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# -*- coding: utf-8 -*-
# Copyright 2014, 2015 OpenMarket Ltd
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from twisted.internet import defer
import logging
logger = logging.getLogger(__name__)
class Lock(object):
def __init__(self, deferred, key):
self._deferred = deferred
self.released = False
self.key = key
def release(self):
self.released = True
self._deferred.callback(None)
def __del__(self):
if not self.released:
logger.critical("Lock was destructed but never released!")
self.release()
def __enter__(self):
return self
def __exit__(self, type, value, traceback):
logger.debug("Releasing lock for key=%r", self.key)
self.release()
class LockManager(object):
""" Utility class that allows us to lock based on a `key` """
def __init__(self):
self._lock_deferreds = {}
@defer.inlineCallbacks
def lock(self, key):
""" Allows us to block until it is our turn.
Args:
key (str)
Returns:
Lock
"""
new_deferred = defer.Deferred()
old_deferred = self._lock_deferreds.get(key)
self._lock_deferreds[key] = new_deferred
if old_deferred:
logger.debug("Queueing on lock for key=%r", key)
yield old_deferred
logger.debug("Obtained lock for key=%r", key)
else:
logger.debug("Entering uncontended lock for key=%r", key)
defer.returnValue(Lock(new_deferred, key))
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