Asynchronous Programming in .NET

Asynchronous programming lets you improve responsiveness and scalability by performing work without blocking threads. In .NET, the async and await keywords simplify the creation of asynchronous methods.

Key Concepts

• Task – Represents an asynchronous operation.
• Task<TResult> – Returns a result when the operation completes.
• async – Marks a method as asynchronous.
• await – Suspends execution until the awaited task finishes.

Creating an Async Method

public async Task<string> GetContentAsync(string url)
{
    using var client = new HttpClient();
    var response = await client.GetAsync(url);
    response.EnsureSuccessStatusCode();
    return await response.Content.ReadAsStringAsync();
}

Explanation

The method returns Task<string>, allowing callers to await its completion. The await operator releases the current thread while the I/O operation is in progress.

Best Practices

1. Use ConfigureAwait(false) in library code to avoid capturing the synchronization context.
2. Avoid async void except for event handlers.
3. Prefer Task.WhenAll and Task.WhenAny for parallel async operations.

Sample: Parallel Data Fetch

public async Task<IEnumerable<string>> FetchAllAsync(IEnumerable<string> urls)
{
    var tasks = urls.Select(url => GetContentAsync(url));
    var results = await Task.WhenAll(tasks);
    return results;
}

FAQ

Can I call async code from synchronous methods?

Yes, but you should block only at the top‑level entry point (e.g., Main) using Task.Wait or .Result. Excessive blocking defeats the purpose of async.

What does ConfigureAwait(false) do?

It tells the awaiter not to marshal the continuation back to the original synchronization context, which can improve performance in library code.