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gtask: Emit a debug message if a GTask is finalised without returning

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This typically indicates a bug in the program, where a GTask has been
created, but a bug in the control flow has caused it to not return a
value.

There is one situation where it might be legitimate to finalise a GTask
without returning: if an error happens in your *_async() start function
after you’ve created a GTask, but before the async operation returns to
the main loop; and you report the error using g_task_report_*error()
rather than reporting it using the newly constructed GTask.

Another situation is where you are just using GTask as a convenient way
to move some work to another thread, without the complexity of creating
and running your own thread pool. GDBus does this with
g_dbus_interface_method_dispatch_helper(), for example.

In most other cases, it’s a bug. Emit a debug message about it, but not
a full-blown warning, as that would create noise in the legitimate
cases.

Signed-off-by: Philip Withnall <withnall@endlessm.com>
This commit is contained in:
Philip Withnall 2018-10-07 17:15:49 +01:00 committed by Philip Withnall
parent 1d7dfb68e8
commit fe89940572
2 changed files with 71 additions and 0 deletions
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32
gio/gtask.c
View File

@ -64,6 +64,10 @@
* #GTask was constructed to be running at least until the task has completed
* and its data has been freed.
*
* If a #GTask has been constructed and its callback set, it is an error to
* not call `g_task_return_*()` on it. GLib will warn at runtime if this happens
* (since 2.76).
*
* Here is an example for using GTask as a GAsyncResult:
* |[<!-- language="C" -->
* typedef struct {
@ -659,6 +663,34 @@ g_task_finalize (GObject *object)
{
GTask *task = G_TASK (object);
/* Warn if a #GTask is finalised without g_task_return() ever having been
* called on it.
*
* Tasks without a callback or which are run in g_task_run_in_thread{,_sync}()
* only trigger a debug message as that’s sometimes used as a pattern for
* running work in a worker thread without caring about the result. */
if (!task->ever_returned)
{
gchar *owned_task_name = NULL;
const gchar *task_name = g_task_get_name (task);
if (task_name == NULL)
task_name = owned_task_name = g_strdup_printf ("%p", task);
if (task->callback != NULL && !G_TASK_IS_THREADED (task))
g_critical ("GTask %s (source object: %p, source tag: %p) finalized without "
"ever returning (using g_task_return_*()). This potentially "
"indicates a bug in the program.",
task_name, task->source_object, task->source_tag);
else
g_debug ("GTask %s (source object: %p, source tag: %p) finalized without "
"ever returning (using g_task_return_*()). This potentially "
"indicates a bug in the program.",
task_name, task->source_object, task->source_tag);
g_free (owned_task_name);
}
g_clear_object (&task->source_object);
g_clear_object (&task->cancellable);
if (!task->name_is_static)

39
gio/tests/task.c
View File

@ -2451,6 +2451,44 @@ test_attach_source_set_name (void)
g_object_unref (task);
}
static void
test_finalize_without_return (void)
{
GTask *task = NULL;
guint n_calls = 0;
/* With a callback set. */
task = g_task_new (NULL, NULL, task_complete_cb, &n_calls);
g_test_expect_message (G_LOG_DOMAIN, G_LOG_LEVEL_CRITICAL,
"GTask * (source object: *, source tag: *) finalized without "
"ever returning (using g_task_return_*()). This potentially "
"indicates a bug in the program.");
g_object_unref (task);
g_test_assert_expected_messages ();
/* With a callback and task name set. */
task = g_task_new (NULL, NULL, task_complete_cb, &n_calls);
g_task_set_static_name (task, "oogly boogly");
g_test_expect_message (G_LOG_DOMAIN, G_LOG_LEVEL_CRITICAL,
"GTask oogly boogly (source object: *, source tag: *) finalized without "
"ever returning (using g_task_return_*()). This potentially "
"indicates a bug in the program.");
g_object_unref (task);
g_test_assert_expected_messages ();
/* Without a callback set. */
task = g_task_new (NULL, NULL, NULL, NULL);
g_test_expect_message (G_LOG_DOMAIN, G_LOG_LEVEL_DEBUG,
"GTask * (source object: *, source tag: *) finalized without "
"ever returning (using g_task_return_*()). This potentially "
"indicates a bug in the program.");
g_object_unref (task);
g_test_assert_expected_messages ();
}
int
main (int argc, char **argv)
{
@ -2494,6 +2532,7 @@ main (int argc, char **argv)
g_test_add_func ("/gtask/return/error-first", test_return_error_first);
g_test_add_func ("/gtask/return/value-first", test_return_value_first);
g_test_add_func ("/gtask/attach-source/set-name", test_attach_source_set_name);
g_test_add_func ("/gtask/finalize-without-return", test_finalize_without_return);
ret = g_test_run();