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今天小編給大家分享一下C語言如何實現經典多級時間輪定時器的相關知識點,內容詳細,邏輯清晰,相信大部分人都還太了解這方面的知識,所以分享這篇文章給大家參考一下,希望大家閱讀完這篇文章后有所收獲,下面我們一起來了解一下吧。
參考Linux源碼中的實現
上圖是5個時間輪級聯的效果圖。中間的大輪是工作輪,只有在它上的任務才會被執行;其他輪上的任務時間到后遷移到下一級輪上,他們最終都會遷移到工作輪上而被調度執行。
多級時間輪的原理也容易理解:就拿時鐘做說明,秒針轉動一圈分針轉動一格;分針轉動一圈時針轉動一格;同理時間輪也是如此:當低級輪轉動一圈時,高一級輪轉動一格,同時會將高一級輪上的任務重新分配到低級輪上。從而實現了多級輪級聯的效果。
多級時間輪應該至少包括以下內容:
每一級時間輪對象
輪子上指針的位置
關于輪子上指針的位置有一個比較巧妙的辦法:那就是位運算。比如定義一個無符號整型的數:
==通過獲取當前的系統時間便可以通過位操作轉換為時間輪上的時間,通過與實際時間輪上的時間作比較,從而確定時間輪要前進調度的時間,進而操作對應時間輪槽位對應的任務==。
為什么至少需要這兩個成員呢?
定義多級時間輪,首先需要明確的便是級聯的層數,也就是說需要確定有幾個時間輪。
輪子上指針位置,就是當前時間輪運行到的位置,它與真實時間的差便是后續時間輪需要調度執行,它們的差值是時間輪運作起來的驅動力。
多級時間輪對象的定義
//實現5級時間輪 范圍為0~ (2^8 * 2^6 * 2^6 * 2^6 *2^6)=2^32 struct tvec_base { unsigned long current_index; pthread_t thincrejiffies; pthread_t threadID; struct tvec_root tv1; /*第一個輪*/ struct tvec tv2; /*第二個輪*/ struct tvec tv3; /*第三個輪*/ struct tvec tv4; /*第四個輪*/ struct tvec tv5; /*第五個輪*/ };
我們知道每一個輪子實際上都是一個哈希表,上面我們只是實例化了五個輪子的對象,但是五個輪子具體包含什么,有幾個槽位等等沒有明確(即struct tvec和struct tvec_root)。
#define TVN_BITS 6 #define TVR_BITS 8 #define TVN_SIZE (1<<TVN_BITS) #define TVR_SIZE (1<<TVR_BITS) struct tvec { struct list_head vec[TVN_SIZE];/*64個格子*/ }; struct tvec_root{ struct list_head vec[TVR_SIZE];/*256個格子*/ };
此外,每一個時間輪都是哈希表,因此它的類型應該至少包含兩個指針域來實現雙向鏈表的功能。這里我們為了方便使用通用的struct list_head的雙向鏈表結構。
定時器的主要工作是為了在未來的特定時間完成某項任務,而這個任務經常包含以下內容:
任務的處理邏輯(回調函數)
任務的參數
雙向鏈表節點
到時時間
定時任務對象的定義
typedef void (*timeouthandle)(unsigned long ); struct timer_list{ struct list_head entry; //將時間連接成鏈表 unsigned long expires; //超時時間 void (*function)(unsigned long); //超時后的處理函數 unsigned long data; //處理函數的參數 struct tvec_base *base; //指向時間輪 };
在時間輪上的效果圖:
在時間輪上我們采用雙向鏈表的數據類型。采用雙向鏈表的除了操作上比單鏈表復雜,多占一個指針域外沒有其他不可接收的問題。而多占一個指針域在今天大內存的時代明顯不是什么問題。至于雙向鏈表操作的復雜性,我們可以通過使用通用的struct list結構來解決,因為雙向鏈表有眾多的標準操作函數,我們可以通過直接引用list.h頭文件來使用他們提供的接口。
struct list可以說是一個萬能的雙向鏈表操作框架,我們只需要在自定義的結構中定義一個struct list對象即可使用它的標準操作接口。同時它還提供了一個類似container_of的接口,在應用層一般叫做list_entry,因此我們可以很方便的通過struct list成員找到自定義的結構體的起始地址。
關于應用層的log.h, 我將在下面的代碼中附上該文件。如果需要內核層的實現,可以直接從linux源碼中獲取。
多級時間輪效果圖:
提到雙向鏈表,很多的源碼工程中都會實現一系列的統一的雙向鏈表操作函數。它們為雙向鏈表封裝了統計的接口,使用者只需要在自定義的結構中添加一個struct list_head結構,然后調用它們提供的接口,便可以完成雙向鏈表的所有操作。這些操作一般都在list.h的頭文件中實現。Linux源碼中也有實現(內核態的實現)。他們實現的方式基本完全一樣,只是實現的接口數量和功能上稍有差別。可以說這個==list.h文件是學習操作雙向鏈表的不二選擇==,它幾乎實現了所有的操作:增、刪、改、查、遍歷、替換、清空等等。這里我拼湊了一個源碼中的log.h函數,終于湊夠了多級時間輪中使用到的接口(原來的博主沒有提供list.h文件,只能自己去東拼西湊)。
#if !defined(_BLKID_LIST_H) && !defined(LIST_HEAD) #define _BLKID_LIST_H #ifdef __cplusplus extern "C" { #endif /* * Simple doubly linked list implementation. * * Some of the internal functions ("__xxx") are useful when * manipulating whole lists rather than single entries, as * sometimes we already know the next/prev entries and we can * generate better code by using them directly rather than * using the generic single-entry routines. */ struct list_head { struct list_head *next, *prev; }; #define LIST_HEAD_INIT(name) { &(name), &(name) } #define LIST_HEAD(name) struct list_head name = LIST_HEAD_INIT(name) #define INIT_LIST_HEAD(ptr) do { (ptr)->next = (ptr); (ptr)->prev = (ptr); } while (0) static inline void __list_add(struct list_head *entry, struct list_head *prev, struct list_head *next) { next->prev = entry; entry->next = next; entry->prev = prev; prev->next = entry; } /** * Insert a new element after the given list head. The new element does not * need to be initialised as empty list. * The list changes from: * head → some element → ... * to * head → new element → older element → ... * * Example: * struct foo *newfoo = malloc(...); * list_add(&newfoo->entry, &bar->list_of_foos); * * @param entry The new element to prepend to the list. * @param head The existing list. */ static inline void list_add(struct list_head *entry, struct list_head *head) { __list_add(entry, head, head->next); } /** * Append a new element to the end of the list given with this list head. * * The list changes from: * head → some element → ... → lastelement * to * head → some element → ... → lastelement → new element * * Example: * struct foo *newfoo = malloc(...); * list_add_tail(&newfoo->entry, &bar->list_of_foos); * * @param entry The new element to prepend to the list. * @param head The existing list. */ static inline void list_add_tail(struct list_head *entry, struct list_head *head) { __list_add(entry, head->prev, head); } static inline void __list_del(struct list_head *prev, struct list_head *next) { next->prev = prev; prev->next = next; } /** * Remove the element from the list it is in. Using this function will reset * the pointers to/from this element so it is removed from the list. It does * NOT free the element itself or manipulate it otherwise. * * Using list_del on a pure list head (like in the example at the top of * this file) will NOT remove the first element from * the list but rather reset the list as empty list. * * Example: * list_del(&foo->entry); * * @param entry The element to remove. */ static inline void list_del(struct list_head *entry) { __list_del(entry->prev, entry->next); } static inline void list_del_init(struct list_head *entry) { __list_del(entry->prev, entry->next); INIT_LIST_HEAD(entry); } static inline void list_move_tail(struct list_head *list, struct list_head *head) { __list_del(list->prev, list->next); list_add_tail(list, head); } /** * Check if the list is empty. * * Example: * list_empty(&bar->list_of_foos); * * @return True if the list contains one or more elements or False otherwise. */ static inline int list_empty(struct list_head *head) { return head->next == head; } /** * list_replace - replace old entry by new one * @old : the element to be replaced * @new : the new element to insert * * If @old was empty, it will be overwritten. */ static inline void list_replace(struct list_head *old, struct list_head *new) { new->next = old->next; new->next->prev = new; new->prev = old->prev; new->prev->next = new; } /** * Retrieve the first list entry for the given list pointer. * * Example: * struct foo *first; * first = list_first_entry(&bar->list_of_foos, struct foo, list_of_foos); * * @param ptr The list head * @param type Data type of the list element to retrieve * @param member Member name of the struct list_head field in the list element. * @return A pointer to the first list element. */ #define list_first_entry(ptr, type, member) list_entry((ptr)->next, type, member) static inline void list_replace_init(struct list_head *old, struct list_head *new) { list_replace(old, new); INIT_LIST_HEAD(old); } /** * list_entry - get the struct for this entry * @ptr: the &struct list_head pointer. * @type: the type of the struct this is embedded in. * @member: the name of the list_struct within the struct. */ #define list_entry(ptr, type, member) ((type *)((char *)(ptr)-(unsigned long)(&((type *)0)->member))) /** * list_for_each - iterate over elements in a list * @pos: the &struct list_head to use as a loop counter. * @head: the head for your list. */ #define list_for_each(pos, head) for (pos = (head)->next; pos != (head); pos = pos->next) /** * list_for_each_safe - iterate over elements in a list, but don"t dereference * pos after the body is done (in case it is freed) * @pos: the &struct list_head to use as a loop counter. * @pnext: the &struct list_head to use as a pointer to the next item. * @head: the head for your list (not included in iteration). */ #define list_for_each_safe(pos, pnext, head) for (pos = (head)->next, pnext = pos->next; pos != (head); pos = pnext, pnext = pos->next) #ifdef __cplusplus } #endif #endif /* _BLKID_LIST_H */
這里面一般會用到一個重要實現:==container_of==, 它的原理如果不清楚的話,可以閱讀另一篇專門介紹該函數的博文:container of()函數簡介
這個頭文件實際上不是必須的,我只是用它來添加調試信息(代碼中的errlog(), log()都是log.h中的宏函數)。它的效果是給打印的信息加上顏色,效果如下:
log.h的代碼如下:
#ifndef _LOG_h_ #define _LOG_h_ #include <stdio.h> #define COL(x) "33[;" #x "m" #define RED COL(31) #define GREEN COL(32) #define YELLOW COL(33) #define BLUE COL(34) #define MAGENTA COL(35) #define CYAN COL(36) #define WHITE COL(0) #define GRAY "33[0m" #define errlog(fmt, arg...) do{ printf(RED"[#ERROR: Toeny Sun:"GRAY YELLOW" %s:%d]:"GRAY WHITE fmt GRAY, __func__, __LINE__, ##arg); }while(0) #define log(fmt, arg...) do{ printf(WHITE"[#DEBUG: Toeny Sun: "GRAY YELLOW"%s:%d]:"GRAY WHITE fmt GRAY, __func__, __LINE__, ##arg); }while(0) #endif
/* *毫秒定時器 采用多級時間輪方式 借鑒linux內核中的實現 *支持的范圍為1 ~ 2^32 毫秒(大約有49天) *若設置的定時器超過最大值 則按最大值設置定時器 **/ #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <pthread.h> #include <sys/time.h> #include "list.h" #include "log.h" #define TVN_BITS 6 #define TVR_BITS 8 #define TVN_SIZE (1<<TVN_BITS) #define TVR_SIZE (1<<TVR_BITS) #define TVN_MASK (TVN_SIZE - 1) #define TVR_MASK (TVR_SIZE - 1) #define SEC_VALUE 0 #define USEC_VALUE 2000 struct tvec_base; #define INDEX(N) ((ba->current_index >> (TVR_BITS + (N) * TVN_BITS)) & TVN_MASK) typedef void (*timeouthandle)(unsigned long ); struct timer_list{ struct list_head entry; //將時間連接成鏈表 unsigned long expires; //超時時間 void (*function)(unsigned long); //超時后的處理函數 unsigned long data; //處理函數的參數 struct tvec_base *base; //指向時間輪 }; struct tvec { struct list_head vec[TVN_SIZE]; }; struct tvec_root{ struct list_head vec[TVR_SIZE]; }; //實現5級時間輪 范圍為0~ (2^8 * 2^6 * 2^6 * 2^6 *2^6)=2^32 struct tvec_base { unsigned long current_index; pthread_t thincrejiffies; pthread_t threadID; struct tvec_root tv1; /*第一個輪*/ struct tvec tv2; /*第二個輪*/ struct tvec tv3; /*第三個輪*/ struct tvec tv4; /*第四個輪*/ struct tvec tv5; /*第五個輪*/ }; static void internal_add_timer(struct tvec_base *base, struct timer_list *timer) { struct list_head *vec; unsigned long expires = timer->expires; unsigned long idx = expires - base->current_index; #if 1 if( (signed long)idx < 0 ) /*這里是沒有辦法區分出是過時還是超長定時的吧?*/ { vec = base->tv1.vec + (base->current_index & TVR_MASK);/*放到第一個輪的當前槽*/ } else if ( idx < TVR_SIZE ) /*第一個輪*/ { int i = expires & TVR_MASK; vec = base->tv1.vec + i; } else if( idx < 1 << (TVR_BITS + TVN_BITS) )/*第二個輪*/ { int i = (expires >> TVR_BITS) & TVN_MASK; vec = base->tv2.vec + i; } else if( idx < 1 << (TVR_BITS + 2 * TVN_BITS) )/*第三個輪*/ { int i = (expires >> (TVR_BITS + TVN_BITS)) & TVN_MASK; vec = base->tv3.vec + i; } else if( idx < 1 << (TVR_BITS + 3 * TVN_BITS) )/*第四個輪*/ { int i = (expires >> (TVR_BITS + 2 * TVN_BITS)) & TVN_MASK; vec = base->tv4.vec + i; } else /*第五個輪*/ { int i; if (idx > 0xffffffffUL) { idx = 0xffffffffUL; expires = idx + base->current_index; } i = (expires >> (TVR_BITS + 3 * TVN_BITS)) & TVN_MASK; vec = base->tv5.vec + i; } #else /*上面可以優化吧*/; #endif list_add_tail(&timer->entry, vec); } static inline void detach_timer(struct timer_list *timer) { struct list_head *entry = &timer->entry; __list_del(entry->prev, entry->next); entry->next = NULL; entry->prev = NULL; } static int __mod_timer(struct timer_list *timer, unsigned long expires) { if(NULL != timer->entry.next) detach_timer(timer); internal_add_timer(timer->base, timer); return 0; } //修改定時器的超時時間外部接口 int mod_timer(void *ptimer, unsigned long expires) { struct timer_list *timer = (struct timer_list *)ptimer; struct tvec_base *base; base = timer->base; if(NULL == base) return -1; expires = expires + base->current_index; if(timer->entry.next != NULL && timer->expires == expires) return 0; if( NULL == timer->function ) { errlog("timer"s timeout function is null "); return -1; } timer->expires = expires; return __mod_timer(timer,expires); } //添加一個定時器 static void __ti_add_timer(struct timer_list *timer) { if( NULL != timer->entry.next ) { errlog("timer is already exist "); return; } mod_timer(timer, timer->expires); } /*添加一個定時器 外部接口 *返回定時器 */ void* ti_add_timer(void *ptimewheel, unsigned long expires,timeouthandle phandle, unsigned long arg) { struct timer_list *ptimer; ptimer = (struct timer_list *)malloc( sizeof(struct timer_list) ); if(NULL == ptimer) return NULL; bzero( ptimer,sizeof(struct timer_list) ); ptimer->entry.next = NULL; ptimer->base = (struct tvec_base *)ptimewheel; ptimer->expires = expires; ptimer->function = phandle; ptimer->data = arg; __ti_add_timer(ptimer); return ptimer; } /* *刪除一個定時器 外部接口 * * */ void ti_del_timer(void *p) { struct timer_list *ptimer =(struct timer_list*)p; if(NULL == ptimer) return; if(NULL != ptimer->entry.next) detach_timer(ptimer); free(ptimer); } /*時間輪級聯*/ static int cascade(struct tvec_base *base, struct tvec *tv, int index) { struct list_head *pos,*tmp; struct timer_list *timer; struct list_head tv_list; /*將tv[index]槽位上的所有任務轉移給tv_list,然后清空tv[index]*/ list_replace_init(tv->vec + index, &tv_list);/*用tv_list替換tv->vec + index*/ list_for_each_safe(pos, tmp, &tv_list)/*遍歷tv_list雙向鏈表,將任務重新添加到時間輪*/ { timer = list_entry(pos,struct timer_list,entry);/*struct timer_list中成員entry的地址是pos, 獲取struct timer_list的首地址*/ internal_add_timer(base, timer); } return index; } static void *deal_function_timeout(void *base) { struct timer_list *timer; int ret; struct timeval tv; struct tvec_base *ba = (struct tvec_base *)base; for(;;) { gettimeofday(&tv, NULL); while( ba->current_index <= (tv.tv_sec*1000 + tv.tv_usec/1000) )/*單位:ms*/ { struct list_head work_list; int index = ba->current_index & TVR_MASK;/*獲取第一個輪上的指針位置*/ struct list_head *head = &work_list; /*指針指向0槽時,級聯輪需要更新任務列表*/ if(!index && (!cascade(ba, &ba->tv2, INDEX(0))) &&( !cascade(ba, &ba->tv3, INDEX(1))) && (!cascade(ba, &ba->tv4, INDEX(2))) ) cascade(ba, &ba->tv5, INDEX(3)); ba->current_index ++; list_replace_init(ba->tv1.vec + index, &work_list); while(!list_empty(head)) { void (*fn)(unsigned long); unsigned long data; timer = list_first_entry(head, struct timer_list, entry); fn = timer->function; data = timer->data; detach_timer(timer); (*fn)(data); } } } } static void init_tvr_list(struct tvec_root * tvr) { int i; for( i = 0; i<TVR_SIZE; i++ ) INIT_LIST_HEAD(&tvr->vec[i]); } static void init_tvn_list(struct tvec * tvn) { int i; for( i = 0; i<TVN_SIZE; i++ ) INIT_LIST_HEAD(&tvn->vec[i]); } //創建時間輪 外部接口 void *ti_timewheel_create(void ) { struct tvec_base *base; int ret = 0; struct timeval tv; base = (struct tvec_base *) malloc( sizeof(struct tvec_base) ); if( NULL==base ) return NULL; bzero( base,sizeof(struct tvec_base) ); init_tvr_list(&base->tv1); init_tvn_list(&base->tv2); init_tvn_list(&base->tv3); init_tvn_list(&base->tv4); init_tvn_list(&base->tv5); gettimeofday(&tv, NULL); base->current_index = tv.tv_sec*1000 + tv.tv_usec/1000;/*當前時間毫秒數*/ if( 0 != pthread_create(&base->threadID,NULL,deal_function_timeout,base) ) { free(base); return NULL; } return base; } static void ti_release_tvr(struct tvec_root *pvr) { int i; struct list_head *pos,*tmp; struct timer_list *pen; for(i = 0; i < TVR_SIZE; i++) { list_for_each_safe(pos,tmp,&pvr->vec[i]) { pen = list_entry(pos,struct timer_list, entry); list_del(pos); free(pen); } } } static void ti_release_tvn(struct tvec *pvn) { int i; struct list_head *pos,*tmp; struct timer_list *pen; for(i = 0; i < TVN_SIZE; i++) { list_for_each_safe(pos,tmp,&pvn->vec[i]) { pen = list_entry(pos,struct timer_list, entry); list_del(pos); free(pen); } } } /* *釋放時間輪 外部接口 * */ void ti_timewheel_release(void * pwheel) { struct tvec_base *base = (struct tvec_base *)pwheel; if(NULL == base) return; ti_release_tvr(&base->tv1); ti_release_tvn(&base->tv2); ti_release_tvn(&base->tv3); ti_release_tvn(&base->tv4); ti_release_tvn(&base->tv5); free(pwheel); } /************demo****************/ struct request_para{ void *timer; int val; }; void mytimer(unsigned long arg) { struct request_para *para = (struct request_para *)arg; log("%d ",para->val); mod_timer(para->timer,3000); //進行再次啟動定時器 sleep(10);/*定時器依然被阻塞*/ //定時器資源的釋放是在這里完成的 //ti_del_timer(para->timer); } int main(int argc,char *argv[]) { void *pwheel = NULL; void *timer = NULL; struct request_para *para; para = (struct request_para *)malloc( sizeof(struct request_para) ); if(NULL == para) return 0; bzero(para,sizeof(struct request_para)); //創建一個時間輪 pwheel = ti_timewheel_create(); if(NULL == pwheel) return -1; //添加一個定時器 para->val = 100; para->timer = ti_add_timer(pwheel, 3000, &mytimer, (unsigned long)para); while(1) { sleep(2); } //釋放時間輪 ti_timewheel_release(pwheel); return 0; }
toney@ubantu:/mnt/hgfs/em嵌入式學習記錄/4. timerwheel/2. 多級時間輪$ ls a.out list.h log.h mutiTimeWheel.c toney@ubantu:/mnt/hgfs/em嵌入式學習記錄/4. timerwheel/2. 多級時間輪$ gcc mutiTimeWheel.c -lpthread toney@ubantu:/mnt/hgfs/em嵌入式學習記錄/4. timerwheel/2. 多級時間輪$ ./a.out [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100 [#DEBUG: Toeny Sun: mytimer:370]:100
從結果可以看出:如果添加的定時任務是比較耗時的操作,那么后續的任務也會被阻塞,可能一直到超時,甚至一直阻塞下去,這個取決于當前任務是否耗時。
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