Example of parallel loops in powershell core with variables AND functions

for_each_parallel.ps1

# Define the function to use
Function Times-Two {
    param($j)
    $j*2
}

# Define all functions you want to load into parallel runspaces
# The reason to do this is that functions are not available in the runspaces like variables
$functionsArr = @("Times-Two")

# Load all functions into a variable
$functionsObj = [PSCustomObject]@{}
$functionsArr | ForEach {
    $func = Get-Command -Name $_
    $functionsObj | Add-Member -MemberType NoteProperty -Name $func.Name -Value $func.Definition.toString()
}

# Start the parallel loop
1..5 | ForEach-Object -ThrottleLimit 5 -Parallel {

    # Load the functions into the runspace, all other variables than the input need $using: as prefix
    $using:functionsObj.PSObject.Properties | ForEach {
        $functionsMember = $_
        # Creating a string consisting of "Function", the function name and the definition
        . { Invoke-Expression "Function $( $functionsMember.Name ) { $( $functionsMember.Value ) }" }
    }

    # Use the input object
    $i = $_

    # Do something with the input object and loaded functions
    Write-Host "Hello World $( Times-Two $i )"

    # Show the duration with parallelisation
    Start-Sleep 1

}