csharp-async-patterns

Async/await in C# lets you write non-blocking I/O operations by marking methods with async and awaiting Task-returning calls. This frees threads to handle other work while operations complete, improving responsiveness in UI applications and scalability in server workloads without complex threading.

Task is a reference type allocating heap memory; ValueTask is a value type reducing allocation overhead for synchronous or fast-completing operations. Use ValueTask in hot paths where allocation matters, and Task for general async workflows and when you need reference semantics.

Task.WhenAll waits for all tasks to complete and aggregates results or exceptions; Task.WhenAny returns when the first task completes. Use WhenAll to parallelize independent work and WhenAny to race operations or implement timeouts and cancellation.

ConfigureAwait(false) tells the await to resume on any thread instead of the original context, avoiding deadlocks and improving performance in libraries. Use it in library code and background tasks; avoid it in UI code that must return to the UI thread.

Pass a CancellationToken to async methods and check it periodically or pass it to framework APIs like HttpClient. Cooperative cancellation lets callers signal timeout or abort, enabling graceful shutdown and resource cleanup in responsive applications.

Async streams using async IAsyncEnumerable let you iterate over data fetched asynchronously, yielding results as they arrive. This is ideal for paginated APIs, file processing, and real-time data feeds without loading everything into memory at once.