barbershop2.c

操作系统实验

/* The sleeping barber problem */

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/shm.h>

#define CUSTOMERS 0
#define BARBERS 1
#define MUTEX 2

#define CHAIRS 5

void up(int sem_id,int sem_num,struct sembuf *semaphore) {
  semaphore->sem_num=sem_num;
  semaphore->sem_op=1;
  semaphore->sem_flg=0;
  semop(sem_id,semaphore,1);
}

void down(int sem_id,int sem_num,struct sembuf *semaphore) {
  semaphore->sem_num=sem_num;
  semaphore->sem_op=-1;
  semaphore->sem_flg=0;
  semop(sem_id,semaphore,1);
}

void initSem(int sem_id,int sem_num,int val) {
  union semnum {
    int val;
    struct semid_ds *buf;
    unsigned short *array;
  }argument;
  argument.val=val;
  semctl(sem_id,sem_num,SETVAL,argument);
}

int main() {
  int sem_key=1111,shm_key=2222;
  int sem_id,shm_id;
  int *waiting;
  struct sembuf semaphore;
  int count=1;
  shm_id=shmget(shm_key,sizeof(int),IPC_CREAT|0666);
  sem_id=semget(sem_key,3,IPC_CREAT|0666);
  waiting=shmat(shm_id,NULL,0);
  *waiting=0;
  initSem(sem_id,CUSTOMERS,0);
  initSem(sem_id,BARBERS,0);
  initSem(sem_id,MUTEX,1);
  printf("There are %d chairs.\n",CHAIRS);
  if(fork()) {
    /* The barber part. */
    while(1) {
      down(sem_id,CUSTOMERS,&semaphore);
      down(sem_id,MUTEX,&semaphore);
      *waiting=*waiting-1;
      up(sem_id,BARBERS,&semaphore);
      up(sem_id,MUTEX,&semaphore);
      printf("The barber is now cutting hair.\n");	
      sleep(6);			/* Slowly cut the hair */
    }
  }
  else {
    /* The customer part. */
    while(1) {
      sleep(1);			/* Customers come in fast */
      down(sem_id,MUTEX,&semaphore);
      if(*waiting < CHAIRS) {
	printf("Customer %d is seated.\n",count++);
	*waiting=*waiting+1;
	up(sem_id,CUSTOMERS,&semaphore);
	up(sem_id,MUTEX,&semaphore);

      }
      else {
	printf("Customer %d left the shop.\n",count++);
	up(sem_id,MUTEX,&semaphore);
      }
    }
  }
}