System V semaphore——demo

 

#include sys/types.h>
#include sys/ipc.h>
#include sys/sem.h>
union semun{
    int val;
    struct semid_ds *buf;
    unsigned short *array;
    struct seminfo *__buf;
};

// create the semaphore set,
// if key is IPC_PRIVATE, the semaphore is anonymous
int semaphore_create(key_t key, int number)
{
    return semget(key, number, IPC_CREAT|IPC_EXCL|0666);
}

// set all semaphores to val
int semaphore_setAll(int semid, int number, int val)
{
    int i;
    union semun initVal;
    unsigned short valList[number];
    for (i = 0; i < number; i++)
    {
        valList[i] = val;
    }
    initVal.array = &valList[0];
    return semctl(semid, 0, SETALL, initVal);
}

// get all semaphores to val
int semaphore_getAll(int semid, unsigned short** val)
{
    union semun ret;
    ret.array = *val;
    return semctl(semid, 0, GETALL, ret);
}

// set index-th semaphore to val
int semaphore_set(int semid, int index, int val)
{
    union semun un;
    un.val = val;
    return semctl(semid, index, SETVAL, un);
}

// get index-th semaphore to val
int semaphore_get(int semid, int index, int *val)
{
    union semun un;
    un.val = *val;
    return semctl(semid, index, GETVAL, un);
}

// delete the semaphore set
int semaphore_del(int semid)
{
    return semctl(semid, 0, IPC_RMID);
}

// v operation, here we just add one for example
int semaphore_v(int semid, int index)
{
    // add the semaphore
    struct sembuf operation;
    operation.sem_num = index;
    operation.sem_op = 1;
    operation.sem_flg = SEM_UNDO;
    return semop(semid, &operation, 1);
}

// p operation, here just del one for example
int semaphore_p(int semid, int index)
{
    struct sembuf operation;
    operation.sem_num = index;
    operation.sem_op = -1;
    operation.sem_flg = SEM_UNDO;
    struct timespec delay;
    delay.tv_sec = 2;
    delay.tv_nsec = 0;
    return semtimedop(semid, &operation, 1, &delay);
}