Netflix Coding: Bounded Blocking Queue Implementation

Question overview

You must implement a thread-safe, bounded blocking queue with a fixed positive integer capacity supplied at construction. You are expected to provide offer(item) that blocks when the queue is full until space is available, poll() that blocks when the queue is empty until an element arrives and returns the removed head, peek() that is non-blocking and returns the head or None if empty, and size() that returns the current count. Synchronization should use explicit wait/signal (condition variable) style primitives.

How the interview will typically flow

You’ll start by clarifying capacity semantics (capacity > 0), blocking/non-blocking behavior, and whether spurious wakeups/timeouts or shutdown signals are required. Then sketch the design: a mutex/lock, an internal buffer (e.g., array or deque), and two condition variables (not_full and not_empty). Next, discuss correctness under concurrency (use while loops around waits), then implement or pseudocode the key methods and discuss edge cases.

Skills and signals the interviewer is looking for

You should demonstrate knowledge of locks and condition variables, correct use of wait in a loop to handle spurious wakeups, how to maintain invariants (0 ≤ size ≤ capacity), safe notifications (notify vs notify_all), and capacity enforcement. Mentioning alternative implementations (semaphores, ReentrantLock+Condition) and trade-offs (fairness, performance) is a plus.

This question tests core concurrency, multithreading, and concurrent data structure design—use clear reasoning about liveness and safety as you code.