How do I Write-Progress in Powershell based on events from object? - multithreading

Question

I have a small C# file that defines a SumCalculator class. It has a method CalculateSum(int totalSteps) that calculates the sum of numbers from 1 to totalSteps and raises a CalculationStep event returning arguments of LongOperationArgs class on each consecutive number. I want to create an instance of the Calculator class in my PowerShell 5.0 script and report the calculation progress using Write-Progress cmdlet. Here's the code:
$csharpSource = #'
using System;
namespace Test
{
public class LongOperationArgs : EventArgs {
public int TotalSteps { get; private set; }
public int CurrentStep { get; private set; }
public LongOperationArgs(int totalSteps, int currentStep) {
TotalSteps = totalSteps;
CurrentStep = currentStep;
}
}
public class SumCalculator {
public event EventHandler<LongOperationArgs> CalculationStep;
private void OnCalculationStep(LongOperationArgs e) {
EventHandler<LongOperationArgs> handler = CalculationStep;
if (handler != null) {
handler(this, e);
}
}
public int CalculateSum(int totalSteps) {
var sum = 0;
for(var i = 1; i <= totalSteps; i++) {
sum += i;
OnCalculationStep(new LongOperationArgs(totalSteps, i));
}
return sum;
}
}
}
'#
Add-Type -TypeDefinition "$csharpSource"
$calculator = New-Object Test.SumCalculator
$action =
{
$jobId = 1;
$jobActivity = "Calculating...";
if ($EventArgs.CurrentStep -eq $EventArgs.TotalSteps)
{
Write-Progress -Id $jobId -Activity $jobActivity -Completed;
}
else
{
Write-Progress -Id $jobId -Activity $jobActivity -Status "Step $($EventArgs.CurrentStep) of $($EventArgs.TotalSteps)" -PercentComplete ($EventArgs.CurrentStep / $EventArgs.TotalSteps * 100);
}
}
$bar = Register-ObjectEvent -InputObject $calculator -EventName "CalculationStep" -Action $action
$calculator.CalculateSum(100);
My problem is that Powershell runs CalculateSum() and Write-Progress in the same thread. So first CalculateSum() runs to completion, and only then Write-Progress starts reporting progress. My first response was to change the last line of my script from
$calculator.CalculateSum(100);
to
$job = Start-Job { $calculator.CalculateSum(100); }
but that caused the progress to stop being reported (Write-Progress likely wants events from $calculator to be thrown in the same thread). Is there any way to make Write-Progress respond to $calculator events when calculation is done in a different thread?