Async/Await in C#: Writing Clean and Safe Asynchronous Code

Asynchrony is crucial for creating performant and responsive applications, especially when dealing with I/O, network calls, or long-running operations.

In C#, the async/await pattern has revolutionized asynchronous programming by making it much more readable and easier to write.

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Why use async/await?

• Prevents blocking the main thread (UI or server).

• Improves server application scalability.

• Makes the code more readable compared to callbacks or traditional Tasks.

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How does async/await work?

• async indicates that a method contains asynchronous operations.

• await suspends the method execution until the Task completes, without blocking the thread.

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Basic rules for using async/await

• Async methods must return Task or Task<T>, or void only for event handlers.

• Always use await to call asynchronous methods, to avoid blocking the thread.

• Avoid using .Result or .Wait() on a Task to prevent deadlocks.

• Propagate async up to the top of the call stack when possible.

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Writing clean asynchronous code

• Avoid async void, except for specific cases (event handlers).

• Name asynchronous methods with the Async suffix (e.g., GetDataAsync).

• Use ConfigureAwait(false) in libraries to avoid context issues (when you don't need to return to the original context).

• Properly handle exceptions in async methods with try/catch.

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Practical example

public async Task<string> GetWebPageAsync(string url)
{
    using var client = new HttpClient();
    var response = await client.GetAsync(url);
    response.EnsureSuccessStatusCode();
    var content = await response.Content.ReadAsStringAsync();
    return content;
}

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Be cautious about...

• Deadlock: Never block asynchronous methods with .Result or .Wait() in synchronization contexts (e.g., UI).

• Unhandled exceptions: Errors in async methods propagate through Tasks, so always use try/catch.

• Parallelism vs. Asynchrony: Async does not mean running in parallel; it means not blocking.

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Testing asynchronous code

• Tests should be async Task and use await to call asynchronous methods.

• Frameworks like xUnit natively support asynchronous tests.

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Conclusion

Correctly using async/await significantly improves the quality and responsiveness of C# applications.

Writing clean asynchronous code requires attention to best practices and a good understanding of the model.