bus.c

设公共汽车上

#include<sys/types.h>
#include<unistd.h>
#include<stdio.h>
#include<linux/sem.h>
#include<linux/shm.h>
#include<pthread.h>

void P(int semid,int index)
{ struct sembuf sem;
  sem.sem_num=index;
  sem.sem_op=-1;
  sem.sem_flg=0;
  semop(semid,&sem,1);
  return;
}
void V(int semid,int index)
{ struct sembuf sem;
  sem.sem_num=index;
  sem.sem_op=1;
  sem.sem_flg=0;
  semop(semid,&sem,1);
  return;
}
int semid;
driver()
{ int i=0;
  while(i<2)
  { P(semid,0);
    printf("start the bus\n");
    sleep(3);
    printf("running normally\n");
    sleep(3);
    printf("then stop the bus\n");
    sleep(3);
    V(semid,1);
    i++;
  }
}
seller()
{ int j=0;
  while(j<2)
  { printf("men get on\n");
    sleep(3);
    printf("close the door\n");
    sleep(3);
    V(semid,0);
    printf("sell the tickets\n");
    sleep(3);
    P(semid,1);
    printf("open the door\n");
    sleep(3);
    printf("men get off\n");
    sleep(3);
    j++;
  }
}

main()
{ union semun semopts;
  int res,i,status;
  pid_t d,s;
  pid_t t1,t2;
  
  semid = semget(300,2,IPC_CREAT|0666);
  if(semid<0)
  { printf("error");
    return;
  }
  semopts.val=0;
  res=semctl(semid,0,SETVAL,semopts);
  if(res<0)  return;
  semopts.val=0;
  res=semctl(semid,0,SETVAL,semopts);
  if(res<0)  return;
  d=fork();
  if(d==0)
  driver();
   { s=fork();
     if(s==0)
     seller();
     else
      { t1=waitpid(d,&status,0);
        t2=waitpid(s,&status,0);
        semctl(semid,0,IPC_RMID,0);
        semctl(semid,1,IPC_RMID,0);
      }
   }
}

输出结果：
men get on
close the door
sell the tickets
start the bus
running normally
then stop the bus
open the door
men get off
men get on
close the door
sell the tickets
start the bus
running normally
then stop the bus
open the door
men get off