1.生产者消费者问题
      一个消费者一个生产者时
      semaphore full , empty;
      empty = n , full = 0;
      int in = 0 , out = 0; 
      cobegin 
      process producer () {                       process consumer () { 
               while(true){                                       while(true){
                     produce();                                          P(full);
                     P(empty);                                           out = (out+1)%n;
                     in = (in+1)%n;                                    V(empty);
                     V(full);                                                comsumer();
               }                                                           }
      }                                                       }
      coend      

      而一组消费者，一组生产者时，不仅生产者与消费者之间要同步，而且各个生产者之间、各个消费者之间还必须互斥地访问缓冲区。
      所以要多一个互斥的信号mutex
      semaphore full , empty , mutex;
      empty = n , full = 0 , mutex = 1;
       int in = 0 , out = 0; 
      cobegin 
      process producer () {                       process consumer () { 
               while(true){                                       while(true){
                     produce();                                          P(full);
                     P(empty);                                           P(mutex) ;  
                     P(mutex) ;                                          out = (out+1)%n;
                     in = (in+1)%n;                                    V(mutex) ; 
                     V(mutex) ;                                          V(empty);
                     V(full);                                                comsumer();
               }                                                           }
      }                                                       }
      coend