Use weak refs for endpoint context cache

fastapi/routing.py

@@ -76,6 +76,7 @@ from starlette.routing import Mount as Mount  # noqa
 from starlette.types import AppType, ASGIApp, Lifespan, Receive, Scope, Send
 from starlette.websockets import WebSocket
 from typing_extensions import deprecated
+from weakref import WeakKeyDictionary
 
 
 # Copy of starlette.routing.request_response modified to include the
@@ -212,15 +213,17 @@ def _merge_lifespan_context(
 
 
 # Cache for endpoint context to avoid re-extracting on every request
-_endpoint_context_cache: dict[int, EndpointContext] = {}
+_endpoint_context_cache: WeakKeyDictionary[Any, EndpointContext] = WeakKeyDictionary()
 
 
 def _extract_endpoint_context(func: Any) -> EndpointContext:
     """Extract endpoint context with caching to avoid repeated file I/O."""
-    func_id = id(func)
-
-    if func_id in _endpoint_context_cache:
-        return _endpoint_context_cache[func_id]
+    try:
+        cached = _endpoint_context_cache.get(func)
+    except TypeError:
+        cached = None
+    if cached is not None:
+        return cached
 
     try:
         ctx: EndpointContext = {}
@@ -234,7 +237,10 @@ def _extract_endpoint_context(func: Any) -> EndpointContext:
     except Exception:
         ctx = EndpointContext()
 
-    _endpoint_context_cache[func_id] = ctx
+    try:
+        _endpoint_context_cache[func] = ctx
+    except TypeError:
+        pass
     return ctx
 
 

tests/test_routing_endpoint_context_cache.py

@@ -0,0 +1,25 @@
+import gc
+import weakref
+
+from fastapi.routing import _endpoint_context_cache, _extract_endpoint_context
+
+
+def _make_endpoint():
+    def endpoint():
+        return None
+
+    return endpoint
+
+
+def test_endpoint_context_cache_releases_endpoints():
+    endpoint = _make_endpoint()
+    _extract_endpoint_context(endpoint)
+    assert endpoint in _endpoint_context_cache
+
+    ref = weakref.ref(endpoint)
+    size_with_endpoint = len(_endpoint_context_cache)
+    del endpoint
+    gc.collect()
+
+    assert ref() is None
+    assert len(_endpoint_context_cache) <= size_with_endpoint - 1