Updating console UI from RunnableState / sub-process

Anyone got a simple example on how I should update a UI/ui model from a
subprocess inside a RunnableState object?

Currently my TestNG plugin is running TestNG directly inside the
RunnableState and IDEAs JVM which is wrong.

If I launch a new JVM process to run TestNG, whats the suggested manner
of controlling a UI from the running process ( much like how the JUnit
plugin works ).

Do I just parse the output stream in a ProcessHandler?