bpo-31034: Reliable signal handler for test_asyncio (#2867) (#2876)

* bpo-31034: Reliable signal handler for test_asyncio

Don't rely on the current SIGHUP signal handler, make sure that it's
set to the "default" signal handler: SIG_DFL.

* Add comments

(cherry picked from commit 83008091)

Lib/test/test_asyncio/test_events.py

@@ -1980,6 +1980,11 @@ class SubprocessTestsMixin:
 
     @unittest.skipIf(sys.platform == 'win32', "Don't have SIGHUP")
     def test_subprocess_send_signal(self):
+        # bpo-31034: Make sure that we get the default signal handler (killing
+        # the process). The parent process may have decided to ignore SIGHUP,
+        # and signal handlers are inherited.
+        old_handler = signal.signal(signal.SIGHUP, signal.SIG_DFL)
+        try:
             prog = os.path.join(os.path.dirname(__file__), 'echo.py')
 
             connect = self.loop.subprocess_exec(
@@ -1993,6 +1998,8 @@ class SubprocessTestsMixin:
             self.loop.run_until_complete(proto.completed)
             self.assertEqual(-signal.SIGHUP, proto.returncode)
             transp.close()
+        finally:
+            signal.signal(signal.SIGHUP, old_handler)
 
     def test_subprocess_stderr(self):
         prog = os.path.join(os.path.dirname(__file__), 'echo2.py')

Lib/test/test_asyncio/test_subprocess.py

@@ -166,6 +166,11 @@ class SubprocessMixin:
 
     @unittest.skipIf(sys.platform == 'win32', "Don't have SIGHUP")
     def test_send_signal(self):
+        # bpo-31034: Make sure that we get the default signal handler (killing
+        # the process). The parent process may have decided to ignore SIGHUP,
+        # and signal handlers are inherited.
+        old_handler = signal.signal(signal.SIGHUP, signal.SIG_DFL)
+        try:
             code = 'import time; print("sleeping", flush=True); time.sleep(3600)'
             args = [sys.executable, '-c', code]
             create = asyncio.create_subprocess_exec(*args,
@@ -185,6 +190,8 @@ class SubprocessMixin:
 
             returncode = self.loop.run_until_complete(send_signal(proc))
             self.assertEqual(-signal.SIGHUP, returncode)
+        finally:
+            signal.signal(signal.SIGHUP, old_handler)
 
     def prepare_broken_pipe_test(self):
         # buffer large enough to feed the whole pipe buffer