Lesson 14 of 40 Async Intermediate ⏱ 40 min

Async / Await & Task-Based Programming

Write responsive, scalable applications with C#'s async/await — understand Tasks, ConfigureAwait, cancellation, and common pitfalls.

Part 1: async and await Basics

// Mark method async, return Task or Task<T>
public async Task<string> FetchUserAsync(int id)
{
var response = await _http.GetStringAsync($"/users/{id}");
return response;
}

Part 2: Task.WhenAll & Task.WhenAny

// Run multiple tasks concurrently
var (user, orders) = await (
FetchUserAsync(id),
FetchOrdersAsync(id)
);

// Alternatively with Task.WhenAll
await Task.WhenAll(tasks);

// First to complete wins
var first = await Task.WhenAny(tasks);

Part 3: CancellationToken

public async Task<List<Order>> GetOrdersAsync(CancellationToken ct = default)
{
ct.ThrowIfCancellationRequested();
return await _db.Orders.ToListAsync(ct);
}

// With timeout
using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
await GetOrdersAsync(cts.Token);

Part 4: Common Async Mistakes

Anti-Pattern	Why Bad	Fix
`.Result` or `.Wait()`	Deadlocks on UI/ASP threads	Always await
`async void`	Exceptions can't be caught	Return Task
Missing ConfigureAwait(false)	Unnecessary context switch in libs	Add it in library code
Forgetting cancellation token	Can't cancel long operations	Accept and pass CancellationToken

Async / Await & Task-Based Programming

Part 1: async and await Basics

Part 2: Task.WhenAll & Task.WhenAny

Part 3: CancellationToken

Part 4: Common Async Mistakes

C# in Visual Studio 2026