Concurrency Production Problems

Deadlocks, race conditions, ThreadPool starvation, async-over-sync, sync-over-async, blocking in ASP.NET Core, unbounded concurrency and backpressure.

1. A .NET service hangs with no CPU usage. How do you diagnose and fix a deadlock, whether it comes from locks or from async code?

   Deadlock conditions, lock-ordering and async deadlocks, diagnosis with dotnet-dump (syncblk, clrstack, parallelstacks, dumpasync) and prevention.

   Senior Debugging Concurrency Production Problems · 🔗 3 follow-ups · 🛠 1 real-world
2. What is a race condition? Give examples in .NET, including async and database races, and explain how you find and fix them.

   Check-then-act and read-modify-write races, non-thread-safe collections, async interleaving, lost updates in databases, and detection and fixes.

   Senior Debugging Concurrency Production Problems · 🔗 3 follow-ups · 🛠 1 real-world
3. How do you recognise, diagnose and fix ThreadPool starvation in a production ASP.NET Core service?

   Starvation symptoms, Kestrel heartbeat warnings, dotnet-counters and dotnet-trace evidence, dump analysis, root causes and short- versus long-term fixes.

   Senior Debugging Concurrency Production Problems · 🔗 3 follow-ups · 🛠 1 real-world
4. What is async-over-sync, why is wrapping synchronous code in Task.Run often a mistake, and when is it acceptable?

   Fake async wrappers, why they do not scale on servers, when offloading is right (UI responsiveness), and how to integrate blocking legacy SDKs safely.

   Senior Architecture Concurrency Production Problems · 🔗 3 follow-ups · 🛠 1 real-world
5. What is sync-over-async, where does it sneak into .NET code, and how do you remove it?

   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.

   Senior CodeReview Concurrency Production Problems · 🔗 3 follow-ups · 🛠 1 real-world
6. Which blocking calls cause problems in ASP.NET Core, how do you find them, and what should replace them?

   Synchronous I/O and AllowSynchronousIO, EF Core sync APIs, HttpClient.Send, Thread.Sleep, long locks, heavy synchronous logging; detection with analysers, traces and load tests.

   Mid-Level CodeReview Concurrency Production Problems · 🔗 3 follow-ups · 🛠 1 real-world
7. What is unbounded concurrency, why does it take systems down, and how do you put limits in place in .NET?

   Unbounded Task.WhenAll, Task.Run per request, unlimited queues and connections; Little's law; limits with SemaphoreSlim, Parallel.ForEachAsync, bounded channels, rate limiting middleware and bulkheads.

   Senior Architecture Concurrency Production Problems · 🔗 3 follow-ups · 🛠 1 real-world
8. What is backpressure, and how do you implement it across a .NET system, from in-process queues to message brokers and HTTP APIs?

   Backpressure strategies (block, buffer, drop, reject), bounded channels, pull-based streams, broker prefetch and concurrency settings, HTTP 429/503 with Retry-After, and metrics.

   Staff / Architect SystemDesign Concurrency Production Problems · 🔗 3 follow-ups · 🛠 1 real-world