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@@ -12,9 +12,15 @@
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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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+
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+from twisted.internet import defer
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from synapse.util.async import ObservableDeferred
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from synapse.util.caches import metrics as cache_metrics
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+from synapse.util.logcontext import make_deferred_yieldable, run_in_background
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+
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+logger = logging.getLogger(__name__)
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class ResponseCache(object):
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@@ -31,6 +37,7 @@ class ResponseCache(object):
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self.clock = hs.get_clock()
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self.timeout_sec = timeout_ms / 1000.
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+ self._name = name
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self._metrics = cache_metrics.register_cache(
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"response_cache",
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size_callback=lambda: self.size(),
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@@ -43,15 +50,21 @@ class ResponseCache(object):
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def get(self, key):
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"""Look up the given key.
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- Returns a deferred which doesn't follow the synapse logcontext rules,
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- so you'll probably want to make_deferred_yieldable it.
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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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+
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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 (str):
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+ key (hashable):
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Returns:
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- twisted.internet.defer.Deferred|None: None if there is no entry
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- for this key; otherwise a deferred result.
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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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@@ -68,19 +81,17 @@ class ResponseCache(object):
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you should wrap normal synapse deferreds with
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logcontext.run_in_background).
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- Returns a new Deferred which also doesn't follow the synapse logcontext
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- rules, so you will want to make_deferred_yieldable it
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-
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- (TODO: before using this more widely, it might make sense to refactor
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- it and get() so that they do the necessary wrapping rather than having
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- to do it everywhere ResponseCache is used.)
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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 (str):
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- deferred (twisted.internet.defer.Deferred):
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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
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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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@@ -97,3 +108,52 @@ class ResponseCache(object):
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result.addBoth(remove)
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return result.observe()
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+
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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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+
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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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+
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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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+
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+ Example usage:
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+
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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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+
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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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+
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+ Args:
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+ key (hashable): key to get/set in the cache
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+
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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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+
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+ *args: positional parameters to pass to the callback, if it is used
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+
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+ **kwargs: named paramters to pass to the callback, if it is used
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+
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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("[%s]: no cached result for [%s], calculating new one",
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+ self._name, key)
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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]",
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+ self._name, key)
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+ else:
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+ logger.info("[%s]: using incomplete cached result for [%s]",
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+ self._name, key)
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+ return make_deferred_yieldable(result)
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