Problem solved

Keep looking a head is the name of the game in software. I looked ahead.

We have two rectangles, the command line and the flush window. The flush window interleaves printfs with command line scroll as normal.  The fwrites to flush window go to a non blocking fd fifo, so they can be redirected. If the response to write is not ready, then the standard is to cll the IO manager flush buffer routine immediately and move the fifo to the flush screen. We can put a mutext lock on the flush window, any one cn fprintf to it all day long.  IO manager can do that, a necessary default function.