Fix potential resource leak in CloudFetchQueue (#624)

* add close() for Queue, add ResultSet invocation

Signed-off-by: varun-edachali-dbx <varun.edachali@databricks.com>

* move Queue closure to finally: block to ensure client-side cleanup regardless of server side state

Signed-off-by: varun-edachali-dbx <varun.edachali@databricks.com>

* add unit test assertions to ensure Queue closure

Signed-off-by: varun-edachali-dbx <varun.edachali@databricks.com>

* move results closure to try block

Signed-off-by: varun-edachali-dbx <varun.edachali@databricks.com>

---------

Signed-off-by: varun-edachali-dbx <varun.edachali@databricks.com>

Author: varun-edachali-dbx

src/databricks/sql/client.py

@@ -1596,6 +1596,7 @@ def close(self) -> None:
         been closed on the server for some other reason, issue a request to the server to close it.
         """
         try:
+            self.results.close()
             if (
                 self.op_state != self.thrift_backend.CLOSED_OP_STATE
                 and not self.has_been_closed_server_side

src/databricks/sql/utils.py

@@ -46,6 +46,10 @@ def next_n_rows(self, num_rows: int):
     def remaining_rows(self):
         pass
 
+    @abstractmethod
+    def close(self):
+        pass
+
 
 class ResultSetQueueFactory(ABC):
     @staticmethod
@@ -157,6 +161,9 @@ def remaining_rows(self):
         self.cur_row_index += slice.num_rows
         return slice
 
+    def close(self):
+        return
+
 
 class ArrowQueue(ResultSetQueue):
     def __init__(
@@ -192,6 +199,9 @@ def remaining_rows(self) -> "pyarrow.Table":
         self.cur_row_index += slice.num_rows
         return slice
 
+    def close(self):
+        return
+
 
 class CloudFetchQueue(ResultSetQueue):
     def __init__(
@@ -341,6 +351,9 @@ def _create_empty_table(self) -> "pyarrow.Table":
         # Create a 0-row table with just the schema bytes
         return create_arrow_table_from_arrow_file(self.schema_bytes, self.description)
 
+    def close(self):
+        self.download_manager._shutdown_manager()
+
 
 ExecuteResponse = namedtuple(
     "ExecuteResponse",

tests/unit/test_client.py

@@ -267,33 +267,39 @@ def test_arraysize_buffer_size_passthrough(
     def test_closing_result_set_with_closed_connection_soft_closes_commands(self):
         mock_connection = Mock()
         mock_backend = Mock()
+        mock_results = Mock()
         result_set = client.ResultSet(
             connection=mock_connection,
             thrift_backend=mock_backend,
             execute_response=Mock(),
         )
+        result_set.results = mock_results
         mock_connection.open = False
 
         result_set.close()
 
         self.assertFalse(mock_backend.close_command.called)
         self.assertTrue(result_set.has_been_closed_server_side)
+        mock_results.close.assert_called_once()
 
     def test_closing_result_set_hard_closes_commands(self):
         mock_results_response = Mock()
         mock_results_response.has_been_closed_server_side = False
         mock_connection = Mock()
         mock_thrift_backend = Mock()
+        mock_results = Mock()
         mock_connection.open = True
         result_set = client.ResultSet(
             mock_connection, mock_results_response, mock_thrift_backend
         )
+        result_set.results = mock_results
 
         result_set.close()
 
         mock_thrift_backend.close_command.assert_called_once_with(
             mock_results_response.command_handle
         )
+        mock_results.close.assert_called_once()
 
     @patch("%s.client.ResultSet" % PACKAGE_NAME)
     def test_executing_multiple_commands_uses_the_most_recent_command(