To build on the threading library I mentioned here, I've added some functionality to make it easier to communicate with the seperate thread. Still, keep in mind that PowerShell will only allow one pipeline to be executing in a runspace at any given time. So, these new functions can only be used while the thread is inactive. But, they provide power into setting up the thread to be run and communicating with the original runspace.
Ok, so this solution really isn't threading, but a neat way to get async scripts to run! The important thing to remember is that each "thread" is actually a PowerShell "runspace". Meaning, scripts run within the thread don't have access to objects or functions defined outside the thread. The script is composed of the following commands: