How to call a function within a foreach parallel loop

Question

Good evening.

I'm trying to use parallelism for the first time but I don't understand how to call a function within foreach loop.

I get a series of this error: Cannot bind argument to parameter 'Path' because it is null.

This is what I've done so far:


$FolderPath = "C:\myfolder\"

function AppendLog ($client) {
    $so = New-CimSessionOption -Protocol 'DCOM'
    $s = New-CimSession -ComputerName $client -SessionOption $so
    Add-Content -Path (join-path $folderpath "LOGS.txt") -Value ( (get-date -Format "[yyyy.MM.dd HH:mm:ss]").tostring() + $client + " -PING: OK")
    $arch = Get-CimInstance –query "select * from win32_operatingsystem" -CimSession $s | select -expandproperty osarchitecture
    Add-Content -Path (join-path $folderpath "LOGS.txt") -Value ( (get-date -Format "[yyyy.MM.dd HH:mm:ss]").tostring() + $client + " -ARCH:" + $arch )   
    $lastboot = Get-CimInstance –query "select * from win32_operatingsystem" -CimSession $s | select -expandproperty lastbootuptime
    Add-Content -Path (join-path $folderpath "LOGS.txt") -Value ( (get-date -Format "[yyyy.MM.dd HH:mm:ss]").tostring() + $client + " -BOOT:" + $lastboot )   

}



$funcDef = $function:AppendLog.ToString()

$clients = get-content -path (join-path $folderPath "client.txt")
$clients | ForEach-Object -parallel  {

    if (test-connection $_ -count 2 -Quiet) 
            {                              
                $function:AppendLog = $using:funcDef
                AppendLog ($_)
            }
     }       -throttlelimit 3

Could you explain me how to pass my path?

Try with $using:_. By the way, you can establish a CimSession with multiple computers as well as query multiple computers at the same time with CimInstace which is far more efficient than ForEach -Parallel. — Santiago Squarzon
– Santiago Squarzon, Commented Jun 19, 2021 at 21:18
You should be able to just use AppendLog $_ without the parenthesis around the psitem ($_). To include attempting to expand it — Abraham Zinala
– Abraham Zinala, Commented Jun 19, 2021 at 21:27

Santiago Squarzon · Accepted Answer · 2021-06-19 23:10:03Z

My bad on the comment, the error you're getting is most likely coming from your function. The error is being thrown by Join-Path:

PS /> Join-Path $null 'Logs.txt'
Join-Path : Cannot bind argument to parameter 'Path' because it is null.
At line:1 char:11
+ Join-Path $null 'Logs.txt'
+           ~~~~~
    + CategoryInfo          : InvalidData: (:) [Join-Path], ParameterBindingValidationException
    + FullyQualifiedErrorId : ParameterArgumentValidationErrorNullNotAllowed,Microsoft.PowerShell.Commands.JoinPathCommand

The reason is because $FolderPath doesn't exist in the scope of your parallel loop. $folderpath should be replace with $using:folderpath inside your function.

As a side note, adding information to the same file on a parallel execution doesn't seem to be a good idea.

Last edit, I understand if this is meant to test how ForEach-Object -Parallel works but again, if the cmdlet allows remote querying / remote execution with multiple hosts at the same time, let the cmdlet handle that for you, it is more efficient.

As for the code, this is what I would use with what you already have:

$FolderPath = "C:\myfolder\"
$sessionOption = New-CimSessionOption -Protocol 'DCOM'

$clients = Get-Content -Path (Join-Path $FolderPath -ChildPath "Client.txt")
$results = $clients | ForEach-Object -Parallel {

    $out = @{
        Time = [datetime]::Now.ToString('[yyyy.MM.dd HH:mm:ss]')
        ComputerName = $_
    }

    if ($ping = Test-Connection $_ -Count 2 -Quiet)
    {
        $session = New-CimSession -ComputerName $_ -SessionOption $using:sessionOption
        $OSInfo = Get-CimInstance -CimSession $session -ClassName win32_operatingSystem
        Remove-CimSession $session
    }

    $out.Ping = $ping
    $out.Arch = $OSInfo.OSArchitecture
    $out.LastBoot = $OSInfo.LastBootUpTime

    [pscustomobject]$out

} -ThrottleLimit 3

$results | Export-Csv "$myFolder\LOGS.csv" -NoTypeInformation

This will output an object like this below:

Time                  ComputerName   Ping   OSArchitecture LastBoot             
----                  ------------   ----   -------------- --------             
[2021.06.19 20:06:00] ComputerName01 True   64-bit         6/16/2021 11:47:16 AM
[2021.06.19 20:07:00] ComputerName02 False
[2021.06.19 20:08:00] ComputerName03 True   64-bit         6/13/2021 11:47:16 AM
[2021.06.19 20:09:00] ComputerName04 True   64-bit         6/14/2021 11:47:16 AM
[2021.06.19 20:10:00] ComputerName05 True   64-bit         6/15/2021 11:47:16 AM

Which can be exported nicely to a CSV instead of a text file. P.D.: sorry for the syntax highlighting :(

Thank you Santiago both for the alternative code that for the advice of $using. You wrote that is a bad idea but my code was just a simple example. I have a script with a lot of functions that has to copy file to several clients and has to do a lot of operations. The script works but I'd like to speed up it and this is the reason why I want to use parallelism calling those functions.

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