/usr/lib/python2.7/dist-packages/kazoo/recipe/barrier.py is in python-kazoo 2.2.1-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 | """Zookeeper Barriers
:Maintainer: None
:Status: Unknown
"""
import os
import socket
import uuid
from kazoo.protocol.states import EventType
from kazoo.exceptions import KazooException
from kazoo.exceptions import NoNodeError
from kazoo.exceptions import NodeExistsError
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.
"""
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
def create(self):
"""Establish the barrier if it doesn't exist already"""
self.client.retry(self.client.ensure_path, self.path)
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
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()
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.
"""
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
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
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
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