TopolearnParallel and remote execution turn slow, one-machine-at-a-time scripts into fleet automation.
PowerShell has several ways to run work concurrently:
- Start-Job runs a script block in a separate background process. Isolated but heavy (a new pwsh starts each time).
- Start-ThreadJob runs it on a thread in the same process: much lighter, the usual choice. Both return job objects; collect results with
Receive-Job(-Waitto block) and clean up withRemove-Job. - ForEach-Object -Parallel (PowerShell 7) processes pipeline items concurrently in runspaces, with
-ThrottleLimit(default 5) capping concurrency.
Code in a job or a parallel block cannot see your variables. Pass values with the `$using:` scope modifier, which copies them in: $using:token. Do not modify shared collections from parallel blocks; output results and collect them instead.
Parallelism pays off for I/O-bound work like web calls, remote commands and file copies. For tiny CPU tasks, the overhead of runspaces can make it slower than a plain loop.
Remoting runs commands on other machines: Invoke-Command -ComputerName srv1, srv2 -ScriptBlock { ... } executes in parallel on all of them over WinRM (Windows), and -HostName uses SSH, which works cross-platform. Enter-PSSession gives an interactive remote prompt; New-PSSession keeps a reusable connection. Results come back as deserialized objects (properties only, no methods).
Example
$job = Start-ThreadJob { Start-Sleep -Milliseconds 300; (Get-Date).Year }
Receive-Job $job -Wait -AutoRemoveJob # 2026
$pj = Start-Job { $PID } # a separate process
(Receive-Job $pj -Wait) -ne $PID # True
Remove-Job $pj
$factor = 10
1..5 | ForEach-Object -Parallel {
Start-Sleep -Milliseconds (Get-Random -Maximum 200)
$_ * $using:factor # $using: copies a local value in
} -ThrottleLimit 3 # 10..50, in any order
# Remoting (WinRM on Windows, or SSH everywhere):
# Invoke-Command -HostName web1, web2 -UserName ops -ScriptBlock { Get-Uptime }
# Enter-PSSession -HostName web1 # interactive remote prompt
# $s = New-PSSession -HostName web1 -UserName ops
# Invoke-Command -Session $s { $env:HOSTNAME }Remember
- Start-ThreadJob is light, Start-Job isolates in a process
- ForEach-Object -Parallel with -ThrottleLimit for concurrent pipelines
- $using:var passes local values into jobs, parallel blocks and remote sessions
Watch out for
- Referencing $myVar inside -Parallel or a job without $using: and getting $null.