Issue #23209, #23225: selectors.BaseSelector.close() now clears its internal

reference to the selector mapping to break a reference cycle. Initial patch
written by Martin Richard.

Lib/selectors.py

@@ -175,6 +175,8 @@ class BaseSelector(metaclass=ABCMeta):
         """
         mapping = self.get_map()
         try:
+            if mapping is None:
+                raise KeyError
             return mapping[fileobj]
         except KeyError:
             raise KeyError("{!r} is not registered".format(fileobj)) from None
@@ -256,6 +258,7 @@ class _BaseSelectorImpl(BaseSelector):
 
     def close(self):
         self._fd_to_key.clear()
+        self._map = None
 
     def get_map(self):
         return self._map

Lib/test/test_selectors.py

@@ -180,6 +180,7 @@ class BaseSelectorTestCase(unittest.TestCase):
         s = self.SELECTOR()
         self.addCleanup(s.close)
 
+        mapping = s.get_map()
         rd, wr = self.make_socketpair()
 
         s.register(rd, selectors.EVENT_READ)
@@ -188,6 +189,8 @@ class BaseSelectorTestCase(unittest.TestCase):
         s.close()
         self.assertRaises(KeyError, s.get_key, rd)
         self.assertRaises(KeyError, s.get_key, wr)
+        self.assertRaises(KeyError, mapping.__getitem__, rd)
+        self.assertRaises(KeyError, mapping.__getitem__, wr)
 
     def test_get_key(self):
         s = self.SELECTOR()

Misc/NEWS

@@ -44,6 +44,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #23209, #23225: selectors.BaseSelector.close() now clears its internal
+  reference to the selector mapping to break a reference cycle. Initial patch
+  written by Martin Richard.
+
 - Issue #21356: Make ssl.RAND_egd() optional to support LibreSSL. The
   availability of the function is checked during the compilation. Patch written
   by Bernard Spil.