Async and await in C#

ASP.NET Core is built for async I/O. Database calls, HTTP client requests, and file reads use async Task methods with await—similar to JavaScript promises but with compile-time checking.

Basic pattern

public async Task<List<User>> GetUsersAsync() {
    return await _db.Users.ToListAsync();
}

Action methods return Task<IActionResult> and await services—Kestrel handles many concurrent requests efficiently.

Rules of thumb

• Suffix async methods with Async
• Await all the way—avoid .Result or .Wait() (deadlock risk)
• Use ConfigureAwait(false) in library code; ASP.NET Core doesn't need it in controllers
• CPU-bound work may use Task.Run sparingly—not for every loop

Important interview questions and answers

1. Q: async improves throughput how?
   A: Threads aren't blocked during I/O waits—they return to the pool until the operation completes.
2. Q: async void?
   A: Avoid except event handlers—exceptions can't be caught by callers; prefer async Task.

Self-check

1. Why avoid .Result on async calls in ASP.NET?
2. What return type should an async API action use?

Pitfall: Blocking async with .Result or .Wait() can deadlock ASP.NET request threads—await all the way through the call stack.