RT_Thread内核机制学习（二）

对于RTT来说，每个线程创建时都自带一个定时器

rt_err_t rt_thread_sleep(rt_tick_t tick)
{
    register rt_base_t temp;
    struct rt_thread *thread;

    /* set to current thread */
    thread = rt_thread_self();
    RT_ASSERT(thread != RT_NULL);
    RT_ASSERT(rt_object_get_type((rt_object_t)thread) == RT_Object_Class_Thread);

    /* disable interrupt */
    temp = rt_hw_interrupt_disable();

    /* suspend thread */
    rt_thread_suspend(thread); //从就绪链表移除

    /* reset the timeout of thread timer and start it */
    rt_timer_control(&(thread->thread_timer), RT_TIMER_CTRL_SET_TIME, &tick); //设置定时器定时时间
    rt_timer_start(&(thread->thread_timer)); //开启定时器

    /* enable interrupt */
    rt_hw_interrupt_enable(temp);

    rt_schedule();

    /* clear error number of this thread to RT_EOK */
    if (thread->error == -RT_ETIMEOUT)
        thread->error = RT_EOK;

    return RT_EOK;
}

延时过程：

1. 将线程从就绪链表移除。
2. 设置/启动定时器
3. 每个Tick判断，定时器是否超时，调用超时函数。

/**
 * This function is the timeout function for thread, normally which is invoked
 * when thread is timeout to wait some resource.
 *
 * @param parameter the parameter of thread timeout function
 */
void rt_thread_timeout(void *parameter)
{
    struct rt_thread *thread;

    thread = (struct rt_thread *)parameter;

    /* thread check */
    RT_ASSERT(thread != RT_NULL);
    RT_ASSERT((thread->stat & RT_THREAD_STAT_MASK) == RT_THREAD_SUSPEND);
    RT_ASSERT(rt_object_get_type((rt_object_t)thread) == RT_Object_Class_Thread);

    /* set error number */
    thread->error = -RT_ETIMEOUT; //表示被唤醒原因是：超时

    /* remove from suspend list */
    rt_list_remove(&(thread->tlist)); //可能因为等待队列等原因而挂起，先移除

    /* insert to schedule ready list */
    rt_schedule_insert_thread(thread);

    /* do schedule */
    rt_schedule();
}
RTM_EXPORT(rt_thread_timeout);

超时函数：

1. 将线程放入就绪链表尾部
2. 发起调度

void rt_schedule_remove_thread(struct rt_thread *thread)
{
    register rt_base_t level;

    RT_ASSERT(thread != RT_NULL);

    /* disable interrupt */
    level = rt_hw_interrupt_disable();

    RT_DEBUG_LOG(RT_DEBUG_SCHEDULER, ("remove thread[%.*s], the priority: %d\n",
                                      RT_NAME_MAX, thread->name,
                                      thread->current_priority));

    /* remove thread from ready list */
    rt_list_remove(&(thread->tlist));
    if (rt_list_isempty(&(rt_thread_priority_table[thread->current_priority])))
    {
#if RT_THREAD_PRIORITY_MAX > 32
        rt_thread_ready_table[thread->number] &= ~thread->high_mask;
        if (rt_thread_ready_table[thread->number] == 0)
        {
            rt_thread_ready_priority_group &= ~thread->number_mask;
        }
#else
        rt_thread_ready_priority_group &= ~thread->number_mask;
#endif
    }

    /* enable interrupt */
    rt_hw_interrupt_enable(level);
}

将线程从就绪链表中移除，首先从链表中删除，再判断优先级对应的链表是否空了？

可以快速查找到哪一位是1。

每次Tick中断还需要检查定时器

/**
 * This function will check timer list, if a timeout event happens, the
 * corresponding timeout function will be invoked.
 *
 * @note this function shall be invoked in operating system timer interrupt.
 */
void rt_timer_check(void)
{
    struct rt_timer *t;
    rt_tick_t current_tick;
    register rt_base_t level;

    RT_DEBUG_LOG(RT_DEBUG_TIMER, ("timer check enter\n"));

    current_tick = rt_tick_get();

    /* disable interrupt */
    level = rt_hw_interrupt_disable();

    while (!rt_list_isempty(&rt_timer_list[RT_TIMER_SKIP_LIST_LEVEL - 1]))
    {
        t = rt_list_entry(rt_timer_list[RT_TIMER_SKIP_LIST_LEVEL - 1].next,
                          struct rt_timer, row[RT_TIMER_SKIP_LIST_LEVEL - 1]); //从链表中取出定时器

        /*
         * It supposes that the new tick shall less than the half duration of
         * tick max.
         */
        if ((current_tick - t->timeout_tick) < RT_TICK_MAX / 2) //判断时间是否到了
        {
            RT_OBJECT_HOOK_CALL(rt_timer_enter_hook, (t));

            /* remove timer from timer list firstly */
            _rt_timer_remove(t);

            /* call timeout function */
            t->timeout_func(t->parameter);

            /* re-get tick */
            current_tick = rt_tick_get();

            RT_OBJECT_HOOK_CALL(rt_timer_exit_hook, (t));
            RT_DEBUG_LOG(RT_DEBUG_TIMER, ("current tick: %d\n", current_tick));

            if ((t->parent.flag & RT_TIMER_FLAG_PERIODIC) &&
                (t->parent.flag & RT_TIMER_FLAG_ACTIVATED))
            {
                /* start it */
                t->parent.flag &= ~RT_TIMER_FLAG_ACTIVATED;
                rt_timer_start(t);
            }
            else
            {
                /* stop timer */
                t->parent.flag &= ~RT_TIMER_FLAG_ACTIVATED;
            }
        }
        else
            break;
    }

    /* enable interrupt */
    rt_hw_interrupt_enable(level);

    RT_DEBUG_LOG(RT_DEBUG_TIMER, ("timer check leave\n"));
}

依次判断定时器时间是否到了，到了的话就调用定时器超时函数。

定时器启动后放到链表中。

Tick中断检查定时器时，也是从链表中取出判断。