Create simple runspaces in PowerShell.

CreateRunspaces.ps1

$watch = [System.Diagnostics.Stopwatch]::StartNew()
# BLOCK 1: Create and open runspace pool, setup runspaces array with min and max threads
$pool = [RunspaceFactory]::CreateRunspacePool(1, [int]$env:NUMBER_OF_PROCESSORS+1)
$pool.Open()
$runspaces = $results = @()
    
# BLOCK 2: Create reusable scriptblock. This is the workhorse of the runspace. Think of it as a function.
$scriptblock = {
    param (
        [string]$Data
    )

    Start-Sleep -Seconds 1
}

foreach($num in 1..20) {
    # BLOCK 3: Create runspace and add to runspace pool
    $runspace = [PowerShell]::Create()
    $null = $runspace.AddScript($scriptblock)
    $null = $runspace.AddArgument($num)
    $runspace.RunspacePool = $pool
    
    # BLOCK 4: Add runspace to runspaces collection and "start" it
    # Asynchronously runs the commands of the PowerShell object pipeline
    $runspaces += [PSCustomObject]@{ Pipe = $runspace; Status = $runspace.BeginInvoke() }
}


# BLOCK 5: Wait for runspaces to finish
while ($runspaces.Status.IsCompleted -notcontains $true) {}

# BLOCK 6: Clean up
foreach ($runspace in $runspaces) {
    # EndInvoke method retrieves the results of the asynchronous call
    $results += $runspace.Pipe.EndInvoke($runspace.Status)
    $runspace.Pipe.Dispose()
}
    
$pool.Close() 
$pool.Dispose()

# Bonus block 7
# Look at $results to see any errors or whatever was returned from the runspaces
$watch.Stop()
$watch.ElapsedMilliseconds / 1000

NoRunspaces.ps1

$watch = [System.Diagnostics.Stopwatch]::StartNew()
$items = Get-ChildItem -Path "master:" -ID "{F8FD1710-E835-402D-B0DB-0537887DBE00}"
foreach($item in $items) {
    $yaml = $item | ConvertTo-RainbowYaml
    $rainbowItem = ConvertFrom-RainbowYaml -Yaml $yaml
    Import-RainbowItem -Item $rainbowItem
}
$watch.Stop()
$watch.ElapsedMilliseconds / 1000

RunspacesWithSPE.ps1

$watch = [System.Diagnostics.Stopwatch]::StartNew()
$script = {
    $yaml = $item | ConvertTo-RainbowYaml
    $rainbowItem = ConvertFrom-RainbowYaml -Yaml $yaml
    Import-RainbowItem -Item $rainbowItem
    $true
}

$maxParallel = 20
$sessions = [System.Collections.ArrayList]@()
$requestItemQueue = [System.Collections.Generic.Queue[Item]]@()
$items = Get-ChildItem -Path "master:" -ID "{110D559F-DEA5-42EA-9C1C-8A5DF7E70EF9}" -Recurse
foreach($item in $items) {
    $requestItemQueue.Enqueue($item)
}
$finishedSessions = [System.Collections.ArrayList]@()
while($requestItemQueue.Count -gt 0) {
    if($sessions.Count -ge $maxParallel) {
        $finished = @($sessions | Wait-ScriptSession -Any)
        $finishedSessions.AddRange($finished) > $null
        foreach($fin in $finished) {
            $sessions.Remove($fin) > $null
        }
    }
    $requestItem = $requestItemQueue.Dequeue()
    $s = Start-ScriptSession -ScriptBlock $script -ArgumentList @{"item"=$requestItem}
    $sessions.Add($s) > $null
}
if($sessions.Count -gt 0) {
    $finished = @($sessions | Wait-ScriptSession)
    $finishedSessions.AddRange($finished) > $null
}
$finishedSessions | Receive-ScriptSession
$watch.Stop()
$watch.ElapsedMilliseconds / 1000