154 lines
5.2 KiB
Python
154 lines
5.2 KiB
Python
# -*- 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 synapse.util.async import ObservableDeferred
|
|
from synapse.util.caches import metrics as cache_metrics
|
|
from synapse.util.logcontext import make_deferred_yieldable, run_in_background
|
|
|
|
logger = logging.getLogger(__name__)
|
|
|
|
|
|
class ResponseCache(object):
|
|
"""
|
|
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.
|
|
"""
|
|
|
|
def __init__(self, hs, name, timeout_ms=0):
|
|
self.pending_result_cache = {} # Requests that haven't finished yet.
|
|
|
|
self.clock = hs.get_clock()
|
|
self.timeout_sec = timeout_ms / 1000.
|
|
|
|
self._name = name
|
|
self._metrics = cache_metrics.register_cache(
|
|
"response_cache",
|
|
size_callback=lambda: self.size(),
|
|
cache_name=name,
|
|
)
|
|
|
|
def size(self):
|
|
return len(self.pending_result_cache)
|
|
|
|
def get(self, key):
|
|
"""Look up the given key.
|
|
|
|
Returns a deferred which doesn't follow the synapse logcontext rules,
|
|
so you'll probably want to make_deferred_yieldable it.
|
|
|
|
Args:
|
|
key (hashable):
|
|
|
|
Returns:
|
|
twisted.internet.defer.Deferred|None: None if there is no entry
|
|
for this key; otherwise a deferred result.
|
|
"""
|
|
result = self.pending_result_cache.get(key)
|
|
if result is not None:
|
|
self._metrics.inc_hits()
|
|
return result.observe()
|
|
else:
|
|
self._metrics.inc_misses()
|
|
return None
|
|
|
|
def set(self, key, deferred):
|
|
"""Set the entry for the given key to the given deferred.
|
|
|
|
*deferred* should run its callbacks in the sentinel logcontext (ie,
|
|
you should wrap normal synapse deferreds with
|
|
logcontext.run_in_background).
|
|
|
|
Returns a new Deferred which also doesn't follow the synapse logcontext
|
|
rules, so you will want to make_deferred_yieldable it
|
|
|
|
(TODO: before using this more widely, it might make sense to refactor
|
|
it and get() so that they do the necessary wrapping rather than having
|
|
to do it everywhere ResponseCache is used.)
|
|
|
|
Args:
|
|
key (hashable):
|
|
deferred (twisted.internet.defer.Deferred):
|
|
|
|
Returns:
|
|
twisted.internet.defer.Deferred
|
|
"""
|
|
result = ObservableDeferred(deferred, consumeErrors=True)
|
|
self.pending_result_cache[key] = result
|
|
|
|
def remove(r):
|
|
if self.timeout_sec:
|
|
self.clock.call_later(
|
|
self.timeout_sec,
|
|
self.pending_result_cache.pop, key, None,
|
|
)
|
|
else:
|
|
self.pending_result_cache.pop(key, None)
|
|
return r
|
|
|
|
result.addBoth(remove)
|
|
return result.observe()
|
|
|
|
def wrap(self, key, callback, *args, **kwargs):
|
|
"""Wrap together a *get* and *set* call, taking care of logcontexts
|
|
|
|
First looks up the key in the cache, and if it is present makes it
|
|
follow the synapse logcontext rules and returns it.
|
|
|
|
Otherwise, makes a call to *callback(*args, **kwargs)*, which should
|
|
follow the synapse logcontext rules, and adds the result to the cache.
|
|
|
|
Example usage:
|
|
|
|
@defer.inlineCallbacks
|
|
def handle_request(request):
|
|
# etc
|
|
defer.returnValue(result)
|
|
|
|
result = yield response_cache.wrap(
|
|
key,
|
|
handle_request,
|
|
request,
|
|
)
|
|
|
|
Args:
|
|
key (hashable): key to get/set in the cache
|
|
|
|
callback (callable): function to call if the key is not found in
|
|
the cache
|
|
|
|
*args: positional parameters to pass to the callback, if it is used
|
|
|
|
**kwargs: named paramters to pass to the callback, if it is used
|
|
|
|
Returns:
|
|
twisted.internet.defer.Deferred: yieldable result
|
|
"""
|
|
result = self.get(key)
|
|
if not result:
|
|
logger.info("[%s]: no cached result for [%s], calculating new one",
|
|
self._name, key)
|
|
d = run_in_background(callback, *args, **kwargs)
|
|
result = self.set(key, d)
|
|
elif result.called:
|
|
logger.info("[%s]: using completed cached result for [%s]",
|
|
self._name, key)
|
|
else:
|
|
logger.info("[%s]: using incomplete cached result for [%s]",
|
|
self._name, key)
|
|
return make_deferred_yieldable(result)
|