diff options
Diffstat (limited to 'synapse/util/caches')
| -rw-r--r-- | synapse/util/caches/response_cache.py | 88 |
1 files changed, 74 insertions, 14 deletions
diff --git a/synapse/util/caches/response_cache.py b/synapse/util/caches/response_cache.py index 066fa423fd..7f79333e96 100644 --- a/synapse/util/caches/response_cache.py +++ b/synapse/util/caches/response_cache.py @@ -12,9 +12,15 @@ # 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 metrics as cache_metrics +from synapse.util.logcontext import make_deferred_yieldable, run_in_background + +logger = logging.getLogger(__name__) class ResponseCache(object): @@ -31,6 +37,7 @@ class ResponseCache(object): 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(), @@ -43,15 +50,21 @@ class ResponseCache(object): 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. + 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 (str): + key (hashable): Returns: - twisted.internet.defer.Deferred|None: None if there is no entry - for this key; otherwise a deferred result. + 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: @@ -68,19 +81,17 @@ class ResponseCache(object): 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.) + 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 (str): - deferred (twisted.internet.defer.Deferred): + key (hashable): + deferred (twisted.internet.defer.Deferred[T): Returns: - twisted.internet.defer.Deferred + twisted.internet.defer.Deferred[T]|T: a new deferred, or the actual + result. """ result = ObservableDeferred(deferred, consumeErrors=True) self.pending_result_cache[key] = result @@ -97,3 +108,52 @@ class ResponseCache(object): 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) |