MatrixSynapse/synapse/util/caches/dictionary_cache.py

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# -*- coding: utf-8 -*-
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# Copyright 2015, 2016 OpenMarket Ltd
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#
# 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.lrucache import LruCache
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from collections import namedtuple
from . import register_cache
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import threading
import logging
logger = logging.getLogger(__name__)
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class DictionaryEntry(namedtuple("DictionaryEntry", ("full", "value"))):
def __len__(self):
return len(self.value)
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class DictionaryCache(object):
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"""Caches key -> dictionary lookups, supporting caching partial dicts, i.e.
fetching a subset of dictionary keys for a particular key.
"""
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def __init__(self, name, max_entries=1000):
self.cache = LruCache(max_size=max_entries, size_callback=len)
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self.name = name
self.sequence = 0
self.thread = None
# caches_by_name[name] = self.cache
class Sentinel(object):
__slots__ = []
self.sentinel = Sentinel()
self.metrics = register_cache(name, self.cache)
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def check_thread(self):
expected_thread = self.thread
if expected_thread is None:
self.thread = threading.current_thread()
else:
if expected_thread is not threading.current_thread():
raise ValueError(
"Cache objects can only be accessed from the main thread"
)
def get(self, key, dict_keys=None):
entry = self.cache.get(key, self.sentinel)
if entry is not self.sentinel:
self.metrics.inc_hits()
if dict_keys is None:
return DictionaryEntry(entry.full, dict(entry.value))
else:
return DictionaryEntry(entry.full, {
k: entry.value[k]
for k in dict_keys
if k in entry.value
})
self.metrics.inc_misses()
return DictionaryEntry(False, {})
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def invalidate(self, key):
self.check_thread()
# Increment the sequence number so that any SELECT statements that
# raced with the INSERT don't update the cache (SYN-369)
self.sequence += 1
self.cache.pop(key, None)
def invalidate_all(self):
self.check_thread()
self.sequence += 1
self.cache.clear()
def update(self, sequence, key, value, full=False):
self.check_thread()
if self.sequence == sequence:
# Only update the cache if the caches sequence number matches the
# number that the cache had before the SELECT was started (SYN-369)
if full:
self._insert(key, value)
else:
self._update_or_insert(key, value)
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def _update_or_insert(self, key, value):
entry = self.cache.setdefault(key, DictionaryEntry(False, {}))
entry.value.update(value)
def _insert(self, key, value):
self.cache[key] = DictionaryEntry(True, value)