participating = True except KazooException: # We failed to enter, best effort cleanup self._best_effort_cleanup() self.participating = False
def _inner_enter(self): # make sure our barrier parent node exists if not self.assured_path: self.client.ensure_path(self.path) self.assured_path = True ready = self.client.handler.event_object() try: self.client.create( self.create_path, self._identifier.encode('utf-8'), ephemeral=True) except NodeExistsError: pass def created(event): if event.type == EventType.CREATED: ready.set() self.client.exists(self.path + '/' + 'ready', watch=created) children = self.client.get_children(self.path) if len(children) < self.num_clients: ready.wait() else: self.client.ensure_path(self.path + '/ready') return True
[docs] def leave(self): """Leave the barrier, blocks until all nodes have left""" try: self.client.retry(self._inner_leave) except KazooException: # pragma: nocover # Failed to cleanly leave self._best_effort_cleanup() self.participating = False
def _inner_leave(self): # Delete the ready node if its around try: self.client.delete(self.path + '/ready') except NoNodeError: pass while True: children = self.client.get_children(self.path) if not children: return True if len(children) == 1 and children[0] == self.node_name: self.client.delete(self.create_path) return True children.sort() ready = self.client.handler.event_object() def deleted(event): if event.type == EventType.DELETED: ready.set() if self.node_name == children[0]: # We're first, wait on the highest to leave if not self.client.exists(self.path + '/' + children[-1], watch=deleted): continue ready.wait() continue # Delete our node self.client.delete(self.create_path) # Wait on the first if not self.client.exists(self.path + '/' + children[0], watch=deleted): continue # Wait for the lowest to be deleted ready.wait() def _best_effort_cleanup(self): try: self.client.retry(self.client.delete, self.create_path) except NoNodeError: pass