1 總程序架構(gòu)的重要性

很多人尤其是初學(xué)者在寫代碼的時(shí)候往往都是想一點(diǎn)寫一點(diǎn)，最開(kāi)始沒(méi)有一個(gè)整體的規(guī)劃，導(dǎo)致后面代碼越寫越亂，bug不斷。

最終代碼跑起來(lái)看似沒(méi)有問(wèn)題(有可能也真的沒(méi)有問(wèn)題)，但是要加一個(gè)功能的時(shí)候會(huì)浪費(fèi)大量的時(shí)間，甚至導(dǎo)致整個(gè)代碼的崩潰。

所以，在一個(gè)項(xiàng)目開(kāi)始的時(shí)候多花一些時(shí)間在代碼的架構(gòu)設(shè)計(jì)上是十分有必要的。代碼架構(gòu)確定好了之后你會(huì)發(fā)現(xiàn)敲代碼的時(shí)候會(huì)特別快，并且在后期調(diào)試的時(shí)候也不會(huì)像無(wú)頭蒼蠅一樣胡亂找問(wèn)題。當(dāng)然，調(diào)試也是一門技術(shù)。

在學(xué)習(xí)實(shí)時(shí)操作系統(tǒng)的過(guò)程中，發(fā)現(xiàn)實(shí)時(shí)操作系統(tǒng)框架與個(gè)人的業(yè)務(wù)代碼之間的耦合性就非常低，都是只需要將業(yè)務(wù)代碼通過(guò)一定的接口函數(shù)注冊(cè)好后就交給操作系統(tǒng)托管了，十分方便。

但是操作系統(tǒng)的調(diào)度過(guò)于復(fù)雜，這里就使用操作系統(tǒng)的思維方式來(lái)重構(gòu)這個(gè)時(shí)間片輪詢框架。實(shí)現(xiàn)該框架的完全解耦，用戶只需要包含頭文件，并且在使用過(guò)程中不需要改動(dòng)已經(jīng)寫好的庫(kù)文件。

2 參考代碼

首先來(lái)個(gè)demo，該demo是使用電腦開(kāi)兩個(gè)線程：一個(gè)線程模擬單片機(jī)的定時(shí)器中斷產(chǎn)生時(shí)間片輪詢個(gè)時(shí)鐘，另一個(gè)線程則模擬主函數(shù)中一直運(yùn)行的時(shí)間片輪詢調(diào)度程序。

  #include 
  #include 
  #include 
  #include "timeslice.h"
  
  // 創(chuàng)建5個(gè)任務(wù)對(duì)象
  TimesilceTaskObj task_1, task_2, task_3, task_4, task_5;
  
  // 具體的任務(wù)函數(shù)
 void task1_hdl()
{
     printf(">> task 1 is running ...
");
 }
 
 void task2_hdl()
{
     printf(">> task 2 is running ...
");
 }
 
 void task3_hdl()
{
     printf(">> task 3 is running ...
");
 }
 
 void task4_hdl()
{
     printf(">> task 4 is running ...
");
 }
 
 void task5_hdl()
{
     printf(">> task 5 is running ...
");
 }
 
 // 初始化任務(wù)對(duì)象，并且將任務(wù)添加到時(shí)間片輪詢調(diào)度中
 void task_init()
{
     timeslice_task_init(&task_1, task1_hdl, 1, 10);
     timeslice_task_init(&task_2, task2_hdl, 2, 20);
     timeslice_task_init(&task_3, task3_hdl, 3, 30);
     timeslice_task_init(&task_4, task4_hdl, 4, 40);
     timeslice_task_init(&task_5, task5_hdl, 5, 50);
     timeslice_task_add(&task_1);
     timeslice_task_add(&task_2);
     timeslice_task_add(&task_3);
     timeslice_task_add(&task_4);
     timeslice_task_add(&task_5);
 }
 
 
 // 開(kāi)兩個(gè)線程模擬在單片機(jī)上的運(yùn)行過(guò)程
 void timeslice_exec_thread()
{
     while (true)
     {
         timeslice_exec();
     }
 }
 
 void timeslice_tick_thread()
{
     while (true)
     {
         timeslice_tick();
         Sleep(10);
     }
 }
 
 int main()
{
     task_init();
 
     printf(">> task num: %d
", timeslice_get_task_num());
     printf(">> task len: %d
", timeslice_get_task_timeslice_len(&task_3));
 
     timeslice_task_del(&task_2);
     printf(">> delet task 2
");
     printf(">> task 2 is exist: %d
", timeslice_task_isexist(&task_2));
 
     printf(">> task num: %d
", timeslice_get_task_num());
 
     timeslice_task_del(&task_5);
     printf(">> delet task 5
");
 
     printf(">> task num: %d
", timeslice_get_task_num());
 
     printf(">> task 3 is exist: %d
", timeslice_task_isexist(&task_3));
     timeslice_task_add(&task_2);
     printf(">> add task 2
");
     printf(">> task 2 is exist: %d
", timeslice_task_isexist(&task_2));
 
     timeslice_task_add(&task_5);
     printf(">> add task 5
");
 
     printf(">> task num: %d
", timeslice_get_task_num());
 
     printf("

========timeslice running===========
");
 
     std::thread thread_1(timeslice_exec_thread);
    std::thread thread_2(timeslice_tick_thread);


    thread_1.join();
    thread_2.join();




    return 0;
}

運(yùn)行結(jié)果如下：

由以上例子可見(jiàn)，這個(gè)框架使用十分方便，甚至可以完全不知道其原理，僅僅通過(guò)幾個(gè)簡(jiǎn)單的接口就可以迅速創(chuàng)建任務(wù)并加入到時(shí)間片輪詢的框架中，十分好用。

3時(shí)間片輪詢架構(gòu)
其實(shí)該部分主要使用了面向?qū)ο蟮乃季S，使用結(jié)構(gòu)體作為對(duì)象，并使用結(jié)構(gòu)體指針作為參數(shù)傳遞，這樣作可以節(jié)省資源，并且有著極高的運(yùn)行效率。

其中最難的部分是侵入式鏈表的使用，這種鏈表在一些操作系統(tǒng)內(nèi)核中使用十分廣泛，這里是參考RT-Thread實(shí)時(shí)操作系統(tǒng)中的侵入式鏈表實(shí)現(xiàn)。

h文件：

 #ifndef _TIMESLICE_H
 #define _TIMESLICE_H
 
 #include "./list.h"
 
 typedef enum {
     TASK_STOP,
     TASK_RUN
 } IsTaskRun;


typedef struct timesilce
{
    unsigned int id;
    void (*task_hdl)(void);
    IsTaskRun is_run;
    unsigned int timer;
    unsigned int timeslice_len;
    ListObj timeslice_task_list;
} TimesilceTaskObj;


void timeslice_exec(void);
void timeslice_tick(void);
void timeslice_task_init(TimesilceTaskObj* obj, void (*task_hdl)(void), unsigned int id, unsigned int timeslice_len);
void timeslice_task_add(TimesilceTaskObj* obj);
void timeslice_task_del(TimesilceTaskObj* obj);
unsigned int timeslice_get_task_timeslice_len(TimesilceTaskObj* obj);
unsigned int timeslice_get_task_num(void);
unsigned char timeslice_task_isexist(TimesilceTaskObj* obj);


#endif

.c文件：

 #include "./timeslice.h"
 
 static LIST_HEAD(timeslice_task_list);
 
 void timeslice_exec()
{
     ListObj* node;
     TimesilceTaskObj* task;
 
    list_for_each(node, ×lice_task_list)
    {


        task = list_entry(node, TimesilceTaskObj, timeslice_task_list);
        if (task->is_run == TASK_RUN)
        {
            task->task_hdl();
            task->is_run = TASK_STOP;
        }
    }
}


void timeslice_tick()
{
    ListObj* node;
    TimesilceTaskObj* task;


    list_for_each(node, ×lice_task_list)
    {
        task = list_entry(node, TimesilceTaskObj, timeslice_task_list);
        if (task->timer != 0)
        {
            task->timer--;
            if (task->timer == 0)
            {
                task->is_run = TASK_RUN;
                task->timer = task->timeslice_len;
            }
        }
    }
}


unsigned int timeslice_get_task_num()
{
    return list_len(×lice_task_list);
}


void timeslice_task_init(TimesilceTaskObj* obj, void (*task_hdl)(void), unsigned int id, unsigned int timeslice_len)
{
    obj->id = id;
    obj->is_run = TASK_STOP;
    obj->task_hdl = task_hdl;
    obj->timer = timeslice_len;
    obj->timeslice_len = timeslice_len;
}


void timeslice_task_add(TimesilceTaskObj* obj)
{
    list_insert_before(×lice_task_list, &obj->timeslice_task_list);
}


void timeslice_task_del(TimesilceTaskObj* obj)
{
    if (timeslice_task_isexist(obj))
        list_remove(&obj->timeslice_task_list);
    else
        return;
}




unsigned char timeslice_task_isexist(TimesilceTaskObj* obj)
{
    unsigned char isexist = 0;
    ListObj* node;
    TimesilceTaskObj* task;


    list_for_each(node, ×lice_task_list)
    {
        task = list_entry(node, TimesilceTaskObj, timeslice_task_list);
        if (obj->id == task->id)
            isexist = 1;
    }


    return isexist;
}


unsigned int timeslice_get_task_timeslice_len(TimesilceTaskObj* obj)
{
    return obj->timeslice_len;
}

4底層侵入式雙向鏈表

該鏈表是linux內(nèi)核中使用十分廣泛，也十分經(jīng)典，其原理具體可以參考文章。 .h文件：

 #ifndef _LIST_H
 #define _LIST_H
 
 #define offset_of(type, member)             (unsigned long) &((type*)0)->member
 #define container_of(ptr, type, member)     ((type *)((char *)(ptr) - offset_of(type, member)))
 
 typedef struct list_structure
 {
     struct list_structure* next;
    struct list_structure* prev;
} ListObj;


#define LIST_HEAD_INIT(name)    {&(name), &(name)}
#define LIST_HEAD(name)         ListObj name = LIST_HEAD_INIT(name)


void list_init(ListObj* list);
void list_insert_after(ListObj* list, ListObj* node);
void list_insert_before(ListObj* list, ListObj* node);
void list_remove(ListObj* node);
int list_isempty(const ListObj* list);
unsigned int list_len(const ListObj* list);


#define list_entry(node, type, member) 
    container_of(node, type, member)


#define list_for_each(pos, head) 
    for (pos = (head)->next; pos != (head); pos = pos->next)


#define list_for_each_safe(pos, n, head) 
  for (pos = (head)->next, n = pos->next; pos != (head); 
    pos = n, n = pos->next)


#endif

.c文件：

 #include "list.h"
 
 void list_init(ListObj* list)
 {
     list->next = list->prev = list;
 }
 
 void list_insert_after(ListObj* list, ListObj* node)
 {
    list->next->prev = node;
    node->next = list->next;


    list->next = node;
    node->prev = list;
}


void list_insert_before(ListObj* list, ListObj* node)
{
    list->prev->next = node;
    node->prev = list->prev;


    list->prev = node;
    node->next = list;
}


void list_remove(ListObj* node)
{
    node->next->prev = node->prev;
    node->prev->next = node->next;


    node->next = node->prev = node;
}


int list_isempty(const ListObj* list)
{
    return list->next == list;
}


unsigned int list_len(const ListObj* list)
{
    unsigned int len = 0;
    const ListObj* p = list;
    while (p->next != list)
    {
        p = p->next;
        len++;
    }


    return len;
}

到此，一個(gè)全新的，完全解耦的，十分方便易用時(shí)間片輪詢框架完成。

審核編輯：湯梓紅