asynchronous code execution on PowerShell? - powershell

Question

Help me please figure out how asynchronous loop execution works.
In many forums, examples are very cumbersome and not understandable
During execution, the program window freezes, and at the end of the cycle it shows the final number
for example
[void][System.Reflection.Assembly]::LoadWithPartialName('presentationframework')
[xml]$XAML = #"
<Window
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
Title="Рассылка интернет-трафика" Height="200" Width="300" ResizeMode="NoResize">
<Grid Width="300">
<TextBox Name="text_result" TextWrapping="Wrap" Margin="0,0,0,0" VerticalAlignment="Top" Height="31" Width="200" />
<Button Name="button_start" Content="Start" Height="31" Margin="0,50,0,0" VerticalAlignment="Top" Width="200" />
<Button Name="button_close" Content="Close" Height="31" Margin="0,100,0,0" VerticalAlignment="Top" Width="200"/>
</Grid>
</Window>
"#
#Read XAML
$reader=(New-Object System.Xml.XmlNodeReader $xaml)
try{$Form=[Windows.Markup.XamlReader]::Load( $reader )}
catch{Write-Host "Unable to load Windows.Markup.XamlReader"; exit}
# Store Form Objects In PowerShell
$xaml.SelectNodes("//*[#Name]") | ForEach-Object {Set-Variable -Name ($_.Name) -Value $Form.FindName($_.Name)}
$button_start.Add_Click({
for ($row = 2; $row -le 1000; $row++) {
$text_result.Text = $row
}
})
#Загружаем главную форму
$Form.ShowDialog() | out-null

Answer 1

It took me quite a while to figure this one out. Let me preface by saying that Adam the Automator has a fantastic breakdown:
https://adamtheautomator.com/building-asynchronous-powershell-functions/
The easiest way to think about executing an asynchronous loop is to think about tricking powershell. In short, you just want it to do something in the background while your script is running. So, you just need to turn the loop you would like into a script block and use start-job, a.k.a. &.
Let's use a common task, such as looking through a bunch of files. Here, we'll use gci.
$scriptblock = {
param ($folder)
Get-ChildItem -Path $folder}
Start-job -ScriptBlock $scriptblock -ArgumentList "C:\Windows" -name "stackexample"
The name is important so that you can reference it later. Now you have a job in the background, and you're good to continue with your script. But what happens if you want to see if the job is done? There's a command for checking on the status of your job (code below).
Get-Job -Name stackexample
One thing to note, make sure to CLOSE your jobs once they're done.
$status = (Get-Job -Name stackexample).state
if ($status -eq "completed")
{
Remove-Job -Name stackexample
}
Wait, I need to know what those folders were! No problem. We just need to tell the scriptblock to output data (write-host, for example). Then, we receive the job before we close it. So a full circuit might look like this:
$scriptblock = {
param ($folder)
$folders = Get-ChildItem -Path $folder
write-host $folders
}
Start-job -ScriptBlock $scriptblock -ArgumentList "C:\Windows" -name "stackexample"
Start-Sleep -Seconds 5
$status = (Get-Job -Name stackexample).state
if ($status -eq "completed")
{
Receive-Job -Name StackExample -Wait
Remove-Job -Name stackexample
}
You can get so much fancier from here, but that is the core of what 'asynchronous code execution' is - telling powershell to do something time consuming while you're doing other stuff.
As applied to your code, you can use the button click to set off a job and run in the background, then receive the final results.
$xaml.SelectNodes("//*[#Name]") | ForEach-Object {Set-Variable -Name ($_.Name) -Value $Form.FindName($_.Name)}
$scriptblock = {
for ($row = 2; $row -le 1000; $row++)
{
$result = $row
}
return $result
}
$button_start.Add_Click({
Start-job -ScriptBlock $scriptblock -Name scriptblock
While ((Get-Job -Name scriptblock).State -ne "Completed")
{
start-sleep 1
}
$results = receive-job -Name scriptblock -keep
remove-job -Name scriptblock
$text_result.Text = $results
})
Above the button click we've defined the script block. When the button is clicked, it kicks off the job and then watches it with the while loop. Once the job is finished, we can extract the result (done here with return $result in the scriptblock). Receive the job and you have your final variable which you can now display for the user.

Answer 2

With no cycle.
The form is just a name in this case. You can remove all GUI elements from it if you want.
$Script:SyncHashTable = [Hashtable]::Synchronized(#{})
$RunSpace = [Management.Automation.Runspaces.RunspaceFactory]::CreateRunspace()
$RunSpace.ApartmentState = "STA"
$RunSpace.ThreadOptions = "ReuseThread"
$RunSpace.Open()
$RunSpace.SessionStateProxy.SetVariable("SyncHashTable", $Script:SyncHashTable)
$PowerShellCmd = [Management.Automation.PowerShell]::Create().AddScript({
[void] [System.Reflection.Assembly]::LoadWithPartialName("System.Drawing")
[void] [System.Reflection.Assembly]::LoadWithPartialName("System.Windows.Forms")
$Script:SyncHashTable.objForm = New-Object System.Windows.Forms.Form
$Script:SyncHashTable.InitialFormWindowState = New-Object System.Windows.Forms.FormWindowState
$Script:SyncHashTable.objForm.Size = New-Object System.Drawing.Size(340, 200)
$Script:SyncHashTable.objForm.Name = "objForm"
$Script:SyncHashTable.objForm.Text = "Test form"
$Script:SyncHashTable.objLabel = New-Object System.Windows.Forms.Label
$Script:SyncHashTable.objLabel.Location = New-Object System.Drawing.Size(10,20)
$Script:SyncHashTable.objLabel.Size = New-Object System.Drawing.Size(320,20)
$Script:SyncHashTable.objLabel.Text = "Enter the data and press the OK button or key Enter"
$Script:SyncHashTable.objForm.Controls.Add($Script:SyncHashTable.objLabel)
$Script:SyncHashTable.objTextBox = New-Object System.Windows.Forms.TextBox
$Script:SyncHashTable.objTextBox.Location = New-Object System.Drawing.Size(10,40)
$Script:SyncHashTable.objTextBox.Size = New-Object System.Drawing.Size(300,20)
$Script:SyncHashTable.objForm.Controls.Add($Script:SyncHashTable.objTextBox)
$Script:SyncHashTable.objForm.KeyPreview = $True
$Script:SyncHashTable.objForm.Add_KeyDown( { if ($_.KeyCode -eq "Enter") { $Script:SyncHashTable.X = $Script:SyncHashTable.objTextBox.Text;$Script:SyncHashTable.objForm.Close() } })
$Script:SyncHashTable.objForm.Add_KeyDown( { if ($_.KeyCode -eq "Escape") { $objForm.Close() } })
$Script:SyncHashTable.OKButton = New-Object System.Windows.Forms.Button
$Script:SyncHashTable.OKButton.Location = New-Object System.Drawing.Size(75,120)
$Script:SyncHashTable.OKButton.Size = New-Object System.Drawing.Size(75,23)
$Script:SyncHashTable.OKButton.Text = "OK"
$Script:SyncHashTable.OKButton.Add_Click( { $Script:SyncHashTable.X = $Script:SyncHashTable.objTextBox.Text;$Script:SyncHashTable.objForm.Close() } )
$Script:SyncHashTable.objForm.Controls.Add($Script:SyncHashTable.OKButton)
$Script:SyncHashTable.InitialFormWindowState = $Script:SyncHashTable.objForm.WindowState
$Script:SyncHashTable.objForm.add_Load($Script:SyncHashTable.OnLoadForm_StateCorrection)
[void] $Script:SyncHashTable.objForm.ShowDialog()
})
$PowerShellCmd.Runspace = $RunSpace
$obj=$PowerShellCmd.BeginInvoke()
#Time to retrieve our missing object $AsyncObject
$BindingFlags = [Reflection.BindingFlags]'nonpublic','instance'
$Field = $PowerShellCmd.GetType().GetField('invokeAsyncResult',$BindingFlags)
$AsyncObject = $Field.GetValue($PowerShellCmd)
Write-Host 'Here is your code that will be executed in parallel with the form code'
Write-Host '(any length and execution time)'
Write-Host "`$PowerShellCmd.EndInvoke(`$AsyncObject) will wait for results from the form,"
Write-Host "or pick them up if they are ready."
Write-Host "=================================="
#Closing the execution space when getting the result
$PowerShellCmd.EndInvoke($AsyncObject)
'This is the result of executing the form code: {0}' -f $Script:SyncHashTable.X