dotnet-asynclisted

# C# Async Patterns C#'s async/await model is powerful but has a handful of well-known pitfalls — most production async bugs fall into three categories: deadlocks from blocking on async code, unobserved exceptions from `async void`, and missing cancellation support. Know these cold. ## Never block on async code Calling `.Result` or `.Wait()` on a Task blocks the current thread and can deadlock in contexts with a synchronization context (WinForms, WPF, old ASP.NET): ```csharp // Bad: can deadlock in sync-context environments var user = GetUserAsync(id).Result; var data = FetchDataAsync().GetAwaiter().GetResult(); // Good: async all the way up var user = await GetUserAsync(id); ``` In ASP.NET Core there is no synchronization context, so `.GetAwaiter().GetResult()` won't deadlock there — but it still blocks a thread pool thread, defeating the purpose of async. Make it async all the way. If you genuinely need to call async from sync (e.g., a console app entry point or legacy code), use `Task.Run(() => method()).GetAwaiter().GetResult()` as a last resort — but don't normalize it. ## `async void` is dangerous `async void` methods can't be awaited. If they throw, the exception is unobservable and crashes the process (or is silently swallowed depending on the host). Use `async Task` everywhere except event handlers. ```csharp // Bad: exception from SendEmailAsync is unobservable async void NotifyUser(User user) { await SendEmailAsync(user.Email); } // Good: exception c