使用共享内存作为进程互斥锁的代码

pthread_mutex_t* init_shm_mutex(const key_t mutex_key)
{
    int shmid = shmget(mutex_key, sizeof(pthread_mutex_t), 0666 | IPC_CREAT);
    if (shmid == -1)
    {
        return NULL;
    }
    void* shm_addr = shmat(shmid, NULL, 0);
    if (shm_addr == (void *) -1)
    {
        return NULL;
    }
    pthread_mutexattr_t mutex_attr;
    pthread_mutexattr_init(      &mutex_attr);
    pthread_mutexattr_setpshared(&mutex_attr, PTHREAD_PROCESS_SHARED);
    pthread_mutexattr_setrobust( &mutex_attr, PTHREAD_MUTEX_ROBUST);
    pthread_mutex_t* shm_mutex = (pthread_mutex_t *)shm_addr;
    pthread_mutex_init(shm_mutex,&mutex_attr);
    return shm_mutex;
}  

#define PROCESS_MUTEX_KEY 20181217
//process
pthread_mutex_t* g_ProcessMutex = NULL
void write_data_to_shared_memory(const uchar* data)
{
    if (g_ProcessMutex == NULL)
    {
        g_ProcessMutex = init_shm_mutex(PROCESS_MUTEX_KEY);
    }
    pthread_mutex_lock(g_ProcessMutex);
    //do something
    pthread_mutex_unlock(g_ProcessMutex);
}