Execute parallel powershell thread using runspace objects

ForEach-Parallel.ps1

function ForEach-Parallel
{
	<#
	.DESCRIPTION
	.SYNOPSIS
	.NOTES
		Source: http://powertoe.wordpress.com/2012/05/03/foreach-parallel/
	.EXAMPLE
		(0..50) |ForEach-Parallel -MaxThreads 4{
			$_
			sleep (Get-Random -Minimum 0 -Maximum 5)
		}
	
	#>
	[CmdletBinding()]
	param (
		[Parameter(Mandatory = $true, position = 0)]
		[System.Management.Automation.ScriptBlock] $ScriptBlock,
		[Parameter(Mandatory = $true, ValueFromPipeline = $true)]
		[PSObject]$InputObject,
		[Parameter(Mandatory = $false)]
		[int]$MaxThreads = 5
	)
	BEGIN
	{
		$iss = [system.management.automation.runspaces.initialsessionstate]::CreateDefault()
		$pool = [Runspacefactory]::CreateRunspacePool(1, $maxthreads, $iss, $host)
		$pool.open()
		$threads = @()
		$ScriptBlock = $ExecutionContext.InvokeCommand.NewScriptBlock("param(`$_)`r`n" + $Scriptblock.ToString())
	}
	PROCESS
	{
		$powershell = [powershell]::Create().addscript($scriptblock).addargument($InputObject)
		$powershell.runspacepool = $pool
		$threads += @{
			instance = $powershell
			handle = $powershell.begininvoke()
		}
	}
	END
	{
		$notdone = $true
		while ($notdone)
		{
			$notdone = $false
			for ($i = 0; $i -lt $threads.count; $i++)
			{
				$thread = $threads[$i]
				if ($thread)
				{
					if ($thread.handle.iscompleted)
					{
						$thread.instance.endinvoke($thread.handle)
						$thread.instance.dispose()
						$threads[$i] = $null
					}
					else
					{
						$notdone = $true
					}
				}
			}
		}
	}
}