Questions about sharing desktops

hello: I am a java programmer and have a question about sharing remote desktops. How to implement a shared desktop at the code level?I simulated two users using the same GuacamoleTunnel to achieve shared desktop??but the result is that neither user can connect to the remote desktop.I would like

The VNC console response slowly or get stuck after opening more than five console windows

no idea about this。Do you kown why？ -- Thanks Wenhu Liu