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