Csharp Async

Performance

• Use Task.WhenAll() for parallel execution of multiple tasks
• Use Task.WhenAny() for implementing timeouts or taking the first completed task
• Use Task.WhenEach() (.NET 9+) to process tasks as they complete, rather than waiting for all
• Avoid unnecessary async/await when simply passing through task results
• Consider cancellation tokens for long-running operations
• Compose cancellation tokens with CancellationTokenSource.CreateLinkedTokenSource() for layered timeout scenarios

Common Pitfalls

• Never use .Wait(), .Result, or .GetAwaiter().GetResult() in async code
• Avoid mixing blocking and async code
• Don't create async void methods (except for event handlers)
• Always await Task-returning methods

ConfigureAwait Guidance

• In ASP.NET Core, ConfigureAwait(false) has no effect because there is no SynchronizationContext; omit it in application code for clarity
• In library code that may run outside ASP.NET Core (WPF, WinForms, legacy ASP.NET), use ConfigureAwait(false) to avoid deadlocks
• When in doubt about the consumer, use ConfigureAwait(false) in shared libraries

Async Streams

• Use IAsyncEnumerable<T> for producing sequences of values asynchronously
• Accept [EnumeratorCancellation] CancellationToken in async iterator methods
• Consume with await foreach and pass cancellation via .WithCancellation(token)
• Prefer async streams over returning Task<List<T>> when results can be yielded incrementally

Implementation Patterns

• Implement the async command pattern for long-running operations
• Use async streams (IAsyncEnumerable<T>) for processing sequences asynchronously
• Consider the task-based asynchronous pattern (TAP) for public APIs

When reviewing my C# code, identify these issues and suggest improvements that follow these best practices.