Async and await

async/await lets you write non-blocking code that looks synchronous—ideal for I/O-bound work. The CLR rewrites async methods into state machines; this lesson uses Task.Delay to simulate I/O without blocking threads—unlike callback pyramids in older JavaScript.

Basic pattern

async Task<int> FetchCountAsync() {
    await Task.Delay(100);  // simulated I/O
    return 42;
}

int n = await FetchCountAsync();

await yields the thread while waiting—important for scalable servers covered later in ASP.NET.

Rules of thumb

• Suffix async methods with Async
• Avoid .Result and .Wait() on async code—they can deadlock UI/ASP.NET contexts
• Use async Task for void-like async work; avoid async void except event handlers

Important interview questions and answers

1. Q: async vs multithreading?
   A: Async frees threads during I/O waits; CPU-bound parallelism uses Task.Run or Parallel separately.
2. Q: What does await return?
   A: It unwraps the task result (or propagates exceptions) once the operation completes.

Self-check

1. Why avoid blocking .Result on ASP.NET requests?
2. What return type for async methods with no result?

Pitfall: Never block on async code with .Result or .Wait() on UI or ASP.NET threads—use await all the way.