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

* 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

Lib/test/test_asyncio/test_events.py

@@ -1980,19 +1980,26 @@ class SubprocessTestsMixin:
 
     @unittest.skipIf(sys.platform == 'win32', "Don't have SIGHUP")
     def test_subprocess_send_signal(self):
-        prog = os.path.join(os.path.dirname(__file__), 'echo.py')
-
-        connect = self.loop.subprocess_exec(
-                        functools.partial(MySubprocessProtocol, self.loop),
-                        sys.executable, prog)
-        transp, proto = self.loop.run_until_complete(connect)
-        self.assertIsInstance(proto, MySubprocessProtocol)
-        self.loop.run_until_complete(proto.connected)
-
-        transp.send_signal(signal.SIGHUP)
-        self.loop.run_until_complete(proto.completed)
-        self.assertEqual(-signal.SIGHUP, proto.returncode)
-        transp.close()
+        # 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(
+                            functools.partial(MySubprocessProtocol, self.loop),
+                            sys.executable, prog)
+            transp, proto = self.loop.run_until_complete(connect)
+            self.assertIsInstance(proto, MySubprocessProtocol)
+            self.loop.run_until_complete(proto.connected)
+
+            transp.send_signal(signal.SIGHUP)
+            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

@@ -166,25 +166,32 @@ class SubprocessMixin:
 
     @unittest.skipIf(sys.platform == 'win32', "Don't have SIGHUP")
     def test_send_signal(self):
-        code = 'import time; print("sleeping", flush=True); time.sleep(3600)'
-        args = [sys.executable, '-c', code]
-        create = asyncio.create_subprocess_exec(*args,
-                                                stdout=subprocess.PIPE,
-                                                loop=self.loop)
-        proc = self.loop.run_until_complete(create)
-
-        @asyncio.coroutine
-        def send_signal(proc):
-            # basic synchronization to wait until the program is sleeping
-            line = yield from proc.stdout.readline()
-            self.assertEqual(line, b'sleeping\n')
+        # 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,
+                                                    stdout=subprocess.PIPE,
+                                                    loop=self.loop)
+            proc = self.loop.run_until_complete(create)
 
-            proc.send_signal(signal.SIGHUP)
-            returncode = (yield from proc.wait())
-            return returncode
-
-        returncode = self.loop.run_until_complete(send_signal(proc))
-        self.assertEqual(-signal.SIGHUP, returncode)
+            @asyncio.coroutine
+            def send_signal(proc):
+                # basic synchronization to wait until the program is sleeping
+                line = yield from proc.stdout.readline()
+                self.assertEqual(line, b'sleeping\n')
+
+                proc.send_signal(signal.SIGHUP)
+                returncode = (yield from proc.wait())
+                return returncode
+
+            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