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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 twisted.internet import defer
- from synapse.util.async import ObservableDeferred
- from synapse.util.caches import register_cache
- 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 = register_cache(
- "response_cache", name, self
- )
- def size(self):
- return len(self.pending_result_cache)
- def __len__(self):
- return self.size()
- def get(self, key):
- """Look up the given key.
- Can return either a new Deferred (which also doesn't follow the synapse
- logcontext rules), or, if the request has completed, the actual
- result. You will probably want to make_deferred_yieldable the result.
- If there is no entry for the key, returns None. It is worth noting that
- this means there is no way to distinguish a completed result of None
- from an absent cache entry.
- Args:
- key (hashable):
- Returns:
- twisted.internet.defer.Deferred|None|E: None if there is no entry
- for this key; otherwise either a deferred result or the result
- itself.
- """
- 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).
- Can return either a new Deferred (which also doesn't follow the synapse
- logcontext rules), or, if *deferred* was already complete, the actual
- result. You will probably want to make_deferred_yieldable the result.
- Args:
- key (hashable):
- deferred (twisted.internet.defer.Deferred[T):
- Returns:
- twisted.internet.defer.Deferred[T]|T: a new deferred, or the actual
- result.
- """
- 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 not isinstance(result, defer.Deferred) or 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)
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