bpo-30014: make poll-like selector's modify() method faster (#1030)

* #30014: make selectors.DefaultSelector.modify() faster by relying on selector's modify() method instead of un/register()ing the fd

* #30014: add unit test

* speedup poll/epoll/devpoll modify() method by using internal modify() call

* update doc

* address PR comments

* update NEWS entries

* use != instead of 'is not'

1 files changed, 27 insertions, 0 deletions

diff --git a/Lib/test/test_selectors.py b/Lib/test/test_selectors.py
index 852b2fe..f2594a6 100644
--- a/Lib/test/test_selectors.py
+++ b/Lib/test/test_selectors.py
@@ -175,6 +175,33 @@ class BaseSelectorTestCase(unittest.TestCase):
         self.assertFalse(s.register.called)
         self.assertFalse(s.unregister.called)
 
+    def test_modify_unregister(self):
+        # Make sure the fd is unregister()ed in case of error on
+        # modify(): http://bugs.python.org/issue30014
+        if self.SELECTOR.__name__ == 'EpollSelector':
+            patch = unittest.mock.patch(
+                'selectors.EpollSelector._selector_cls')
+        elif self.SELECTOR.__name__ == 'PollSelector':
+            patch = unittest.mock.patch(
+                'selectors.PollSelector._selector_cls')
+        elif self.SELECTOR.__name__ == 'DevpollSelector':
+            patch = unittest.mock.patch(
+                'selectors.DevpollSelector._selector_cls')
+        else:
+            raise self.skipTest("")
+
+        with patch as m:
+            m.return_value.modify = unittest.mock.Mock(
+                side_effect=ZeroDivisionError)
+            s = self.SELECTOR()
+            self.addCleanup(s.close)
+            rd, wr = self.make_socketpair()
+            s.register(rd, selectors.EVENT_READ)
+            self.assertEqual(len(s._map), 1)
+            with self.assertRaises(ZeroDivisionError):
+                s.modify(rd, selectors.EVENT_WRITE)
+            self.assertEqual(len(s._map), 0)
+
     def test_close(self):
         s = self.SELECTOR()
         self.addCleanup(s.close)