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The 30-Day .NET Challenge Day 14: Limit Concurrent Async Operations

by Sukhpinder SinghApril 2nd, 2024

Too Long; Didn't Read

The article highlights the importance of limiting the concurrent asynchronous operations which in turn improves performance. Prerequisites for Developers include basic understanding of C# programming language and understanding of asynchronous programming using await. The article can be found on GitHub and can be downloaded from: http://www.gitHub.com/uk/sshpinder/30DayChallenge/Main.php.

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Introduction

The article highlights the importance of limiting the concurrent asynchronous operations, which in turn improves performance.

Learning Objectives

The common mistake all developers do
How to use limit concurrent async operations
Best Practices

Prerequisites for Developers

Basic understanding of C# programming language
Basic understanding of asynchronous programming using async await

Getting Started

The common mistake all developers do

Consider an example where the user wants to load data asynchronously within a method, and it highlights the common mistake developers make.

(async item => await ProcessItem(item));
/// <summary>
/// Old approach with classic async await 
/// </summary>
/// <returns></returns>
public async static Task OldApproach(List<string> items)
{
    var tasks = items.Select(async item => await ProcessItem(item));
    await Task.WhenAll(tasks);
}

The approach may look clean and simple, but it initiates tasks for each item in the collection concurrently. This can cause system strain under heavy List<string> items, which will produce poor application performance.

Optimized approach with Concurrency Limit

Let’s transform the above method using SemaphoreSlim to limit the number of concurrent asynchronous operations. The following code snippet demonstrates the more refined approach.

/// <summary>
/// Optimized approach with limit concurrency
/// </summary>
/// <returns></returns>
public static async Task OptimizedApproachAsync(List<string> items, int maxConcurrency = 10)
{
    using (var semaphore = new SemaphoreSlim(maxConcurrency))
    {
        var tasks = items.Select(async item =>
        {
            await semaphore.WaitAsync(); // Limit concurrency by waiting for the semaphore.
            try
            {
                await ProcessItem(item);
            }
            finally
            {
                semaphore.Release(); // Release the semaphore to allow other operations.
            }
        });

        await Task.WhenAll(tasks);
    }
}

The aforementioned code prevents the system from being choked by too many concurrent tasks.

Best Practices

Please find below the best practices

Limit Concurrency

To balance system load and resources, it is recommended to use SemaphoreSlim

Avoid Blocking Calls

Avoid using .Result or .Wait(), as they can lead to deadlocks and degrade performance.

Async all the way

Avoid mixing async and sync code. Ensure all methods are async from top to bottom to prevent deadlock and make optimal use of resources.

Conclusion

Asynchronous programming in C# involves more than just understanding the async and await keywords; it requires more features like concurrency, resource utilization, and code structure