gst: Add gst_deinit_register_notify() API

Add an API so that user can install a callback function to be
called when gst_deinit() is executed, then performs library specific
teardown operations such as clearing resources or reporting live
objects.

subprojects/gstreamer/gst/gst.c

@@ -172,6 +172,23 @@ static gboolean parse_goption_arg (const gchar * s_opt,
 
 GSList *_priv_gst_preload_plugins = NULL;
 
+/* deinit callbacks */
+static GList *_gst_deinit_notifies = NULL;
+
+typedef struct _GstDeinitNotify
+{
+  GstDeinitNotifyFunc func;
+  gpointer user_data;
+} GstDeinitNotify;
+
+static void
+gst_deinit_notify_free (GstDeinitNotify * cb)
+{
+  if (cb->func)
+    cb->func (cb->user_data);
+  g_free (cb);
+}
+
 enum
 {
   ARG_VERSION = 1,
@@ -1092,6 +1109,10 @@ gst_deinit (void)
   }
 
   GST_INFO ("deinitializing GStreamer");
+
+  g_list_free_full (_gst_deinit_notifies,
+      (GDestroyNotify) gst_deinit_notify_free);
+
   g_thread_pool_set_max_unused_threads (0);
   bin_class = (GstBinClass *) g_type_class_peek (gst_bin_get_type ());
   if (bin_class && bin_class->pool != NULL) {
@@ -1326,3 +1347,40 @@ gst_segtrap_set_enabled (gboolean enabled)
 {
   _gst_disable_segtrap = !enabled;
 }
+
+/**
+ * gst_deinit_register_notify:
+ * @func: (scope async): a #GstDeinitNotifyFunc
+ * @user_data: (nullable): private user data
+ *
+ * Registers a callback notified when gst_deinit() is called.
+ * This could be useful for a GStreamer library where the library holds
+ * persistent resources but prefers the resources to be released
+ * when gst_deinit() is called, so that any expected resource leaks
+ * (either GStreamer object or native handle/memory) can be addressed.
+ *
+ * Applications or GStreamer components can register callbacks
+ * before GStreamer is initialized, but installing notify after gst_deinit()
+ * is not allowed.
+ *
+ * Since: 1.26
+ */
+void
+gst_deinit_register_notify (GstDeinitNotifyFunc func, gpointer user_data)
+{
+  GstDeinitNotify *cb;
+
+  g_rec_mutex_lock (&init_lock);
+  if (gst_deinitialized) {
+    g_warning ("GStreamer was deinitialized already.");
+    g_rec_mutex_unlock (&init_lock);
+    return;
+  }
+
+  cb = g_new0 (GstDeinitNotify, 1);
+  cb->func = func;
+  cb->user_data = user_data;
+
+  _gst_deinit_notifies = g_list_prepend (_gst_deinit_notifies, cb);
+  g_rec_mutex_unlock (&init_lock);
+}

subprojects/gstreamer/gst/gst.h

@@ -144,6 +144,18 @@ gboolean        gst_update_registry             (void);
 GST_API
 const gchar *   gst_get_main_executable_path    (void);
 
+/**
+ * GstDeinitNotifyFunc:
+ * @user_data: User data registered along with this function via gst_deinit_register_notify()
+ *
+ * Since: 1.26
+ */
+typedef void  (*GstDeinitNotifyFunc)            (gpointer user_data);
+
+GST_API
+void            gst_deinit_register_notify      (GstDeinitNotifyFunc func,
+                                                 gpointer user_data);
+
 G_END_DECLS
 
 #endif /* __GST_H__ */

subprojects/gstreamer/tests/check/gst/gstdeinit2.c

@@ -0,0 +1,49 @@
+/* GStreamer
+ * Copyright (C) 2024 Seungha Yang <seungha@centricular.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <gst/gst.h>
+
+static void
+deinit_cb (guint * cb_count)
+{
+  *cb_count += 1;
+}
+
+int
+main (int argc, char **argv)
+{
+  guint cb_count = 0;
+
+  /* Installing callback before gst_init() is allowed */
+  gst_deinit_register_notify ((GstDeinitNotifyFunc) deinit_cb, &cb_count);
+
+  gst_init (NULL, NULL);
+
+  /* Install callback again */
+  gst_deinit_register_notify ((GstDeinitNotifyFunc) deinit_cb, &cb_count);
+
+  gst_deinit ();
+
+  g_assert (cb_count == 2);
+
+  return 0;
+}

subprojects/gstreamer/tests/check/meson.build

@@ -16,6 +16,7 @@ core_tests = [
   [ 'gst/gstcapsfeatures.c' ],
   [ 'gst/gstdatetime.c' ],
   [ 'gst/gstdeinit.c' ],
+  [ 'gst/gstdeinit2.c' ],
   [ 'gst/gstdevice.c' ],
   [ 'gst/gstelement.c', not gst_registry or not gst_parse],
   [ 'gst/gstelementfactory.c', not gst_registry ],