Fixed - async __call__ not run/awaited in the BackgroundTask

starlette/background.py

@@ -1,17 +1,23 @@
-import asyncio
+import inspect
 import typing
 
 from starlette.concurrency import run_in_threadpool
 
 
+def iscoroutinefunction(obj: object) -> bool:
+    if inspect.iscoroutinefunction(obj):
+        return True
+    return callable(obj) and inspect.iscoroutinefunction(obj.__call__)
+
+
 class BackgroundTask:
     def __init__(
         self, func: typing.Callable, *args: typing.Any, **kwargs: typing.Any
     ) -> None:
         self.func = func
         self.args = args
         self.kwargs = kwargs
-        self.is_async = asyncio.iscoroutinefunction(func)
+        self.is_async = iscoroutinefunction(func)
 
     async def __call__(self) -> None:
         if self.is_async:

tests/test_background.py

@@ -21,6 +21,26 @@ async def app(scope, receive, send):
     assert TASK_COMPLETE
 
 
+def test_async_callable_task(test_client_factory):
+    TASK_COMPLETE = False
+
+    class async_callable_task:
+        async def __call__(self):
+            nonlocal TASK_COMPLETE
+            TASK_COMPLETE = True
+
+    task = BackgroundTask(async_callable_task())
+
+    async def app(scope, receive, send):
+        response = Response("task initiated", media_type="text/plain", background=task)
+        await response(scope, receive, send)
+
+    client = test_client_factory(app)
+    response = client.get("/")
+    assert response.text == "task initiated"
+    assert TASK_COMPLETE
+
+
 def test_sync_task(test_client_factory):
     TASK_COMPLETE = False