autoconvert: Remove unused elements from the bin

Instead of letting all the elements that were added into the bin,
add them only when strictly needed and removed them when we stop using
them.

With previous refactoring we are keeping them in our own hashmap in
amy case so we can keep reusing the same elements as before.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/899>

subprojects/gst-plugins-bad/gst/autoconvert/gstautoconvert.c

@@ -427,22 +427,22 @@ gst_auto_convert_get_property (GObject * object,
 static GstElement *
 gst_auto_convert_get_element_by_type (GstAutoConvert * autoconvert, GType type)
 {
-  GList *item;
+  GList *item, *elements;
-  GstBin *bin = GST_BIN (autoconvert);
   GstElement *element = NULL;
 
   g_return_val_if_fail (type != 0, NULL);
 
-  GST_OBJECT_LOCK (autoconvert);
+  GST_AUTOCONVERT_LOCK (autoconvert);
-
+  elements = g_hash_table_get_keys (autoconvert->elements);
-  for (item = bin->children; item; item = item->next) {
+  for (item = elements; item; item = item->next) {
-    if (G_OBJECT_TYPE(item->data) == type) {
+    if (G_OBJECT_TYPE (item->data) == type) {
       element = gst_object_ref (item->data);
       break;
     }
   }
+  GST_AUTOCONVERT_UNLOCK (autoconvert);
 
-  GST_OBJECT_UNLOCK (autoconvert);
+  g_list_free (elements);
 
   return element;
 }
@@ -569,9 +569,6 @@ gst_auto_convert_add_element (GstAutoConvert * autoconvert,
 {
   GstElement *element = NULL;
   InternalPads *pads;
-  GstPad *sinkpad = NULL;
-  GstPad *srcpad = NULL;
-  GstPadLinkReturn padlinkret;
 
   GST_DEBUG_OBJECT (autoconvert, "Adding element %s to the autoconvert bin",
       gst_plugin_feature_get_name (GST_PLUGIN_FEATURE (factory)));
@@ -580,33 +577,9 @@ gst_auto_convert_add_element (GstAutoConvert * autoconvert,
   if (!element)
     return NULL;
 
-  if (!gst_bin_add (GST_BIN (autoconvert), element)) {
-    GST_ERROR_OBJECT (autoconvert, "Could not add element %s to the bin",
-        GST_OBJECT_NAME (element));
-    gst_object_unref (element);
-    return NULL;
-  }
-
   pads = internal_pads_new (autoconvert, GST_OBJECT_NAME (element));
   g_hash_table_insert (autoconvert->elements, element, pads);
 
-  srcpad = get_pad_by_direction (element, GST_PAD_SRC);
-  if (!srcpad) {
-    GST_ERROR_OBJECT (autoconvert, "Could not find source in %s",
-        GST_OBJECT_NAME (element));
-    goto error;
-  }
-
-  sinkpad = get_pad_by_direction (element, GST_PAD_SINK);
-  if (!sinkpad) {
-    GST_ERROR_OBJECT (autoconvert, "Could not find sink in %s",
-        GST_OBJECT_NAME (element));
-    goto error;
-  }
-
-  gst_pad_set_active (pads->sink, TRUE);
-  gst_pad_set_active (pads->src, TRUE);
-
   gst_pad_set_chain_function (pads->sink,
       GST_DEBUG_FUNCPTR (gst_auto_convert_internal_sink_chain));
   gst_pad_set_chain_list_function (pads->sink,
@@ -621,47 +594,7 @@ gst_auto_convert_add_element (GstAutoConvert * autoconvert,
   gst_pad_set_query_function (pads->src,
       GST_DEBUG_FUNCPTR (gst_auto_convert_internal_src_query));
 
-  padlinkret = gst_pad_link_full (pads->src, sinkpad,
+  return gst_object_ref (element);
-      GST_PAD_LINK_CHECK_NOTHING);
-  if (GST_PAD_LINK_FAILED (padlinkret)) {
-    GST_WARNING_OBJECT (autoconvert, "Could not links pad %s:%s to %s:%s"
-        " for reason %d",
-        GST_DEBUG_PAD_NAME (pads->src),
-        GST_DEBUG_PAD_NAME (sinkpad), padlinkret);
-    goto error;
-  }
-
-  padlinkret = gst_pad_link_full (srcpad, pads->sink,
-      GST_PAD_LINK_CHECK_NOTHING);
-  if (GST_PAD_LINK_FAILED (padlinkret)) {
-    GST_WARNING_OBJECT (autoconvert, "Could not links pad %s:%s to %s:%s"
-        " for reason %d",
-        GST_DEBUG_PAD_NAME (pads->src),
-        GST_DEBUG_PAD_NAME (sinkpad), padlinkret);
-    goto error;
-  }
-
-  gst_element_sync_state_with_parent (element);
-
-  /* Increment the reference count we will return to the caller */
-  gst_object_ref (element);
-
-  /* unref sink and src pad */
-  gst_object_unref (srcpad);
-  gst_object_unref (sinkpad);
-  return element;
-
-error:
-  gst_element_set_locked_state (element, TRUE);
-  gst_element_set_state (element, GST_STATE_NULL);
-  gst_bin_remove (GST_BIN (autoconvert), element);
-
-  if (srcpad)
-    gst_object_unref (srcpad);
-  if (sinkpad)
-    gst_object_unref (sinkpad);
-
-  return NULL;
 }
 
 static GstElement *
@@ -773,6 +706,10 @@ static gboolean
 gst_auto_convert_activate_element (GstAutoConvert * autoconvert,
     GstElement * element, GstCaps * caps)
 {
+  gboolean res = TRUE;
+  GstPad *sinkpad = NULL, *srcpad = NULL;
+  GstPadLinkReturn padlinkret;
+  GstElement *current_subelement = NULL;
   InternalPads *pads =
       gst_auto_convert_get_element_internal_pads (autoconvert, element);
 
@@ -783,11 +720,61 @@ gst_auto_convert_activate_element (GstAutoConvert * autoconvert,
     if (!gst_pad_peer_query_accept_caps (pads->src, caps)) {
       GST_DEBUG_OBJECT (autoconvert, "Could not set %s:%s to %"
           GST_PTR_FORMAT, GST_DEBUG_PAD_NAME (pads->src), caps);
-      internal_pads_unref (pads);
+      goto error;
-      return FALSE;
     }
   }
 
+  current_subelement = gst_auto_convert_get_subelement (autoconvert);
+  gst_element_set_locked_state (element, FALSE);
+  if (!gst_bin_add (GST_BIN (autoconvert), gst_object_ref (element))) {
+    GST_ERROR_OBJECT (autoconvert, "Could not add element %s to the bin",
+        GST_OBJECT_NAME (element));
+    goto error;
+  }
+
+  if (!gst_element_sync_state_with_parent (element)) {
+    GST_WARNING_OBJECT (autoconvert, "Could sync %" GST_PTR_FORMAT " state",
+        element);
+    goto error;
+  }
+
+  srcpad = get_pad_by_direction (element, GST_PAD_SRC);
+  if (!srcpad) {
+    GST_ERROR_OBJECT (autoconvert, "Could not find source in %s",
+        GST_OBJECT_NAME (element));
+    goto error;
+  }
+
+  sinkpad = get_pad_by_direction (element, GST_PAD_SINK);
+  if (!sinkpad) {
+    GST_ERROR_OBJECT (autoconvert, "Could not find sink in %s",
+        GST_OBJECT_NAME (element));
+    goto error;
+  }
+
+  gst_pad_set_active (pads->sink, TRUE);
+  gst_pad_set_active (pads->src, TRUE);
+
+  padlinkret = gst_pad_link_full (pads->src, sinkpad,
+      GST_PAD_LINK_CHECK_NOTHING);
+  if (GST_PAD_LINK_FAILED (padlinkret)) {
+    GST_WARNING_OBJECT (autoconvert, "Could not links pad %s:%s to %s:%s"
+        " for reason %d",
+        GST_DEBUG_PAD_NAME (pads->src),
+        GST_DEBUG_PAD_NAME (sinkpad), padlinkret);
+    goto error;
+  }
+
+  padlinkret = gst_pad_link_full (srcpad, pads->sink,
+      GST_PAD_LINK_CHECK_NOTHING);
+  if (GST_PAD_LINK_FAILED (padlinkret)) {
+    GST_WARNING_OBJECT (autoconvert, "Could not links pad %s:%s to %s:%s"
+        " for reason %d",
+        GST_DEBUG_PAD_NAME (pads->src),
+        GST_DEBUG_PAD_NAME (sinkpad), padlinkret);
+    goto error;
+  }
+
   GST_AUTOCONVERT_LOCK (autoconvert);
   gst_object_replace ((GstObject **) & autoconvert->current_subelement,
       GST_OBJECT (element));
@@ -797,6 +784,12 @@ gst_auto_convert_activate_element (GstAutoConvert * autoconvert,
       GST_OBJECT (pads->sink));
   GST_AUTOCONVERT_UNLOCK (autoconvert);
 
+  if (current_subelement) {
+    gst_element_set_locked_state (current_subelement, TRUE);
+    gst_element_set_state (current_subelement, GST_STATE_NULL);
+    gst_bin_remove (GST_BIN (autoconvert), current_subelement);
+  }
+
   gst_pad_sticky_events_foreach (autoconvert->sinkpad, sticky_event_push,
       autoconvert);
 
@@ -805,10 +798,24 @@ gst_auto_convert_activate_element (GstAutoConvert * autoconvert,
   GST_INFO_OBJECT (autoconvert, "Selected element %s",
       GST_OBJECT_NAME (GST_OBJECT (element)));
 
+done:
   gst_object_unref (element);
   internal_pads_unref (pads);
+  gst_clear_object (&srcpad);
+  gst_clear_object (&sinkpad);
+  gst_clear_object (&current_subelement);
 
-  return TRUE;
+  return res;
+
+error:
+  gst_element_set_locked_state (element, TRUE);
+  gst_element_set_state (element, GST_STATE_NULL);
+
+  if (GST_OBJECT_PARENT (element))
+    gst_bin_remove (GST_BIN (autoconvert), element);
+
+  res = FALSE;
+  goto done;
 }
 
 static GstIterator *