举例来说，这边从某处读取数据到缓冲区，那边将缓冲区数据进行处理。

pthread_cond_t  data_cond;
pthread_mutex_t data_mutex;

#define DATA_SIZE 4096
int   data_flag = 0;
int   data_size = 0;
char  data_buffer[DATA_SIZE];


void read_to_databuffer()
{
    //init fd
    while (1)
    {
        //已读取的数据还没有被处理，等待。或者用另外的条件锁？
        while (data_flag == 1)
        {
            usleep(1000);
            continue;
        }

        pthread_mutex_lock(&data_mutex);

        data_size = read(fd, data_buffer, DATA_SIZE);

        //已经没有数据，中断。
        if (data_size <= 0)
        {
            pthread_mutex_unlock(&data_mutex);
            break;
        }

        //设置数据标志，发出通知
        data_flag = 1;
        pthread_cond_signal( &data_cond);
        pthread_mutex_unlock(&data_mutex);
    }

    //release
}

void databuffer_to_process()
{
    while (1)
    {
        pthread_mutex_lock(&data_mutex);

        //没有数据，进入条件锁
        if (data_flag == 0)
        {
            //有人问，两边都先lock……其实这里有一个先释放锁的动作。
            pthread_cond_wait(&data_cond, &data_mutex);
        }

        //处理数据

        //结束处理
        data_flag = 0;
        pthread_mutex_unlock(&data_mutex);
    }

    //release
}

void start()
{
    pthread_t tid1, tid2;

    pthread_mutex_init(&data_mutex, NULL);
    pthread_cond_init( &data_cond,  NULL);

    pthread_create(&tid1, NULL, read_to_databuffer,    NULL);
    pthread_create(&tid2, NULL, databuffer_to_process, NULL);
}