# 2021-04-06 `ilkclord`

## 測驗 `1`
## 測驗 `2`

static void dequeue(queue_t *q, int *fd)
{
    node_t *old_head;
    pthread_mutex_lock(q->head_lock);
    /* Wait until signaled that queue is non_empty.
     * Need while loop in case a new thread manages to steal the queue
     * element after the waiting thread is signaled, but before it can
     * re-acquire head_lock.
     */
    pthread_cond_wait(&q->non_empty ,&q->head_lock); // prevent empty dequeue
    
    /*start poping*/
    old_head = q->tail ;
    q->tail->pre->next = NULL ;
    fd = old_head->fd 
    pthread_mutex_unlock(q->head_lock);
    free(old_head);
}

1 . greeter 控管連接伺服器的連接 ,並控制單位時間內的連線數
worker_routine 將資料傳輸倒伺服器並寫入檔案

2 . 利用 pthread_cond_wait(,) 和 pthread_cond_signal( , )的組合確保dequeue不會在空元素的狀況下操作 .

## 測驗 `3`

### Struct of Ring Buffer

typedef struct {
    struct {                          /** Ring producer status. */
        uint32_t watermark;           /**< Maximum items before EDQUOT. */
        uint32_t size;                /**< Size of ring. */
        uint32_t mask;                /**< Mask (size - 1) of ring. */
        volatile uint32_t head, tail; /**< Producer head and tail. */
    } prod __attribute__((__aligned__(CACHE_LINE_SIZE)));

    struct {                          /** Ring consumer status. */
        uint32_t size;                /**< Size of the ring. */
        uint32_t mask;                /**< Mask (size - 1) of ring. */
        volatile uint32_t head, tail; /**< Consumer head and tail. */
    } cons __attribute__((__aligned__(CACHE_LINE_SIZE)));

    void *ring[] __attribute__((__aligned__(CACHE_LINE_SIZE)));
} ringbuf_t;