Use WeakValueDictionary to drop a key's Lock as soon as nothing is contending for it

Author: JWCook

HISTORY.md

@@ -3,6 +3,7 @@
 ## Not released
 
 - Added `_ExpandedRequestOptions.refresh` to satisfy Pyright type checking.
+- Revert `lru_cache` for request lock to avoid binding to multiple event loops (`RuntimeError: ...Lock is bound to a different event loop`)
 
 ## 0.14.3 (2026-01-07)
 

aiohttp_client_cache/session.py

@@ -5,10 +5,10 @@
 import sys
 import warnings
 from asyncio import Lock
-from collections import defaultdict
 from contextlib import asynccontextmanager
 from logging import getLogger
 from typing import TYPE_CHECKING, cast
+from weakref import WeakValueDictionary
 
 from aiohttp import ClientSession
 from aiohttp.typedefs import StrOrURL
@@ -61,7 +61,8 @@ def __init__(
         **kwargs,
     ):
         self.cache = cache or CacheBackend()
-        self._locks: dict[str, Lock] = defaultdict(Lock)
+        # Drops a key's Lock as soon as nothing is contending for it
+        self._locks: WeakValueDictionary[str, Lock] = WeakValueDictionary()
         self._null_lock = nullcontext()
 
         # Pass along any valid kwargs for ClientSession (or custom session superclass)
@@ -89,7 +90,10 @@ async def _request(
         if actions.skip_read:
             lock: Lock | nullcontext = self._null_lock
         else:
-            lock = self._locks[key]
+            try:
+                lock = self._locks[key]
+            except KeyError:
+                lock = self._locks[key] = Lock()
 
         async with lock:
             response = await self.cache.request(actions)

test/unit/test_session.py

@@ -194,6 +194,22 @@ class CustomSession(CacheMixin, ClientSession):
     assert mock_request.called is False
 
 
+@patch.object(ClientSession, '_request', return_value=FakeClientResponse)
+async def test_session__locks_do_not_leak(mock_request):
+    """Locks are only needed while requests are actively contending for a cache key, so distinct
+    keys should not accumulate indefinitely.
+    """
+    cache = MagicMock(spec=CacheBackend)
+    cache.request.return_value = None
+    cache.create_key.side_effect = lambda method, url, **kwargs: str(url)
+
+    async with CachedSession(cache=cache) as session:
+        for i in range(1000):
+            await session.get(f'http://test.url/{i}')
+
+        assert len(session._locks) == 0
+
+
 @patch.object(ClientSession, '_request', return_value=FakeCachedResponse)
 async def test_session__cache_include_headers(mock_request):
     async with CachedSession(cache=CacheBackend(include_headers=True)) as session: