Created attachment 283432 [details]
demo code to trigger the bug

while pipeline dynamic changed, gst_gl_mixer_decide_allocation (runs on app main thread) will re-allocate fbo/depth_texture, 
but gst_gl_mixer_process_textures(runs on GstAggregator's own main context thread,) may still runs. leads invalid gl object access .


the demo code is modified "dynamic change pipeline element " from gstreamer manual , this demo will trigger 

*: gint gst_gl_shader_get_attribute_location(GstGLShader *, const gchar *): assertion 'priv->program_handle != 0' failed

or fbo !=0 assert while changing elements 

(the GstAggregator use buffer timestamp to decide which buffers to display,so it didn't fit dynamic element very well. only first a few element changes can be viewed)