Function rt_data_queue_pop

components/drivers/ipc/dataqueue.c:210–317

* @brief This function will pop data from the data queue. If the data queue is empty,the thread * will suspend for the specified amount of time. * * @note When the number of data in the data queue is less than lwm(low water mark), will * wake up the thread waiting for write data. * * @param queue is a pointer to the data queue object. * * @param data_ptr is

 *           When the return value is -RT_ETIMEOUT, it means the specified time out.
 */
rt_err_t rt_data_queue_pop(struct rt_data_queue *queue,
                           const void **data_ptr,
                           rt_size_t *size,
                           rt_int32_t timeout)
{
    rt_base_t level;
    rt_thread_t thread;
    rt_err_t    result;

    RT_ASSERT(queue != RT_NULL);
    RT_ASSERT(queue->magic == DATAQUEUE_MAGIC);
    RT_ASSERT(data_ptr != RT_NULL);
    RT_ASSERT(size != RT_NULL);

    /* current context checking */
    RT_DEBUG_SCHEDULER_AVAILABLE(timeout != 0);

    result = RT_EOK;
    thread = rt_thread_self();

    level = rt_spin_lock_irqsave(&(queue->spinlock));
    while (queue->is_empty)
    {
        /* queue is empty */
        if (timeout == 0)
        {
            result = -RT_ETIMEOUT;
            goto __exit;
        }

        /* reset thread error number */
        thread->error = RT_EOK;

        /* suspend thread on the pop list */
        result = rt_thread_suspend_to_list(thread, &queue->suspended_pop_list,
                                           RT_IPC_FLAG_FIFO, RT_UNINTERRUPTIBLE);
        if (result == RT_EOK)
        {
            /* start timer */
            if (timeout > 0)
            {
                rt_tick_t timeout_tick = timeout;
                /* reset the timeout of thread timer and start it */
                rt_timer_control(&(thread->thread_timer),
                                RT_TIMER_CTRL_SET_TIME,
                                &timeout_tick);
                rt_timer_start(&(thread->thread_timer));
            }

            /* enable interrupt */
            rt_spin_unlock_irqrestore(&(queue->spinlock), level);

            /* do schedule */
            rt_schedule();

            /* thread is waked up */
            level  = rt_spin_lock_irqsave(&(queue->spinlock));
            result = thread->error;