159 lines
5.5 KiB
Python
159 lines
5.5 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright 2016 OpenMarket Ltd
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import logging
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from twisted.internet import defer
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from synapse.util.async_helpers import ObservableDeferred
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from synapse.util.caches import register_cache
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from synapse.util.logcontext import make_deferred_yieldable, run_in_background
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logger = logging.getLogger(__name__)
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class ResponseCache(object):
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"""
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This caches a deferred response. Until the deferred completes it will be
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returned from the cache. This means that if the client retries the request
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while the response is still being computed, that original response will be
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used rather than trying to compute a new response.
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"""
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def __init__(self, hs, name, timeout_ms=0):
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self.pending_result_cache = {} # Requests that haven't finished yet.
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self.clock = hs.get_clock()
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self.timeout_sec = timeout_ms / 1000.0
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self._name = name
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self._metrics = register_cache("response_cache", name, self)
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def size(self):
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return len(self.pending_result_cache)
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def __len__(self):
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return self.size()
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def get(self, key):
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"""Look up the given key.
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Can return either a new Deferred (which also doesn't follow the synapse
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logcontext rules), or, if the request has completed, the actual
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result. You will probably want to make_deferred_yieldable the result.
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If there is no entry for the key, returns None. It is worth noting that
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this means there is no way to distinguish a completed result of None
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from an absent cache entry.
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Args:
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key (hashable):
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Returns:
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twisted.internet.defer.Deferred|None|E: None if there is no entry
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for this key; otherwise either a deferred result or the result
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itself.
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"""
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result = self.pending_result_cache.get(key)
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if result is not None:
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self._metrics.inc_hits()
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return result.observe()
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else:
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self._metrics.inc_misses()
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return None
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def set(self, key, deferred):
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"""Set the entry for the given key to the given deferred.
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*deferred* should run its callbacks in the sentinel logcontext (ie,
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you should wrap normal synapse deferreds with
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logcontext.run_in_background).
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Can return either a new Deferred (which also doesn't follow the synapse
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logcontext rules), or, if *deferred* was already complete, the actual
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result. You will probably want to make_deferred_yieldable the result.
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Args:
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key (hashable):
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deferred (twisted.internet.defer.Deferred[T):
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Returns:
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twisted.internet.defer.Deferred[T]|T: a new deferred, or the actual
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result.
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"""
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result = ObservableDeferred(deferred, consumeErrors=True)
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self.pending_result_cache[key] = result
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def remove(r):
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if self.timeout_sec:
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self.clock.call_later(
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self.timeout_sec, self.pending_result_cache.pop, key, None
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)
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else:
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self.pending_result_cache.pop(key, None)
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return r
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result.addBoth(remove)
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return result.observe()
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def wrap(self, key, callback, *args, **kwargs):
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"""Wrap together a *get* and *set* call, taking care of logcontexts
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First looks up the key in the cache, and if it is present makes it
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follow the synapse logcontext rules and returns it.
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Otherwise, makes a call to *callback(*args, **kwargs)*, which should
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follow the synapse logcontext rules, and adds the result to the cache.
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Example usage:
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@defer.inlineCallbacks
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def handle_request(request):
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# etc
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defer.returnValue(result)
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result = yield response_cache.wrap(
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key,
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handle_request,
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request,
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)
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Args:
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key (hashable): key to get/set in the cache
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callback (callable): function to call if the key is not found in
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the cache
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*args: positional parameters to pass to the callback, if it is used
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**kwargs: named parameters to pass to the callback, if it is used
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Returns:
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twisted.internet.defer.Deferred: yieldable result
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"""
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result = self.get(key)
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if not result:
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logger.info(
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"[%s]: no cached result for [%s], calculating new one", self._name, key
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)
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d = run_in_background(callback, *args, **kwargs)
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result = self.set(key, d)
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elif not isinstance(result, defer.Deferred) or result.called:
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logger.info("[%s]: using completed cached result for [%s]", self._name, key)
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else:
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logger.info(
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"[%s]: using incomplete cached result for [%s]", self._name, key
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)
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return make_deferred_yieldable(result)
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