Oct 15, 2025 - 12 MIN READ

Async/Await Mastery in C#: Patterns, Pitfalls, and Performance

Deep dive into asynchronous programming in C# covering async/await patterns, deadlock prevention, concurrent operations, and optimization strategies.

Your Name

Asynchronous programming is one of the most powerful features in modern C#, but it's also where I've encountered some of the most subtle and devastating bugs.

Understanding Async/Await

Async/await is syntactic sugar around Tasks and continuations. When you write await, you're telling C# to suspend execution and resume later when the operation completes.

Phase 1: Proper Async/Await Patterns

Never Block on Async Operations

// BAD - Deadlock risk
public IActionResult GetOrder(int id)
{
    var order = _orderService.GetOrderAsync(id).Result;
    return Ok(order);
}

// GOOD - Truly async
public async Task<IActionResult> GetOrder(int id)
{
    var order = await _orderService.GetOrderAsync(id);
    return Ok(order);
}

Proper Task Composition

// BAD - Sequential when independent
var payment = await _paymentService.ProcessAsync();
var inventory = await _inventoryService.ReserveAsync();

// GOOD - Parallel for independent operations
var paymentTask = _paymentService.ProcessAsync();
var inventoryTask = _inventoryService.ReserveAsync();

var results = await Task.WhenAll(paymentTask, inventoryTask);

Phase 2: Concurrent Operations

// BAD - Unbounded task creation
var tasks = userIds.Select(id => FetchUserAsync(id)).ToList();
await Task.WhenAll(tasks);

// GOOD - Limit concurrency with SemaphoreSlim
var semaphore = new SemaphoreSlim(50);

var tasks = userIds.Select(async id =>
{
    await semaphore.WaitAsync();
    try
    {
        return await FetchUserAsync(id);
    }
    finally
    {
        semaphore.Release();
    }
});

Phase 3: Avoiding Common Pitfalls

Async Void Anti-Pattern

// BAD - Never use async void except for events
public async void BadAsyncVoid()
{
    await SomeOperationAsync();
}

// GOOD - Return Task instead
public async Task GoodAsyncTask()
{
    await SomeOperationAsync();
}

ConfigureAwait for Libraries

// In library code
public async Task<User> GetUserAsync(int userId)
{
    var response = await _httpClient.GetAsync($"/api/users/{userId}")
        .ConfigureAwait(false);
    
    return await response.Content.ReadAsAsync<User>()
        .ConfigureAwait(false);
}

Conclusion

Mastering async/await transforms how you build scalable systems. The patterns I've shared aren't theoretical—they come from debugging production issues.

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