The 30-Day .NET Challenge - Day 20: Task vs. ValueTask

Heap allocations aren’t entirely bad, but when an object is allocated on a heap, it contributes to the garbage collection cycles, which in turn reduces overall application performance.

Introduction

One approach to optimizing resource usage in async code is by using ValueTask<TResult> syntax to minimize heap allocations, which in turn reduces pressure on garbage collection and enhances overall performance.

Learning Objectives

• The Problem with Heap Allocations
• Optimizing with ValueTask<TResult>
• When to Use ValueTask<TResult>

Prerequisites for Developers

• Basic understanding of C# programming language.

Getting Started

Heap allocations aren’t entirely bad, but when an object is allocated on a heap, it contributes to the garbage collection cycles, which in turn reduces overall application performance. In the case of excessive heap allocation, the garbage collector can cause GC pauses.

Bad Practice: Excessive Use of Task<TResult>

Let’s consider a common asynchronous pattern that developers commonly use:

    public async Task<string> ReadDataAsync()
    {
        var data = await ReadFromStreamAsync(_stream);
        return ProcessData(data);
    }

If the above-mentioned method is called more frequently, each request results in a new Task instance being allocated on heap memory. Over time, it leads to increased garbage collection overhead.

Optimizing with ValueTask<TResult>

By changing the return type from Task<TResult> to ValueTask<TResult>, we can reduce heap allocations

    public async ValueTask<string> ReadDataAsync()
    {
        var data = await ReadFromStreamAsync(_stream);
        return ProcessData(data);
    }

The aforementioned optimization is beneficial for high-frequency async operations or methods that are expected to complete synchronously in a significant portion of time.

When to Use ValueTask<TResult>

• High-frequency methods
• Performance-sensitive code
• Methods that often complete synchronously

Create another class named TaskVsValueTask and add the following code snippet

    public static class TaskVsValueTask
    {
        public static async Task<string> FetchDataAsync()
        {
            // Simulate a delay to mimic fetching data
            await Task.Delay(1000);
            return "Data fetched using Task";
        }
    
        public static async ValueTask<string> FetchDataValueTaskAsync()
        {
            // Simulate a delay to mimic fetching data
            await Task.Delay(1000); // Note: Use Task.Delay for the sake of example.
            return "Data fetched using ValueTask";
        }
    }

Execute from the main method as follows

    #region Day 20: Task vs. Value Task
    static async Task<string> ExecuteDay20()
    {
        Console.WriteLine("Fetching data with Task...");
        string result = await TaskVsValueTask.FetchDataAsync();
        Console.WriteLine(result);
    
        Console.WriteLine("Fetching data with ValueTask...");
        string resultValueTask = await TaskVsValueTask.FetchDataValueTaskAsync();
        Console.WriteLine(resultValueTask);
    
        return "Executed Day 20 successfully..!!";
    }
    #endregion

Console Output

    Fetching data with Task...
    Data fetched using Task
    Fetching data with ValueTask...
    Data fetched using ValueTask

Complete Code on GitHub

GitHub — ssukhpinder/30DayChallenge.Net

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