Wait, I'm sleeping

What this C++ concurrency interview question tests

This is an easy concurrency question that quant firms use to check whether candidates understand the subtle pitfalls of synchronisation primitives and thread coordination. It probes your ability to spot a classic race condition or deadlock scenario in producer–consumer patterns.

The question asks you to reason about the order of operations when a consumer thread checks a shared queue and then waits on a semaphore. The core skill being tested is recognising the gap between checking a condition and acting on it—a window where another thread's action can invalidate your assumption. Strong answers identify the specific synchronisation failure and explain why the current approach leaves the consumer vulnerable.

• Race conditions between check and wait
• Atomicity of compound operations
• Semaphore semantics and signalling guarantees
• Mutex-semaphore interaction in producer–consumer designs