linux定时器(Linux定时器实现)

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准备好linux编程环境,现场手撕定时器实现【linux服务器开发】

工程师的圣地—Linux内核， 谈谈内核的架构

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上图是5个时间轮级联的效果图。中间的大轮是工作轮，只有在它上的任务才会被执行；其他轮上的任务时间到后迁移到下一级轮上，他们最终都会迁移到工作轮上而被调度执行。

多级时间轮的原理也容易理解：就拿时钟做说明，秒针转动一圈分针转动一格；分针转动一圈时针转动一格；同理时间轮也是如此：当低级轮转动一圈时，高一级轮转动一格，同时会将高一级轮上的任务重新分配到低级轮上。从而实现了多级轮级联的效果。

1.1 多级时间轮对象

多级时间轮应该至少包括以下内容：

关于轮子上指针的位置有一个比较巧妙的办法：那就是位运算。比如定义一个无符号整型的数：

通过获取当前的系统时间便可以通过位操作转换为时间轮上的时间，通过与实际时间轮上的时间作比较，从而确定时间轮要前进调度的时间，进而操作对应时间轮槽位对应的任务。

为什么至少需要这两个成员呢？

多级时间轮对象的定义

//实现5级时间轮 范围为0~ (2^8 * 2^6 * 2^6 * 2^6 *2^6)=2^32struct tvec_ba{ unsigned long current_index; pthread_t thincrejiffies; pthread_t threadID; struct tvec_root tv1; /*第一个轮*/ struct tvec tv2; /*第二个轮*/ struct tvec tv3; /*第三个轮*/ struct tvec tv4; /*第四个轮*/ struct tvec tv5; /*第五个轮*/};

1.2 时间轮对象

我们知道每一个轮子实际上都是一个哈希表，上面我们只是实例化了五个轮子的对象，但是五个轮子具体包含什么，有几个槽位等等没有明确(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个格子*/}; struct tvec_root{ struct list_head vec[TVR_SIZE];/*256个格子*/};

此外，每一个时间轮都是哈希表，因此它的类型应该至少包含两个指针域来实现双向链表的功能。这里我们为了方便使用通用的struct list_head的双向链表结构。

1.3 定时任务对象

定时器的主要工作是为了在未来的特定时间完成某项任务，而这个任务经常包含以下内容：

定时任务对象的定义

typedef void (*timeouthandle)(unsigned long ); struct timer_list{ struct list_head entry; //将时间连接成链表 unsigned long expires; //超时时间 void (*function)(unsigned long); //超时后的处理函数 unsigned long data; //处理函数的参数 struct tvec_ba *ba; //指向时间轮};

在时间轮上的效果图：

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1.4 双向链表

在时间轮上我们采用双向链表的数据类型。采用双向链表的除了操作上比单链表复杂，多占一个指针域外没有其他不可接收的问题。而多占一个指针域在今天大内存的时代明显不是什么问题。至于双向链表操作的复杂性，我们可以通过使用通用的struct list结构来解决，因为双向链表有众多的标准操作函数，我们可以通过直接引用list.h头文件来使用他们提供的接口。

struct list可以说是一个万能的双向链表操作框架，我们只需要在自定义的结构中定义一个struct list对象即可使用它的标准操作接口。同时它还提供了一个类似container_of的接口，在应用层一般叫做list_entry，因此我们可以很方便的通过struct list成员找到自定义的结构体的起始地址。

关于应用层的log.h, 我将在下面的代码中附上该文件。如果需要内核层的实现，可以直接从linux源码中获取。

1.5 联结方式

多级时间轮效果图：

2.1 双向链表头文件: list.h

提到双向链表，很多的源码工程中都会实现一系列的统一的双向链表操作函数。它们为双向链表封装了统计的接口，使用者只需要在自定义的结构中添加一个struct list_head结构，然后调用它们提供的接口，便可以完成双向链表的所有操作。这些操作一般都在list.h的头文件中实现。Linux源码中也有实现（内核态的实现）。他们实现的方式基本完全一样，只是实现的接口数量和功能上稍有差别。可以说这个list.h文件是学习操作双向链表的不二选择，它几乎实现了所有的操作：增、删、改、查、遍历、替换、清空等等。这里我拼凑了一个源码中的log.h函数，终于凑够了多级时间轮中使用到的接口。

#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 uful 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;}/** * Inrt a new element after the given list head. The new element does not * need to be initialid 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 voidlist_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 voidlist_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 ret * the pointers to/from this element so it is removed from the list. It does * NOT free the element itlf or manipulate it otherwi. * * 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 ret the list as empty list. * * Example: * list_del(&foo->entry); * * @param entry The element to remove. */static inline voidlist_del(struct list_head *entry){ __list_del(entry->prev, entry->next);}static inline voidlist_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 Fal otherwi. */static inline intlist_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 inrt * * 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 u 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 ca it is freed) * @pos: the &struct list_head to u as a loop counter. * @pnext: the &struct list_head to u 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 */

这里面一般会用到一个重要实现：container_of, 它的原理这里不叙述

2.2 调试信息头文件: log.h

这个头文件实际上不是必须的，我只是用它来添加调试信息(代码中的errlog(), log()都是log.h中的宏函数)。它的效果是给打印的信息加上颜色，效果如下：

log.h的代码如下：

#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

2.3 时间轮代码: timewheel.c

/* *毫秒定时器 采用多级时间轮方式 借鉴linux内核中的实现 *支持的范围为1 ~ 2^32 毫秒(大约有49天) *若设置的定时器超过最大值 则按最大值设置定时器 **/#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_ba;#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; //将时间连接成链表 unsigned long expires; //超时时间 void (*function)(unsigned long); //超时后的处理函数 unsigned long data; //处理函数的参数 struct tvec_ba *ba; //指向时间轮}; struct tvec { struct list_head vec[TVN_SIZE];}; struct tvec_root{ struct list_head vec[TVR_SIZE];}; //实现5级时间轮 范围为0~ (2^8 * 2^6 * 2^6 * 2^6 *2^6)=2^32struct tvec_ba{ unsigned long current_index; pthread_t thincrejiffies; pthread_t threadID; struct tvec_root tv1; /*第一个轮*/ struct tvec tv2; /*第二个轮*/ struct tvec tv3; /*第三个轮*/ struct tvec tv4; /*第四个轮*/ struct tvec tv5; /*第五个轮*/}; static void internal_add_timer(struct tvec_ba *ba, struct timer_list *timer){ struct list_head *vec; unsigned long expires = timer->expires; unsigned long idx = expires - ba->current_index;#if 1 if( (signed long)idx < 0 ) /*这里是没有办法区分出是过时还是超长定时的吧?*/ { vec = ba->tv1.vec + (ba->current_index & TVR_MASK);/*放到第一个轮的当前槽*/ } el if ( idx < TVR_SIZE ) /*第一个轮*/ { int i = expires & TVR_MASK; vec = ba->tv1.vec + i; } el if( idx < 1 << (TVR_BITS + TVN_BITS) )/*第二个轮*/ { int i = (expires >> TVR_BITS) & TVN_MASK; vec = ba->tv2.vec + i; } el if( idx < 1 << (TVR_BITS + 2 * TVN_BITS) )/*第三个轮*/ { int i = (expires >> (TVR_BITS + TVN_BITS)) & TVN_MASK; vec = ba->tv3.vec + i; } el if( idx < 1 << (TVR_BITS + 3 * TVN_BITS) )/*第四个轮*/ { int i = (expires >> (TVR_BITS + 2 * TVN_BITS)) & TVN_MASK; vec = ba->tv4.vec + i; } el /*第五个轮*/ { int i; if (idx > 0xffffffffUL) { idx = 0xffffffffUL; expires = idx + ba->current_index; } i = (expires >> (TVR_BITS + 3 * TVN_BITS)) & TVN_MASK; vec = ba->tv5.vec + i; }#el /*上面可以优化吧*/;#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->ba, timer); return 0;} //修改定时器的超时时间外部接口int mod_timer(void *ptimer, unsigned long expires){ struct timer_list *timer = (struct timer_list *)ptimer; struct tvec_ba *ba; ba = timer->ba; if(NULL == ba) return -1; expires = expires + ba->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);} //添加一个定时器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); } /*添加一个定时器 外部接口 *返回定时器 */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->ba = (struct tvec_ba *)ptimewheel; ptimer->expires = expires; ptimer->function = phandle; ptimer->data = arg; __ti_add_timer(ptimer); return ptimer;} /* *删除一个定时器 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);}/*时间轮级联*/ static int cascade(struct tvec_ba *ba, struct tvec *tv, int index){ struct list_head *pos,*tmp; struct timer_list *timer; struct list_head tv_list; /*将tv[index]槽位上的所有任务转移给tv_list,然后清空tv[index]*/ list_replace_init(tv->vec + index, &tv_list);/*用tv_list替换tv->vec + index*/ list_for_each_safe(pos, tmp, &tv_list)/*遍历tv_list双向链表，将任务重新添加到时间轮*/ { timer = list_entry(pos,struct timer_list,entry);/*struct timer_list中成员entry的地址是pos, 获取struct timer_list的首地址*/ internal_add_timer(ba, timer); } return index;} static void *deal_function_timeout(void *ba){ struct timer_list *timer; int ret; struct timeval tv; struct tvec_ba *ba = (struct tvec_ba *)ba; for(;;) { gettimeofday(&tv, NULL); while( ba->current_index <= (tv.tv_c*1000 + tv.tv_uc/1000) )/*单位：ms*/ { struct list_head work_list; int index = ba->current_index & TVR_MASK;/*获取第一个轮上的指针位置*/ struct list_head *head = &work_list; /*指针指向0槽时，级联轮需要更新任务列表*/ 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]);} //创建时间轮 外部接口void *ti_timewheel_create(void ){ struct tvec_ba *ba; int ret = 0; struct timeval tv; ba = (struct tvec_ba *) malloc( sizeof(struct tvec_ba) ); if( NULL==ba ) return NULL; bzero( ba,sizeof(struct tvec_ba) ); init_tvr_list(&ba->tv1); init_tvn_list(&ba->tv2); init_tvn_list(&ba->tv3); init_tvn_list(&ba->tv4); init_tvn_list(&ba->tv5); gettimeofday(&tv, NULL); ba->current_index = tv.tv_c*1000 + tv.tv_uc/1000;/*当前时间毫秒数*/ if( 0 != pthread_create(&ba->threadID,NULL,deal_function_timeout,ba) ) { free(ba); return NULL; } return ba;} static void ti_relea_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_relea_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); } }} /* *释放时间轮 外部接口 * */void ti_timewheel_relea(void * pwheel){ struct tvec_ba *ba = (struct tvec_ba *)pwheel; if(NULL == ba) return; ti_relea_tvr(&ba->tv1); ti_relea_tvn(&ba->tv2); ti_relea_tvn(&ba->tv3); ti_relea_tvn(&ba->tv4); ti_relea_tvn(&ba->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); //进行再次启动定时器 sleep(10);/*定时器依然被阻塞*/ //定时器资源的释放是在这里完成的 //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)); //创建一个时间轮 pwheel = ti_timewheel_create(); if(NULL == pwheel) return -1; //添加一个定时器 para->val = 100; para->timer = ti_add_timer(pwheel, 3000, &mytimer, (unsigned long)para); while(1) { sleep(2); } //释放时间轮 ti_timewheel_relea(pwheel); return 0;}

2.4 编译运行

toney@ubantu:/mnt/hgfs/em嵌入式学习记录/4. timerwheel/2. 多级时间轮$ lsa.out list.h log.h mutiTimeWheel.ctoney@ubantu:/mnt/hgfs/em嵌入式学习记录/4. timerwheel/2. 多级时间轮$ gcc mutiTimeWheel.c -lpthreadtoney@ubantu:/mnt/hgfs/em嵌入式学习记录/4. timerwheel/2. 多级时间轮$ ./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

从结果可以看出：如果添加的定时任务是比较耗时的操作，那么后续的任务也会被阻塞，可能一直到超时，甚至一直阻塞下去，这个取决于当前任务是否耗时。这个理论上是绝不能接受的：一个任务不应该也不能去影响其他的任务吧。但是目前没有对此问题进行改进和完善，以后有机会再继续完善吧。