gh-87079: Warn on unintended signal wakeup fd override in `asyncio` (#96807)

Warn on loop initialization, when setting the wakeup fd disturbs a previously set wakeup fd, and on loop closing, when upon resetting the wakeup fd, we find it has been changed by someone else.

1 files changed, 24 insertions, 0 deletions

diff --git a/Lib/test/test_asyncio/test_unix_events.py b/Lib/test/test_asyncio/test_unix_events.py
index 5bad21ecbae..1ec627f63ee 100644
--- a/Lib/test/test_asyncio/test_unix_events.py
+++ b/Lib/test/test_asyncio/test_unix_events.py
@@ -89,6 +89,17 @@ class SelectorEventLoopSignalTests(test_utils.TestCase):
             signal.SIGINT, lambda: True)
 
     @mock.patch('asyncio.unix_events.signal')
+    def test_add_signal_handler_setup_warn(self, m_signal):
+        m_signal.NSIG = signal.NSIG
+        m_signal.valid_signals = signal.valid_signals
+        m_signal.set_wakeup_fd.return_value = -1000
+
+        with self.assertWarnsRegex(
+            ResourceWarning, 'Signal wakeup fd was already set'
+        ):
+            self.loop.add_signal_handler(signal.SIGINT, lambda: True)
+
+    @mock.patch('asyncio.unix_events.signal')
     def test_add_signal_handler_coroutine_error(self, m_signal):
         m_signal.NSIG = signal.NSIG
 
@@ -214,6 +225,19 @@ class SelectorEventLoopSignalTests(test_utils.TestCase):
         self.assertTrue(m_logging.info)
 
     @mock.patch('asyncio.unix_events.signal')
+    def test_remove_signal_handler_cleanup_warn(self, m_signal):
+        m_signal.NSIG = signal.NSIG
+        m_signal.valid_signals = signal.valid_signals
+        self.loop.add_signal_handler(signal.SIGHUP, lambda: True)
+
+        m_signal.set_wakeup_fd.return_value = -1000
+
+        with self.assertWarnsRegex(
+            ResourceWarning, 'Got unexpected signal wakeup fd'
+        ):
+            self.loop.remove_signal_handler(signal.SIGHUP)
+
+    @mock.patch('asyncio.unix_events.signal')
     def test_remove_signal_handler_error(self, m_signal):
         m_signal.NSIG = signal.NSIG
         m_signal.valid_signals = signal.valid_signals