Async/Await and Async Controllers in ASP.NET Core
💡 Concept Name
Async/Await and Async Controllers
📘 Quick Intro
Async/await are C# features that help write non-blocking, asynchronous code. In ASP.NET Core, controllers can be async, making your web API more scalable. Async controllers free up threads during long-running I/O tasks.
🧠 Analogy / Short Story
Imagine you’re in a restaurant. A waiter takes your order and doesn’t wait by your table; instead, he serves other tables while the kitchen prepares your food. That’s how async works—your thread doesn’t wait but continues doing other work until the result is ready.
🔧 Technical Explanation
The `async` modifier allows a method to run asynchronously. The `await` keyword tells the program to pause and resume once the awaited task completes.
Async controllers return `Task
🎯 Purpose & Use Case
- ✅ Improve scalability by freeing up threads
- ✅ Handle high concurrency with fewer resources
- ✅ Avoid UI freezes or blocked threads in web apps
- ✅ Efficiently handle I/O-bound operations (DB, file, network)
- ✅ Align with modern async-first APIs (EF Core, HttpClient)
💻 Real Code Example
public class ProductController : ControllerBase
{
private readonly IProductService _service;
public ProductController(IProductService service)
{
_service = service;
}
[HttpGet(""api/products/{id}"")]
public async Task<IActionResult> GetProduct(int id)
{
var product = await _service.GetProductByIdAsync(id);
return Ok(product);
}
}
❓ Interview Q&A
Q1: What is the purpose of async/await?
A: To write non-blocking, asynchronous code in a readable way.
Q2: What does `await` do in C#?
A: It pauses execution until the awaited task completes.
Q3: What is returned by an async controller?
A: `Task
Q4: Are async controllers faster?
A: Not necessarily faster, but more scalable under load.
Q5: Can we use async in constructors?
A: No, constructors cannot be async in C#.
Q6: What is `ConfigureAwait(false)`?
A: It avoids capturing the current context, often used in libraries.
Q7: What is an I/O-bound operation?
A: A task that waits for external operations like DB, file, or network access.
Q8: What if we don’t use `await` in an async method?
A: It runs synchronously, and a warning may appear.
Q9: What happens if an exception occurs in async method?
A: It’s captured in the returned Task and must be awaited to catch.
Q10: What is deadlock in async code?
A: It occurs when blocking async code with `.Result` or `.Wait()`.
📝 MCQs
Q1. Which keyword is used to pause execution in async?
- yield
- delay
- await
- pause
Q2. What does an async controller return?
- void
- string
- Task
- Task<IActionResult>
Q3. Can constructors be async in C#?
- Yes
- No
- Only static
- Only public
Q4. What does ConfigureAwait(false) do?
- Waits synchronously
- Avoids capturing context
- Throws exception
- Enables retry
Q5. Which operation benefits most from async?
- CPU-bound
- I/O-bound
- Memory-bound
- UI-bound
Q6. Which method creates a delay?
- Wait.Delay
- Thread.Sleep
- Task.Delay
- Timer.Sleep
Q7. What is the return type of an async method?
- void
- int
- Task
- Func
Q8. What happens if an exception is thrown in async method?
- Crashes app
- Ignored
- Stored in Task
- Stops immediately
Q9. How to avoid deadlock in async code?
- Use lock
- Avoid async
- Use await properly
- Add timeout
Q10. Which is more scalable under load?
- Sync controller
- Async controller
- Task.Run controller
- None
💡 Bonus Insight
Async controllers shine in scenarios like API gateways, microservices, and cloud apps where non-blocking operations reduce latency and resource usage. Use async wherever external I/O like DB or API calls are involved to maximize performance.
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