Foreach -parallel (Part 1: PowerShell 7)

by Dec 6, 2019

PowerShell 7 comes with a built-in parameter to run different tasks in parallel. Here is a simple example:

1..100 | ForEach-Object -ThrottleLimit 20 -Parallel { Start-Sleep -Seconds 1 $_ }

In a normal ForEach-Object loop, this would take 100 seconds to execute. Thanks to -parallel, the code is executed in parallel. -ThrottleLimit defines the “chunks”, so in this example, there are 20 threads running in parallel, reducing the total execution time to 5 seconds.

Before you get too enthusiastic, keep in mind that each thread runs in its own PowerShell environment. Fortunately, you can access local variables with the prefix “using:”:

$text = "Output: "

1..100 | ForEach-Object -ThrottleLimit 20 -Parallel { Start-Sleep -Seconds 1 "$using:text $_" }

Once you start using multi-threading, you need to know about thread-safety, though. Complex objects such as ADUser objects may not be shared across multiple threads, so it depends on the individual use case whether or not parallelization will work for you.

While parallel ForEach-Object loops are built-in in PowerShell 7, that does not mean you cannot use parallelization in Windows PowerShell. There are plenty of modules that implement this functionality in Windows PowerShell. We’ll talk about that in an upcoming trick.

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