377 questions for senior .NET engineer interviews, each with a 30-second answer, the full answer, a deep dive, the follow-ups interviewers ask next, and real-world production problems.
Threads, tasks, synchronisation primitives, advanced async patterns and the concurrency problems seen in production .NET systems.
SpinLock and SpinWait, busy-waiting versus blocking, struct copying pitfalls, owner tracking and why most code should not use it.
Read, write and upgradeable read locks, recursion policy, thread affinity, performance reality and lock-free alternatives for read-mostly data.
Atomic Increment, Add, Exchange, CompareExchange, Read, And and Or; full fences; CAS loops; ABA and when lock-free is worth it.
Compiler and CPU reordering, acquire and release semantics, the volatile keyword, Volatile class, x64 versus Arm64 memory models and what volatile does not guarantee.
Store buffers and reordering, full versus half fences, Interlocked.MemoryBarrier, implicit barriers in locks and Interlocked, double-checked locking and MemoryBarrierProcessWide.
SynchronizationContext Post and Send, UI and legacy ASP.NET contexts, ASP.NET Core having none, and the blocking-on-async deadlock.
Context capture, library versus application code, the already-completed caveat, ASP.NET Core relevance, CA2007 and ConfigureAwaitOptions.
CancellationTokenSource and token, ThrowIfCancellationRequested, Register, OperationCanceledException, RequestAborted in ASP.NET Core, disposal and where not to cancel.
CreateLinkedTokenSource, disposal to avoid leaks, telling which source fired, and combining request, shutdown and timeout cancellation.
CancelAfter, WaitAsync, HttpClient.Timeout, resilience handlers, ASP.NET Core request timeouts middleware, TimeProvider and layered timeout budgets.
Async iterators with yield return and await, await foreach, EnumeratorCancellation, ConfigureAwait, LINQ over async streams in .NET 10, EF Core and ASP.NET Core streaming.
Bounded and unbounded channels, full modes, single reader and writer options, completion, ReadAllAsync and backpressure in background processing.
Dataflow blocks, linking with completion propagation, MaxDegreeOfParallelism, BoundedCapacity, SendAsync versus Post, batching and when it is the right tool.
Parallel LINQ partitioning, degree of parallelism, ordering, merge options, cancellation, exceptions, and why it is for CPU-bound work only.
Parallel.ForEachAsync in .NET 6+, MaxDegreeOfParallelism defaults, cancellation and exception behaviour, collecting results, Parallel.ForAsync and alternatives.
Deadlock conditions, lock-ordering and async deadlocks, diagnosis with dotnet-dump (syncblk, clrstack, parallelstacks, dumpasync) and prevention.
Check-then-act and read-modify-write races, non-thread-safe collections, async interleaving, lost updates in databases, and detection and fixes.
Starvation symptoms, Kestrel heartbeat warnings, dotnet-counters and dotnet-trace evidence, dump analysis, root causes and short- versus long-term fixes.
Fake async wrappers, why they do not scale on servers, when offloading is right (UI responsiveness), and how to integrate blocking legacy SDKs safely.
Blocking on tasks with .Result, .Wait and GetResult; hidden places such as constructors, DI factories, Dispose and sync interfaces; async initialisation patterns and safe boundaries.