I don’t know if this is canonical but, does this count?

Also here are examples of queues in SDL-88
http://www.sdl-forum.org/sdl88tutorial/4.ProcessCommunication/4.1_Signal_input_queue.htm
I don’t know if this is canonical but, does this count?

Also here are examples of queues in SDL-88
http://www.sdl-forum.org/sdl88tutorial/4.ProcessCommunication/4.1_Signal_input_queue.htm