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function Invoke-Parallel {
Function to control parallel processing using runspaces
Function to control parallel processing using runspaces
Note that each runspace will not have access to variables and commands loaded in your session or in other runspaces by default.
This behaviour can be changed with parameters.
File to run against all input objects. Must include parameter to take in the input object, or use $args. Optionally, include parameter to take in parameter. Example: C:\script.ps1
.PARAMETER ScriptBlock
Scriptblock to run against all computers.
You may use $Using:<Variable> language in PowerShell 3 and later.
The parameter block is added for you, allowing behaviour similar to foreach-object:
Refer to the input object as $_.
Refer to the parameter parameter as $parameter
.PARAMETER InputObject
Run script against these specified objects.
.PARAMETER Parameter
This object is passed to every script block. You can use it to pass information to the script block; for example, the path to a logging folder
Reference this object as $parameter if using the scriptblock parameterset.
.PARAMETER ImportVariables
If specified, get user session variables and add them to the initial session state
.PARAMETER ImportModules
If specified, get loaded modules and pssnapins, add them to the initial session state
Maximum number of threads to run at a single time.
Milliseconds to sleep after checking for completed runspaces and in a few other spots. I would not recommend dropping below 200 or increasing above 500
.PARAMETER RunspaceTimeout
Maximum time in seconds a single thread can run. If execution of your code takes longer than this, it is disposed. Default: 0 (seconds)
WARNING: Using this parameter requires that maxQueue be set to throttle (it will be by default) for accurate timing. Details here:
.PARAMETER NoCloseOnTimeout
Do not dispose of timed out tasks or attempt to close the runspace if threads have timed out. This will prevent the script from hanging in certain situations where threads become non-responsive, at the expense of leaking memory within the PowerShell host.
Maximum number of powershell instances to add to runspace pool. If this is higher than $throttle, $timeout will be inaccurate
If this is equal or less than throttle, there will be a performance impact
The default value is $throttle times 3, if $runspaceTimeout is not specified
The default value is $throttle, if $runspaceTimeout is specified
Path to a file where we can log results, including run time for each thread, whether it completes, completes with errors, or times out.
Append to existing log
Disable progress bar
Each example uses Test-ForPacs.ps1 which includes the following code:
if(test-connection $computer -count 1 -quiet -BufferSize 16){
$object = [pscustomobject] @{
if((test-path "\\$computer\c$\users\public\desktop\Kodak Direct View Pacs.url") -or (test-path "\\$computer\c$\documents and settings\all users\desktop\Kodak Direct View Pacs.url") ){"1"}else{"0"}
$object = [pscustomobject] @{
Invoke-Parallel -scriptfile C:\public\Test-ForPacs.ps1 -inputobject $(get-content C:\pcs.txt) -runspaceTimeout 10 -throttle 10
Pulls list of PCs from C:\pcs.txt,
Runs Test-ForPacs against each
If any query takes longer than 10 seconds, it is disposed
Only run 10 threads at a time
Invoke-Parallel -scriptfile C:\public\Test-ForPacs.ps1 -inputobject c-is-ts-91, c-is-ts-95
Runs against c-is-ts-91, c-is-ts-95 (-computername)
Runs Test-ForPacs against each
$stuff = [pscustomobject] @{
ContentFile = "windows\system32\drivers\etc\hosts"
Logfile = "C:\temp\log.txt"
$computers | Invoke-Parallel -parameter $stuff {
$contentFile = join-path "\\$_\c$" $parameter.contentfile
Get-Content $contentFile |
set-content $parameter.logfile
This example uses the parameter argument. This parameter is a single object. To pass multiple items into the script block, we create a custom object (using a PowerShell v3 language) with properties we want to pass in.
Inside the script block, $parameter is used to reference this parameter object. This example sets a content file, gets content from that file, and sets it to a predefined log file.
$test = 5
1..2 | Invoke-Parallel -ImportVariables {$_ * $test}
Add variables from the current session to the session state. Without -ImportVariables $Test would not be accessible
$test = 5
1..2 | Invoke-Parallel {$_ * $Using:test}
Reference a variable from the current session with the $Using:<Variable> syntax. Requires PowerShell 3 or later. Note that -ImportVariables parameter is no longer necessary.
PowerShell Language
Credit to Boe Prox for the base runspace code and $Using implementation
Credit to T Bryce Yehl for the Quiet and NoCloseOnTimeout implementations
Credit to Sergei Vorobev for the many ideas and contributions that have improved functionality, reliability, and ease of use
Param (
[ValidateScript({Test-Path $_ -pathtype leaf})]
[int]$Throttle = 20,
[int]$SleepTimer = 200,
[int]$RunspaceTimeout = 0,
[switch]$NoCloseOnTimeout = $false,
[validatescript({Test-Path (Split-Path $_ -parent)})]
[switch] $AppendLog = $false,
[switch] $Quiet = $false
begin {
#No max queue specified? Estimate one.
#We use the script scope to resolve an odd PowerShell 2 issue where MaxQueue isn't seen later in the function
if( -not $PSBoundParameters.ContainsKey('MaxQueue') ) {
if($RunspaceTimeout -ne 0){ $script:MaxQueue = $Throttle }
else{ $script:MaxQueue = $Throttle * 3 }
else {
$script:MaxQueue = $MaxQueue
$ProgressId = Get-Random
Write-Verbose "Throttle: '$throttle' SleepTimer '$sleepTimer' runSpaceTimeout '$runspaceTimeout' maxQueue '$maxQueue' logFile '$logFile'"
#If they want to import variables or modules, create a clean runspace, get loaded items, use those to exclude items
if ($ImportVariables -or $ImportModules -or $ImportFunctions) {
$StandardUserEnv = [powershell]::Create().addscript({
#Get modules, snapins, functions in this clean runspace
$Modules = Get-Module | Select-Object -ExpandProperty Name
$Snapins = Get-PSSnapin | Select-Object -ExpandProperty Name
$Functions = Get-ChildItem function:\ | Select-Object -ExpandProperty Name
#Get variables in this clean runspace
#Called last to get vars like $? into session
$Variables = Get-Variable | Select-Object -ExpandProperty Name
#Return a hashtable where we can access each.
Variables = $Variables
Modules = $Modules
Snapins = $Snapins
Functions = $Functions
if ($ImportVariables) {
#Exclude common parameters, bound parameters, and automatic variables
Function _temp {[cmdletbinding(SupportsShouldProcess=$True)] param() }
$VariablesToExclude = @( (Get-Command _temp | Select-Object -ExpandProperty parameters).Keys + $PSBoundParameters.Keys + $StandardUserEnv.Variables )
Write-Verbose "Excluding variables $( ($VariablesToExclude | Sort-Object ) -join ", ")"
# we don't use 'Get-Variable -Exclude', because it uses regexps.
# One of the veriables that we pass is '$?'.
# There could be other variables with such problems.
# Scope 2 required if we move to a real module
$UserVariables = @( Get-Variable | Where-Object { -not ($VariablesToExclude -contains $_.Name) } )
Write-Verbose "Found variables to import: $( ($UserVariables | Select-Object -expandproperty Name | Sort-Object ) -join ", " | Out-String).`n"
if ($ImportModules) {
$UserModules = @( Get-Module | Where-Object {$StandardUserEnv.Modules -notcontains $_.Name -and (Test-Path $_.Path -ErrorAction SilentlyContinue)} | Select-Object -ExpandProperty Path )
$UserSnapins = @( Get-PSSnapin | Select-Object -ExpandProperty Name | Where-Object {$StandardUserEnv.Snapins -notcontains $_ } )
if($ImportFunctions) {
$UserFunctions = @( Get-ChildItem function:\ | Where-Object { $StandardUserEnv.Functions -notcontains $_.Name } )
#region functions
Function Get-RunspaceData {
param( [switch]$Wait )
#loop through runspaces
#if $wait is specified, keep looping until all complete
Do {
#set more to false for tracking completion
$more = $false
#Progress bar if we have inputobject count (bound parameter)
if (-not $Quiet) {
Write-Progress -Id $ProgressId -Activity "Running Query" -Status "Starting threads"`
-CurrentOperation "$startedCount threads defined - $totalCount input objects - $script:completedCount input objects processed"`
-PercentComplete $( Try { $script:completedCount / $totalCount * 100 } Catch {0} )
#run through each runspace.
Foreach($runspace in $runspaces) {
#get the duration - inaccurate
$currentdate = Get-Date
$runtime = $currentdate - $runspace.startTime
$runMin = [math]::Round( $runtime.totalminutes ,2 )
#set up log object
$log = "" | Select-Object Date, Action, Runtime, Status, Details
$log.Action = "Removing:'$($runspace.object)'"
$log.Date = $currentdate
$log.Runtime = "$runMin minutes"
#If runspace completed, end invoke, dispose, recycle, counter++
If ($runspace.Runspace.isCompleted) {
#check if there were errors
if($runspace.powershell.Streams.Error.Count -gt 0) {
#set the logging info and move the file to completed
$log.status = "CompletedWithErrors"
Write-Verbose ($log | ConvertTo-Csv -Delimiter ";" -NoTypeInformation)[1]
foreach($ErrorRecord in $runspace.powershell.Streams.Error) {
Write-Error -ErrorRecord $ErrorRecord
else {
#add logging details and cleanup
$log.status = "Completed"
Write-Verbose ($log | ConvertTo-Csv -Delimiter ";" -NoTypeInformation)[1]
#everything is logged, clean up the runspace
$runspace.Runspace = $null
$runspace.powershell = $null
#If runtime exceeds max, dispose the runspace
ElseIf ( $runspaceTimeout -ne 0 -and $runtime.totalseconds -gt $runspaceTimeout) {
$timedOutTasks = $true
#add logging details and cleanup
$log.status = "TimedOut"
Write-Verbose ($log | ConvertTo-Csv -Delimiter ";" -NoTypeInformation)[1]
Write-Error "Runspace timed out at $($runtime.totalseconds) seconds for the object:`n$($runspace.object | out-string)"
#Depending on how it hangs, we could still get stuck here as dispose calls a synchronous method on the powershell instance
if (!$noCloseOnTimeout) { $runspace.powershell.dispose() }
$runspace.Runspace = $null
$runspace.powershell = $null
#If runspace isn't null set more to true
ElseIf ($runspace.Runspace -ne $null ) {
$log = $null
$more = $true
#log the results if a log file was indicated
if($logFile -and $log) {
($log | ConvertTo-Csv -Delimiter ";" -NoTypeInformation)[1] | out-file $LogFile -append
#Clean out unused runspace jobs
$temphash = $runspaces.clone()
$temphash | Where-Object { $_.runspace -eq $Null } | ForEach-Object {
#sleep for a bit if we will loop again
if($PSBoundParameters['Wait']){ Start-Sleep -milliseconds $SleepTimer }
#Loop again only if -wait parameter and there are more runspaces to process
} while ($more -and $PSBoundParameters['Wait'])
#End of runspace function
#endregion functions
#region Init
if($PSCmdlet.ParameterSetName -eq 'ScriptFile') {
$ScriptBlock = [scriptblock]::Create( $(Get-Content $ScriptFile | out-string) )
elseif($PSCmdlet.ParameterSetName -eq 'ScriptBlock') {
#Start building parameter names for the param block
[string[]]$ParamsToAdd = '$_'
if( $PSBoundParameters.ContainsKey('Parameter') ) {
$ParamsToAdd += '$Parameter'
$UsingVariableData = $Null
# This code enables $Using support through the AST.
# This is entirely from Boe Prox, and his module; all credit to Boe!
if($PSVersionTable.PSVersion.Major -gt 2) {
#Extract using references
$UsingVariables = $ScriptBlock.ast.FindAll({$args[0] -is [System.Management.Automation.Language.UsingExpressionAst]},$True)
If ($UsingVariables) {
$List = New-Object 'System.Collections.Generic.List`1[System.Management.Automation.Language.VariableExpressionAst]'
ForEach ($Ast in $UsingVariables) {
$UsingVar = $UsingVariables | Group-Object -Property SubExpression | ForEach-Object {$_.Group | Select-Object -First 1}
#Extract the name, value, and create replacements for each
$UsingVariableData = ForEach ($Var in $UsingVar) {
try {
$Value = Get-Variable -Name $Var.SubExpression.VariablePath.UserPath -ErrorAction Stop
Name = $Var.SubExpression.Extent.Text
Value = $Value.Value
NewName = ('$__using_{0}' -f $Var.SubExpression.VariablePath.UserPath)
NewVarName = ('__using_{0}' -f $Var.SubExpression.VariablePath.UserPath)
catch {
Write-Error "$($Var.SubExpression.Extent.Text) is not a valid Using: variable!"
$ParamsToAdd += $UsingVariableData | Select-Object -ExpandProperty NewName -Unique
$NewParams = $UsingVariableData.NewName -join ', '
$Tuple = [Tuple]::Create($list, $NewParams)
$bindingFlags = [Reflection.BindingFlags]"Default,NonPublic,Instance"
$GetWithInputHandlingForInvokeCommandImpl = ($ScriptBlock.ast.gettype().GetMethod('GetWithInputHandlingForInvokeCommandImpl',$bindingFlags))
$StringScriptBlock = $GetWithInputHandlingForInvokeCommandImpl.Invoke($ScriptBlock.ast,@($Tuple))
$ScriptBlock = [scriptblock]::Create($StringScriptBlock)
Write-Verbose $StringScriptBlock
$ScriptBlock = $ExecutionContext.InvokeCommand.NewScriptBlock("param($($ParamsToAdd -Join ", "))`r`n" + $Scriptblock.ToString())
else {
Throw "Must provide ScriptBlock or ScriptFile"; Break
Write-Debug "`$ScriptBlock: $($ScriptBlock | Out-String)"
Write-Verbose "Creating runspace pool and session states"
#If specified, add variables and modules/snapins to session state
$sessionstate = [System.Management.Automation.Runspaces.InitialSessionState]::CreateDefault()
if($ImportVariables -and $UserVariables.count -gt 0) {
foreach($Variable in $UserVariables) {
$sessionstate.Variables.Add((New-Object -TypeName System.Management.Automation.Runspaces.SessionStateVariableEntry -ArgumentList $Variable.Name, $Variable.Value, $null) )
if ($ImportModules) {
if($UserModules.count -gt 0) {
foreach($ModulePath in $UserModules) {
if($UserSnapins.count -gt 0) {
foreach($PSSnapin in $UserSnapins) {
[void]$sessionstate.ImportPSSnapIn($PSSnapin, [ref]$null)
if($ImportFunctions -and $UserFunctions.count -gt 0) {
foreach ($FunctionDef in $UserFunctions) {
$sessionstate.Commands.Add((New-Object System.Management.Automation.Runspaces.SessionStateFunctionEntry -ArgumentList $FunctionDef.Name,$FunctionDef.ScriptBlock))
#Create runspace pool
$runspacepool = [runspacefactory]::CreateRunspacePool(1, $Throttle, $sessionstate, $Host)
Write-Verbose "Creating empty collection to hold runspace jobs"
$Script:runspaces = New-Object System.Collections.ArrayList
#If inputObject is bound get a total count and set bound to true
$bound = $PSBoundParameters.keys -contains "InputObject"
if(-not $bound) {
[System.Collections.ArrayList]$allObjects = @()
#Set up log file if specified
if( $LogFile -and (-not (Test-Path $LogFile) -or $AppendLog -eq $false)){
New-Item -ItemType file -Path $logFile -Force | Out-Null
("" | Select-Object -Property Date, Action, Runtime, Status, Details | ConvertTo-Csv -NoTypeInformation -Delimiter ";")[0] | Out-File $LogFile
#write initial log entry
$log = "" | Select-Object -Property Date, Action, Runtime, Status, Details
$log.Date = Get-Date
$log.Action = "Batch processing started"
$log.Runtime = $null
$log.Status = "Started"
$log.Details = $null
if($logFile) {
($log | convertto-csv -Delimiter ";" -NoTypeInformation)[1] | Out-File $LogFile -Append
$timedOutTasks = $false
#endregion INIT
process {
#add piped objects to all objects or set all objects to bound input object parameter
if($bound) {
$allObjects = $InputObject
else {
[void]$allObjects.add( $InputObject )
end {
#Use Try/Finally to catch Ctrl+C and clean up.
try {
#counts for progress
$totalCount = $allObjects.count
$script:completedCount = 0
$startedCount = 0
foreach($object in $allObjects) {
#region add scripts to runspace pool
#Create the powershell instance, set verbose if needed, supply the scriptblock and parameters
$powershell = [powershell]::Create()
if ($VerbosePreference -eq 'Continue') {
[void]$PowerShell.AddScript({$VerbosePreference = 'Continue'})
if ($parameter) {
# $Using support from Boe Prox
if ($UsingVariableData) {
Foreach($UsingVariable in $UsingVariableData) {
Write-Verbose "Adding $($UsingVariable.Name) with value: $($UsingVariable.Value)"
#Add the runspace into the powershell instance
$powershell.RunspacePool = $runspacepool
#Create a temporary collection for each runspace
$temp = "" | Select-Object PowerShell, StartTime, object, Runspace
$temp.PowerShell = $powershell
$temp.StartTime = Get-Date
$temp.object = $object
#Save the handle output when calling BeginInvoke() that will be used later to end the runspace
$temp.Runspace = $powershell.BeginInvoke()
#Add the temp tracking info to $runspaces collection
Write-Verbose ( "Adding {0} to collection at {1}" -f $temp.object, $temp.starttime.tostring() )
$runspaces.Add($temp) | Out-Null
#loop through existing runspaces one time
#If we have more running than max queue (used to control timeout accuracy)
#Script scope resolves odd PowerShell 2 issue
$firstRun = $true
while ($runspaces.count -ge $Script:MaxQueue) {
#give verbose output
if($firstRun) {
Write-Verbose "$($runspaces.count) items running - exceeded $Script:MaxQueue limit."
$firstRun = $false
#run get-runspace data and sleep for a short while
Start-Sleep -Milliseconds $sleepTimer
#endregion add scripts to runspace pool
Write-Verbose ( "Finish processing the remaining runspace jobs: {0}" -f ( @($runspaces | Where-Object {$_.Runspace -ne $Null}).Count) )
Get-RunspaceData -wait
if (-not $quiet) {
Write-Progress -Id $ProgressId -Activity "Running Query" -Status "Starting threads" -Completed
finally {
#Close the runspace pool, unless we specified no close on timeout and something timed out
if ( ($timedOutTasks -eq $false) -or ( ($timedOutTasks -eq $true) -and ($noCloseOnTimeout -eq $false) ) ) {
Write-Verbose "Closing the runspace pool"
#collect garbage
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