Powershell module loading stops in C# code when Write-Progress is used

Question

I have this service that, when request is received, runs a powershell command and returns result. Here is the invoker class code:

public class PowerShellScript {

    public PowerShellScript() {
    }

    public Object[] Invoke( String strScriptName, NameValueCollection nvcParams ) {
        Boolean bResult = true;
        int n = 0;
        Object[] objResult = null;
        PowerShell ps = PowerShell.Create();
        String strScript = strScriptName;

        for (n = 0; n < nvcParams.Count; n++) {
            strScript += String.Format( " -{0} {1}", nvcParams.GetKey( n ), nvcParams[n] );
        }

        //ps.AddScript( @"E:\snapins\Init-profile.ps1" );
        ps.AddScript( strScript );
        Collection<PSObject> colpsOutput = ps.Invoke();
        if (colpsOutput.Count > 0)
            objResult = new Object[colpsOutput.Count];

        n = 0;
        foreach (PSObject psOutput in colpsOutput) {
            if (psOutput != null) {
                try {
                    objResult[n] = psOutput.BaseObject;
                }
                catch (Exception ex) { 
                    //exception should be handeled properly in powershell script
                }
            }
            n++;
        }
        colpsOutput.Clear();
        ps.Dispose();

        return objResult;
    }
}

Method Invoke returns all results returned by powershell script. The problem though is that if the called script contains Write-Progress either in imported module or script itself, the Powershell class somehow believes that this is real output and completes script execution instantly, thus returning null as an object.

Ideally, one could block output with Out-Null cmdlet, but it doesn't work for Write-Progress. Any ideas as ot how to block Write-Progress?

Answer 1

I tried your code and it worked in a trivial Console application and even in a Windows application with a simple script with some output and calls of Write-Progress. Thus, the problem is not that easy reproducible...

Powershell class somehow believes that this is real output and completes script execution instantly

Hmm, perhaps it just fails, not “treats output differently” and that is why the output is empty. Can you check the error collection after execution?

Any ideas as ot how to block Write-Progress?

If you are just about blocking it then this should work: before invoking your worker script invoke a “profile” script with this command installing a dummy replacement:

function global:Write-Progress {}

Thus, when your script calls Write-Progress then the dummy function Write-Progress is actually called and this in fact “blocks Write-Progress” effectively.