CODEWITHSUNDEEP
multithreadingpowershellrunspace
Collin Craige
Collin Craige

Reputation: 129

Powershell runspace output behaves differently depending on how returning custom object is defined

I am experimenting with Powershell runspaces and have noticed a difference in how output is written to the console depending on where I create my custom object. If I create the custom object directly in my script block, the output is written to the console in a table format. However, the table appears to be held open while the runspace pool still has open threads, i.e. it creates a table but I can see the results from finished jobs being appended dynamically to the table. This is the desired behavior. I'll refer to this as behavior 1.

The discrepancy occurs when I add a custom module to the runspace pool and then call a function contained in that module, which then creates a custom object. This object is printed to the screen in a list format for each returned object. This is not the desired behavior. I'll call this behavior 2

I have tried piping the output from behavior 2 to Format-Table but this just creates a new table for each returned object. I can achieve the desired effect somewhat by using Write-Host to print a line of the object values but I don't think this is appropriate considering it seems there is a built in behavior that can achieve my desired result if I can understand it.

My thoughts on the matter are that it has something to do with the asynchronous behavior of the runspace. I'm new to powershell but perhaps when the custom object comes directly from the script block there is a hidden method or type declaration telling powershell to hold the table open and wait for result? This would be overridden when using the second technique because its coming from my custom function?

I would like to understand why this is occurring and how I can achieve behavior 1 while being able to use the custom module, which will eventually be very large. I'm open to a different method technique as well, so long as its possible to essentially see the table of outputs grow as jobs finish. The code used is below.

$ISS = [InitialSessionState]::CreateDefault()
[void]$ISS.ImportPSModule(".\Modules\Test-Item.psm1")
$Pool = [RunspaceFactory]::CreateRunspacePool(1, 5, $ISS, $Host)
$Pool.Open()
$Runspaces = @()

# Script block to run code in
$ScriptBlock = {
    Param ( [string]$Server, [int]$Count )
    Test-Server -Server $Server -Count $Count

    # Uncomment the three lines below and comment out the two
    # lines above to test behavior 1.
    #[int] $SleepTime = Get-Random -Maximum 4 -Minimum 1
    #Start-Sleep -Seconds $SleepTime
    #[pscustomobject]@{Server=$Server; Count=$Count;}
}


# Create runspaces and assign to runspace pool
1..10 | ForEach-Object {
    $ParamList = @{ Server = "Server A" Count = $_ }
    $Runspace = [PowerShell]::Create()
    [void]$Runspace.AddScript($ScriptBlock)
    [void]$Runspace.AddParameters($ParamList)
    $Runspace.RunspacePool = $Pool
    $Runspaces += [PSCustomObject]@{
        Id = $_
        Pipe = $Runspace
        Handle = $Runspace.BeginInvoke()
        Object = $Object
    }
}

# Check for things to be finished
while ($Runspaces.Handle -ne $null)
{
    $Completed = $Runspaces | Where-Object { $_.Handle.IsCompleted -eq $true }

    foreach ($Runspace in $Completed)
    {
        $Runspace.Pipe.EndInvoke($Runspace.Handle)
        $Runspace.Handle = $null
    }

    Start-Sleep -Milliseconds 100
}

$Pool.Close()
$Pool.Dispose()

The custom module I'm using is as follows.

function Test-Server {
    Param ([string]$Server, [int]$Count )
    [int] $SleepTime = Get-Random -Maximum 4 -Minimum 1
    Start-Sleep -Seconds $SleepTime

    [pscustomobject]@{Server = $Server;Item = $Count}
}

Upvotes: 0

Views: 1322

Answers (2)

Collin Craige
Collin Craige

Reputation: 129

It appears that my primary issue, aside from errors in my code, was a lack of understanding related to powershell's default object handling. Powershell displays the output of objects as a table when there are less than four key-value pairs and as a list when there are more.

The custom object returned in my test module had more than for key-value pairs while the custom object I returned directly only had two. This resulted in what I thought was odd behavior. I compounded the issue by removing some key-value pairs in my posted code to shorten it and then didn't test it (sorry).

This stackoverflow post has a lengthy answer explaining the behavior some and providing examples for changing the default output.

Upvotes: 0

Sid
Sid

Reputation: 2676

What you have mentioned sounds completely normal to me. That is how powershell is designed because it shares the burden of display. If the user has not specified how to display, PowerShell decides how to.

I couldn't reproduce your issue with the code provided but I think this will solve your problem.

$FinalTable = foreach ($Runspace in $Completed)
{
    $Runspace.Pipe.EndInvoke($Runspace.Handle)
    $Runspace.Handle = $null
}

$FinalResult will now have the table format you expect.

Upvotes: 0

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