Modifies a pointer to a GstMessage to point to a different GstMessage. The
modification is done atomically (so this is useful for ensuring thread safety
in some cases), and the reference counts are updated appropriately (the old
message is unreffed, the new one is reffed).
Either new_message or the GstMessage pointed to by old_message may be NULL.
Modifies a pointer to a GstMessage to point to a different GstMessage. The modification is done atomically (so this is useful for ensuring thread safety in some cases), and the reference counts are updated appropriately (the old message is unreffed, the new one is reffed). Either new_message or the GstMessage pointed to by old_message may be NULL.