GH-94597: deprecate SafeChildWatcher, FastChildWatcher and MultiLoopChildWatcher child watchers (#98089)

Lib/test/test_asyncio/test_subprocess.py

@@ -4,7 +4,6 @@ import signal
 import sys
 import unittest
 import warnings
-import functools
 from unittest import mock
 
 import asyncio
@@ -31,19 +30,6 @@ PROGRAM_CAT = [
               'sys.stdout.buffer.write(data)'))]
 
 
-@functools.cache
-def _has_pidfd_support():
-    if not hasattr(os, 'pidfd_open'):
-        return False
-
-    try:
-        os.close(os.pidfd_open(os.getpid()))
-    except OSError:
-        return False
-
-    return True
-
-
 def tearDownModule():
     asyncio.set_event_loop_policy(None)
 
@@ -688,7 +674,7 @@ if sys.platform != 'win32':
             self.loop = policy.new_event_loop()
             self.set_event_loop(self.loop)
 
-            watcher = self.Watcher()
+            watcher = self._get_watcher()
             watcher.attach_loop(self.loop)
             policy.set_child_watcher(watcher)
 
@@ -703,32 +689,38 @@ if sys.platform != 'win32':
     class SubprocessThreadedWatcherTests(SubprocessWatcherMixin,
                                          test_utils.TestCase):
 
-        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
+        def _get_watcher(self):
+            return unix_events.ThreadedChildWatcher()
 
     class SubprocessSafeWatcherTests(SubprocessWatcherMixin,
                                      test_utils.TestCase):
 
-        Watcher = unix_events.SafeChildWatcher
+        def _get_watcher(self):
+            with self.assertWarns(DeprecationWarning):
+                return unix_events.SafeChildWatcher()
+
+    class MultiLoopChildWatcherTests(test_utils.TestCase):
+
+        def test_warns(self):
+            with self.assertWarns(DeprecationWarning):
+                unix_events.MultiLoopChildWatcher()
 
     class SubprocessFastWatcherTests(SubprocessWatcherMixin,
                                      test_utils.TestCase):
 
-        Watcher = unix_events.FastChildWatcher
+        def _get_watcher(self):
+            with self.assertWarns(DeprecationWarning):
+                return unix_events.FastChildWatcher()
 
     @unittest.skipUnless(
-        _has_pidfd_support(),
+        unix_events.can_use_pidfd(),
         "operating system does not support pidfds",
     )
     class SubprocessPidfdWatcherTests(SubprocessWatcherMixin,
                                       test_utils.TestCase):
-        Watcher = unix_events.PidfdChildWatcher
+
+        def _get_watcher(self):
+            return unix_events.PidfdChildWatcher()
 
 
     class GenericWatcherTests(test_utils.TestCase):
@@ -758,7 +750,7 @@ if sys.platform != 'win32':
 
 
         @unittest.skipUnless(
-            _has_pidfd_support(),
+            unix_events.can_use_pidfd(),
             "operating system does not support pidfds",
         )
         def test_create_subprocess_with_pidfd(self):