信号量
创建信号量
int sem_creat(key_t key){
int semid = 0;
semid = semget(key,1,0666| IPC_CREAT | IPC_EXCL);
if(semid == -1){
perror("semget");
if(errno == EEXIST){
printf("检测到信号量集已经存在\n");
return 0;
}
}
return semid;
}
打开信号量
int sem_open(key_t key){
int semid = 0;
semid =semget(key,1,0666);
if(semid == -1){
perror("semget");
return -1;
}
return semid;
}
设置信号量的值(资源的个数)
union semun {
int val; /* Value for SETVAL */
struct semid_ds *buf; /* Buffer for IPC_STAT, IPC_SET */
unsigned short *array; /* Array for GETALL, SETALL */
struct seminfo *__buf; /* Buffer for IPC_INFO
(Linux-specific) */
};
int sem_setval(int semid , int val){
int ret =0;
union semun su;
su.val = val;
ret = semctl(semid,0,SETVAL,su);
return ret;
}
获取信号量的值
int sem_getval(int semid){
int ret =0;
union semun su;
ret = semctl(semid,0,GETVAL,su);
printf("val:%d\n",su.val);
return ret;
}
信号量PV操作
int sem_p(int semid){
struct sembuf buf={0,-1,0};
int ret =0;
ret = semop(semid,&buf,1);
return ret;
}
int sem_v(int semid){
struct sembuf buf={0,1,0};
int ret =0;
ret = semop(semid,&buf,1);
return ret;
}
sembuf结构体
{
unsigned short int sem_num; /* semaphore number */
short int sem_op; /* semaphore operation */
short int sem_flg; /* operation flag */
};
struct sembuf buf={0,1,0};
信号量的编好, pv操作 P-1 V+1 ,操作0阻塞
