Add task_group as application attribute

starlette/applications.py

@@ -1,6 +1,7 @@
 import typing
 
 import anyio
+from anyio.abc import TaskGroup
 
 from starlette.datastructures import State, URLPath
 from starlette.exceptions import ExceptionMiddleware
@@ -38,6 +39,8 @@ class Starlette:
     standard functions, or async functions.
     """
 
+    task_group: TaskGroup
+
     def __init__(
         self,
         debug: bool = False,
@@ -111,8 +114,8 @@ def url_path_for(self, name: str, **path_params: str) -> URLPath:
 
     async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
         scope["app"] = self
-        task_group = scope["task_group"] = anyio.create_task_group()
-        async with task_group:
+        self.task_group = anyio.create_task_group()
+        async with self.task_group:
             await self.middleware_stack(scope, receive, send)
 
     # The following usages are now discouraged in favour of configuration

starlette/middleware/base.py

@@ -29,13 +29,12 @@ async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
     async def call_next(self, request: Request) -> Response:
         send_stream, recv_stream = anyio.create_memory_object_stream()
         scope = request.scope
-        task_group = scope["task_group"]
 
         async def coro() -> None:
             async with send_stream:
                 await self.app(scope, request.receive, send_stream.send)
 
-        task_group.start_soon(coro)
+        scope["app"].task_group.start_soon(coro)
 
         try:
             message = await recv_stream.receive()