Fix #835. patch_select deals better with unexpected import order.

changelog.rst

@@ -69,6 +69,9 @@ Stdlib Compatibility
   libev would tend to return the descriptor as ready. In the worst
   case, this adds an extra system call, but may also reduce latency if
   descriptors are ready at the time of entry.
+- :class:`selectors.SelectSelector` is properly monkey-patched
+  regardless of the order of imports. Reported in :issue:`835` by
+  Przemysław Węgrzyn.
 - :meth:`gevent.select.poll.unregister` raises an exception if *fd* is not
   registered, like the standard library.
 - :meth:`gevent.select.poll.poll` returns an event with

src/gevent/monkey.py

@@ -495,12 +495,18 @@ def patch_select(aggressive=True):
         # not a builtin and doesn't get the magic auto-static that they do)
         #    r, w, _ = self._select(self._readers, self._writers, [], timeout)
         #    TypeError: select() takes from 3 to 4 positional arguments but 5 were given
-        select = __import__('select')
+        # Note that this obviously only happens if selectors was imported after we had patched
+        # select; but there is a code path that leads to it being imported first (but now we've
+        # patched select---so we can't compare them identically)
+        select = __import__('select') # Should be gevent-patched now
+        orig_select_select = get_original('select', 'select')
+        assert select.select is not orig_select_select
         selectors = __import__('selectors')
-        if selectors.SelectSelector._select is select.select:
+        if selectors.SelectSelector._select in (select.select, orig_select_select):
             def _select(self, *args, **kwargs): # pylint:disable=unused-argument
                 return select.select(*args, **kwargs)
             selectors.SelectSelector._select = _select
+            _select._gevent_monkey = True
 
         if aggressive:
             # If `selectors` had already been imported before we removed

src/greentest/test__monkey_selectors.py

+
+import sys
+import greentest
+try:
+    import selectors # Do this before the patch, just to force it
+except ImportError:
+    pass
+from gevent.monkey import patch_all
+patch_all()
+
+if sys.platform != 'win32' and sys.version_info[:2] >= (3, 4):
+
+    class TestSelectors(greentest.TestCase):
+
+        def test_selectors_select_is_patched(self):
+            # https://github.com/gevent/gevent/issues/835
+            _select = selectors.SelectSelector._select
+            self.assertTrue(hasattr(_select, '_gevent_monkey'), dir(_select))
+
+
+if __name__ == '__main__':
+    greentest.main()