$jobItems = "a", "b", "c", "d", "e"
$jobMax = 2
$jobs = @()

$jobWork = {
    param ($MyInput)
    if ($MyInput -eq "d") {
        throw "an example of an error"
    } else {
        write-output "Processed $MyInput"
    }
}

foreach ($jobItem in $jobItems) {
    if ($jobs.Count -le $jobMax) {
        $jobs += Start-Job -ScriptBlock $jobWork -ArgumentList $jobItem
    } else {
        $jobs | Wait-Job -Any
    }
}
$jobs | Wait-Job