Resolved: ThreadJob in powershell is not working with global variables

In this post, we will see how to resolve ThreadJob in powershell is not working with global variables

Question:

I have the below code where myValues will be updated by multiple functions (in this file) and I want to capture that change and process myValues in a different thread so that the current execution of updating myValues is not stopped. But logsToDashboard is not event getting called in here. Not sure what am i missing. Would appreciate any leads.

$global:myValues = New-Object System.Collections.ArrayList
$global:myValuesProcessed = New-Object System.Collections.ArrayList

for ($i = 0; $i -lt 5; $i++) {
    Start-Sleep 10
    Build-DashboardLogValues -message "test $i"
    Start-Sleep 10
}

function Build-DashboardLogValues {
    param (
        [string] $message
    )
    $value = New-Object System.Collections.ArrayList
    $value.Add("timestamp")
    $value.Add($message)
    $global:myValues.Add($value)
}

function LogsToDashboard 
{
    while ($true) {
        if ($global:myValues.Count -gt 0 ) {
            $headers = @{ 'Authorization' = "my token" }
            $jsonBase = @{} 
            # doing something with the "myValues" and updating the json base and removing the processed values from "myValues"
            $bodyJson = $jsonBase | ConvertTo-Json -Depth 20

            
            Invoke-WebRequest -Uri "myurl" -Method Post -Headers $headers -Body $bodyJson -ContentType "application/json"
        }
    }
}

$Dashboardjob = Start-ThreadJob -ScriptBlock ${function:LogsToDashboard}

Best Answer:

You need to use the using: scope modifier to reference a local a variable in your new thread. Also using global: is pointless in your code.

$myValues = New-Object System.Collections.ArrayList

function LogsToDashboard {
    $myValues = $using:myValues
    while ($true) {
        if ($myValues.Count -gt 0 ) {
            # Code here
        }
    }
}

$Dashboardjob = Start-ThreadJob -ScriptBlock ${function:LogsToDashboard}

Another way to do it is with -ArgumentList and, you can but not mandatory, add a param block to your function. Without the param block you would refer to the list using $args[0] instead of $list.

$myValues = New-Object System.Collections.ArrayList

function LogsToDashboard {
    param($list)

    while ($true) {
        if ($list.Count -gt 0 ) {
            # Code here
        }
    }
}

$Dashboardjob = Start-ThreadJob -ScriptBlock ${function:LogsToDashboard} -ArgumentList (, $myValues)

If you have better answer, please add a comment about this, thank you!

Source: Stackoverflow.com

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