<skill_overview> <purpose>Build reliable async flows and safe multi-threaded code</purpose> <triggers> <trigger>Writing async methods</trigger> <trigger>Coordinating multiple tasks</trigger> <trigger>Adding cancellation support</trigger> <trigger>Working with concurrent collections</trigger> </triggers> <sources> <source url="https://learn.microsoft.com/en-us/dotnet/csharp/asynchronous-programming/async-scenarios">Async Scenarios</source> <source url="https://learn.microsoft.com/en-us/dotnet/standard/collections/thread-safe/">Thread-Safe Collections</source> <source url="https://learn.microsoft.com/en-us/dotnet/core/extensions/channels">System.Threading.Channels</source> </sources> </skill_overview> <async_await_rules> <rules> <rule>Use async/await end-to-end; avoid blocking waits</rule> <rule>Return Task/ValueTask, not void (except event handlers)</rule> <rule>Use ConfigureAwait(false) in library code</rule> </rules> </async_await_rules> <task_coordination> <rules> <rule>Use Task.WhenAll for independent work</rule> <rule>Use Task.WhenAny for first-completion patterns</rule> <rule>Handle exceptions from all tasks</rule> </rules> <example> <code> await Task.WhenAll(fetchUserTask, fetchOrdersTask); </code> </example> </task_coordination> <cancellation> <rules> <rule>Accept CancellationToken in cancellable APIs</rule> <rule>Pass the token to all awaited operations</rule> <rule>Respect cancellation promptly</rule> </rules> </cancellation> <concurrency_primitives> <rules> <rule>Use ConcurrentDictionary, ConcurrentQueue, ConcurrentBag for shared collections</rule> <rule>Use Channel for producer-consumer pipelines</rule> <rule>Keep lock scope minimal and consistent</rule> </rules> </concurrency_primitives> <deadlocks> <rules> <rule>Never use .Result or .Wait on async operations</rule> <rule>Avoid blocking inside async methods</rule> <rule>Do not capture synchronization context in libraries</rule> </rules> </deadlocks> <anti_patterns> <avoid name="sync_over_async">Blocking on async tasks</avoid> <avoid name="async_void">async void outside event handlers</avoid> <avoid name="shared_mutable_state">Mutable shared state without synchronization</avoid> </anti_patterns>