经典胡睡觉理发师问题，利用信号量实现进程同步-Classic Hu sleeping barber problem using semaphores to achieve process synchronization

其实际为生产者消费者问题，理发师忙时，顾客等待，理发师闲时，给顾客理发。(In fact, it is the problem of producer consumers, when the barber is busy, the customer is waiting, and the barber is free to make a haircut for the customer.)