diff --git a/synapse/util/caches/response_cache.py b/synapse/util/caches/response_cache.py
index 0c2c347953..7f79333e96 100644
--- a/synapse/util/caches/response_cache.py
+++ b/synapse/util/caches/response_cache.py
@@ -14,6 +14,8 @@
# 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
@@ -48,15 +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 (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:
@@ -73,19 +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 (hashable):
- deferred (twisted.internet.defer.Deferred):
+ 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
@@ -144,7 +150,7 @@ class ResponseCache(object):
self._name, key)
d = run_in_background(callback, *args, **kwargs)
result = self.set(key, d)
- elif result.called:
+ elif not isinstance(result, defer.Deferred) or result.called:
logger.info("[%s]: using completed cached result for [%s]",
self._name, key)
else:
|
