Yaseer Arafat

🚦 Mastering CancellationToken in C#

🧠 Why It Matters

In modern .NET applications, asynchronous programming is essential—but with it comes the risk of runaway tasks, unresponsive UIs, or server overloads.

Enter CancellationToken: a smart way to inject cancellation logic into your async workflows.

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🎯 Key Concepts

▶️ Inject Control

🔹 External signal stops task execution gracefully

▶️ Graceful Shutdown

🔹 Check IsCancellationRequested inside the task

▶️ Linked Tokens

🔹 Combine multiple cancellation sources

▶️ Real-World Use

🔹 Cancel API calls when the user navigates away

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🛠️ Sample Code

using System;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;

class Program
{
    static async Task Main()
    {
        using CancellationTokenSource cts = new CancellationTokenSource();

        Console.WriteLine("Press any key to cancel...");
        Task.Run(() =>
        {
            Console.ReadKey();
            cts.Cancel();
        });

        try
        {
            await FetchDataAsync(cts.Token);
        }
        catch (OperationCanceledException)
        {
            Console.WriteLine("Operation was cancelled.");
        }
    }

    static async Task FetchDataAsync(CancellationToken token)
    {
        using HttpClient client = new HttpClient();

        Console.WriteLine("Fetching data...");
        HttpResponseMessage response = await client.GetAsync(
            "https://jsonplaceholder.typicode.com/posts", token
        );

        response.EnsureSuccessStatusCode();
        string content = await response.Content.ReadAsStringAsync(token);
        Console.WriteLine("Data fetched successfully.");
    }
}

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✅ Takeaway

Using CancellationToken not only protects your application from wasteful processing, it also keeps user experience snappy and systems resilient.

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