RT-thread内核之空闲线程

空闲线程初始化：
/**
 * @ingroup SystemInit
 *
 * This function will initialize idle thread, then start it.
 *
 * @note this function must be invoked when system init.
 */
void rt_thread_idle_init(void)
{
    /* initialize thread */
    rt_thread_init(&idle,
                   "tidle",
                   rt_thread_idle_entry,      //空闲线程入口函数
                   RT_NULL,                   //入口函数参数为空
                   &rt_thread_stack[0],       //空闲线程栈地址
                   sizeof(rt_thread_stack),   //栈大小，默认为128字节，若使用钩子函数或动态堆时为256字节，在idle.c中宏定义
                   RT_THREAD_PRIORITY_MAX - 1,//空闲线程优先级最低
                   32);                       //时间片为32个时钟节拍

    /* startup */
    rt_thread_startup(&idle);
}

空闲线程入口函数：
static void rt_thread_idle_entry(void *parameter)
{
    while (1)
    {
        #ifdef RT_USING_HOOK
        if (rt_thread_idle_hook != RT_NULL)
            rt_thread_idle_hook();//若使用钩子且钩子函数不为空，则执行钩子函数
        #endif

        rt_thread_idle_excute();  //空闲线程的真正执行函数
    }
}

空闲线程执行函数：
void rt_thread_idle_excute(void)
{
    /* Loop until there is no dead thread. So one call to rt_thread_idle_excute
     * will do all the cleanups. */
    while (_has_defunct_thread())        //检查僵尸线程链表中是否存在僵尸线程，以前的版本中用if (!rt_list_isempty(&rt_thread_defunct))来判断，这样每次只能清除一个僵尸线程
    {
        rt_base_t lock;
        rt_thread_t thread;
#ifdef RT_USING_MODULE
        rt_module_t module = RT_NULL;
#endif
        RT_DEBUG_NOT_IN_INTERRUPT;      //确保此函数不是在中断服务中，若RT_DEBUG_CONTEXT_CHECK is 1 in rtdebug.h,则该宏表示这个函数不能用于中断ISR中。通过检查rt_interrupt_nest中断嵌套计数器是否为0来判断

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

        /* re-check whether list is empty */
        if (_has_defunct_thread())      //再次判断rt_thread_defunct是否为空，若不为空
        {
            /* get defunct thread */
            thread = rt_list_entry(rt_thread_defunct.next,
                                   struct rt_thread,
                                   tlist);          //获取待回收的僵尸线程 
#ifdef RT_USING_MODULE
            /* get thread‘s parent module */
            module = (rt_module_t)thread->module_id;//得到模块ID

            /* if the thread is module‘s main thread */
            if (module != RT_NULL && module->module_thread == thread)
            {
                /* detach module‘s main thread */
                module->module_thread = RT_NULL;    //清空模块线程  
            }
#endif
            /* remove defunct thread */
            rt_list_remove(&(thread->tlist));       //重置线程链表节点为初始值，即节点next与prev均指向自身节点，即将线程从僵尸线程链表中移除  
            /* invoke thread cleanup */
            if (thread->cleanup != RT_NULL)
                thread->cleanup(thread);            //执行线程清理函数 

            /* if it‘s a system object, not delete it */
            if (rt_object_is_systemobject((rt_object_t)thread) == RT_TRUE)//若该僵尸线程内核对象为静态对象，则不删除该对程内核对象
            {
                /* enable interrupt */
                rt_hw_interrupt_enable(lock);

                return;
            }
        }
        else                        //若再次判断rt_thread_defunct僵尸线程链表为空
        {
            /* enable interrupt */
            rt_hw_interrupt_enable(lock);

            /* may the defunct thread list is removed by others, just return */
            return;
        }

        /* enable interrupt */
        rt_hw_interrupt_enable(lock);

#ifdef RT_USING_HEAP                //程序运行到这，说明上文处理的僵尸线程为动态创建的线程
#if defined(RT_USING_MODULE) && defined(RT_USING_SLAB)
        /* the thread belongs to an application module */
        if (thread->flags & RT_OBJECT_FLAG_MODULE)
            rt_module_free((rt_module_t)thread->module_id, thread->stack_addr);//释放模块主线程栈所占内存
        else
#endif
        /* release thread‘s stack */
        RT_KERNEL_FREE(thread->stack_addr);   //释放动态线程栈所占内存
        /* delete thread object */
        rt_object_delete((rt_object_t)thread);//删除动态线程内核对象，即从当前类型的内核对象链表中移除，同时释放内核对象所占空间（若使用了模块功能，还要释放模块ID所占空间）
#endif

#ifdef RT_USING_MODULE
        if (module != RT_NULL)
        {
            extern rt_err_t rt_module_destroy(rt_module_t module);

                      /* if sub thread list and main thread are all empty */  //若模块主线程为空，且子线程对象链表为空
            if ((module->module_thread == RT_NULL) &&
                rt_list_isempty(&module->module_object[RT_Object_Class_Thread].object_list))
            {
                module->nref --;
            }

            /* destroy module */
            if (module->nref == 0)
                rt_module_destroy(module);//销毁模块  
        }
#endif
    }
}