thread: Add support for posting async task

This uses the queue that was introduced when migrating impl task
management from MetaThread to MetaThreadImpl, with the exception that
it's now fully used as an actual queue. It now has a GSource that sits
on the right GMainContext that is dispatched whenever there are tasks to
execute.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2777>

src/backends/native/meta-thread-impl.c

@@ -37,6 +37,12 @@ enum
 
 static GParamSpec *obj_props[N_PROPS];
 
+typedef struct _MetaThreadImplSource
+{
+  GSource base;
+  MetaThreadImpl *thread_impl;
+} MetaThreadImplSource;
+
 typedef struct _MetaThreadImplPrivate
 {
   MetaThread *thread;
@@ -44,6 +50,7 @@ typedef struct _MetaThreadImplPrivate
   gboolean in_impl_task;
 
   GMainContext *thread_context;
+  GSource *impl_source;
   GAsyncQueue *task_queue;
 } MetaThreadImplPrivate;
 
@@ -51,8 +58,13 @@ struct _MetaThreadTask
 {
   MetaThreadTaskFunc func;
   gpointer user_data;
+
   MetaThreadTaskFeedbackFunc feedback_func;
   gpointer feedback_user_data;
+  MetaThreadTaskFeedbackType feedback_type;
+
+  gpointer retval;
+  GError *error;
 };
 
 G_DEFINE_TYPE_WITH_PRIVATE (MetaThreadImpl, meta_thread_impl, G_TYPE_OBJECT)
@@ -105,12 +117,74 @@ meta_thread_impl_set_property (GObject      *object,
     }
 }
 
+static gboolean
+impl_source_prepare (GSource *source,
+                     int     *timeout)
+{
+  MetaThreadImplSource *impl_source = (MetaThreadImplSource *) source;
+  MetaThreadImpl *thread_impl = impl_source->thread_impl;
+  MetaThreadImplPrivate *priv =
+    meta_thread_impl_get_instance_private (thread_impl);
+
+  g_assert (g_source_get_context (source) == priv->thread_context);
+
+  *timeout = -1;
+
+  return g_async_queue_length (priv->task_queue) > 0;
+}
+
+static gboolean
+impl_source_check (GSource *source)
+{
+  MetaThreadImplSource *impl_source = (MetaThreadImplSource *) source;
+  MetaThreadImpl *thread_impl = impl_source->thread_impl;
+  MetaThreadImplPrivate *priv =
+    meta_thread_impl_get_instance_private (thread_impl);
+
+  g_assert (g_source_get_context (source) == priv->thread_context);
+
+  return g_async_queue_length (priv->task_queue) > 0;
+}
+
+static gboolean
+impl_source_dispatch (GSource     *source,
+                      GSourceFunc  callback,
+                      gpointer     user_data)
+{
+  MetaThreadImplSource *impl_source = (MetaThreadImplSource *) source;
+  MetaThreadImpl *thread_impl = impl_source->thread_impl;
+  MetaThreadImplPrivate *priv =
+    meta_thread_impl_get_instance_private (thread_impl);
+
+  g_assert (g_source_get_context (source) == priv->thread_context);
+
+  meta_thread_impl_dispatch (thread_impl);
+
+  return G_SOURCE_CONTINUE;
+}
+
+static GSourceFuncs impl_source_funcs = {
+  .prepare = impl_source_prepare,
+  .check = impl_source_check,
+  .dispatch = impl_source_dispatch,
+};
+
 static void
 meta_thread_impl_constructed (GObject *object)
 {
   MetaThreadImpl *thread_impl = META_THREAD_IMPL (object);
   MetaThreadImplPrivate *priv =
     meta_thread_impl_get_instance_private (thread_impl);
+  GSource *source;
+  MetaThreadImplSource *impl_source;
+
+  source = g_source_new (&impl_source_funcs, sizeof (MetaThreadImplSource));
+  impl_source = (MetaThreadImplSource *) source;
+  impl_source->thread_impl = thread_impl;
+  g_source_attach (source, priv->thread_context);
+  g_source_unref (source);
+
+  priv->impl_source = source;
 
   priv->task_queue = g_async_queue_new ();
 
@@ -124,6 +198,7 @@ meta_thread_impl_finalize (GObject *object)
   MetaThreadImplPrivate *priv =
     meta_thread_impl_get_instance_private (thread_impl);
 
+  g_clear_pointer (&priv->impl_source, g_source_destroy);
   g_clear_pointer (&priv->task_queue, g_async_queue_unref);
   g_clear_pointer (&priv->thread_context, g_main_context_unref);
 
@@ -186,7 +261,8 @@ MetaThreadTask *
 meta_thread_task_new (MetaThreadTaskFunc         func,
                       gpointer                   user_data,
                       MetaThreadTaskFeedbackFunc feedback_func,
-                      gpointer                   feedback_user_data)
+                      gpointer                   feedback_user_data,
+                      MetaThreadTaskFeedbackType feedback_type)
 {
   MetaThreadTask *task;
 
@@ -196,6 +272,7 @@ meta_thread_task_new (MetaThreadTaskFunc         func,
     .user_data = user_data,
     .feedback_func = feedback_func,
     .feedback_user_data = feedback_user_data,
+    .feedback_type = feedback_type,
   };
 
   return task;
@@ -204,6 +281,7 @@ meta_thread_task_new (MetaThreadTaskFunc         func,
 void
 meta_thread_task_free (MetaThreadTask *task)
 {
+  g_clear_error (&task->error);
   g_free (task);
 }
 
@@ -365,6 +443,17 @@ meta_thread_impl_is_in_impl (MetaThreadImpl *thread_impl)
   return priv->in_impl_task;
 }
 
+static void
+invoke_task_feedback (MetaThread *thread,
+                      gpointer    user_data)
+{
+  MetaThreadTask *task = user_data;
+
+  meta_assert_not_in_thread_impl (thread);
+
+  task->feedback_func (task->retval, task->error, task->feedback_user_data);
+}
+
 void
 meta_thread_impl_dispatch (MetaThreadImpl *thread_impl)
 {
@@ -380,9 +469,24 @@ meta_thread_impl_dispatch (MetaThreadImpl *thread_impl)
   retval = task->func (thread_impl, task->user_data, &error);
 
   if (task->feedback_func)
-    task->feedback_func (retval, error, task->feedback_user_data);
+    {
+      switch (task->feedback_type)
+        {
+        case META_THREAD_TASK_FEEDBACK_TYPE_IMPL:
+          task->feedback_func (retval, error, task->feedback_user_data);
+          break;
+        case META_THREAD_TASK_FEEDBACK_TYPE_CALLBACK:
+          task->retval = retval;
+          task->error = g_steal_pointer (&error);
+          meta_thread_queue_callback (priv->thread,
+                                      invoke_task_feedback,
+                                      g_steal_pointer (&task),
+                                      (GDestroyNotify) meta_thread_task_free);
+          break;
+        }
+    }
 
-  meta_thread_task_free (task);
+  g_clear_pointer (&task, meta_thread_task_free);
 
   priv->in_impl_task = FALSE;
 }

src/backends/native/meta-thread-impl.h

@@ -37,11 +37,13 @@ struct _MetaThreadImplClass
   GObjectClass parent_class;
 };
 
-typedef struct _MetaThreadTask MetaThreadTask;
+typedef enum _MetaThreadTaskFeedbackType
+{
+  META_THREAD_TASK_FEEDBACK_TYPE_CALLBACK,
+  META_THREAD_TASK_FEEDBACK_TYPE_IMPL,
+} MetaThreadTaskFeedbackType;
 
-typedef void (* MetaThreadTaskFeedbackFunc) (gpointer      retval,
-                                             const GError *error,
-                                             gpointer      user_data);
+typedef struct _MetaThreadTask MetaThreadTask;
 
 META_EXPORT_TEST
 MetaThread * meta_thread_impl_get_thread (MetaThreadImpl *thread_impl);
@@ -70,7 +72,8 @@ gboolean meta_thread_impl_is_in_impl (MetaThreadImpl *thread_impl);
 MetaThreadTask * meta_thread_task_new (MetaThreadTaskFunc         func,
                                        gpointer                   user_data,
                                        MetaThreadTaskFeedbackFunc feedback_func,
-                                       gpointer                   feedback_user_data);
+                                       gpointer                   feedback_user_data,
+                                       MetaThreadTaskFeedbackType feedback_type);
 
 void meta_thread_task_free (MetaThreadTask *task);
 

src/backends/native/meta-thread.c

@@ -298,7 +298,8 @@ meta_thread_run_impl_task_sync (MetaThread          *thread,
   MetaSyncTaskData data = { 0 };
 
   task = meta_thread_task_new (func, user_data,
-                               sync_task_done_in_impl, &data);
+                               sync_task_done_in_impl, &data,
+                               META_THREAD_TASK_FEEDBACK_TYPE_IMPL);
   meta_thread_impl_queue_task (priv->impl, task);
 
   priv->waiting_for_impl_task = TRUE;
@@ -314,6 +315,22 @@ meta_thread_run_impl_task_sync (MetaThread          *thread,
   return data.retval;
 }
 
+void
+meta_thread_post_impl_task (MetaThread                 *thread,
+                            MetaThreadTaskFunc          func,
+                            gpointer                    user_data,
+                            MetaThreadTaskFeedbackFunc  feedback_func,
+                            gpointer                    feedback_user_data)
+{
+  MetaThreadPrivate *priv = meta_thread_get_instance_private (thread);
+  MetaThreadTask *task;
+
+  task = meta_thread_task_new (func, user_data,
+                               feedback_func, feedback_user_data,
+                               META_THREAD_TASK_FEEDBACK_TYPE_CALLBACK);
+  meta_thread_impl_queue_task (priv->impl, task);
+}
+
 MetaBackend *
 meta_thread_get_backend (MetaThread *thread)
 {

src/backends/native/meta-thread.h

@@ -44,6 +44,9 @@ typedef void (* MetaThreadCallback) (MetaThread *thread,
 typedef gpointer (* MetaThreadTaskFunc) (MetaThreadImpl  *thread_impl,
                                          gpointer         user_data,
                                          GError         **error);
+typedef void (* MetaThreadTaskFeedbackFunc) (gpointer      retval,
+                                             const GError *error,
+                                             gpointer      user_data);
 
 META_EXPORT_TEST
 void meta_thread_queue_callback (MetaThread         *thread,
@@ -60,6 +63,13 @@ gpointer meta_thread_run_impl_task_sync (MetaThread          *thread,
                                          gpointer             user_data,
                                          GError             **error);
 
+META_EXPORT_TEST
+void meta_thread_post_impl_task (MetaThread                 *thread,
+                                 MetaThreadTaskFunc          func,
+                                 gpointer                    user_data,
+                                 MetaThreadTaskFeedbackFunc  feedback_func,
+                                 gpointer                    feedback_user_data);
+
 META_EXPORT_TEST
 MetaBackend * meta_thread_get_backend (MetaThread *thread);
 

src/tests/native-thread.c

@@ -193,6 +193,48 @@ add_idle_func (MetaThreadImpl  *thread_impl,
   return GINT_TO_POINTER (TRUE);
 }
 
+typedef struct
+{
+  MetaThread *thread;
+  GMainLoop *loop;
+
+  GMutex mutex;
+  int state;
+} AsyncData;
+
+static gpointer
+async_func (MetaThreadImpl  *thread_impl,
+            gpointer         user_data,
+            GError         **error)
+{
+  AsyncData *async_data = user_data;
+
+  meta_assert_in_thread_impl (async_data->thread);
+
+  g_mutex_lock (&async_data->mutex);
+  g_assert_cmpint (async_data->state, ==, 0);
+  async_data->state = 1;
+  g_mutex_unlock (&async_data->mutex);
+
+  return GINT_TO_POINTER (TRUE);
+}
+
+static void
+async_feedback_func (gpointer      retval,
+                     const GError *error,
+                     gpointer      user_data)
+{
+  AsyncData *async_data = user_data;
+
+  meta_assert_not_in_thread_impl (async_data->thread);
+
+  g_mutex_lock (&async_data->mutex);
+  g_assert_cmpint (async_data->state, ==, 1);
+  async_data->state = 2;
+  g_main_loop_quit (async_data->loop);
+  g_mutex_unlock (&async_data->mutex);
+}
+
 static void
 run_thread_tests (MetaThread *thread)
 {
@@ -204,6 +246,7 @@ run_thread_tests (MetaThread *thread)
   int buf;
   PipeData pipe_data;
   IdleData idle_data;
+  AsyncData async_data;
 
   meta_assert_not_in_thread_impl (thread);
 
@@ -254,6 +297,24 @@ run_thread_tests (MetaThread *thread)
   g_main_loop_run (idle_data.loop);
   g_assert_cmpint (idle_data.state, ==, 3);
   g_main_loop_unref (idle_data.loop);
+
+  /* Test async tasks */
+  g_debug ("Test async task");
+  async_data = (AsyncData) { 0 };
+  g_mutex_init (&async_data.mutex);
+  async_data.thread = thread;
+  async_data.loop = g_main_loop_new (NULL, FALSE);
+  g_mutex_lock (&async_data.mutex);
+  meta_thread_post_impl_task (thread, async_func, &async_data,
+                              async_feedback_func, &async_data);
+  g_assert_cmpint (async_data.state, ==, 0);
+  g_mutex_unlock (&async_data.mutex);
+  g_main_loop_run (async_data.loop);
+  g_mutex_lock (&async_data.mutex);
+  g_assert_cmpint (async_data.state, ==, 2);
+  g_mutex_unlock (&async_data.mutex);
+  g_main_loop_unref (async_data.loop);
+  g_mutex_clear (&async_data.mutex);
 }
 
 static void