Powershell Guide: How to Efficiently Add Results to an Array with ForEach-Object -Parallel

Discover how to manage results in `Powershell` using `ForEach-Object -Parallel` and thread-safe collections for effective programming!
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Powershell Guide: How to Efficiently Add Results to an Array with ForEach-Object -Parallel

As technology professionals, we often find ourselves needing to perform batch operations that involve collecting data and managing it efficiently in scripts. One common scenario is using Powershell to retrieve and store information concurrently, especially when operating in a cloud environment. However, there can be some challenges when trying to aggregate results from parallel operations. This guide will guide you through how to solve such an issue specifically when using ForEach-Object -Parallel in PowerShell 7 and above.

The Problem

You're running a script where you're using ForEach-Object -Parallel to fetch data from multiple Azure subscriptions. You define a variable to hold the results, but when you attempt to add results to this variable using the standard + = operator, you encounter an error message indicating that the assignment expression is not valid. The use of the $using: scope also doesn't resolve the issue, which can be frustrating. So, what’s the solution?

Understanding the Core Issue

When working with the ForEach-Object -Parallel command, each parallel execution runs in its own runspace or thread. This means that variables aren't shared directly between these runspaces, making it impossible to use traditional array operations like + = to concatenate results. Instead, you need a thread-safe way to manage shared data.

The Solution

To successfully store results from parallel operations, you will need to:

Use a Thread-Safe Collection: Instead of a standard array, utilize a concurrent collection that allows safe operations from multiple threads.

Obtain a Local Reference: Extract a reference to the collection within the parallel block to manage the contents safely.

Here’s how you can implement this in your script:

[[See Video to Reveal this Text or Code Snippet]]

Breakdown of the Code:

Creating a Concurrent Bag:
The line $Costs = [System.Collections.Concurrent.ConcurrentBag[psobject]]::new() initializes a new concurrent collection, which can dynamically store objects securely during concurrent operations.

Using ForEach-Object -Parallel:
Within the ForEach-Object loop, you set up the Azure context and log the fetching activity for better tracking.

Adding to Local Reference:
By assigning $using:Costs to a local variable called $localCostsVariable, you can safely add data to the concurrent bag without running into threading issues.

Conclusion

By using a concurrent collection in PowerShell with ForEach-Object -Parallel, you can effectively manage shared data in multi-threaded scenarios. This practice not only enhances performance but also ensures that your script runs smoothly without errors related to variable assignments. Whether you're fetching costs from Azure subscriptions or performing any other batch operations in parallel, implementing thread-safe techniques can significantly improve reliability and efficiency in your scripts.

Now that you know how to add results back into a variable safely while using ForEach-Object -Parallel, you can confidently tackle more complex PowerShell scripting tasks. Happy scripting!