计数信号量相对互斥锁 的优点：

1，不会出现反复无效解锁，信号量就代表实际的产品空间数量，而不是不管三七二十一先上锁再判断；
2，提高了效率，只要一方一提供资源，另一方马上就可以解锁，响应度更高

1 有两个信号量，要用setall，不是setval

        int ret =semctl(semid,0,SETALL,a);//xx1

2 要while循环不然走一轮就结束了；

另外，还有个容易错的，是信号量的数值是unsigned short不是int！！！

 unsigned short a[2]={10,0};

3 被坑最多的，就是信号量结构体写错。要么写重复了，要么就是格式不对，特别是写重了，用接口判断不出bug

                sopv.sem_num= 0;//xx3  not sopp.sem_num
                sopv.sem_op = 1;//xx3 not sopv.op   not sopv.sem_num

4 sleep1，2，不能反了，不然打印的结果会很懵逼，因为产品多，那就消费者多一点

```
#include <func.h>

int main(){
        int semid=semget(10,2,0600|IPC_CREAT);
        ERROR_CHECK(semid,-1,"semget");
        unsigned short a[2]={10,0};// 0 for food 1 for space
        int ret =semctl(semid,0,SETALL,a);//xx1
        ERROR_CHECK(ret,-1,"semctl");
        if(!fork()){//cus
                struct sembuf sopp,sopv;
                sopp.sem_num = 0;
                sopp.sem_op = -1;
                sopp.sem_flg = SEM_UNDO;
                sopv.sem_num = 1;
                sopv.sem_op = 1;
                sopv.sem_flg = SEM_UNDO;
                while(1){//xx2
                        printf("i am customer ,food :%d , space : %d \n",semctl(semid,0,GETVAL),semctl(semid,1,GETVAL));
                        ret =   semop(semid,&sopp,1);
                        ERROR_CHECK(ret,-1,"semop");
                        printf("eatting..\n");
                        ret =   semop(semid,&sopv,1);
                        ERROR_CHECK(ret,-1,"semop");
                        printf("i am customer ,food :%d , space : %d \n",semctl(semid,0,GETVAL),semctl(semid,1,GETVAL));
                        sleep(1);//xx4
                }
        }else{
                struct sembuf sopp,sopv;
                sopp.sem_num = 1;
                sopp.sem_op = -1;
                sopp.sem_flg = SEM_UNDO;
                sopv.sem_num= 0;//xx3  not sopp.sem_num
                sopv.sem_op = 1;//xx3 not sopv.op   not sopv.sem_num
                sopv.sem_flg = SEM_UNDO;
                while(1){
                        printf("i am producer,food:%d,spce :%d\n",semctl(semid,0,GETVAL),semctl(semid,1,GETVAL));
                        ret =   semop(semid,&sopp,1);
                        ERROR_CHECK(ret,-1,"semop");
                        printf("i am producing .. \n");
                        ret =   semop(semid,&sopv,1);
                        ERROR_CHECK(ret,-1,"semop");
                        printf("i am producer ,food :%d , space : %d \n",semctl(semid,0,GETVAL),semctl(semid,1,GETVAL));
                        sleep(2);//xx4
                }
                wait(NULL);
        }
        return 0;
}
```