Can shared memory data be used as a signal like gtk-input-add doe s with a pipe?

["Norris, Kendall P." <Kendall Norris Honeywell com>]

I am writing an application with a gtk process for user interface and a
seperate process for my test application.  I was using pipes for
communication between the processes but am now using shared memory as my
IPC.  I used gdk-input-add to emit a signal when the pipe had a message.  Is
there a way I can use a variable in the shared memory space,  monitor the
memory address with gtk looking for a change of state and cause a signal to
be emitted?

Thanks for any help, Ken