进程间通信问题： 银行有n个柜员，顾客进入银行先取一个号码，然后等着叫号。柜员空闲下来就叫号。 用P、V操作实现顾客和柜员的同步。-Interprocess communication problems: Bank n a teller, the customer enters the bank to take a number, and then waiting for the called number. Teller idle down called. P, V opera