How to pass a variable with the current value to runspace?

Question

I'm writing a script that will download the selected programs I need (thank you Santiago Squarzon for your help). The script works well when I need to download one program, but to download several in a row I need to start the next one at the end of the download. I made a list of downloads $FileList and I want to pass its value to runspace in order to start downloading the next program (and remove the already downloaded one from the list). And so on until I go through the entire list. There will be more programs later. For now, two are enough for the test.

Add-Type -assembly System.Windows.Forms

$webMain = New-Object System.Net.WebClient
$FileList = @()

$MainForm = New-Object System.Windows.Forms.Form
$MainForm.Width = 420
$MainForm.Height = 200
$MainForm.FormBorderStyle = "Fixed3d"
$MainForm.MaximizeBox = $false
$MainForm.StartPosition = "CenterScreen"

$Button1 = New-Object System.Windows.Forms.Button
$Button1.Location = New-Object System.Drawing.Size(120,50)
$Button1.Size = New-Object System.Drawing.Size(160,50)
$Button1.Text = "Download selected"
$Button1.Name = "Button1"
$Button1.Add_Click({
    $Button1.Enabled = $false
    if ($CheckBox1.Checked) {
        $FileList += @{Link = "https://dl.google.com/chrome/install/standalonesetup64.exe"; Path = "D:\chrome.exe"}
    }
    if ($CheckBox2.Checked) {
        $FileList += @{Link = "https://download.mozilla.org/?product=firefox-latest-ssl&os=win64&lang=ru"; Path = "D:\firefox.exe"}
    }
    $FileList = [System.Collections.ArrayList]$FileList
    Wait-Event -Timeout 5
    if ($FileList.count -gt 0) {
        $webMain.DownloadFileAsync($FileList[0].Link, $FileList[0].Path)
        $FileList.Remove($FileList[0])
    }
    
})
$MainForm.Controls.Add($Button1)

$CheckBox1 = New-Object System.Windows.Forms.CheckBox
$CheckBox1.Location = New-Object System.Drawing.Size(10,10)
$CheckBox1.Size = New-Object System.Drawing.Size(100,20)
$CheckBox1.Text = "Chrome"
$MainForm.Controls.Add($CheckBox1)

$CheckBox2 = New-Object System.Windows.Forms.CheckBox
$CheckBox2.Location = New-Object System.Drawing.Size(10,30)
$CheckBox2.Size = New-Object System.Drawing.Size(100,20)
$CheckBox2.Text = "Firefox"
$MainForm.Controls.Add($CheckBox2)

$ProgressBar1 = New-Object System.Windows.Forms.ProgressBar
$ProgressBar1.Location = New-Object System.Drawing.Size(5,120)
$ProgressBar1.Size = New-Object System.Drawing.Size(400,40)
$ProgressBar1.Name = "ProgressBar1"
$MainForm.Controls.Add($ProgressBar1)

$rs = [runspacefactory]::CreateRunspace($Host)
$rs.Open()
$rs.SessionStateProxy.PSVariable.Set([psvariable]::new('form', $MainForm))
$rs.SessionStateProxy.PSVariable.Set([psvariable]::new('FileList', $FileList))

$ps = [powershell]::Create().AddScript({

    Register-ObjectEvent -InputObject $args[0] -EventName 'DownloadProgressChanged' -SourceIdentifier 'WebMainDownloadProgressChanged' -Action {
        [System.Threading.Monitor]::Enter($form)
        $progress = $form.Controls.Find('ProgressBar1', $false)[0]
        $progress.Value = $eventArgs.ProgressPercentage
        [System.Threading.Monitor]::Exit($form)
    }
     
    Register-ObjectEvent -InputObject $args[0] -EventName 'DownloadFileCompleted' -SourceIdentifier 'WebMainDownloadFileCompleted' -Action {
        [System.Threading.Monitor]::Enter($form)
        $progress = $form.Controls.Find('ProgressBar1', $false)[0]
        $progress.Value = 0
        [System.Threading.Monitor]::Exit($form)
        if ($FileList.count -gt 0) {
            $webMain.DownloadFileAsync($FileList[0].Link, $FileList[0].Path)
            $FileList.Remove($FileList[0])
        }
        if ($FileList.count -eq 0) {
            $form.Controls.Find('Button1', $false)[0].Enabled = $true
        }
    }

}).AddArgument($webMain)

$ps.Runspace = $rs
$task = $ps.BeginInvoke()
$MainForm.ShowDialog()

As far as I understand, $rs.SessionStateProxy.PSVariable.Set([psvariable]::new('FileList', $FileList)) transmits the current value at the time the script starts, and not at the time the button is pressed. How can I correctly pass the $FileList variable to runspace so that it contains the current value at the time the button is pressed?

Answer 1

Although I still haven’t figured out why $rs.SessionStateProxy.PSVariable.Set([psvariable]::new('form', $MainForm)) transmits the "current" form with which you can work, and $rs.SessionStateProxy.PSVariable.Set ([psvariable]::new('FileList', $FileList)) transmits only the value of the variable at the moment the script is launched and does not “update” it when changed, but I realized that you can simply transfer all processing to that separate runspace and then there is no need will transmit nothing.

This is what I ended up with:

Add-Type -assembly System.Windows.Forms

$MainForm = New-Object System.Windows.Forms.Form
$MainForm.Width = 420
$MainForm.Height = 200
$MainForm.FormBorderStyle = "Fixed3d"
$MainForm.MaximizeBox = $false
$MainForm.StartPosition = "CenterScreen"

$Button1 = New-Object System.Windows.Forms.Button
$Button1.Location = New-Object System.Drawing.Size(120,50)
$Button1.Size = New-Object System.Drawing.Size(160,50)
$Button1.Text = "Download selected"
$Button1.Name = "Button1"
$MainForm.Controls.Add($Button1)

$CheckBox1 = New-Object System.Windows.Forms.CheckBox
$CheckBox1.Location = New-Object System.Drawing.Size(10,10)
$CheckBox1.Size = New-Object System.Drawing.Size(100,20)
$CheckBox1.Text = "Chrome"
$CheckBox1.Name = "CheckBox1"
$MainForm.Controls.Add($CheckBox1)

$CheckBox2 = New-Object System.Windows.Forms.CheckBox
$CheckBox2.Location = New-Object System.Drawing.Size(10,30)
$CheckBox2.Size = New-Object System.Drawing.Size(100,20)
$CheckBox2.Text = "Firefox"
$CheckBox2.Name = "CheckBox2"
$MainForm.Controls.Add($CheckBox2)

$ProgressBar1 = New-Object System.Windows.Forms.ProgressBar
$ProgressBar1.Location = New-Object System.Drawing.Size(5,120)
$ProgressBar1.Size = New-Object System.Drawing.Size(400,40)
$ProgressBar1.Name = "ProgressBar1"
$MainForm.Controls.Add($ProgressBar1)

$rs = [runspacefactory]::CreateRunspace($Host)
$rs.Open()
$rs.SessionStateProxy.PSVariable.Set([psvariable]::new('form', $MainForm))

$ps = [powershell]::Create().AddScript({

    $FileList = @()
    $webMain = New-Object System.Net.WebClient
    $Button1 = $form.Controls.Find('Button1', $false)[0]

    $Button1.Add_Click({
        $Button1.Enabled = $false
        if ($form.Controls.Find('CheckBox1', $false)[0].Checked) {
            $Global:FileList += @{Link = "https://dl.google.com/chrome/install/standalonesetup64.exe"; Path = "D:\chrome.exe"}
        }
        if ($form.Controls.Find('CheckBox2', $false)[0].Checked) {
            $Global:FileList += @{Link = "https://download.mozilla.org/?product=firefox-latest-ssl&os=win64&lang=ru"; Path = "D:\firefox.exe"}
        }
        $Global:FileList = [System.Collections.ArrayList]$Global:FileList
        Wait-Event -Timeout 5
        if ($Global:FileList.count -gt 0) {
            $webMain.DownloadFileAsync($Global:FileList[0].Link, $Global:FileList[0].Path)
            $Global:FileList.Remove($Global:FileList[0])
        }
    })

    Register-ObjectEvent -InputObject $webMain -EventName 'DownloadProgressChanged' -SourceIdentifier 'WebMainDownloadProgressChanged' -Action {
        [System.Threading.Monitor]::Enter($form)
        $progress = $form.Controls.Find('ProgressBar1', $false)[0]
        $progress.Value = $eventArgs.ProgressPercentage
        [System.Threading.Monitor]::Exit($form)
    }
     
    Register-ObjectEvent -InputObject $webMain -EventName 'DownloadFileCompleted' -SourceIdentifier 'WebMainDownloadFileCompleted' -Action {
        [System.Threading.Monitor]::Enter($form)
        $progress = $form.Controls.Find('ProgressBar1', $false)[0]
        $progress.Value = 0
        if ($Global:FileList.count -eq 0) {
            $form.Controls.Find('Button1', $false)[0].Enabled = $true
        }
        [System.Threading.Monitor]::Exit($form)
        if ($Global:FileList.count -gt 0) {
            $webMain.DownloadFileAsync($Global:FileList[0].Link, $Global:FileList[0].Path)
            $Global:FileList.Remove($FileList[0])
        }
    }

})

$ps.Runspace = $rs
$ps.BeginInvoke()
$MainForm.ShowDialog()

Answer 2

The code from the past implementation gets increasingly more complicated if you want to handle the "enqueueing" of multiple async downloads. Basically, the code from the past answer was able to handle a single download without blocking the form (the main thread), however for handling multiple downloads it needs to be refactored.

This implementation sets up a worker thread that handles downloads "enqueued" from the main thread (the form), this worker will remain active awaiting for new downloads to be enqueued and is only terminated when the parent process is terminated.

I have added a few pointer comments that might help you understand the logic behind the code.

Demo

Code

Add-Type -Assembly System.Windows.Forms

[System.Windows.Forms.Application]::EnableVisualStyles()

$MainForm = New-Object System.Windows.Forms.Form
$MainForm.Width = 420
$MainForm.Height = 200
$MainForm.FormBorderStyle = "Fixed3d"
$MainForm.MaximizeBox = $false
$MainForm.StartPosition = "CenterScreen"

$Button1 = New-Object System.Windows.Forms.Button
$Button1.Location = New-Object System.Drawing.Size(120,50)
$Button1.Size = New-Object System.Drawing.Size(160,50)
$Button1.Text = "Download selected"
$Button1.Name = "Button1"
$Button1.Add_Click({
    # from this event handler we just enqueue downloads, there is no need to disable
    # this button because the current implementation will allow as many downloads as you like
    # and the download is limited by a `SemaphoreSlim` to handle throttling.
    if ($CheckBox1.Checked) {
        $queue.Enqueue(@{
            Link = "https://www.w3.org/WAI/ER/tests/xhtml/testfiles/resources/pdf/dummy.pdf"
            Path = Join-Path $pwd -ChildPath ('chrome' + [guid]::NewGuid() + '.exe')
        })
    }
    if ($CheckBox2.Checked) {
        $queue.Enqueue(@{
            Link = "https://www.w3.org/WAI/ER/tests/xhtml/testfiles/resources/pdf/dummy.pdf"
            Path = Join-Path $pwd -ChildPath ('firefox' + [guid]::NewGuid() + '.exe')
        })
    }
})
$MainForm.Controls.Add($Button1)

$CheckBox1 = New-Object System.Windows.Forms.CheckBox
$CheckBox1.Location = New-Object System.Drawing.Size(10,10)
$CheckBox1.Size = New-Object System.Drawing.Size(100,20)
$CheckBox1.Text = "Chrome"
$MainForm.Controls.Add($CheckBox1)

$CheckBox2 = New-Object System.Windows.Forms.CheckBox
$CheckBox2.Location = New-Object System.Drawing.Size(10,30)
$CheckBox2.Size = New-Object System.Drawing.Size(100,20)
$CheckBox2.Text = "Firefox"
$MainForm.Controls.Add($CheckBox2)

$ProgressBar1 = New-Object System.Windows.Forms.ProgressBar
$ProgressBar1.Location = New-Object System.Drawing.Size(5,120)
$ProgressBar1.Size = New-Object System.Drawing.Size(390,30)
$ProgressBar1.Name = "ProgressBar1"
$MainForm.Controls.Add($ProgressBar1)

$queue = [System.Collections.Concurrent.ConcurrentQueue[hashtable]]::new()

$rs = [runspacefactory]::CreateRunspace($Host)
$rs.Open()
# the 2 objects that we need available in the worker thread are the queue and the progressbar,
# if you want more objects available from the form itslef it might be better to pass in `$MainForm`
# then use `.Controls.Find(...)` as shown in the previous answer
$rs.SessionStateProxy.PSVariable.Set('queue', $queue)
$rs.SessionStateProxy.PSVariable.Set('progress', $ProgressBar1)

$ps = [powershell]::Create().AddScript({
    $client = [System.Net.WebClient]::new()
    $task = $null
    # allow only 1 download at a time
    $throttleLimit = [System.Threading.SemaphoreSlim]::new(1, 1)
    # NOTE: A single instance of `WebClient` can handle more than one download at the same
    #       but you need additional logic, i.e. check for `$client.IsBusy` before downloading async.

    $registerObjectEventSplat = @{
        InputObject = $client
        EventName   = 'DownloadProgressChanged'
        Action      = {
            $progress.Value = $eventArgs.ProgressPercentage
            Write-Progress -Activity 'Downloading...' -PercentComplete $eventArgs.ProgressPercentage
        }
    }

    Register-ObjectEvent @registerObjectEventSplat

    $registerObjectEventSplat = @{
        InputObject = $client
        EventName   = 'DownloadFileCompleted'
        Action      = {
            # Release the Semaphore handle here once the download is completed
            $throttleLimit.Release()
            "A download was completed...", "Items in Queue: $($queue.Count)" | Out-Host
            Write-Progress -Activity 'Downloading...' -Completed
        }
    }

    Register-ObjectEvent @registerObjectEventSplat

    while ($true) {
        # if there is nothing in queue
        if (-not $queue.TryDequeue([ref] $task)) {
            # sleep for a bit
            Start-Sleep -Milliseconds 200
            # and go to the next iteration
            continue
        }

        # else, we know there is a download here but we want to allow only 1 at a time
        # so, this inner `while` will unblock only when the SemaphoreSlim allows it
        while (-not $throttleLimit.Wait(200)) { }
        # once we have the handle of the Semaphore we can start the download here
        $client.DownloadFileAsync($task['Link'], $task['Path'])
        "A download has started...", "Items in Queue: $($queue.Count)" | Out-Host
        $task | Out-Host
    }
}, $false)

$ps.Runspace = $rs
$task = $ps.BeginInvoke()

$MainForm.ShowDialog()

# this should be a must in your code,
# always dispose the resources when done
$ps.Stop()
$ps.Dispose()
$rs.Dispose()