gh-82504: deprecate the MultiLoopChildWatcher

Doc/library/asyncio-policy.rst

@@ -232,6 +232,7 @@ implementation used by the asyncio event loop:
    :py:data:`SIGCHLD` is received).
 
    .. versionadded:: 3.8
+   .. deprecated-removed:: 3.12 3.14
 
 .. class:: SafeChildWatcher
 

Doc/whatsnew/3.12.rst

@@ -139,6 +139,18 @@ CPython bytecode changes
 Deprecated
 ==========
 
+The following modules and APIs have been deprecated in this Python release,
+and will be removed in Python 3.14.
+
+APIs:
+
+* :class:`asyncio.MultiLoopChildWatcher` (:gh:`94648`)
+
+The following APIs were deprecated in this Python release and will be removed,
+although there is currently no date scheduled for their removal.
+
+APIs:
+
 * :class:`typing.Hashable` and :class:`typing.Sized` aliases for :class:`collections.abc.Hashable`
   and :class:`collections.abc.Sized`. (:gh:`94309`.)
 

Lib/asyncio/unix_events.py

@@ -1229,6 +1229,7 @@ class MultiLoopChildWatcher(AbstractChildWatcher):
     # but retrieves the current loop by get_running_loop()
 
     def __init__(self):
+        warnings._deprecated("asyncio.MultiLoopChildWatcher", remove=(3, 14))
         self._callbacks = {}
         self._saved_sighandler = None
 

Lib/test/test_asyncio/test_subprocess.py

@@ -666,13 +666,6 @@ class SubprocessThreadedWatcherTests(SubprocessWatcherMixin,
 
         Watcher = unix_events.ThreadedChildWatcher
 
-    @unittest.skip("bpo-38323: MultiLoopChildWatcher has a race condition \
-                    and these tests can hang the test suite")
-    class SubprocessMultiLoopWatcherTests(SubprocessWatcherMixin,
-                                          test_utils.TestCase):
-
-        Watcher = unix_events.MultiLoopChildWatcher
-
     class SubprocessSafeWatcherTests(SubprocessWatcherMixin,
                                      test_utils.TestCase):
 
@@ -701,6 +694,11 @@ class SubprocessPidfdWatcherTests(SubprocessWatcherMixin,
         Watcher = unix_events.PidfdChildWatcher
 
 
+    class MultiLoopChildWatcherTests(unittest.TestCase):
+        def test_deprecated(self):
+            with self.assertWarns(DeprecationWarning):
+                asyncio.MultiLoopChildWatcher()
+
     class GenericWatcherTests(test_utils.TestCase):
 
         def test_create_subprocess_fails_with_inactive_watcher(self):

Misc/NEWS.d/next/Library/2022-07-07-09-04-49.gh-issue-82504.6xtYAz.rst

@@ -0,0 +1 @@
+Deprecate :class:`asyncio.MultiLoopChildWatcher` to be removed in Python 3.14.