说明：  理发店里有一位理发师，一把理发椅和 N 把供等候理发的顾客坐的椅子 如果没有顾客,则理发师便在理发椅上睡觉。当一个顾客到来时，他必须先唤醒理发师。如果顾客到来时理发师正在理发，则如果有空椅子，可坐下来等；否 则离开。操作系统信号量控制进程同步。
(Barbershop, a hairdresser, a barber chair and N customer sat waiting Barber chair if no customers, the barber would sleep in the barber chair. When a customer comes, he must wake up to the barber. If the customer comes barber is Barber, if the empty chair, sit down and so on otherwise leave. The semaphore control of the operating system process synchronization.)