Display problems with program-framework & multi-processing

[David Vinayak Wallace <Gumby@MCC.COM>]

    Date: Tue, 16 Aug 88 15:11 EDT
    From: pan@Athena.Pangaro.Dialnet.Symbolics.Com (Paul Pangaro)

    Then, I run an additional process in the background, which is merely to
    update the simulation per time slice. It reads the current parameter
    values, runs the simulation, and then updates the screen, possibly the
    same displays that the user modifies via mouse clicks.

Why don't you wrap some sort of with-lock-held around your redisplay
functions?  Your sensitivity function (I forget what it's called --
"applicability" or "context" or whatever) can return if the lock is
held.  Don't forget that your handlers themselves need to seize the
lock.  Also, make sure that, despite your thinking that updating is done
by the background, that the program command loop isn't also doing
redisplay, which some do by default.

    NOW: Sometimes all hell breaks lose, and the display updates get messed
    up:  added characters strewn about in the wrong places...

I get this kind of garbage when using vanilla redisplayable-output too.
I don't think it works as well as as just using tv:scroll-parse-item.