How to execute a PowerShell function several times in parallel?

Here's a quick bogus scriptblock for the purpose of testing:

$Code = {
    param ($init)
    $start = Get-Date
    (1..30) | % { Start-Sleep -Seconds 1; $init +=1 }
    $stop = Get-Date
    Write-Output "Counted from $($init - 30) until $init in $($stop - $start)."
}

This scriptblock can then be passed on to Start-Job, with for example 3 parameters (10, 15, 35)

$jobs = @()
(10,15,35) | % { $jobs += Start-Job -ArgumentList $_ -ScriptBlock $Code }

Wait-Job -Job $jobs | Out-Null
Receive-Job -Job $jobs

This creates 3 jobs, assign them to the $jobs variable, runs them in parallel and then waits for these 3 jobs to finish, and retrieves the results:

Counted from 10 until 40 in 00:00:30.0147167.
Counted from 15 until 45 in 00:00:30.0057163.
Counted from 35 until 65 in 00:00:30.0067163.

This did not take 90 seconds to execute, only 30.

One of the tricky parts is to provide -Argumentlist to Start-Job, and include a param() block inside the ScriptBlock. Otherwise, your values are never seen by the scriptblock.

No update necessary for this. Define a script block and use Start-Job to run the script block as many times as necessary. Example:

$cmd = {
  param($a, $b)
  Write-Host $a $b
}

$foo = "foo"

1..5 | ForEach-Object {
  Start-Job -ScriptBlock $cmd -ArgumentList $_, $foo
}

The script block takes 2 parameters $a and $b which are passed by the -ArgumentList option. In the example above, the assignments are $_ → $a and $foo → $b. $foo is just an example for a configurable, but static parameter.

Run Get-Job | Remove-Job at some point to remove the finished jobs from the queue (or Get-Job | % { Receive-Job $_.Id; Remove-Job $_.Id } if you want to retrieve the output).