Powershell 中的线程

Question

I have a basic script to generate a Windows Form. In this script, a button is supposed to trigger and operation. In order to prevent lagging, I would like to use multiple threads.

After reading several tutorials, I still don't seem to get the fundamentals of it. This is my function for dthe button click:

Function Click ()
{
    Get-Job | Remove-Job
    $MaximumThreads = 4
    For ($i=0;$i -lt 5; $i++)
    {
        $ScriptBlock =
        {
            Write-Host "Job started!"
        }
        While ($(Get-Job -state running).count -ge $MaximumThreads)
        {
            Write-Host "Wait"
            Start-Sleep -Seconds 1
        }
        Start-Job -ScriptBlock $ScriptBlock
    }
    Write-Host "All jobs complete!"
}

I get this output:

Wait
Wait
Wait
Wait
Wait
Wait
All jobs complete!
Cancel

What I would expect is that the first threads start piling up until the threshold is reached before the "Wait" condition would kick in. But it appears as though the Jobs are not getting started in the first place, which leads me to believe I am missing something fundamental...

Any suggestions? Thanks!

Answer 1

I think you have to move the while outside the for-loop.

Function Click()
{
    Get-Job | Remove-Job
    $MaximumThreads = 4
    For ($i=0;$i -lt 5; $i++)
    {
        $ScriptBlock =
        {
            Write-Host "Job started!"
        }
        Start-Job -ScriptBlock $ScriptBlock
    }

    While ($(Get-Job -state running).count -ge $MaximumThreads)
    {
        Write-Host "Wait"
        Start-Sleep -Seconds 1
    }

    Write-Host "All jobs complete!"
}

Answer 2

In your code, you are creating jobs in a loop, and inside that same loop you are waiting for them to complete in a while loop. Only after that while loop you start the job.

Try:

function Click {
    Get-Job | Remove-Job
    $MaximumThreads = 4
    # create and start the jobs
    for ($i = 0; $i -lt $MaximumThreads; $i++) {
        $ScriptBlock = { Write-Host "Job started!" }
        # Start-job outputs job information. 
        # If you don't want that, append | Out-Null
        Start-Job -ScriptBlock $ScriptBlock
    }
    # now wait for the jobs to complete.
    while ((Get-Job -State Completed).Count -lt $MaximumThreads) {
        Write-Host "Wait"
        Start-Sleep -Seconds 1
    }
    Write-Host "All jobs complete!"
}

Click

Output:

Id     Name            PSJobTypeName   State         HasMoreData     Location             Command                  
--     ----            -------------   -----         -----------     --------             -------                  
41     Job41           BackgroundJob   Running       True            localhost             Write-Host "Job start...
43     Job43           BackgroundJob   Running       True            localhost             Write-Host "Job start...
45     Job45           BackgroundJob   Running       True            localhost             Write-Host "Job start...
47     Job47           BackgroundJob   Running       True            localhost             Write-Host "Job start...
Wait
All jobs complete!