Building Powershell GUIs that won't freeze when you use them

A few days ago I wrote about how important I think it is that you build a GUI for your scripts if they are to be used by anoyone else.

If you have ever built a GUI using Powershell however, you know there is a problem with it that I didn't mention, that is, whenever your script is actually doing anything the GUI will freeze and windows will tell you it isn't responding. This is not good as most users will then try to close it and try again. We don't want that.

The reason this happens is because you are running your form (GUI) and logic in the same thread, something you should never do, problem is, Powershells support for multithreading is limited at best.

In the last post I also talked about my module EasyGUI and mentioned that there are features I wouldnt go in to in that post, one of those features is an easy way to use threads.

There are two ways to use threads in EasyGUI, I go through both of them below as well as a tip on how I prefer to use them.

Method 1.

Passing in a scriptblock to the thread, here I am creating it on the fly but you could also store the scriptblock in a variable and pass that to the function instead

New-Thread {
    0..60|Foreach-Object{
        $SYNC.myLabel.Text = $_
    }
}

Method 2.

You could also write the code for the thread in a separate script file and then pass that to the New-Thread function like this

New-Thread "D:\Program\Powershell\myThread.ps1"

One thing to be aware of is that the threads will start running emediatly when you create them. Often you might not want that. What I usually do is create the threads inside a scriptblock that I store in a variable, then when I need the tread to run I run that scriptblock. That would look something like this.

$myThread = {
    New-Thread {
        0...60|Foreach-Object{
            $SYNC.myLabel.Text = $_
        }
    }
}

#Now it's time to run the thread, simply type the & sign and then the variable containing the scriptblock
&$myThread

$SYNC ? Where did that come from?

Noticed that did you?

This is a variable that's automatically created when you initialize the EasyGUI module. It's a hashtable that's synced between all threads so you can communicate between them. In the examples you see that I am using $SYNC.myLabel. This is created in the GUI like this.

$SYNC.myLabel = New-Label @{
    Location = "15, 15"
}

or like this

$myLabel = New-Label @{
    Location = "15, 15"
}
$SYNC.myLabel = $myLabel

If you want to see a complete example of a GUI script with threading implemented there is an example availiable in the Easy GUI repository.