[tracker/wip/carlosg/service-fixes: 7/8] libtracker-sparql: Handle TrackerEndpointDBus cursor writes on a thread

[Carlos Garnacho <carlosg src gnome org>]

commit bbae610ecba527edb3ff4acc88bd56d7013bcee8
Author: Carlos Garnacho <carlosg gnome org>
Date:   Tue Jun 9 18:02:02 2020 +0200

    libtracker-sparql: Handle TrackerEndpointDBus cursor writes on a thread
    
    Take this off the main thread, so other queries may be handled at the same
    time while we are writing a cursor.
    
    Fixes: https://gitlab.gnome.org/GNOME/tracker/-/issues/222

 src/libtracker-sparql/tracker-endpoint-dbus.c | 75 +++++++++++++++++++--------
 1 file changed, 54 insertions(+), 21 deletions(-)
---
diff --git a/src/libtracker-sparql/tracker-endpoint-dbus.c b/src/libtracker-sparql/tracker-endpoint-dbus.c
index 1369b868b..4ecf5d8e6 100644
--- a/src/libtracker-sparql/tracker-endpoint-dbus.c
+++ b/src/libtracker-sparql/tracker-endpoint-dbus.c
@@ -273,35 +273,50 @@ out:
        }
 }
 
-/* Takes ownership on both cursor and error */
 static void
-handle_cursor_reply (QueryRequest        *request,
-                     TrackerSparqlCursor *cursor,
-                     const GError        *error)
+handle_cursor_reply (GTask        *task,
+                     gpointer      source_object,
+                     gpointer      task_data,
+                     GCancellable *cancellable)
 {
+       TrackerSparqlCursor *cursor = source_object;
+       QueryRequest *request = task_data;
        const gchar **variable_names = NULL;
        GError *write_error = NULL;
        gint i, n_columns;
 
-       if (!error) {
-               n_columns = tracker_sparql_cursor_get_n_columns (cursor);
-               variable_names = g_new0 (const gchar *, n_columns + 1);
-               for (i = 0; i < n_columns; i++)
-                       variable_names[i] = tracker_sparql_cursor_get_variable_name (cursor, i);
+       n_columns = tracker_sparql_cursor_get_n_columns (cursor);
+       variable_names = g_new0 (const gchar *, n_columns + 1);
+       for (i = 0; i < n_columns; i++)
+               variable_names[i] = tracker_sparql_cursor_get_variable_name (cursor, i);
 
-               write_cursor (request, cursor, &write_error);
-       }
+       write_cursor (request, cursor, &write_error);
 
-       if (error)
-               g_dbus_method_invocation_return_gerror (request->invocation, error);
-       else if (write_error)
+       if (write_error)
                g_dbus_method_invocation_return_gerror (request->invocation, write_error);
        else
                g_dbus_method_invocation_return_value (request->invocation, g_variant_new ("(^as)", 
variable_names));
 
        g_free (variable_names);
-       g_clear_object (&cursor);
        g_clear_error (&write_error);
+
+       g_task_return_boolean (task, TRUE);
+}
+
+static void
+finish_query (GObject      *source_object,
+              GAsyncResult *res,
+              gpointer      user_data)
+{
+       TrackerSparqlCursor *cursor = TRACKER_SPARQL_CURSOR (source_object);
+       GError *error = NULL;
+
+       if (!g_task_propagate_boolean (G_TASK (res), &error))
+               g_critical ("Error writing cursor: %s\n", error->message);
+
+       tracker_sparql_cursor_close (cursor);
+       g_object_unref (cursor);
+       g_clear_error (&error);
 }
 
 static void
@@ -312,12 +327,21 @@ query_cb (GObject      *object,
        QueryRequest *request = user_data;
        TrackerSparqlCursor *cursor;
        GError *error = NULL;
+       GTask *task;
 
        cursor = tracker_sparql_connection_query_finish (TRACKER_SPARQL_CONNECTION (object),
                                                         res, &error);
-       handle_cursor_reply (request, cursor, error);
-       query_request_free (request);
-       g_clear_error (&error);
+       if (!cursor) {
+               g_dbus_method_invocation_return_gerror (request->invocation, error);
+               g_error_free (error);
+               query_request_free (request);
+               return;
+       }
+
+       task = g_task_new (cursor, request->endpoint->cancellable, finish_query, NULL);
+       g_task_set_task_data (task, request, (GDestroyNotify) query_request_free);
+       g_task_run_in_thread (task, handle_cursor_reply);
+       g_object_unref (task);
 }
 
 static void
@@ -328,12 +352,21 @@ stmt_execute_cb (GObject      *object,
        QueryRequest *request = user_data;
        TrackerSparqlCursor *cursor;
        GError *error = NULL;
+       GTask *task;
 
        cursor = tracker_sparql_statement_execute_finish (TRACKER_SPARQL_STATEMENT (object),
                                                          res, &error);
-       handle_cursor_reply (request, cursor, error);
-       query_request_free (request);
-       g_clear_error (&error);
+       if (!cursor) {
+               g_dbus_method_invocation_return_gerror (request->invocation, error);
+               g_error_free (error);
+               query_request_free (request);
+               return;
+       }
+
+       task = g_task_new (cursor, request->endpoint->cancellable, finish_query, NULL);
+       g_task_set_task_data (task, request, (GDestroyNotify) query_request_free);
+       g_task_run_in_thread (task, handle_cursor_reply);
+       g_object_unref (task);
 }
 
 static void