query: add new drain query

With the new serialized downstream queries we can implement a drain query that
makes an element waits until a downstream element replies to the query.

gst/gstquark.c

@@ -56,7 +56,7 @@ static const gchar *_quark_strings[] = {
   "GstEventReconfigure", "segment", "GstQueryScheduling", "pull-mode",
   "allocator", "GstEventFlushStop", "options", "GstQueryAcceptCaps",
   "result", "GstQueryCaps", "filter", "modes", "GstEventStreamConfig",
-  "setup-data", "stream-headers", "GstEventGap"
+  "setup-data", "stream-headers", "GstEventGap", "GstQueryDrain"
 };
 
 GQuark _priv_gst_quark_table[GST_QUARK_MAX];

gst/gstquark.h

@@ -162,7 +162,8 @@ typedef enum _GstQuarkId
   GST_QUARK_SETUP_DATA = 133,
   GST_QUARK_STREAM_HEADERS = 134,
   GST_QUARK_EVENT_GAP = 135,
-  GST_QUARK_MAX = 136
+  GST_QUARK_QUERY_DRAIN = 136,
+  GST_QUARK_MAX = 137
 } GstQuarkId;
 
 extern GQuark _priv_gst_quark_table[GST_QUARK_MAX];

gst/gstquery.c

@@ -121,6 +121,7 @@ static GstQueryQuarks query_quarks[] = {
   {GST_QUERY_SCHEDULING, "scheduling", 0},
   {GST_QUERY_ACCEPT_CAPS, "accept-caps", 0},
   {GST_QUERY_CAPS, "caps", 0},
+  {GST_QUERY_DRAIN, "drain", 0},
 
   {0, NULL, 0}
 };
@@ -2147,3 +2148,24 @@ gst_query_intersect_caps_result (GstQuery * query, GstCaps * filter,
   gst_query_set_caps_result (query, res);
   gst_caps_unref (res);
 }
+
+/**
+ * gst_query_new_drain:
+ *
+ * Constructs a new query object for querying the drain state.
+ *
+ * Free-function: gst_query_unref
+ *
+ * Returns: (transfer full): a new #GstQuery
+ */
+GstQuery *
+gst_query_new_drain (void)
+{
+  GstQuery *query;
+  GstStructure *structure;
+
+  structure = gst_structure_new_id_empty (GST_QUARK (QUERY_DRAIN));
+  query = gst_query_new_custom (GST_QUERY_DRAIN, structure);
+
+  return query;
+}

gst/gstquery.h

@@ -101,6 +101,7 @@ typedef enum {
  * @GST_QUERY_SCHEDULING: the scheduling properties
  * @GST_QUERY_ACCEPT_CAPS: the accept caps query
  * @GST_QUERY_CAPS: the caps query
+ * @GST_QUERY_DRAIN: wait till all serialized data is consumed downstream
  *
  * Standard predefined Query types
  */
@@ -123,7 +124,8 @@ typedef enum {
   GST_QUERY_ALLOCATION   = GST_QUERY_MAKE_TYPE (140, FLAG(DOWNSTREAM) | FLAG(SERIALIZED)),
   GST_QUERY_SCHEDULING   = GST_QUERY_MAKE_TYPE (150, FLAG(UPSTREAM)),
   GST_QUERY_ACCEPT_CAPS  = GST_QUERY_MAKE_TYPE (160, FLAG(BOTH)),
-  GST_QUERY_CAPS         = GST_QUERY_MAKE_TYPE (170, FLAG(BOTH))
+  GST_QUERY_CAPS         = GST_QUERY_MAKE_TYPE (170, FLAG(BOTH)),
+  GST_QUERY_DRAIN        = GST_QUERY_MAKE_TYPE (180, FLAG(DOWNSTREAM) | FLAG(SERIALIZED))
 } GstQueryType;
 #undef FLAG
 
@@ -456,6 +458,8 @@ void            gst_query_parse_caps_result        (GstQuery *query, GstCaps **c
 
 void            gst_query_intersect_caps_result    (GstQuery *query, GstCaps *filter,
                                                     GstCapsIntersectMode mode);
+/* drain query */
+GstQuery *      gst_query_new_drain                (void) G_GNUC_MALLOC;
 
 G_END_DECLS
 

win32/common/libgstreamer.def

@@ -825,6 +825,7 @@ EXPORTS
 	gst_query_new_caps
 	gst_query_new_convert
 	gst_query_new_custom
+	gst_query_new_drain
 	gst_query_new_duration
 	gst_query_new_formats
 	gst_query_new_latency