Enhance Cursor close handling and context manager exception management to prevent server side resource leaks (#554)

* Enhance Cursor close handling and context manager exception management

* tests

* fmt

* Fix Cursor.close() to properly handle CursorAlreadyClosedError

* Remove specific test message from Cursor.close() error handling

* Improve error handling in connection and cursor context managers to ensure proper closure during exceptions, including KeyboardInterrupt. Add tests for nested cursor management and verify operation closure on server-side errors.

* add

* add

Author: madhav-db

src/databricks/sql/client.py

@@ -315,7 +315,13 @@ def __enter__(self) -> "Connection":
         return self
 
     def __exit__(self, exc_type, exc_value, traceback):
-        self.close()
+        try:
+            self.close()
+        except BaseException as e:
+            logger.warning(f"Exception during connection close in __exit__: {e}")
+            if exc_type is None:
+                raise
+        return False
 
     def __del__(self):
         if self.open:
@@ -456,7 +462,14 @@ def __enter__(self) -> "Cursor":
         return self
 
     def __exit__(self, exc_type, exc_value, traceback):
-        self.close()
+        try:
+            logger.debug("Cursor context manager exiting, calling close()")
+            self.close()
+        except BaseException as e:
+            logger.warning(f"Exception during cursor close in __exit__: {e}")
+            if exc_type is None:
+                raise
+        return False
 
     def __iter__(self):
         if self.active_result_set:
@@ -1163,7 +1176,21 @@ def cancel(self) -> None:
     def close(self) -> None:
         """Close cursor"""
         self.open = False
-        self.active_op_handle = None
+
+        # Close active operation handle if it exists
+        if self.active_op_handle:
+            try:
+                self.thrift_backend.close_command(self.active_op_handle)
+            except RequestError as e:
+                if isinstance(e.args[1], CursorAlreadyClosedError):
+                    logger.info("Operation was canceled by a prior request")
+                else:
+                    logging.warning(f"Error closing operation handle: {e}")
+            except Exception as e:
+                logging.warning(f"Error closing operation handle: {e}")
+            finally:
+                self.active_op_handle = None
+
         if self.active_result_set:
             self._close_and_clear_active_result_set()
 

tests/e2e/test_driver.py

@@ -50,7 +50,7 @@
 
 from tests.e2e.common.uc_volume_tests import PySQLUCVolumeTestSuiteMixin
 
-from databricks.sql.exc import SessionAlreadyClosedError
+from databricks.sql.exc import SessionAlreadyClosedError, CursorAlreadyClosedError
 
 log = logging.getLogger(__name__)
 
@@ -820,7 +820,6 @@ def test_close_connection_closes_cursors(self):
             ars = cursor.active_result_set
 
             # We must manually run this check because thrift_backend always forces `has_been_closed_server_side` to True
-
             # Cursor op state should be open before connection is closed
             status_request = ttypes.TGetOperationStatusReq(
                 operationHandle=ars.command_id, getProgressUpdate=False
@@ -847,9 +846,104 @@ def test_closing_a_closed_connection_doesnt_fail(self, caplog):
         with self.connection() as conn:
             # First .close() call is explicit here
             conn.close()
-
         assert "Session appears to have been closed already" in caplog.text
 
+        conn = None
+        try:
+            with pytest.raises(KeyboardInterrupt):
+                with self.connection() as c:
+                    conn = c
+                    raise KeyboardInterrupt("Simulated interrupt")
+        finally:
+            if conn is not None:
+                assert not conn.open, "Connection should be closed after KeyboardInterrupt"
+
+    def test_cursor_close_properly_closes_operation(self):
+        """Test that Cursor.close() properly closes the active operation handle on the server."""
+        with self.connection() as conn:
+            cursor = conn.cursor()
+            try:
+                cursor.execute("SELECT 1 AS test")
+                assert cursor.active_op_handle is not None
+                cursor.close()
+                assert cursor.active_op_handle is None
+                assert not cursor.open
+            finally:
+                if cursor.open:
+                    cursor.close()
+
+        conn = None
+        cursor = None
+        try:
+            with self.connection() as c:
+                conn = c
+                with pytest.raises(KeyboardInterrupt):
+                    with conn.cursor() as cur:
+                        cursor = cur
+                        raise KeyboardInterrupt("Simulated interrupt")
+        finally:
+            if cursor is not None:
+                assert not cursor.open, "Cursor should be closed after KeyboardInterrupt"
+
+    def test_nested_cursor_context_managers(self):
+        """Test that nested cursor context managers properly close operations on the server."""
+        with self.connection() as conn:
+            with conn.cursor() as cursor1:
+                cursor1.execute("SELECT 1 AS test1")
+                assert cursor1.active_op_handle is not None
+
+                with conn.cursor() as cursor2:
+                    cursor2.execute("SELECT 2 AS test2")
+                    assert cursor2.active_op_handle is not None
+
+                # After inner context manager exit, cursor2 should be not open
+                assert not cursor2.open
+                assert cursor2.active_op_handle is None
+
+            # After outer context manager exit, cursor1 should be not open
+            assert not cursor1.open
+            assert cursor1.active_op_handle is None
+
+    def test_cursor_error_handling(self):
+        """Test that cursor close handles errors properly to prevent orphaned operations."""
+        with self.connection() as conn:
+            cursor = conn.cursor()
+
+            cursor.execute("SELECT 1 AS test")
+
+            op_handle = cursor.active_op_handle
+
+            assert op_handle is not None
+
+            # Manually close the operation to simulate server-side closure
+            conn.thrift_backend.close_command(op_handle)
+
+            cursor.close()
+
+            assert not cursor.open
+
+    def test_result_set_close(self):
+        """Test that ResultSet.close() properly closes operations on the server and handles state correctly."""
+        with self.connection() as conn:
+            cursor = conn.cursor()
+            try:
+                cursor.execute("SELECT * FROM RANGE(10)")
+
+                result_set = cursor.active_result_set
+                assert result_set is not None
+
+                initial_op_state = result_set.op_state
+
+                result_set.close()
+
+                assert result_set.op_state == result_set.thrift_backend.CLOSED_OP_STATE
+                assert result_set.op_state != initial_op_state
+
+                # Closing the result set again should be a no-op and not raise exceptions
+                result_set.close()
+            finally:
+                cursor.close()
+
 
 # use a RetrySuite to encapsulate these tests which we'll typically want to run together; however keep
 # the 429/503 subsuites separate since they execute under different circumstances.

tests/unit/test_client.py

@@ -20,6 +20,7 @@
 import databricks.sql
 import databricks.sql.client as client
 from databricks.sql import InterfaceError, DatabaseError, Error, NotSupportedError
+from databricks.sql.exc import RequestError, CursorAlreadyClosedError
 from databricks.sql.types import Row
 
 from tests.unit.test_fetches import FetchTests
@@ -283,6 +284,15 @@ def test_context_manager_closes_cursor(self):
             cursor.close = mock_close
         mock_close.assert_called_once_with()
 
+        cursor = client.Cursor(Mock(), Mock())
+        cursor.close = Mock()
+        try:
+            with self.assertRaises(KeyboardInterrupt):
+                with cursor:
+                    raise KeyboardInterrupt("Simulated interrupt")
+        finally:
+            cursor.close.assert_called()
+
     @patch("%s.client.ThriftBackend" % PACKAGE_NAME)
     def test_context_manager_closes_connection(self, mock_client_class):
         instance = mock_client_class.return_value
@@ -298,6 +308,15 @@ def test_context_manager_closes_connection(self, mock_client_class):
         close_session_id = instance.close_session.call_args[0][0].sessionId
         self.assertEqual(close_session_id, b"\x22")
 
+        connection = databricks.sql.connect(**self.DUMMY_CONNECTION_ARGS)
+        connection.close = Mock()
+        try:
+            with self.assertRaises(KeyboardInterrupt):
+                with connection:
+                    raise KeyboardInterrupt("Simulated interrupt")
+        finally:
+            connection.close.assert_called()
+
     def dict_product(self, dicts):
         """
         Generate cartesion product of values in input dictionary, outputting a dictionary
@@ -676,6 +695,116 @@ def test_access_current_query_id(self):
         cursor.close()
         self.assertIsNone(cursor.query_id)
 
+    def test_cursor_close_handles_exception(self):
+        """Test that Cursor.close() handles exceptions from close_command properly."""
+        mock_backend = Mock()
+        mock_connection = Mock()
+        mock_op_handle = Mock()
+        
+        mock_backend.close_command.side_effect = Exception("Test error")
+
+        cursor = client.Cursor(mock_connection, mock_backend)
+        cursor.active_op_handle = mock_op_handle
+
+        cursor.close()
+
+        mock_backend.close_command.assert_called_once_with(mock_op_handle)
+        
+        self.assertIsNone(cursor.active_op_handle)
+        
+        self.assertFalse(cursor.open)
+
+    def test_cursor_context_manager_handles_exit_exception(self):
+        """Test that cursor's context manager handles exceptions during __exit__."""
+        mock_backend = Mock()
+        mock_connection = Mock()
+        
+        cursor = client.Cursor(mock_connection, mock_backend)
+        original_close = cursor.close
+        cursor.close = Mock(side_effect=Exception("Test error during close"))
+        
+        try:
+            with cursor:
+                raise ValueError("Test error inside context")
+        except ValueError:
+            pass
+        
+        cursor.close.assert_called_once()
+
+    def test_connection_close_handles_cursor_close_exception(self):
+        """Test that _close handles exceptions from cursor.close() properly."""
+        cursors_closed = []
+        
+        def mock_close_with_exception():
+            cursors_closed.append(1)
+            raise Exception("Test error during close")
+        
+        cursor1 = Mock()
+        cursor1.close = mock_close_with_exception
+        
+        def mock_close_normal():
+            cursors_closed.append(2)
+        
+        cursor2 = Mock()
+        cursor2.close = mock_close_normal
+        
+        mock_backend = Mock()
+        mock_session_handle = Mock()
+        
+        try:
+            for cursor in [cursor1, cursor2]:
+                try:
+                    cursor.close()
+                except Exception:
+                    pass
+                    
+            mock_backend.close_session(mock_session_handle)
+        except Exception as e:
+            self.fail(f"Connection close should handle exceptions: {e}")
+        
+        self.assertEqual(cursors_closed, [1, 2], "Both cursors should have close called")
+
+    def test_resultset_close_handles_cursor_already_closed_error(self):
+        """Test that ResultSet.close() handles CursorAlreadyClosedError properly."""
+        result_set = client.ResultSet.__new__(client.ResultSet)
+        result_set.thrift_backend = Mock()
+        result_set.thrift_backend.CLOSED_OP_STATE = 'CLOSED'
+        result_set.connection = Mock()
+        result_set.connection.open = True
+        result_set.op_state = 'RUNNING'
+        result_set.has_been_closed_server_side = False
+        result_set.command_id = Mock()
+
+        class MockRequestError(Exception):
+            def __init__(self):
+                self.args = ["Error message", CursorAlreadyClosedError()]
+        
+        result_set.thrift_backend.close_command.side_effect = MockRequestError()
+        
+        original_close = client.ResultSet.close
+        try:
+            try:
+                if (
+                    result_set.op_state != result_set.thrift_backend.CLOSED_OP_STATE
+                    and not result_set.has_been_closed_server_side
+                    and result_set.connection.open
+                ):
+                    result_set.thrift_backend.close_command(result_set.command_id)
+            except MockRequestError as e:
+                if isinstance(e.args[1], CursorAlreadyClosedError):
+                    pass
+            finally:
+                result_set.has_been_closed_server_side = True
+                result_set.op_state = result_set.thrift_backend.CLOSED_OP_STATE
+                
+            result_set.thrift_backend.close_command.assert_called_once_with(result_set.command_id)
+            
+            assert result_set.has_been_closed_server_side is True
+            
+            assert result_set.op_state == result_set.thrift_backend.CLOSED_OP_STATE
+        finally:
+            pass
+
 
 if __name__ == "__main__":
     suite = unittest.TestLoader().loadTestsFromModule(sys.modules[__name__])