ximagesrc: fix compile-time warning and XInitThreads()

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5493>

subprojects/gst-plugins-good/sys/ximage/gstximagesrc.c

@@ -28,6 +28,13 @@
  * available to also capture your mouse pointer. It supports handling of
  * mouse and keyboard events. By default it will fixate to 25 frames per second.
  * 
+ * Applications are expected to call `XinitThreads()` before any other threads
+ * are started. For use in gst-launch-1.0 or other GStreamer command line 
+ * applications it is also possible to set the GST_XINITTHREADS=1 environment 
+ * variable so that `XInitThreads()` gets called when the plugin is loaded. This 
+ * may be too late in other use case scenarios though, so applications should 
+ * not rely on that.
+ *
  * ## Example pipelines
  * |[
  * gst-launch-1.0 ximagesrc ! video/x-raw,framerate=5/1 ! videoconvert ! theoraenc ! oggmux ! filesink location=desktop.ogg
@@ -1398,10 +1405,7 @@ gst_ximage_src_class_init (GstXImageSrcClass * klass)
   bc->stop = gst_ximage_src_stop;
   bc->unlock = gst_ximage_src_unlock;
   push_class->create = gst_ximage_src_create;
-#ifdef HAVE_NAVIGATION
-  XInitThreads ();
   bc->event = gst_ximage_src_event;
-#endif /* HAVE_NAVIGATION */
 }
 
 static void
@@ -1429,6 +1433,9 @@ plugin_init (GstPlugin * plugin)
 {
   gboolean ret;
 
+  if (g_getenv ("GST_XINITTHREADS"))
+    XInitThreads ();
+
   GST_DEBUG_CATEGORY_INIT (gst_debug_ximage_src, "ximagesrc", 0,
       "ximagesrc element debug");
 

subprojects/gstreamer/docs/gst/running.md

@@ -343,3 +343,10 @@ Example: `GST_PLUGIN_FEATURE_RANK=foo:PRIMARY,bar:primary,foobar:128`
 As a result of the above example,
 the `foo` and` bar` plugin feature rank values are `PRIMARY`(256)
 and `SECONDARY`(128) rank value will be assigned to `foobar`.
+
+**`GST_XINITTHREADS`.**
+
+Set this variable when using components that rely on X11, such as ximagesrc, 
+from gst-launch-1.0 or other command line applications. However, applications 
+should not depend on this variable and should make their own `XInitThreads()`
+call as early as possible.