bpo-31479: Always reset the signal alarm in tests (GH-3588) (GH-7314)

* bpo-31479: Always reset the signal alarm in tests

Use "try: ... finally: signal.signal(0)" pattern to make sure that
tests don't "leak" a pending fatal signal alarm.

* Move two more alarm() calls into the try block

Fix also typo: replace signal.signal(0) with signal.alarm(0)

* Move another signal.alarm() into the try block

(cherry picked from commit 9abee722)

Lib/test/test_io.py

@@ -3146,7 +3146,6 @@ class SignalsTest(unittest.TestCase):
         try:
             wio = self.io.open(w, **fdopen_kwargs)
             t.start()
-            signal.alarm(1)
             # Fill the pipe enough that the write will be blocking.
             # It will be interrupted by the timer armed above.  Since the
             # other thread has read one byte, the low-level write will
@@ -3154,10 +3153,13 @@ class SignalsTest(unittest.TestCase):
             # The buffered IO layer must check for pending signal
             # handlers, which in this case will invoke alarm_interrupt().
             try:
+                signal.alarm(1)
                 with self.assertRaises(ZeroDivisionError):
                     wio.write(item * (support.PIPE_MAX_SIZE // len(item) + 1))
             finally:
+                signal.alarm(0)
                 t.join()
+
             # We got one byte, get another one and check that it isn't a
             # repeat of the first one.
             read_results.append(os.read(r, 1))
@@ -3206,6 +3208,7 @@ class SignalsTest(unittest.TestCase):
             if isinstance(exc, RuntimeError):
                 self.assertTrue(str(exc).startswith("reentrant call"), str(exc))
         finally:
+            signal.alarm(0)
             wio.close()
             os.close(r)
 
@@ -3234,6 +3237,7 @@ class SignalsTest(unittest.TestCase):
             # - third raw read() returns b"bar"
             self.assertEqual(decode(rio.read(6)), "foobar")
         finally:
+            signal.alarm(0)
             rio.close()
             os.close(w)
             os.close(r)
@@ -3295,6 +3299,7 @@ class SignalsTest(unittest.TestCase):
             self.assertIsNone(error[0])
             self.assertEqual(N, sum(len(x) for x in read_results))
         finally:
+            signal.alarm(0)
             write_finished = True
             os.close(w)
             os.close(r)

Lib/test/test_pty.py

@@ -70,14 +70,11 @@ class PtyTest(unittest.TestCase):
     def setUp(self):
         # isatty() and close() can hang on some platforms.  Set an alarm
         # before running the test to make sure we don't hang forever.
-        self.old_alarm = signal.signal(signal.SIGALRM, self.handle_sig)
+        old_alarm = signal.signal(signal.SIGALRM, self.handle_sig)
+        self.addCleanup(signal.signal, signal.SIGALRM, old_alarm)
+        self.addCleanup(signal.alarm, 0)
         signal.alarm(10)
 
-    def tearDown(self):
-        # remove alarm, restore old alarm handler
-        signal.alarm(0)
-        signal.signal(signal.SIGALRM, self.old_alarm)
-
     def handle_sig(self, sig, frame):
         self.fail("isatty hung")
 

Lib/test/test_signal.py

@@ -138,6 +138,8 @@ class InterProcessSignalTests(unittest.TestCase):
         else:
             self.fail("pause returned of its own accord, and the signal"
                       " didn't arrive after another second.")
+        finally:
+            signal.alarm(0)
 
     # Issue 3864. Unknown if this affects earlier versions of freebsd also.
     @unittest.skipIf(sys.platform=='freebsd6',
@@ -246,11 +248,15 @@ class WakeupSignalTests(unittest.TestCase):
         import select
 
         signal.alarm(1)
-        before_time = time.time()
-        # We attempt to get a signal during the sleep,
-        # before select is called
-        time.sleep(self.TIMEOUT_FULL)
-        mid_time = time.time()
+        try:
+            before_time = time.time()
+            # We attempt to get a signal during the sleep,
+            # before select is called
+            time.sleep(self.TIMEOUT_FULL)
+            mid_time = time.time()
+        finally:
+            signal.alarm(0)
+
         self.assertTrue(mid_time - before_time < self.TIMEOUT_HALF)
         select.select([self.read], [], [], self.TIMEOUT_FULL)
         after_time = time.time()
@@ -260,11 +266,15 @@ class WakeupSignalTests(unittest.TestCase):
         import select
 
         signal.alarm(1)
-        before_time = time.time()
-        # We attempt to get a signal during the select call
-        self.assertRaises(select.error, select.select,
-            [self.read], [], [], self.TIMEOUT_FULL)
-        after_time = time.time()
+        try:
+            before_time = time.time()
+            # We attempt to get a signal during the select call
+            self.assertRaises(select.error, select.select,
+                [self.read], [], [], self.TIMEOUT_FULL)
+            after_time = time.time()
+        finally:
+            signal.alarm(0)
+
         self.assertTrue(after_time - before_time < self.TIMEOUT_HALF)
 
     def setUp(self):

Lib/test/test_socket.py

@@ -1534,8 +1534,8 @@ class TCPTimeoutTest(SocketTCPTest):
             raise Alarm
         old_alarm = signal.signal(signal.SIGALRM, alarm_handler)
         try:
-            signal.alarm(2)    # POSIX allows alarm to be up to 1 second early
             try:
+                signal.alarm(2)    # POSIX allows alarm to be up to 1 second early
                 foo = self.serv.accept()
             except socket.timeout:
                 self.fail("caught timeout instead of Alarm")

Lib/test/test_socketserver.py

@@ -88,12 +88,13 @@ class SocketServerTest(unittest.TestCase):
     """Test all socket servers."""
 
     def setUp(self):
+        self.addCleanup(signal_alarm, 0)
         signal_alarm(60)  # Kill deadlocks after 60 seconds.
         self.port_seed = 0
         self.test_files = []
 
     def tearDown(self):
-        signal_alarm(0)  # Didn't deadlock.
+        self.doCleanups()
         reap_children()
 
         for fn in self.test_files:

Lib/test/test_subprocess.py

@@ -843,8 +843,11 @@ class _SuppressCoreFiles(object):
             kw = {stream: subprocess.PIPE}
             with subprocess.Popen(args, **kw) as process:
                 signal.alarm(1)
-                # communicate() will be interrupted by SIGALRM
-                process.communicate()
+                try:
+                    # communicate() will be interrupted by SIGALRM
+                    process.communicate()
+                finally:
+                    signal.alarm(0)
 
 
 @unittest.skipIf(mswindows, "POSIX specific tests")

Lib/test/test_threadsignals.py

@@ -52,9 +52,11 @@ class ThreadSignals(unittest.TestCase):
         # wait for it return.
         if signal_blackboard[signal.SIGUSR1]['tripped'] == 0 \
            or signal_blackboard[signal.SIGUSR2]['tripped'] == 0:
-            signal.alarm(1)
-            signal.pause()
-            signal.alarm(0)
+            try:
+                signal.alarm(1)
+                signal.pause()
+            finally:
+                signal.alarm(0)
 
         self.assertEqual( signal_blackboard[signal.SIGUSR1]['tripped'], 1)
         self.assertEqual( signal_blackboard[signal.SIGUSR1]['tripped_by'],