您可以在后台作业中运行循环的每次迭代，该作业不同于单独的线程，因为它是一个完整的其他PowerShell.exe进程.数据是通过序列化从后台进程传递的.

要使用后台作业来处理它，您需要定义一个脚本块来完成实际的工作，然后在循环的每次迭代中使用参数调用该脚本块.脚本块可以通过Write-Output或引发异常来报告状态.

您可能想要限制正在运行的并发后台作业数量.这是节流的示例:

$jobItems = "a", "b", "c", "d", "e"
$jobMax = 2
$jobs = @()

$jobWork = {
    param ($MyInput)
    if ($MyInput -eq "d") {
        throw "an example of an error"
    } else {
        write-output "Processed $MyInput"
    }
}

foreach ($jobItem in $jobItems) {
    if ($jobs.Count -le $jobMax) {
        $jobs += Start-Job -ScriptBlock $jobWork -ArgumentList $jobItem
    } else {
        $jobs | Wait-Job -Any
    }
}
$jobs | Wait-Job

作为替代方法，您可以尝试事件.看看这个线程，了解一些如何使用事件实现并发的示例.

PowerShell:DownloadFileAsync的运行空间问题

您也许可以用 OpenReadAsync 代替DownloadFileAsync >

Basic script idea: Hello. I've created a powershell script which I use to check the filesizes of certain executables, and then keep them in a text file. Next time the script runs, if a filesize differs it will replace the one in the text file with the new one.

The structure: I have a main script and a folder which contains many scripts, each for every executable of which I want to check the filesize. So the scripts in the folder will return a string containing the link to the executable, which will be fed to the main script.

The code:

$progdir = "C:\script\programms"
$items = Get-ChildItem -filter *.ps1 -Path $progdir
$webclient = New-Object System.Net.WebClient

$filesizes = get-content C:\updatechecker\programms\filesizes
if ($filesizes.length -ne $items.length) { 
    if ($filesizes.length -eq $null) {
        Write-Host ("Building filesize database...") -nonewline
    } 
    else { 
        Write-Host ("Rebuilding filesize database...") -nonewline 
    }
    clear-content  C:\programms\filesizes

    for ($i=0; $i -le $items.length-1; $i++) {
        $command = "c:\programms\" + $items[$i].name
        $link = & $command
        $webclient.OpenRead($link) | Out-Null
        $filesize = $webclient.ResponseHeaders["Content-Length"]
        $filesize >> C:\programms\filesizes
    }
    echo "Done." 
} 
else {
    ...

Question: This for loop is the one I want to run in parallel. I need your advice on how to do this since I'm new to powershell. I tried to implement a few things I found but they didn't work correctly (took very long to finish, output errors, multiple entries of filesizes in my filesizes file). I suspect it's a synchronization issue and somehow I need to lock the critical parts. Isn't there anything like omp parallel for in powershell? :P

Any help,advice on how to achieve this would be appreciated :)

edit:

Get-Job | Remove-Job -Force
$progdir = "C:\programms"
$items = Get-ChildItem -filter *.ps1 -Path $progdir
$webclient = New-Object System.Net.WebClient
$filesizes = get-content C:\programms\filesizes

$jobWork = {
    param ($MyInput)
    $command = "c:\programms\" + $MyInput
    $link = & $command
    $webclient.OpenRead($link) | Out-Null
    $filesize = $webclient.ResponseHeaders["Content-Length"]
    $filesize >> C:\programms\filesizes

}
foreach ($item in $items) {

    Start-Job -ScriptBlock $jobWork -ArgumentList $item.name | out-null
}

Get-Job | Wait-Job
Get-Job | Receive-Job | Out-GridView | out-null
echo "Done."

Edit 2: Used code I found here: http://ryan.witschger.net/?p=22

$mutex = new-object -TypeName System.Threading.Mutex -ArgumentList $false, "RandomGlobalMutexName";
$MaxThreads = 4
$SleepTimer = 500


$jobWork = {
    param ($MyInput)
    $webclient = New-Object System.Net.WebClient
    $command = "c:\programms\" + $MyInput
    $link = & $command
    $webclient.OpenRead($link) | Out-Null

    $result = $mutex.WaitOne();

    $file = $webclient.ResponseHeaders["Content-Length"]
    $file >> C:\programms\filesizes

    $mutex.ReleaseMutex();
}

$progdir = "C:\programms"
$items = Get-ChildItem -filter *.ps1 -Path $progdir
$webclient = New-Object System.Net.WebClient
$filesizes = get-content C:\programms\filesizes

Get-Job | Remove-Job -Force

$i = 0

ForEach ($item in $items){
    While ($(Get-Job -state running).count -ge $MaxThreads){

        Start-Sleep -Milliseconds $SleepTimer
    }

    $i++
    Start-Job -ScriptBlock $jobWork -ArgumentList $item.name | Out-Null


}

You can run each iteration of the loop in a background job which is not the same a seperate thread in that it is a whole other PowerShell.exe process. Data is passed from the background processes through serialization.

To approach it using background jobs you'll need to define a script block that will do that actual work and then call the script block with parameters in each iteration of the loop. The script block can report back status via Write-Output or by throwing an exception.

You'll probably want to throttle how many concurrent background jobs are running. Here's an example of how to throttle:

$jobItems = "a", "b", "c", "d", "e"
$jobMax = 2
$jobs = @()

$jobWork = {
    param ($MyInput)
    if ($MyInput -eq "d") {
        throw "an example of an error"
    } else {
        write-output "Processed $MyInput"
    }
}

foreach ($jobItem in $jobItems) {
    if ($jobs.Count -le $jobMax) {
        $jobs += Start-Job -ScriptBlock $jobWork -ArgumentList $jobItem
    } else {
        $jobs | Wait-Job -Any
    }
}
$jobs | Wait-Job

As an alternative you might try eventing. Take a look at this thread for some examples of how to implement concurrency using events.

PowerShell: Runspace problem with DownloadFileAsync

You might be able to replace DownloadFileAsync with OpenReadAsync