Run N parallel jobs in powershell - powershell

Question

I have the following powershell script
$list = invoke-sqlcmd 'exec getOneMillionRows' -Server...
$list | % {
GetData $_ > $_.txt
ZipTheFile $_.txt $_.txt.zip
...
}
How to run the script block ({ GetDatta $_ > $_.txt ....}) in parallel with limited maximum number of job, e.g. at most 8 files can be generated at one time?

Answer 1

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 2

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 3

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 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

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: https://devblogs.microsoft.com/powershell/scaling-and-queuing-powershell-background-jobs/
Using queuing method is probably the best answer to throttling background jobs.

Answer 6

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 7

Old thread, but my contribution to it, is the part where you count the running jobs. Some of the answers above do not work for 0 or 1 running job. A little trick I use is to throw the results in a forced array, and then count it:
[array]$JobCount = Get-job -state Running
$JobCount.Count