What is the async and await pattern in C#? When should you use it?

Question

Ravi Vishwakarma · Answer

The async and await pattern in C# is a language feature used to write
asynchronous, non-blocking code in a clean, readable way.
Instead of using callbacks or threads manually, you can write asynchronous code
as if it were synchronous, while still freeing up threads to do other work (like serving more web requests).
Basic Concept
async keyword: Marks a method as asynchronous.await keyword: Tells the compiler to pause execution until the awaited task completes.
public async Taskandlt;stringandgt; GetDataAsync()
{
    HttpClient client = new HttpClient();
    string result = await client.GetStringAsync("https://example.com");
    return result;
}
Behind the scenes, the method gets "split" into parts that run before and after the
await. The thread is returned to the pool while waiting.
Components of the Pattern
Component
Role
async
Makes the method return a Task, Taskandlt;Tandgt;, or ValueTaskandlt;Tandgt;
await
Pauses method until the awaited task completes
Task/Taskandlt;Tandgt;
Represents an asynchronous operation
Rules to Remember
You can only use await inside a method marked with
async.An async method must return:
Task (if it returns nothing),Taskandlt;Tandgt; (if it returns a value),or void (only for event handlers).
await only works with Task, Taskandlt;Tandgt;, 
ValueTask, or custom awaitables.
Example: Asynchronous Delay
public async Task PrintMessageAsync()
{
    Console.WriteLine("Before delay");
    await Task.Delay(1000); // waits asynchronously for 1 second
    Console.WriteLine("After delay");
}
This method does not block the thread during the delay.
When Should You Use async/await?
Use it when:
Calling I/O-bound operations (e.g., HTTP requests, file I/O, database calls)You want to keep the UI responsive (WinForms, WPF)You’re building scalable web APIs that must serve many concurrent requests
// GOOD: Database call (I/O bound)
public async Taskandlt;Userandgt; GetUserAsync(int id)
{
    return await _dbContext.Users.FindAsync(id);
}
Don’t use it when:
The method is CPU-bound and does not involve any async operationsYou’re just wrapping synchronous code in Task.Run() without a good reasonYou don't have any await inside — this will show a compiler warning
Bad Example
public async Taskandlt;intandgt; CalculateSync()
{
    // BAD: nothing async happening here
    return 1 + 2;
}
Better:
public int CalculateSync()
{
    return 1 + 2;
}
Rule of Thumb
Use async/await for I/O-bound operations to keep your app responsive and scalable. Avoid it for purely CPU-bound tasks unless you need to offload work using Task.Run.

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What is the async and await pattern in C#? When should you use it?

Ravi Vishwakarma

Can you answer this question?

1 Answers

Basic Concept

Components of the Pattern

Rules to Remember

Example: Asynchronous Delay

When Should You Use `async`/`await`?

Use it when:

Don’t use it when:

Bad Example

Rule of Thumb

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Component	Role
`async`	Makes the method return a `Task`, `Task<T>`, or `ValueTask<T>`
`await`	Pauses method until the awaited task completes
`Task`/`Task<T>`	Represents an asynchronous operation