gh-93297: Make asyncio task groups prevent child tasks from being GCed (GH-93299) (#93305)

(cherry picked from commit e6a57678ca)

Co-authored-by: Yury Selivanov <yury@edgedb.com>

Co-authored-by: Yury Selivanov <yury@edgedb.com>

Lib/asyncio/taskgroups.py

@@ -3,8 +3,6 @@
 
 __all__ = ["TaskGroup"]
 
-import weakref
-
 from . import events
 from . import exceptions
 from . import tasks
@@ -19,8 +17,7 @@ class TaskGroup:
         self._loop = None
         self._parent_task = None
         self._parent_cancel_requested = False
-        self._tasks = weakref.WeakSet()
-        self._unfinished_tasks = 0
+        self._tasks = set()
         self._errors = []
         self._base_error = None
         self._on_completed_fut = None
@@ -29,8 +26,6 @@ class TaskGroup:
         info = ['']
         if self._tasks:
             info.append(f'tasks={len(self._tasks)}')
-        if self._unfinished_tasks:
-            info.append(f'unfinished={self._unfinished_tasks}')
         if self._errors:
             info.append(f'errors={len(self._errors)}')
         if self._aborting:
@@ -93,7 +88,7 @@ class TaskGroup:
         # can be cancelled multiple times if our parent task
         # is being cancelled repeatedly (or even once, when
         # our own cancellation is already in progress)
-        while self._unfinished_tasks:
+        while self._tasks:
             if self._on_completed_fut is None:
                 self._on_completed_fut = self._loop.create_future()
 
@@ -114,7 +109,7 @@ class TaskGroup:
 
             self._on_completed_fut = None
 
-        assert self._unfinished_tasks == 0
+        assert not self._tasks
 
         if self._base_error is not None:
             raise self._base_error
@@ -141,7 +136,7 @@ class TaskGroup:
     def create_task(self, coro, *, name=None, context=None):
         if not self._entered:
             raise RuntimeError(f"TaskGroup {self!r} has not been entered")
-        if self._exiting and self._unfinished_tasks == 0:
+        if self._exiting and not self._tasks:
             raise RuntimeError(f"TaskGroup {self!r} is finished")
         if context is None:
             task = self._loop.create_task(coro)
@@ -149,7 +144,6 @@ class TaskGroup:
             task = self._loop.create_task(coro, context=context)
         tasks._set_task_name(task, name)
         task.add_done_callback(self._on_task_done)
-        self._unfinished_tasks += 1
         self._tasks.add(task)
         return task
 
@@ -169,10 +163,9 @@ class TaskGroup:
                 t.cancel()
 
     def _on_task_done(self, task):
-        self._unfinished_tasks -= 1
-        assert self._unfinished_tasks >= 0
+        self._tasks.discard(task)
 
-        if self._on_completed_fut is not None and not self._unfinished_tasks:
+        if self._on_completed_fut is not None and not self._tasks:
             if not self._on_completed_fut.done():
                 self._on_completed_fut.set_result(True)
 

Misc/NEWS.d/next/Library/2022-05-27-13-18-18.gh-issue-93297.e2zuHz.rst

@@ -0,0 +1 @@
+Make asyncio task groups prevent child tasks from being GCed