[3.6] bpo-30980: Fix double close in asyncore.file_wrapper

Lib/asyncore.py

@@ -619,8 +619,9 @@ def getsockopt(self, level, optname, buflen=None):
         def close(self):
             if self.fd < 0:
                 return
-            os.close(self.fd)
+            fd = self.fd
             self.fd = -1
+            os.close(fd)
 
         def fileno(self):
             return self.fd

Lib/test/test_asyncore.py

@@ -433,7 +433,10 @@ def test_close_twice(self):
         f = asyncore.file_wrapper(fd)
         os.close(fd)
 
-        f.close()
+        os.close(f.fd)  # file_wrapper dupped fd
+        with self.assertRaises(OSError):
+            f.close()
+
         self.assertEqual(f.fd, -1)
         # calling close twice should not fail
         f.close()