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Diffstat (limited to 'synapse/util/caches/snapshot_cache.py')
| -rw-r--r-- | synapse/util/caches/snapshot_cache.py | 94 |
1 files changed, 0 insertions, 94 deletions
diff --git a/synapse/util/caches/snapshot_cache.py b/synapse/util/caches/snapshot_cache.py deleted file mode 100644 index 8318db8d2c..0000000000 --- a/synapse/util/caches/snapshot_cache.py +++ /dev/null @@ -1,94 +0,0 @@ -# -*- coding: utf-8 -*- -# Copyright 2015, 2016 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_helpers import ObservableDeferred - - -class SnapshotCache(object): - """Cache for snapshots like the response of /initialSync. - The response of initialSync only has to be a recent snapshot of the - server state. It shouldn't matter to clients if it is a few minutes out - of date. - - This caches a deferred response. Until the deferred completes it will be - returned from the cache. This means that if the client retries the request - while the response is still being computed, that original response will be - used rather than trying to compute a new response. - - Once the deferred completes it will removed from the cache after 5 minutes. - We delay removing it from the cache because a client retrying its request - could race with us finishing computing the response. - - Rather than tracking precisely how long something has been in the cache we - keep two generations of completed responses. Every 5 minutes discard the - old generation, move the new generation to the old generation, and set the - new generation to be empty. This means that a result will be in the cache - somewhere between 5 and 10 minutes. - """ - - DURATION_MS = 5 * 60 * 1000 # Cache results for 5 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() - else: - return None - - 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) - return r - - result.addBoth(shuffle_along) - - return result.observe() |