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)
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