gh-104144: Skip scheduling a done callback if a TaskGroup task completes eagerly (#104140)

Co-authored-by: Carl Meyer <carl@oddbird.net>

Author: itamaro

Diff for: Lib/asyncio/taskgroups.py

@@ -164,8 +164,14 @@ def create_task(self, coro, *, name=None, context=None):
         else:
             task = self._loop.create_task(coro, context=context)
         tasks._set_task_name(task, name)
-        task.add_done_callback(self._on_task_done)
-        self._tasks.add(task)
+        # optimization: Immediately call the done callback if the task is
+        # already done (e.g. if the coro was able to complete eagerly),
+        # and skip scheduling a done callback
+        if task.done():
+            self._on_task_done(task)
+        else:
+            self._tasks.add(task)
+            task.add_done_callback(self._on_task_done)
         return task
 
     # Since Python 3.8 Tasks propagate all exceptions correctly,

Diff for: Misc/NEWS.d/next/Library/2023-05-03-16-51-53.gh-issue-104144.653Q0P.rst

@@ -0,0 +1 @@
+Optimize :class:`asyncio.TaskGroup` when using :func:`asyncio.eager_task_factory`. Skip scheduling done callbacks when all tasks finish without blocking.