Use a set for WheelTimer to better handle duplicates.

synapse/util/wheel_timer.py

@@ -11,17 +11,20 @@
 # 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.
-from typing import Generic, List, TypeVar
+from typing import Generic, Hashable, List, Set, TypeVar
 
-T = TypeVar("T")
+T = TypeVar("T", bound=Hashable)
 
 
 class _Entry(Generic[T]):
     __slots__ = ["end_key", "queue"]
 
     def __init__(self, end_key: int) -> None:
         self.end_key: int = end_key
-        self.queue: List[T] = []
+
+        # We use a set here as otherwise we can end up with a lot of duplicate
+        # entries.
+        self.queue: Set[T] = set()
 
 
 class WheelTimer(Generic[T]):
@@ -55,7 +58,7 @@ def insert(self, now: int, obj: T, then: int) -> None:
 
             if then_key <= max_key:
                 # The max here is to protect against inserts for times in the past
-                self.entries[max(min_key, then_key) - min_key].queue.append(obj)
+                self.entries[max(min_key, then_key) - min_key].queue.add(obj)
                 return
 
         next_key = int(now / self.bucket_size) + 1
@@ -71,7 +74,7 @@ def insert(self, now: int, obj: T, then: int) -> None:
         # to insert. This ensures there are no gaps.
         self.entries.extend(_Entry(key) for key in range(last_key, then_key + 1))
 
-        self.entries[-1].queue.append(obj)
+        self.entries[-1].queue.add(obj)
 
     def fetch(self, now: int) -> List[T]:
         """Fetch any objects that have timed out
@@ -84,7 +87,7 @@ def fetch(self, now: int) -> List[T]:
         """
         now_key = int(now / self.bucket_size)
 
-        ret = []
+        ret: List[T] = []
         while self.entries and self.entries[0].end_key <= now_key:
             ret.extend(self.entries.pop(0).queue)