libevent代码阅读（2）——尾队列的学习

libevent当中大量使用了linux内置的一个数据结构——尾队列

下面是它的使用方法：

#include <iostream>#include <vector>#include <string>#include <stack>#include <math.h>#include <stdlib.h>#include <string>#include <string.h>#include <deque>#include <stdio.h>#include <math.h>#include <algorithm>#include <limits>#include <limits.h>#include <sys/queue.h>using namespace std;int main(){    /*      定义一个结构体，它只是尾队列的一个元素      它必须包含一个TAILQ_ENTRY来指向上一个和下一个元素    */    struct tailq_entry {        int value;        // 指向上一个元素和下一个元素        TAILQ_ENTRY(tailq_entry) entries;    };    //定义队列的头部    TAILQ_HEAD(MyQueType, tailq_entry) my_tailq_head;    // 队列初始化    TAILQ_INIT(&my_tailq_head);    //定义一个结构体指针    struct tailq_entry *item;    //定义另外一个指针    struct tailq_entry *tmp_item;    int i;    //在队列里添加10个元素    for(i=0; i<10; i++)    {        //申请内存空间        item = (tailq_entry*)malloc(sizeof(tailq_entry));        if (item == NULL)        {            perror("malloc failed");            exit(-1);        }        //设置值        item->value = i;        /*               将元素加到队列尾部               参数1：指向队列头的指针               参数2：要添加的元素               参数3：结构体的变量名            */        TAILQ_INSERT_TAIL(&my_tailq_head, item, entries);    }    //遍历队列    printf("Forward traversal: ");    TAILQ_FOREACH(item, &my_tailq_head, entries)    {        printf("%d ",item->value);    }    printf("\n");    return 0;}

尾队列的定义

/* * Tail queue definitions. *//* * 尾队列的定义 * TAILQ_HEAD(name, type)定义一个名字为name，元素类型为type的双向队列 * tqh_first访问第一个元素 * tqh_last指向最后一个TAILQ_ENTRY，最后一个TAILQ_ENTRY的tqe_next为空 * 最后一个TAILQ_ENTRY的tqe_prev指向前一个TAILQ_ENTRY， * 倒数第二个TAILQ_ENTRY的tqe_next指向最后一个元素 */#define TAILQ_HEAD(name, type)\struct name {\struct type *tqh_first;/* first element */\struct type **tqh_last;/*最后一个元素的地址*//* addr of last next element */\}// 尾队列头部初始化#define TAILQ_HEAD_INITIALIZER(head)\{ NULL, &(head).tqh_first }/* * TAILQ_ENTRY(type)定义了尾队列元素访问相邻元素的入口点，即每一个元素中有一个字段为 * 该结构的对象，用于访问相邻元素 */#define TAILQ_ENTRY(type)\struct {\struct type *tqe_next;/* next element */\struct type **tqe_prev;/* address of previous next element */\}/* * tail queue access methods */// 尾队列头元素#defineTAILQ_FIRST(head)((head)->tqh_first)// 尾队列的尾#defineTAILQ_END(head)NULL// 下一个元素，访问下一个元素使用elemt的field域的tqe_next#defineTAILQ_NEXT(elm, field)((elm)->field.tqe_next)// 最后一个元素#define TAILQ_LAST(head, headname)\(*(((struct headname *)((head)->tqh_last))->tqh_last))/* XXX */// 当前元素的上一个元素#define TAILQ_PREV(elm, headname, field)\(*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))// 判断队列是否为空#defineTAILQ_EMPTY(head)\(TAILQ_FIRST(head) == TAILQ_END(head))// 正向遍历#define TAILQ_FOREACH(var, head, field)\for((var) = TAILQ_FIRST(head);\    (var) != TAILQ_END(head);\    (var) = TAILQ_NEXT(var, field))// 反向遍历#define TAILQ_FOREACH_REVERSE(var, head, headname, field)\for((var) = TAILQ_LAST(head, headname);\    (var) != TAILQ_END(head);\    (var) = TAILQ_PREV(var, headname, field))/* * Tail queue functions. */// 尾队列初始化#defineTAILQ_INIT(head) do {\(head)->tqh_first = NULL;\(head)->tqh_last = &(head)->tqh_first;\} while (0)// 在队列头插入元素#define TAILQ_INSERT_HEAD(head, elm, field) do {\if (((elm)->field.tqe_next = (head)->tqh_first) != NULL)\(head)->tqh_first->field.tqe_prev =\    &(elm)->field.tqe_next;\else\(head)->tqh_last = &(elm)->field.tqe_next;\(head)->tqh_first = (elm);\(elm)->field.tqe_prev = &(head)->tqh_first;\} while (0)// 在队列尾插入元素#define TAILQ_INSERT_TAIL(head, elm, field) do {\(elm)->field.tqe_next = NULL;\(elm)->field.tqe_prev = (head)->tqh_last;\*(head)->tqh_last = (elm);\(head)->tqh_last = &(elm)->field.tqe_next;\} while (0)// 在指定元素的后面插入元素#define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {\if (((elm)->field.tqe_next = (listelm)->field.tqe_next) != NULL)\(elm)->field.tqe_next->field.tqe_prev =\    &(elm)->field.tqe_next;\else\(head)->tqh_last = &(elm)->field.tqe_next;\(listelm)->field.tqe_next = (elm);\(elm)->field.tqe_prev = &(listelm)->field.tqe_next;\} while (0)// 在指定元素的前面插入元素#defineTAILQ_INSERT_BEFORE(listelm, elm, field) do {\(elm)->field.tqe_prev = (listelm)->field.tqe_prev;\(elm)->field.tqe_next = (listelm);\*(listelm)->field.tqe_prev = (elm);\(listelm)->field.tqe_prev = &(elm)->field.tqe_next;\} while (0)// 删除一个元素#define TAILQ_REMOVE(head, elm, field) do {\if (((elm)->field.tqe_next) != NULL)\(elm)->field.tqe_next->field.tqe_prev =\    (elm)->field.tqe_prev;\else\(head)->tqh_last = (elm)->field.tqe_prev;\*(elm)->field.tqe_prev = (elm)->field.tqe_next;\} while (0)// 替换一个元素#define TAILQ_REPLACE(head, elm, elm2, field) do {\if (((elm2)->field.tqe_next = (elm)->field.tqe_next) != NULL)\(elm2)->field.tqe_next->field.tqe_prev =\    &(elm2)->field.tqe_next;\else\(head)->tqh_last = &(elm2)->field.tqe_next;\(elm2)->field.tqe_prev = (elm)->field.tqe_prev;\*(elm2)->field.tqe_prev = (elm2);\} while (0)