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# -*- 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.caches.lrucache import LruCache
from collections import namedtuple
from . import register_cache
import threading
import logging
logger = logging.getLogger(__name__)
class DictionaryEntry(namedtuple("DictionaryEntry", ("full", "known_absent", "value"))):
"""Returned when getting an entry from the cache
Attributes:
full (bool): Whether the cache has the full or dict or just some keys.
If not full then not all requested keys will necessarily be present
in `value`
known_absent (set): Keys that were looked up in the dict and were not
there.
value (dict): The full or partial dict value
"""
def __len__(self):
return len(self.value)
class DictionaryCache(object):
"""Caches key -> dictionary lookups, supporting caching partial dicts, i.e.
fetching a subset of dictionary keys for a particular key.
"""
def __init__(self, name, max_entries=1000):
self.cache = LruCache(max_size=max_entries, size_callback=len)
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)
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):
"""Fetch an entry out of the cache
Args:
key
dict_key(list): If given a set of keys then return only those keys
that exist in the cache.
Returns:
DictionaryEntry
"""
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, entry.known_absent, dict(entry.value))
else:
return DictionaryEntry(entry.full, entry.known_absent, {
k: entry.value[k]
for k in dict_keys
if k in entry.value
})
self.metrics.inc_misses()
return DictionaryEntry(False, set(), {})
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, known_absent=None):
"""Updates the entry in the cache
Args:
sequence
key
value (dict): The value to update the cache with.
full (bool): Whether the given value is the full dict, or just a
partial subset there of. If not full then any existing entries
for the key will be updated.
known_absent (set): Set of keys that we know don't exist in the full
dict.
"""
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 known_absent is None:
known_absent = set()
if full:
self._insert(key, value, known_absent)
else:
self._update_or_insert(key, value, known_absent)
def _update_or_insert(self, key, value, known_absent):
# We pop and reinsert as we need to tell the cache the size may have
# changed
entry = self.cache.pop(key, DictionaryEntry(False, set(), {}))
entry.value.update(value)
entry.known_absent.update(known_absent)
self.cache[key] = entry
def _insert(self, key, value, known_absent):
self.cache[key] = DictionaryEntry(True, known_absent, value)
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