This problem was from chapter 5 (Concurrency: Mutual Exclusion and Synchronization) at Operating Systems: Internals and Design Principles (7th Edition) by Williang Stallings.

5.22 The following pseudocode is a correct implementation of the producer/consumer problem with a bounded buffer: item [3] buffer; // initially empty semaphore empty; // initialized to +3 semaphore full; // initialized to 0 binary semaphore mutex; // initialized to 1 void producer () void consumer () while (true) f while (true) f item = produce() ; wait (empty) /wait (mutex) append (item) signal (mutex); signal (full); wait (full); /wait (mutex) item take() ; signal (mutex); signal (empty) consume (item) c1: pl: c2: p2: c3: 3: 5.22 The following pseudocode is a correct implementation of the producer/consumer problem with a bounded buffer: item [3] buffer; // initially empty semaphore empty; // initialized to +3 semaphore full; // initialized to 0 binary semaphore mutex; // initialized to 1 void producer () void consumer () while (true) f while (true) f item = produce() ; wait (empty) /wait (mutex) append (item) signal (mutex); signal (full); wait (full); /wait (mutex) item take() ; signal (mutex); signal (empty) consume (item) c1: pl: c2: p2: c3: 3