Preserve CurrentThreadExecutor across create_task

Fixes django#214.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

asgiref/sync.py

@@ -1,3 +1,4 @@
+import asyncio
 import asyncio.coroutines
 import contextvars
 import functools
@@ -175,6 +176,16 @@ def __call__(self, *args, **kwargs):
             if not (self.main_event_loop and self.main_event_loop.is_running()):
                 # Make our own event loop - in a new thread - and run inside that.
                 loop = asyncio.new_event_loop()
+                create_task = loop.create_task
+
+                def new_create_task(*args, **kwargs):
+                    task = create_task(*args, **kwargs)
+                    setattr(
+                        task, self.executors._attr_name, {"current": current_executor}
+                    )
+                    return task
+
+                loop.create_task = new_create_task
                 loop_executor = ThreadPoolExecutor(max_workers=1)
                 loop_future = loop_executor.submit(
                     self._run_event_loop, loop, awaitable

tests/test_sync.py

@@ -397,15 +397,21 @@ def test_thread_sensitive_outside_sync():
     @async_to_sync
     async def middle():
         await inner()
+        await asyncio.create_task(inner_task())
 
-    # Inner sync function
+    # Inner sync functions
     @sync_to_async
     def inner():
         result["thread"] = threading.current_thread()
 
+    @sync_to_async
+    def inner_task():
+        result["thread2"] = threading.current_thread()
+
     # Run it
     middle()
     assert result["thread"] == threading.current_thread()
+    assert result["thread2"] == threading.current_thread()
 
 
 @pytest.mark.asyncio