diff --git a/changelog.d/8593.misc b/changelog.d/8593.misc
new file mode 100644
index 0000000000..d266ba19a4
--- /dev/null
+++ b/changelog.d/8593.misc
@@ -0,0 +1 @@
+Minor optimisations in caching code.
diff --git a/synapse/util/caches/deferred_cache.py b/synapse/util/caches/deferred_cache.py
index 6c162e9f34..601305487c 100644
--- a/synapse/util/caches/deferred_cache.py
+++ b/synapse/util/caches/deferred_cache.py
@@ -31,6 +31,7 @@ from typing import (
from prometheus_client import Gauge
from twisted.internet import defer
+from twisted.python import failure
from synapse.util.async_helpers import ObservableDeferred
from synapse.util.caches.lrucache import LruCache
@@ -214,9 +215,6 @@ class DeferredCache(Generic[KT, VT]):
callbacks = [callback] if callback else []
self.check_thread()
- observable = ObservableDeferred(value, consumeErrors=True)
- observer = observable.observe()
- entry = CacheEntry(deferred=observable, callbacks=callbacks)
existing_entry = self._pending_deferred_cache.pop(key, None)
if existing_entry:
@@ -224,6 +222,20 @@ class DeferredCache(Generic[KT, VT]):
# XXX: why don't we invalidate the entry in `self.cache` yet?
+ # we can save a whole load of effort if the deferred is ready.
+ if value.called:
+ result = value.result
+ if not isinstance(result, failure.Failure):
+ self.cache.set(key, result, callbacks)
+ return value
+
+ # otherwise, we'll add an entry to the _pending_deferred_cache for now,
+ # and add callbacks to add it to the cache properly later.
+
+ observable = ObservableDeferred(value, consumeErrors=True)
+ observer = observable.observe()
+ entry = CacheEntry(deferred=observable, callbacks=callbacks)
+
self._pending_deferred_cache[key] = entry
def compare_and_pop():
|
