Run N parallel jobs in powershell

Question

I have the following powershell script

$list = invoke-sqlcmd \'exec getOneMillionRows\' -Server...
$list | % {
    GetData $_ > $_.txt
    ZipTheFile $_.t         


        

Answer 1

The Start-Job cmdlet allows you to run code in the background. To do what you'd ask, something like the code below should work.

foreach ($server in $servers) {
    $running = @(Get-Job | Where-Object { $_.State -eq 'Running' })
    if ($running.Count -le 8) {
        Start-Job {
             Add-PSSnapin SQL
             $list = invoke-sqlcmd 'exec getOneMillionRows' -Server...
             ...
        }
    } else {
         $running | Wait-Job
    }
    Get-Job | Receive-Job
}

Hope this helps.

Answer 2

It should be really easy with the Split-Pipeline cmdlet of the SplitPipeline module. The code will look as simple as this:

Import-Module SplitPipeline
$list = invoke-sqlcmd 'exec getOneMillionRows' -Server...
$list | Split-Pipeline -Count 8 {process{
    GetData $_ > $_.txt
    ZipTheFile $_.txt $_.txt.zip
    ...
}}

Answer 3

I use and improove a multithread Function, you can use it like :

$Script = {
    param($Computername)
    get-process -Computername $Computername
}

@('Srv1','Srv2') | Run-Parallel -ScriptBlock $Script

include this code in your script

function Run-Parallel {
    <#
        .Synopsis
            This is a quick and open-ended script multi-threader searcher
            http://www.get-blog.com/?p=189#comment-28834
            Improove by Alban LOPEZ 2016

        .Description
            This script will allow any general, external script to be multithreaded by providing a single
            argument to that script and opening it in a seperate thread.  It works as a filter in the
            pipeline, or as a standalone script.  It will read the argument either from the pipeline
            or from a filename provided.  It will send the results of the child script down the pipeline,
            so it is best to use a script that returns some sort of object.

        .PARAMETER ScriptBlock
            This is where you provide the PowerShell ScriptBlock that you want to multithread.

        .PARAMETER ItemObj
            The ItemObj represents the arguments that are provided to the child script.  This is an open ended
            argument and can take a single object from the pipeline, an array, a collection, or a file name.  The
            multithreading script does it's best to find out which you have provided and handle it as such.
            If you would like to provide a file, then the file is read with one object on each line and will
            be provided as is to the script you are running as a string.  If this is not desired, then use an array.

        .PARAMETER InputParam
            This allows you to specify the parameter for which your input objects are to be evaluated.  As an example,
            if you were to provide a computer name to the Get-Process cmdlet as just an argument, it would attempt to
            find all processes where the name was the provided computername and fail.  You need to specify that the
            parameter that you are providing is the "ComputerName".

        .PARAMETER AddParam
            This allows you to specify additional parameters to the running command.  For instance, if you are trying
            to find the status of the "BITS" service on all servers in your list, you will need to specify the "Name"
            parameter.  This command takes a hash pair formatted as follows:

            @{"key" = "Value"}
            @{"key1" = "Value"; "key2" = 321; "key3" = 1..9}

        .PARAMETER AddSwitch
            This allows you to add additional switches to the command you are running.  For instance, you may want
            to include "RequiredServices" to the "Get-Service" cmdlet.  This parameter will take a single string, or
            an aray of strings as follows:

            "RequiredServices"
            @("RequiredServices", "DependentServices")

        .PARAMETER MaxThreads
            This is the maximum number of threads to run at any given time.  If ressources are too congested try lowering
            this number.  The default value is 20.

        .PARAMETER SleepTimer_ms
            This is the time between cycles of the child process detection cycle.  The default value is 200ms.  If CPU
            utilization is high then you can consider increasing this delay.  If the child script takes a long time to
            run, then you might increase this value to around 1000 (or 1 second in the detection cycle).

        .PARAMETER TimeOutGlobal
            this is the TimeOut in second for listen the last thread, after this timeOut All thread are closed, only each other are returned

        .PARAMETER TimeOutThread
            this is the TimeOut in second for each thread, the thread are aborted at this time

        .PARAMETER PSModules
            List of PSModule name to include for use in ScriptBlock

        .PARAMETER PSSapins
            List of PSSapin name to include for use in ScriptBlock

        .EXAMPLE
            1..20 | Run-Parallel -ScriptBlock {param($i) Start-Sleep $i; "> $i sec <"} -TimeOutGlobal 15 -TimeOutThread 5
        .EXAMPLE
            Both of these will execute the scriptBlock and provide each of the server names in AllServers.txt
            while providing the results to GridView.  The results will be the output of the child script.

            gc AllServers.txt | Run-Parallel $ScriptBlock_GetTSUsers -MaxThreads $findOut_AD.ActiveDirectory.Servers.count -PSModules 'PSTerminalServices' | out-gridview
    #>
    Param(
        [Parameter(ValueFromPipeline=$true,ValueFromPipelineByPropertyName=$true)]
            $ItemObj,
        [ScriptBlock]$ScriptBlock = $null,
        $InputParam = $Null,
        [HashTable] $AddParam = @{},
        [Array] $AddSwitch = @(),
        $MaxThreads = 20,
        $SleepTimer_ms = 100,
        $TimeOutGlobal = 300,
        $TimeOutThread = 100,
        [string[]]$PSSapins = $null,
        [string[]]$PSModules = $null,
        $Modedebug = $true
    )
    Begin{
        $ISS = [system.management.automation.runspaces.initialsessionstate]::CreateDefault()
        ForEach ($Snapin in $PSSapins){
            [void]$ISS.ImportPSSnapIn($Snapin, [ref]$null)
        }
        ForEach ($Module in $PSModules){
            [void]$ISS.ImportPSModule($Module)
        }
        $RunspacePool = [runspacefactory]::CreateRunspacePool(1, $MaxThreads, $ISS, $Host)
        $RunspacePool.CleanupInterval=1000
        $RunspacePool.Open()

        $Jobs = @()
    }
    Process{
        #ForEach ($Object in $ItemObj){
            if ($ItemObj){
                Write-Host $ItemObj -ForegroundColor Yellow
                $PowershellThread = [powershell]::Create().AddScript($ScriptBlock)

                If ($InputParam -ne $Null){
                    $PowershellThread.AddParameter($InputParam, $ItemObj.ToString()) | out-null
                }Else{
                    $PowershellThread.AddArgument($ItemObj.ToString()) | out-null
                }
                ForEach($Key in $AddParam.Keys){
                    $PowershellThread.AddParameter($Key, $AddParam.$key) | out-null
                }
                ForEach($Switch in $AddSwitch){
                    $PowershellThread.AddParameter($Switch) | out-null
                }
                $PowershellThread.RunspacePool = $RunspacePool
                $Handle = $PowershellThread.BeginInvoke()
                $Job =  [pscustomobject][ordered]@{
                    Handle = $Handle
                    Thread = $PowershellThread
                    object = $ItemObj.ToString()
                    Started = Get-Date
                }
                $Jobs += $Job
            }
        #}
    }
    End{
        $GlobalStartTime = Get-Date
        $continue = $true
        While (@($Jobs | Where-Object {$_.Handle -ne $Null}).count -gt 0 -and $continue)  {
            ForEach ($Job in $($Jobs | Where-Object {$_.Handle.IsCompleted -eq $True})){
                $out = $Job.Thread.EndInvoke($Job.Handle)
                $out # return vers la sortie srandard
                #Write-Host $out -ForegroundColor green
                $Job.Thread.Dispose() | Out-Null
                $Job.Thread = $Null
                $Job.Handle = $Null
            }
            foreach ($InProgress in $($Jobs | Where-Object {$_.Handle})) {
                if ($TimeOutGlobal -and (($(Get-Date) - $GlobalStartTime).totalseconds -gt $TimeOutGlobal)){
                    $Continue = $false
                    #Write-Host $InProgress -ForegroundColor magenta
                }
                if (!$Continue -or ($TimeOutThread -and (($(Get-Date) - $InProgress.Started).totalseconds -gt $TimeOutThread))) {
                    $InProgress.thread.Stop() | Out-Null
                    $InProgress.thread.Dispose() | Out-Null
                    $InProgress.Thread = $Null
                    $InProgress.Handle = $Null
                    #Write-Host $InProgress -ForegroundColor red
                }
            }
            Start-Sleep -Milliseconds $SleepTimer_ms
        }
        $RunspacePool.Close() | Out-Null
        $RunspacePool.Dispose() | Out-Null
    }
}

Answer 4

Old thread but I think this could help:

$List = C:\List.txt
$Jobs = 8

Foreach ($PC in Get-Content $List)
{
Do
    {
    $Job = (Get-Job -State Running | measure).count
    } Until ($Job -le $Jobs)

Start-Job -Name $PC -ScriptBlock { "Your command here $Using:PC" }
Get-Job -State Completed | Remove-Job
}

Wait-Job -State Running
Get-Job -State Completed | Remove-Job
Get-Job

The "Do" loop pause the "foreach" when the amount of job "running" exceed the amount of "$jobs" that is allowed to run. Than wait for the remaining to complete and show failed jobs...

Answer 5

Same idea as user "Start-Automating" posted, but corrected the bug about forgetting to start the jobs that are held back when hitting the else clause in his example:

$servers = @('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n')

foreach ($server in $servers) {
    $running = @(Get-Job | Where-Object { $_.State -eq 'Running' })
    if ($running.Count -ge 4) {
        $running | Wait-Job -Any | Out-Null
    }

    Write-Host "Starting job for $server"
    Start-Job {
        # do something with $using:server. Just sleeping for this example.
        Start-Sleep 5
        return "result from $using:server"
    } | Out-Null
}

# Wait for all jobs to complete and results ready to be received
Wait-Job * | Out-Null

# Process the results
foreach($job in Get-Job)
{
    $result = Receive-Job $job
    Write-Host $result
}

Remove-Job -State Completed

Answer 6

Background jobs is the answer. You can also throttle the jobs in the run queue using [System.Collection.Queue]. There is a blog post from PowerShell team on this topic: http://blogs.msdn.com/b/powershell/archive/2011/04/04/scaling-and-queuing-powershell-background-jobs.aspx

Using queuing method is probably the best answer to throttling background jobs.