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# -*- coding: utf-8 -*-
# Copyright 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.caches import cache_counter, caches_by_name
from blist import sorteddict
import logging
logger = logging.getLogger(__name__)
class StreamChangeCache(object):
"""Keeps track of the stream positions of the latest change in a set of entities.
Typically the entity will be a room or user id.
Given a list of entities and a stream position, it will give a subset of
entities that may have changed since that position. If position key is too
old then the cache will simply return all given entities.
"""
def __init__(self, name, current_stream_pos, max_size=10000, prefilled_cache={}):
self._max_size = max_size
self._entity_to_key = {}
self._cache = sorteddict()
self._earliest_known_stream_pos = current_stream_pos
self.name = name
caches_by_name[self.name] = self._cache
for entity, stream_pos in prefilled_cache.items():
self.entity_has_changed(entity, stream_pos)
def has_entity_changed(self, entity, stream_pos):
"""Returns True if the entity may have been updated since stream_pos
"""
assert type(stream_pos) is int
if stream_pos < self._earliest_known_stream_pos:
cache_counter.inc_misses(self.name)
return True
if stream_pos == self._earliest_known_stream_pos:
# If the same as the earliest key, assume nothing has changed.
cache_counter.inc_hits(self.name)
return False
latest_entity_change_pos = self._entity_to_key.get(entity, None)
if latest_entity_change_pos is None:
cache_counter.inc_misses(self.name)
return True
if stream_pos < latest_entity_change_pos:
cache_counter.inc_misses(self.name)
return True
cache_counter.inc_hits(self.name)
return False
def get_entities_changed(self, entities, stream_pos):
"""Returns subset of entities that have had new things since the
given position. If the position is too old it will just return the given list.
"""
assert type(stream_pos) is int
if stream_pos >= self._earliest_known_stream_pos:
keys = self._cache.keys()
i = keys.bisect_right(stream_pos)
result = set(
self._cache[k] for k in keys[i:]
).intersection(entities)
cache_counter.inc_hits(self.name)
else:
result = entities
cache_counter.inc_misses(self.name)
return result
def entity_has_changed(self, entity, stream_pos):
"""Informs the cache that the entity has been changed at the given
position.
"""
assert type(stream_pos) is int
if stream_pos > self._earliest_known_stream_pos:
old_pos = self._entity_to_key.get(entity, None)
if old_pos:
stream_pos = max(stream_pos, old_pos)
self._cache.pop(old_pos, None)
self._cache[stream_pos] = entity
self._entity_to_key[entity] = stream_pos
while len(self._cache) > self._max_size:
k, r = self._cache.popitem()
self._earliest_known_stream_pos = max(k, self._earliest_known_stream_pos)
self._entity_to_key.pop(r, None)
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