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# -*- coding: utf-8 -*-
# Copyright 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 synapse.util.async import ObservableDeferred
class SnapshotCache(object):
DURATION_MS = 5 * 60 * 1000 # Cache results for 2 minutes.
def __init__(self):
self.pending_result_cache = {} # Request that haven't finished yet.
self.prev_result_cache = {} # The older requests that have finished.
self.next_result_cache = {} # The newer requests that have finished.
self.time_last_rotated_ms = 0
def rotate(self, time_now_ms):
# Rotate once if the cache duration has passed since the last rotation.
if time_now_ms - self.time_last_rotated_ms >= self.DURATION_MS:
self.prev_result_cache = self.next_result_cache
self.next_result_cache = {}
self.time_last_rotated_ms += self.DURATION_MS
# Rotate again if the cache duration has passed twice since the last
# rotation.
if time_now_ms - self.time_last_rotated_ms >= self.DURATION_MS:
self.prev_result_cache = self.next_result_cache
self.next_result_cache = {}
self.time_last_rotated_ms = time_now_ms
def get(self, time_now_ms, key):
self.rotate(time_now_ms)
# This cache is intended to deduplicate requests, so we expect it to be
# missed most of the time. So we just lookup the key in all of the
# dictionaries rather than trying to short circuit the lookup if the
# key is found.
result = self.prev_result_cache.get(key)
result = self.next_result_cache.get(key, result)
result = self.pending_result_cache.get(key, result)
if result is not None:
return result.observe()
def set(self, time_now_ms, key, deferred):
self.rotate(time_now_ms)
result = ObservableDeferred(deferred)
self.pending_result_cache[key] = result
def shuffle_along(r):
# When the deferred completes we shuffle it along to the first
# generation of the result cache. So that it will eventually
# expire from the rotation of that cache.
self.next_result_cache[key] = result
self.pending_result_cache.pop(key, None)
result.observe().addBoth(shuffle_along)
return result.observe()
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