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

* 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

1 files changed, 14 insertions, 9 deletions

diff --git a/Lib/test/test_socket.py b/Lib/test/test_socket.py
index 01502c8..84ec429 100644
--- a/Lib/test/test_socket.py
+++ b/Lib/test/test_socket.py
@@ -3854,7 +3854,6 @@ class InterruptedTimeoutBase(unittest.TestCase):
         orig_alrm_handler = signal.signal(signal.SIGALRM,
                                           lambda signum, frame: 1 / 0)
         self.addCleanup(signal.signal, signal.SIGALRM, orig_alrm_handler)
-        self.addCleanup(self.setAlarm, 0)
 
     # Timeout for socket operations
     timeout = 4.0
@@ -3891,9 +3890,12 @@ class InterruptedRecvTimeoutTest(InterruptedTimeoutBase, UDPTestBase):
     def checkInterruptedRecv(self, func, *args, **kwargs):
         # Check that func(*args, **kwargs) raises
         # errno of EINTR when interrupted by a signal.
-        self.setAlarm(self.alarm_time)
-        with self.assertRaises(ZeroDivisionError) as cm:
-            func(*args, **kwargs)
+        try:
+            self.setAlarm(self.alarm_time)
+            with self.assertRaises(ZeroDivisionError) as cm:
+                func(*args, **kwargs)
+        finally:
+            self.setAlarm(0)
 
     def testInterruptedRecvTimeout(self):
         self.checkInterruptedRecv(self.serv.recv, 1024)
@@ -3948,10 +3950,13 @@ class InterruptedSendTimeoutTest(InterruptedTimeoutBase,
         # Check that func(*args, **kwargs), run in a loop, raises
         # OSError with an errno of EINTR when interrupted by a
         # signal.
-        with self.assertRaises(ZeroDivisionError) as cm:
-            while True:
-                self.setAlarm(self.alarm_time)
-                func(*args, **kwargs)
+        try:
+            with self.assertRaises(ZeroDivisionError) as cm:
+                while True:
+                    self.setAlarm(self.alarm_time)
+                    func(*args, **kwargs)
+        finally:
+            self.setAlarm(0)
 
     # Issue #12958: The following tests have problems on OS X prior to 10.7
     @support.requires_mac_ver(10, 7)
@@ -4675,8 +4680,8 @@ 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")