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![Andrew Morgan](/assets/img/avatar_default.png)
Closes #4583 Does slightly less than #5045, which prevented a room from being upgraded multiple times, one after another. This PR still allows that, but just prevents two from happening at the same time. Mostly just to mitigate the fact that servers are slow and it can take a moment for the room upgrade to actually complete. We don't want people sending another request to upgrade the room when really they just thought the first didn't go through.
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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