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synapse/util/lockutils.py

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+# -*- coding: utf-8 -*-
+# Copyright 2014 matrix.org
+#
+# 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):
+        self._deferred = deferred
+        self.released = False
+
+    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):
+        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:
+            yield old_deferred
+
+        defer.returnValue(Lock(new_deferred))