Welcome to your interview.
The question is on your right: Thread-Safe Circular Buffer in C. Take a moment with it first.
Talk your thinking through with me if you like - when you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes). Discussion and graded submissions share your five interviewer interactions, so spend them well.
How would you implement a circular buffer in C, and how would you ensure thread safety when reading and writing from it in a multi-threaded or interrupt-driven environment?