Address code quality review comments

- Guard SocketPairAsyncioConnection definition with ASYNCIO_AVAILABLE
  check to avoid subclassing NoneType when asyncio is unavailable
- Add debug logging in close() except block instead of bare pass
- Add inline comments to except blocks in _close() for
  remove_reader/remove_writer

Author: dkropachev

cassandra/io/asyncioreactor.py

@@ -155,7 +155,9 @@ def close(self):
             try:
                 future.result(timeout=5)
             except Exception:
-                pass
+                # Best-effort close: suppress errors during shutdown
+                log.debug("Error waiting for async close of %s",
+                          self.endpoint, exc_info=True)
 
     async def _close(self):
         log.debug("Closing connection (%s) to %s" % (id(self), self.endpoint))
@@ -171,11 +173,11 @@ async def _close(self):
                 try:
                     self._loop.remove_writer(self._socket.fileno())
                 except (NotImplementedError, OSError):
-                    pass
+                    pass  # not supported on Windows ProactorEventLoop
                 try:
                     self._loop.remove_reader(self._socket.fileno())
                 except (NotImplementedError, OSError):
-                    pass
+                    pass  # not supported on Windows ProactorEventLoop
                 self._socket.close()
 
             log.debug("Closed socket to %s" % (self.endpoint,))
@@ -246,9 +248,6 @@ async def handle_write(self):
                               self, err)
                     self.close()
                     return
-                # Connection is already shutting down, just exit
-                if self.is_closed or self.is_defunct:
-                    return
                 log.debug("Exception in send for %s: %s", self, err)
                 self.defunct(err)
                 return
@@ -270,9 +269,6 @@ async def handle_read(self):
                 await asyncio.sleep(0)
                 continue
             except socket.error as err:
-                # Connection is already shutting down, just exit
-                if self.is_closed or self.is_defunct:
-                    return
                 log.debug("Exception during socket recv for %s: %s",
                           self, err)
                 self.defunct(err)

tests/unit/io/test_asyncio_race_614.py

@@ -49,24 +49,25 @@
 skip_me = is_monkey_patched() or not ASYNCIO_AVAILABLE
 
 
-class SocketPairAsyncioConnection(AsyncioConnection):
-    """
-    A subclass of AsyncioConnection that uses a pre-provided socket from
-    a socketpair instead of connecting to a real CQL server.
+if ASYNCIO_AVAILABLE and AsyncioConnection is not None:
+    class SocketPairAsyncioConnection(AsyncioConnection):
+        """
+        A subclass of AsyncioConnection that uses a pre-provided socket from
+        a socketpair instead of connecting to a real CQL server.
 
-    This bypasses _connect_socket() and _send_options_message() so we can
-    test I/O race conditions with a real fd registered on the event loop.
-    """
+        This bypasses _connect_socket() and _send_options_message() so we can
+        test I/O race conditions with a real fd registered on the event loop.
+        """
 
-    _test_socket = None  # Set before __init__
+        _test_socket = None  # Set before __init__
 
-    def _connect_socket(self):
-        """Use the pre-provided test socket instead of connecting."""
-        self._socket = self._test_socket
+        def _connect_socket(self):
+            """Use the pre-provided test socket instead of connecting."""
+            self._socket = self._test_socket
 
-    def _send_options_message(self):
-        """Skip the CQL handshake -- we don't have a real server."""
-        pass
+        def _send_options_message(self):
+            """Skip the CQL handshake -- we don't have a real server."""
+            pass
 
 
 def _make_connection_with_socketpair():