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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.
import logging
from sortedcontainers import SortedDict
from synapse.util import caches
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=None):
self._max_size = int(max_size * caches.CACHE_SIZE_FACTOR)
self._entity_to_key = {}
self._cache = SortedDict()
self._earliest_known_stream_pos = current_stream_pos
self.name = name
self.metrics = caches.register_cache("cache", self.name, self._cache)
if prefilled_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 or type(stream_pos) is long
if stream_pos < self._earliest_known_stream_pos:
self.metrics.inc_misses()
return True
latest_entity_change_pos = self._entity_to_key.get(entity, None)
if latest_entity_change_pos is None:
self.metrics.inc_hits()
return False
if stream_pos < latest_entity_change_pos:
self.metrics.inc_misses()
return True
self.metrics.inc_hits()
return False
def get_entities_changed(self, entities, stream_pos):
"""
Returns subset of entities that have had new things since the given
position. Entities unknown to the cache will be returned. 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:
not_known_entities = set(entities) - set(self._entity_to_key)
result = (
{self._cache[k] for k in self._cache.islice(
start=self._cache.bisect_right(stream_pos))}
.intersection(entities)
.union(not_known_entities)
)
self.metrics.inc_hits()
else:
result = set(entities)
self.metrics.inc_misses()
return result
def has_any_entity_changed(self, stream_pos):
"""Returns if any entity has changed
"""
assert type(stream_pos) is int
if not self._cache:
# If we have no cache, nothing can have changed.
return False
if stream_pos >= self._earliest_known_stream_pos:
self.metrics.inc_hits()
return self._cache.bisect_right(stream_pos) < len(self._cache)
else:
self.metrics.inc_misses()
return True
def get_all_entities_changed(self, stream_pos):
"""Returns all entites that have had new things since the given
position. If the position is too old it will return None.
"""
assert type(stream_pos) is int
if stream_pos >= self._earliest_known_stream_pos:
return [self._cache[k] for k in self._cache.islice(
start=self._cache.bisect_right(stream_pos))]
else:
return None
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 is not None:
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(0)
self._earliest_known_stream_pos = max(
k, self._earliest_known_stream_pos,
)
self._entity_to_key.pop(r, None)
def get_max_pos_of_last_change(self, entity):
"""Returns an upper bound of the stream id of the last change to an
entity.
"""
return self._entity_to_key.get(entity, self._earliest_known_stream_pos)
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