How to execute a PowerShell function several times in parallel?

Question

I'm not sure whether to call this a need for multi-threading, job-based, or async, but basically I have a Powershell script function that takes several parameters and I need to call it several times with different parameters and have these run in parallel.

Currently, I call the function like this:

Execute "param1" "param2" "param3" "param4"

How can I call this multiple times without waiting for each call to Execute return to the caller?

Currently I'm running v2.0 but I can update if necessary

EDIT: here's what I have so far, which doesn't work:

$cmd = {
    param($vmxFilePath,$machineName,$username,$password,$scriptTpath,$scriptFile,$uacDismissScript,$snapshotName)
    Execute $vmxFilePath $machineName $username $password $scriptTpath $scriptFile $uacDismissScript $snapshotName
}

Start-Job -ScriptBlock $cmd -ArgumentList $vmxFilePath, $machineName, $username $password, $scriptTpath, $scriptFile, $uacDismissScript, $snapshotName

I get an error:

cannot convert 'system.object[]' to the type 'system.management.automation.scriptblock' required by parameter 'initializationscript'. specified method is not supported

EDIT2: I've modified my script but I still get the error mentioned above. Here's my mod:

$cmd = {
    param($vmxFilePath,$machineName,$username,$password,$scriptTpath,$scriptFile,$uacDismissScript,$snapshotName)
    Execute $vmxFilePath $machineName $username $password $scriptTpath $scriptFile $uacDismissScript $snapshotName
}

Start-Job -ScriptBlock $cmd -ArgumentList $vmxFilePath, $machineName, $username $password, $scriptTpath, $scriptFile, $uacDismissScript, $snapshotName

Answer 1

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 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).

Answer 2

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.

Answer 3

You can use an alternative which may be faster than invoking jobs if the function is not a long running one. Max thread is 25 and I'm only invoking this function 10 times, so I expect my total runtime to be 5 seconds. You can wrap Measure-Command around the 'results=' statement to view stats.

Example:

$ScriptBlock = {
    Param ( [int]$RunNumber )
    Start-Sleep -Seconds 5   
    Return $RunNumber
}
$runNumbers = @(1..10)
$MaxThreads = 25
$runspacePool = [RunspaceFactory ]::CreateRunspacePool(1, $MaxThreads)
$runspacePool.Open()
$pipeLines = foreach($num in $runNumbers){
    $pipeline = [powershell]::Create()
    $pipeline.RunspacePool = $runspacePool
    $pipeline.AddScript($ScriptBlock)    | Out-Null   
    $pipeline.AddArgument($num)  | Out-Null
    $pipeline | Add-Member -MemberType NoteProperty -Name 'AsyncResult' -Value $pipeline.BeginInvoke() -PassThru 
}
#obtain results as they come.
$results =  foreach($pipeline in $pipeLines){
    $pipeline.EndInvoke($pipeline.AsyncResult )
}
#cleanup code.
$pipeLines | % { $_.Dispose()}
$pipeLines = $null
if ( $runspacePool ) { $runspacePool.Close()}
#your results
$results

Answer 4

I'm sorry that everyone missed your issue - I know it is far too late now, but...

This error is caused because you are missing a comma between $username and $password in your list.

You can test it out with this snippet, which I modelled off of the previous answers:

$cmd = {
  param($a, $b, $c, $d)
}
$foo = "foo"
$bar = "bar"
start-job -scriptblock $cmd -ArgumentList "a", $foo, $bar, "gold" #added missing comma for this to work

Answer 5

I've made a very versitile function to do this for you, and unlike the other answers you dont need to rejig your code to get it to work.
Just pass your function as a parameter to Async and pipe your input in, each item on the pipeline will run your scriptblock in parallel asynchronously, and emit them as each one is completed.

For your question specifically it would look something like this

@(
    @{vmxFilePath='a';machineName='b';username='c';password='d';scriptTpath='e';scriptFile='f';uacDismissScript='g';snapshotName'h'},
    @{vmxFilePath='i';machineName='j';username='k';password='l';scriptTpath='m';scriptFile='n';uacDismissScript='o';snapshotName'p'}
    ...
) `
| Async `
    -Func { Process {
        Execute $_.vmxFilePath $_.machineName $_.username $_.password $_.scriptTpath $_.scriptFile $_.uacDismissScript $_.snapshotName
    } }

On top of this my function supports not only automatic construction of [powershell] (@binarySalt's answer) but also Job s (utilised in @Joost's, but dont use these as they are much slower than runspaces) and Task s if you're using other people's code that already spawn them (use the -AsJob flag, which I explain at the bottom of this answer).

---

So, that's not useful for new visitors to this question, lets do something more demonstrable that you can run on your machine and see real-world results.
Take this simple code for example, it just takes in some test data for websites and checks if they're up.

$in=TestData | ?{ $_.proto -eq 'tcp' }
$in `
| %{
    $WarningPreference='SilentlyContinue'
    $_ `
    | Add-Member `
        -PassThru `
        -MemberType NoteProperty `
        -Name result `
        -Value $(Test-NetConnection `
            -ComputerName $_.address `
            -Port $_.port `
            -InformationLevel Quiet
        )
} `
| Timer -name 'normal' `
| Format-Table

Here's the test data, just a good few of the same websites on repeat.
And also a timing function to see how performant it is.

Function TestData {
    1..20 | %{
        [PsCustomObject]@{proto='tcp'  ; address='www.w3.org'            ; port=443},
        [PsCustomObject]@{proto='https'; address='www.w3.org'            ; port=443},
        [PsCustomObject]@{proto='icmp' ; address='www.w3.org'            ;         },
        [PsCustomObject]@{proto='tcp'  ; address='developer.mozilla.org' ; port=443},
        [PsCustomObject]@{proto='https'; address='developer.mozilla.org' ; port=443},
        [PsCustomObject]@{proto='icmp' ; address='developer.mozilla.org' ;         },
        [PsCustomObject]@{proto='tcp'  ; address='help.dottoro.com'      ; port=80 },
        [PsCustomObject]@{proto='http' ; address='help.dottoro.com'      ; port=80 },
        [PsCustomObject]@{proto='icmp' ; address='help.dottoro.com'      ;         }
    }
}

Function Timer {
    Param ($name)
    Begin {
        $timer=[system.diagnostics.stopwatch]::StartNew()
    }
    Process { $_ }
    End {
        @(
            $name,
            ' '
            [math]::Floor($timer.Elapsed.TotalMinutes),
            ':',
            ($timer.Elapsed.Seconds -replace '^(.)$','0$1')
        ) -join '' | Out-Host
    }
}

Okay, 15seconds, so how much faster can this get if we use Async ?
And how much do we have to change to get it to work?

$in=TestData | ?{ $_.proto -eq 'tcp' }
$in `
| Async `
    -Expected $in.Count `
    -Func { Process {
        $WarningPreference='SilentlyContinue'
        $_ `
        | Add-Member `
            -PassThru `
            -MemberType NoteProperty `
            -Name result `
            -Value $(Test-NetConnection `
                -ComputerName $_.address `
                -Port $_.port `
                -InformationLevel Quiet
            )
    } } `
| Timer -name 'async' `
| Format-Table

It looks basically identical..
Okay, what's the speed?

Wow, cut it by two thirds!
Not only that, but because we know how many items are in the pipeline I wrote in some smarts to give you a progressbar and an ETA

Don't believe me? Have a video
Or run the code yourself :)

#Requires -Version 5.1

#asynchronously run a pool of tasks,
#and aggregate the results back into a synchronous output
#without waiting to pool all input before seeing the first result
Function Async { Param(
    #maximum permitted simultaneous background tasks
    [int]$BatchSize=[int]$env:NUMBER_OF_PROCESSORS * 3,
    #the task that accepts input on a pipe to execute in the background
    [scriptblock]$Func,
    #because your task is in a subshell you wont have access to your outer scope,
    #you may pass them in here
    [array]$ArgumentList=@(),
    [System.Collections.IDictionary]$Parameters=@{},
    #the title of the progress bar
    [string]$Name='Processing',
    #your -Func may return a [Job] instead of being backgrounded itself,
    #if so it must return @(job;input;args)
    #optionally job may be a [scriptblock] to be backgrounded, or a [Task]
    [switch]$AsJob,
    #if you know the number of tasks ahead of time,
    #providing it here will have the progress bar show an ETA
    [int]$Expected,
    #outputs of this stream will be @(job;input) where job is the result
    [switch]$PassThru,
    #the time it takes to give up on one job type if there are others waiting
    [int]$Retry=5
)   
    Begin {
        $ArgumentList=[Array]::AsReadOnly($ArgumentList)
        $Parameters=$Parameters.GetEnumerator() `
        | &{
            Begin { $params=[ordered]@{} }
            Process { $params.Add($_.Key, $_.Value) }
            End { $params.AsReadOnly() }
        }
        #the currently running background tasks
        $running=@{}
        $counts=[PSCustomObject]@{
            completed=0;
            jobs=0;
            tasks=0;
            results=0;
        }
        #a lazy attempt at uniquely IDing this instance for Write-Progress
        $asyncId=Get-Random
        #a timer for Write-Progress
        $timer=[system.diagnostics.stopwatch]::StartNew()

        $pool=[RunspaceFactory]::CreateRunspacePool(1, $BatchSize)
        $pool.Open()

        #called whenever we want to update the progress bar
        Function Progress { Param($Reason)
            #calculate ETA if applicable
            $eta=-1
            $total=[math]::Max(1, $counts.completed + $running.Count)
            if ($Expected) {
                $total=[math]::Max($total, $Expected)
                if ($counts.completed) {
                    $eta=`
                        ($total - $counts.completed) * `
                        $timer.Elapsed.TotalSeconds / `
                        $counts.completed
                }
            }

            $Reason=Switch -regex ($Reason) {
                '^done$'   { "Finishing up the final $($running.Count) jobs." }
                '^(do|next)$' { "
                    Running
                     $($running.Count)
                     jobs concurrently.
                     $(@('Adding','Waiting to add')[!($Reason -eq 'do')])
                     job #
                    $($counts.completed + $running.Count + 1)
                " -replace '\r?\n\t*','' }
                Default { "
                    Running $($running.Count) jobs concurrently.
                     Emitting
                     $($counts.completed)
                    $(@{1='st';2='nd';3='rd'}[$counts.completed % 10] -replace '^$','th')
                     result.
                " -replace '\r?\n\t*','' }
            }

            Write-Progress `
                -Id $asyncId `
                -Activity $Name `
                -SecondsRemaining $eta `
                -Status ("
                    $($counts.completed)
                     jobs completed in
                     $([math]::Floor($timer.Elapsed.TotalMinutes))
                    :
                    $($timer.Elapsed.Seconds -replace '^(.)$','0$1')
                " -replace '\r?\n\t*','') `
                -CurrentOperation $Reason `
                -PercentComplete (100 * $counts.completed / $total)
        }

        #called with the [Job]'s that have completed 
        Filter Done {
            ++$counts.completed
            $out=$running.Item($_.Id)
            $running.Remove($_.Id)

            Progress

            $out.job=`
            if ($_ -is [System.Management.Automation.Job]) {
                --$counts.jobs
                $_ | Receive-Job
            }
            elseif ($_.pwsh) {
                --$counts.results
                try {
                    $_.pwsh.EndInvoke($_)
                }
                catch {
                    #[System.Management.Automation.MethodInvocationException]
                    $_.Exception.InnerException
                }
                finally {
                    $_.pwsh.Dispose()
                }
            }
            elseif ($_.IsFaulted) {
                --$counts.tasks
                #[System.AggregateException]
                $_.Exception.InnerException
            }
            else {
                --$counts.tasks
                $_.Result
            }

            if ($PassThru) {
                $out
            }
            else {
                $out.job
            }
        }

        $isJob={
            $_ -is [System.Management.Automation.Job]
        }
        $isTask={
            $_ -is [System.Threading.Tasks.Task]
        }
        $isResult={
            $_ -is [IAsyncResult]
        }
        $isFinished={
            $_.IsCompleted -or `
            (
                $_.JobStateInfo.State -gt 1 -and
                $_.JobStateInfo.State -ne 6 -and
                $_.JobStateInfo.State -ne 8
            )
        }
        $handle={
            $_.AsyncWaitHandle
        }

        Function Jobs { Param($Filter)
            $running.Values | %{ $_.job } | ? $Filter
        }

        #called whenever we need to wait for at least one task to completed
        #outputs the completed tasks
        Function Wait { Param([switch]$Finishing)
            #if we are at the max background tasks this instant
            while ($running.Count -ge $BatchSize) {
                Progress -Reason @('done','next')[!$Finishing]

                $value=@('jobs', 'tasks', 'results') `
                | %{ $counts.($_) } `
                | measure -Maximum -Sum
                $wait=if ($value.Maximum -lt $value.Sum) {
                    $Retry
                }
                else {
                    -1
                }

                $value=Switch -exact ($value.Maximum) {
                    $counts.jobs {
                        (Wait-Job `
                            -Any `
                            -Job (Jobs -Filter $isJob) `
                            -Timeout $wait
                        ).Count -lt 1
                        break
                    }
                    Default {
                        [System.Threading.WaitHandle]::WaitAny(
                            (Jobs -Filter $handle | % $handle),
                            [math]::Max($wait * 1000, -1)
                        ) -eq [System.Threading.WaitHandle]::WaitTimeout
                        break
                    }
                }

                (Jobs -Filter $isFinished) | Done
            }
        }
    }

    #accepts inputs to spawn a new background task with
    Process {
        Wait
        Progress -Reason 'do'

        $run=[PSCustomObject]@{
            input=$_;
            job=$Func;
            args=$ArgumentList;
            params=$Parameters;
        }
        if ($AsJob) {
            $run.job=$NULL
            Invoke-Command `
                -ScriptBlock $Func `
                -ArgumentList @($run) `
            | Out-Null
        }

        if ($run.job | % $isJob) {
            ++$counts.jobs
        }
        elseif ($run.job | % $isTask) {
            ++$counts.tasks
        }
        #if we weren't given a [Job] we need to spawn it for them
        elseif ($run.job -is [ScriptBlock]) {
            $pwsh=[powershell]::Create().AddScript($run.job)
            $run.args | %{ $pwsh.AddArgument($_) } | Out-Null
            $pwsh.RunspacePool=$pool
            $run.job=$pwsh.AddParameters($run.params).BeginInvoke(
                [System.Management.Automation.PSDataCollection[PSObject]]::new(
                    [PSObject[]]($run.input)
                )
            )
            $run.job | Add-Member `
                -MemberType NoteProperty `
                -Name pwsh `
                -Value $pwsh `
                -PassThru `
            | Add-Member `
                -MemberType NoteProperty `
                -Name Id `
                -Value $run.job.AsyncWaitHandle.Handle.ToString()
            ++$counts.results
        }
        else {
            throw "$($run.job.GetType()) needs to be a ScriptBlock"
        }

        $running.Add($run.job.Id, $run) | Out-Null
    }

    End {
        #wait for the remaining running processes
        $BatchSize=1
        Wait -Finishing
        Write-Progress -Id $asyncId -Activity $Name -Completed
        $pool.Close()
        $pool.Dispose()
    }
}

---

So you may have noticed three things above, I alluded to -AsJob (using a mix of Job s, Task s and scriptblock s), there are unused protocols mentioned in the test data, and the video had a third test in it.

Here it is. Instead of doing the basic tcp test, using the test data we will also do a http/s check and a icmp ping (idk, maybe the https fails, but you want to narrow down if it's because the machine is down or just the service).

• Test-Connection -AsJob is a cmdlet that returns a Job and checks ping.
  
• WebRequest.GetResponseAsync() which connects to a web resource, returning a Task
  
• And finally Test-NetConnection , which will be the same as before, ran in what we programmed as a synchronous scriptblock, which will be ran asynchronously for us.

$in=TestData
$in `
| Async `
    -Expected $in.Count `
    -PassThru `
    -AsJob `
    <#this would be accessible as a named parameter if needed#>`
    -Parameters @{proxy=[System.Net.WebRequest]::GetSystemWebProxy()} `
    -Func { Param([parameter(Position=0)]$x)
        $x.job=Switch -regex ($x.input.proto) {
            '^icmp$' {
                Test-Connection `
                    -ComputerName $x.input.address `
                    -Count 1 `
                    -ThrottleLimit 1 `
                    -AsJob
            }

            '^tcp$' {
                $x.params=@{address=$x.input.address; port=$x.input.port}
                { Param($address, $port)
                    $WarningPreference='SilentlyContinue'
                    Test-NetConnection `
                        -ComputerName $address `
                        -Port $port `
                        -InformationLevel Quiet
                }
            }

            '^(http|https)$' {
                [Net.ServicePointManager]::SecurityProtocol=[Net.SecurityProtocolType]::Tls12
                $request=[System.Net.HttpWebRequest]::Create((@(
                    $x.input.proto,
                    '://',
                    $x.input.address,
                    ':',
                    $x.input.port
                ) -join ''))
                $request.Proxy=$NULL
                $request.Method='Get'
                $request.GetResponseAsync()
            }
        }
    } `
| %{
    $result=$_
    $result.input `
    | Add-Member `
        -PassThru `
        -MemberType NoteProperty `
        -Name result `
        -Value $(Switch -regex (@($result.input.proto, $result.job.message)[$result.job -is [Exception]]) {
            #[Win32_PingStatus]
            '^icmp$' { $result.job.StatusCode -eq 0 }

            #[bool]
            '^tcp$' { $result.job }

            #[System.Net.HttpWebResponse]
            '^(http|https)$' {
                $result.job.Close()
                Switch ($result.job.StatusCode.value__) {
                    { $_ -ge 200 -and $_ -lt 400 } { $True }
                    Default {$False}
                }
            }

            #[Exception]
            Default { $False }
        })
} `
| Timer -name 'async asjob' `
| Format-Table

As you may have seen, this did more than double the work of the original code, but still finished in around half the time at 8seconds.