Async Method Design

Vaibhav • September 11, 2025

In the previous article, we explored how async and await simplify asynchronous programming by allowing you to write non-blocking code that looks synchronous. But writing async methods isn’t just about sprinkling await everywhere. Good async method design requires careful thought about naming, return types, cancellation, exception handling, and how your method fits into the broader application architecture.

In this article, we’ll walk through how to design async methods that are clear, composable, and robust. We’ll cover naming conventions, cancellation support, exception propagation, and how to expose async APIs to consumers. Along the way, we’ll highlight common mistakes and best practices that help you avoid subtle bugs and performance issues.

Async Naming Conventions

One of the simplest but most important rules in async method design is naming. Always suffix your async methods with Async. This makes it immediately clear to callers that the method is asynchronous and must be awaited.

// Good
Task SaveDocumentAsync(Document doc)

// Bad
Task SaveDocument(Document doc)
    

This convention is widely adopted across .NET libraries and helps avoid confusion. It also prevents accidental misuse-like calling an async method without awaiting it, which can lead to unobserved exceptions or race conditions.

Choosing the Right Return Type

Async methods typically return Task or Task<T>. Avoid using void unless you’re writing an event handler. Returning Task allows callers to await the method and handle exceptions properly.

// Correct
async Task SaveAsync()

// Correct with result
async Task<string> LoadAsync()

// Only for event handlers
async void Button_Click(object sender, EventArgs e)
    

Returning void from non-event methods makes it impossible for callers to know when the method completes or if it failed. This breaks exception propagation and makes debugging harder.

Supporting Cancellation

Long-running async methods should support cancellation. This allows callers to abort the operation if it’s no longer needed-saving resources and improving responsiveness. Use CancellationToken as a parameter and check it periodically.

async Task LoadDataAsync(CancellationToken cancellationToken)
{
    await Task.Delay(1000, cancellationToken);
    cancellationToken.ThrowIfCancellationRequested();
    // Continue loading...
}
    

The Task.Delay method accepts a cancellation token, and ThrowIfCancellationRequested ensures that the method exits early if cancellation is requested. You should pass the token to all cancellable operations and check it before doing expensive work.

Exception Propagation

Async methods propagate exceptions through the returned task. If the caller uses await, the exception is rethrown at the await point. This makes error handling straightforward and consistent.

async Task ProcessAsync()
{
    await Task.Run(() => throw new InvalidOperationException("Oops"));
}

// Caller
try
{
    await ProcessAsync();
}
catch (Exception ex)
{
    Console.WriteLine("Caught: " + ex.Message);
}
    

Avoid catching exceptions inside the async method unless you plan to handle them or transform them. Let the caller decide how to respond. If you do catch exceptions, rethrow them or wrap them in a meaningful error.

Avoiding Async Overhead

Async methods introduce a small overhead due to state machine generation and context switching. For trivial methods that complete synchronously, you can avoid marking them async and return a completed task directly.

// Instead of this
async Task<int> GetValueAsync()
{
    return 42;
}

// Use this
Task<int> GetValueAsync() => Task.FromResult(42);
    

This avoids unnecessary allocations and improves performance. Use this pattern for simple methods that don’t need await.

Composability and Reusability

Async methods should be small and composable. Break large operations into smaller async methods that each do one thing. This improves readability, testability, and reuse.

async Task SaveDocumentAsync(Document doc)
{
    await ValidateAsync(doc);
    await WriteToDiskAsync(doc);
    await LogSaveAsync(doc);
}
    

Each helper method is responsible for a single step. This makes the code easier to understand and maintain. It also allows you to test each method independently.

Avoiding Async Void Outside Events

As mentioned earlier, async void should only be used for event handlers. It breaks exception propagation and makes it impossible to know when the method completes.

// OK
async void Button_Click(object sender, EventArgs e) { ... }

// Not OK
async void SaveAsync() { ... }
    

If you need a fire-and-forget method, return Task and document that callers don’t need to await it. This keeps the method testable and exceptions observable.

Async Method Contracts

Async methods should document their behavior clearly. This includes:

• Whether the method supports cancellation
• What exceptions it may throw
• Whether it must be awaited
• Whether it resumes on the original context

Use XML documentation comments to describe these aspects. This helps consumers use your API correctly and avoid surprises.

/// <summary>
/// Saves the document asynchronously.
/// </summary>
/// <param name="doc">The document to save.</param>
/// <param name="cancellationToken">Token to cancel the operation.</param>
/// <returns>A task that completes when the save is done.</returns>
/// <exception cref="IOException">Thrown if the save fails.</exception>
Task SaveAsync(Document doc, CancellationToken cancellationToken);
    

This makes your API self-documenting and easier to use correctly.

Summary

Designing async methods is about more than just using async and await. It’s about creating clear, predictable, and composable APIs that integrate well with the rest of your application. You’ve learned how to name async methods, choose return types, support cancellation, propagate exceptions, and avoid common pitfalls.

In the next article, we’ll explore Exception Handling in Async, where we’ll dive deeper into how exceptions behave in async code, how to catch and log them properly, and how to avoid silent failures and deadlocks.