Asynchronous Programming

Q: What do async and await do?

await asynchronously waits for a Task, releasing the thread until it completes, then resumes the method; async marks a method that uses await and returns a Task.

Q: What is the difference between Task and Task ?

Task represents async work with no result; Task completes with a value of type T that you get by awaiting it.

Q: How do you run multiple async operations concurrently?

Start the tasks without awaiting each immediately, then await Task.WhenAll to run them in parallel and wait for all.

Q: What does ConfigureAwait(false) do?

It resumes the continuation without capturing the synchronization context, avoiding a needless hop and reducing deadlocks. Use it in library code that doesn't touch UI/HttpContext.

Q: Why can .Result or .Wait() deadlock, and what's the fix?

In a single-threaded context the blocked thread waits for a continuation that needs that same thread — neither proceeds. Fix by awaiting all the way down.

Q: How do you design for scalability and avoid thread-pool starvation?

Use async I/O so request threads return to the pool while waiting; never block on async (sync-over-async) as it holds threads and starves the pool under load.

6 question(s)

What do async and await do?

Beginner

await asynchronously waits for a Task, releasing the thread until it completes, then resumes the method; async marks a method that uses await and returns a Task.

public async Task<string> LoadAsync(HttpClient h) => (await h.GetStringAsync("/x")).Trim();

Real-world example A web server frees the request thread during a DB call so it can serve other requests.

What is the difference between Task and Task<T>?

Beginner

Task represents async work with no result; Task<T> completes with a value of type T that you get by awaiting it.

Task done = Task.Delay(100);
Task<int> n = Task.FromResult(42);
int v = await n;

Real-world example Returning Task<Order> from a repository so callers can await the fetched order.

How do you run multiple async operations concurrently?

Intermediate

Start the tasks without awaiting each immediately, then await Task.WhenAll to run them in parallel and wait for all.

var t1 = h.GetStringAsync(a);
var t2 = h.GetStringAsync(b);
var r = await Task.WhenAll(t1, t2);

Real-world example Fetching price, stock and reviews at once to cut page latency.

What does ConfigureAwait(false) do?

Intermediate

It resumes the continuation without capturing the synchronization context, avoiding a needless hop and reducing deadlocks. Use it in library code that doesn't touch UI/HttpContext.

var body = await h.GetStringAsync(url).ConfigureAwait(false);

Real-world example A reusable NuGet library uses it so apps that block on it don't deadlock.

Why can .Result or .Wait() deadlock, and what's the fix?

Advanced

In a single-threaded context the blocked thread waits for a continuation that needs that same thread — neither proceeds. Fix by awaiting all the way down.

// risky: var d = LoadAsync().Result;
var d = await LoadAsync();

Real-world example A legacy MVC action blocking on an async call hangs under load until made async end-to-end.

How do you design for scalability and avoid thread-pool starvation?

Advanced

Use async I/O so request threads return to the pool while waiting; never block on async (sync-over-async) as it holds threads and starves the pool under load.

public async Task<IActionResult> Get() => Ok(await _repo.GetAsync());

Real-world example Removing blocking .Result calls let a checkout API handle far more concurrent users.