Powershell thread handling problem

Question

I have a powershell problem, and maybe someone can help me. I'm using powershell 2.0, and i want to create, and use threads. I know that i can use jobs, but that is not what i want. I want a script, that creates windows forms, and runs background threads too. Since forms needs STA, this is not easy. Running "powershell.exe -sta" is not a solution.

Below is my script that I wrote, for simple thread handling. But it doesn't work. Even the new thread wont be created. Any suggestion, what is wrong? Please help me if you can!

Regards, Peter.

function ThreadProc() {
    for ($i = 0; $i -lt 10; $i++) {
        $ApartmentState = [System.Threading.Thread]::CurrentThread.GetApartmentState()
        Write-Host "ThreadProc ($ApartmentState): $i"
        # Yield the rest of the time slice.
        [System.Threading.Thread]::Sleep(0)
    }
}

$ApartmentState = [System.Threading.Thread]::CurrentThread.GetApartmentState()
Write-Host "Main thread ($ApartmentState): Start a second thread."

$thread_job = New-Object System.Threading.ThreadStart(ThreadProc)
$thread = New-Object System.Threading.Thread($thread_job)
$thread.CurrentThread.SetApartmentState([System.Threading.ApartmentState]::STA)
$thread.Start()

for ($i = 0; $i -lt 4; $i++) {
    Write-Host("Main thread: Do some work.")
    [System.Threading.Thread]::Sleep(0)
}

Write-Host("Main thread: Call Join(), to wait until ThreadProc ends.")
$thread.Join()
Write-Host("Main thread: ThreadProc.Join has returned. Program end.")

Answer 1

Noticed a couple of mistakes in your script. Firstly $thread_job, try this instead:

[System.Threading.ThreadStart]$thread_job = {ThreadProc};

You need to put the brackets around ThreadProc or it will be evaluated rather than passed as a function. Secondly you can just specify the type for delegates like ThreadStart and PowerShell will convert things for you; no need for New-Object.

Secondly CurrentThread is a static member - I'm guessing $thread.CurrentThread is a typo and you meant:

$thread.SetApartmentState([System.Threading.ApartmentState]::STA);

I imagine you'll still have problems getting it to work though - whenever I've tried using threads in PowerShell before I've always had nasty crashes with no real explanation...

Can you write a cmdlet in C# and call into that instead? Might be easier to do things that way - you could setup a new Runspace and run your command in the other Runspace's thread.

EDIT

Found these links that might help you:

http://weblogs.asp.net/adweigert/archive/2008/04/29/powershell-threading-for-powershell-v1-0.aspx http://blogs.msdn.com/b/powershell/archive/2007/03/23/thread-apartmentstate-and-powershell-execution-thread.aspx

Answer 2

I think that your question is somewhere close to a post called Powershell and Backgroundworker.Background worker is for running .NET code on a background thread.

Powershell, though is working on the top of .NET doesn't produce intermediate language (IL). Its an interpreted language and its code cannot run outside of the context of a powershell runspace. you perhaps can use your code creating our own PowerShell Runspace and running your script there, and marshall the results back to your primary session.