libevent尾队列 && 最小堆

Posted 2020-10-11 Sawyer Ford

本文主要研究libevent中用来存储事件的两个结构体。

尾队列

具体定义位于queue.h中。

#define    TAILQ_HEAD(name, type)                        \\
struct name {                                \\
    struct type *tqh_first;    /* first element */            \\
    struct type **tqh_last;    /* addr of last next element */        \\
}

#define    TAILQ_ENTRY(type)                        \\
struct {                                \\
    struct type *tqe_next;    /* next element */            \\
    struct type **tqe_prev;    /* address of previous next element */    \\
}                                    

#define    TAILQ_EMPTY(head)    ((head)->tqh_first == NULL)
#define    TAILQ_FIRST(head)    ((head)->tqh_first)
#define    TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)

#define    TAILQ_INIT(head) do {                        \\
    TAILQ_FIRST((head)) = NULL;                    \\
    (head)->tqh_last = &TAILQ_FIRST((head));            \\
} while (0)

#define    TAILQ_INSERT_TAIL(head, elm, field) do {            \\
    TAILQ_NEXT((elm), field) = NULL;                \\
    (elm)->field.tqe_prev = (head)->tqh_last;            \\
    *(head)->tqh_last = (elm);                    \\
    (head)->tqh_last = &TAILQ_NEXT((elm), field);            \\
} while (0)

#define    TAILQ_INSERT_HEAD(head, elm, field) do {            \\
    if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)    \\
        TAILQ_FIRST((head))->field.tqe_prev =            \\
            &TAILQ_NEXT((elm), field);                \\
    else                                \\
        (head)->tqh_last = &TAILQ_NEXT((elm), field);        \\
    TAILQ_FIRST((head)) = (elm);                    \\
    (elm)->field.tqe_prev = &TAILQ_FIRST((head));            \\
} while (0)

#define    TAILQ_INSERT_AFTER(head, listelm, elm, field) do {        \\
    if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\\
        TAILQ_NEXT((elm), field)->field.tqe_prev =         \\
            &TAILQ_NEXT((elm), field);                \\
    else {                                \\
        (head)->tqh_last = &TAILQ_NEXT((elm), field);        \\
    }                                \\
    TAILQ_NEXT((listelm), field) = (elm);                \\
    (elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);        \\
} while (0)

#define    TAILQ_INSERT_BEFORE(listelm, elm, field) do {            \\
    (elm)->field.tqe_prev = (listelm)->field.tqe_prev;        \\
    TAILQ_NEXT((elm), field) = (listelm);                \\
    *(listelm)->field.tqe_prev = (elm);                \\
    (listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);        \\
} while (0)

#define    TAILQ_REMOVE(head, elm, field) do {                \\
    if ((TAILQ_NEXT((elm), field)) != NULL)                \\
        TAILQ_NEXT((elm), field)->field.tqe_prev =         \\
            (elm)->field.tqe_prev;                \\
    else {                                \\
        (head)->tqh_last = (elm)->field.tqe_prev;        \\
    }                                \\
    *(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);        \\
} while (0)

从定义可以看出，尾队列是一个双向链表，具体表现为：

一个小DEMO:

#include <stdio.h>
#include <stdlib.h>
#include <sys/queue.h>

#define LIST_SIZE 5

// 声明头结点
TAILQ_HEAD(event_list, event);
// 声明元素结点
struct event {
    int value;
    TAILQ_ENTRY(event) field;
};

int main(int argc, char **argv) {
    event_list *list = (event_list*)malloc(sizeof(event_list));
    TAILQ_INIT(list);
    
    event *item;
    for (int i = 0; i < LIST_SIZE; i++) {
        item = (event*)malloc(sizeof(event));
        item->value = i;
        item->field.tqe_next = NULL;
        item->field.tqe_prev = NULL;
        
        TAILQ_INSERT_TAIL(list, item, field);
    }
    
    printf("当前list: ");
    for (item = list->tqh_first; item; item = item->field.tqe_next) {
        printf("%d ", item->value);
    }
    printf("\\n");
    
    event **test = list->tqh_first->field.tqe_prev;
    if (test == &list->tqh_first) {
        printf("guess right\\n");
    }
    
    printf("尾部插入结点: 10\\n");
    item = (event*)malloc(sizeof(event));
    item->value = 10;
    item->field.tqe_next = NULL;
    item->field.tqe_prev = NULL;
    TAILQ_INSERT_TAIL(list, item, field);
    
    printf("当前list: ");
    for (item = list->tqh_first; item; item = item->field.tqe_next) {
        printf("%d ", item->value);
    }
    printf("\\n");
    
    printf("头部插入结点: 20\\n");
    item = (event*)malloc(sizeof(event));
    item->value = 20;
    item->field.tqe_next = NULL;
    item->field.tqe_prev = NULL;
    TAILQ_INSERT_HEAD(list, item, field);
    
    printf("当前list: ");
    for (item = list->tqh_first; item; item = item->field.tqe_next) {
        printf("%d ", item->value);
    }
    printf("\\n");
    
    printf("在值为3的结点之后插入结点: 30\\n");
    for (item = list->tqh_first; item; item = item->field.tqe_next) {
        if (item->value == 3) {
            event *new_item = (event*)malloc(sizeof(event));
            new_item->value = 30;
            new_item->field.tqe_next = NULL;
            new_item->field.tqe_prev = NULL;
            TAILQ_INSERT_AFTER(list, item, new_item, field);
        }
    }
    
    printf("当前list: ");
    for (item = list->tqh_first; item; item = item->field.tqe_next) {
        printf("%d ", item->value);
    }
    printf("\\n");
    
    printf("在值为1的结点之前插入结点: 40\\n");
    for (item = list->tqh_first; item; item = item->field.tqe_next) {
        if (item->value == 1) {
            event *new_item = (event*)malloc(sizeof(event));
            new_item->value = 40;
            new_item->field.tqe_next = NULL;
            new_item->field.tqe_prev = NULL;
            TAILQ_INSERT_BEFORE(item, new_item, field);
        }
    }
    
    printf("当前list: ");
    for (item = list->tqh_first; item; item = item->field.tqe_next) {
        printf("%d ", item->value);
    }
    printf("\\n");
    
    printf("删除值为3的结点\\n");
    for (item = list->tqh_first; item; item = item->field.tqe_next) {
        if (item->value == 3) {
            TAILQ_REMOVE(list, item, field);
        }
    }
    
    printf("当前list: ");
    for (item = list->tqh_first; item; item = item->field.tqe_next) {
        printf("%d ", item->value);
    }
    printf("\\n");
    
    printf("Done\\n");
}

View Code

最小堆

typedef struct min_heap
{
    struct event** p; // 指向event*指针数组
    unsigned n, a;  　// a表示堆的大小，n表示堆中元素个数
} min_heap_t;

 

void min_heap_ctor(min_heap_t* s) { s->p = 0; s->n = 0; s->a = 0; }
void min_heap_elem_init(struct event* e) { e->ev_timeout_pos.min_heap_idx = -1; }
unsigned min_heap_size(min_heap_t* s) { return s->n; }

 

参考资料:

do {...} while (0) 的用途汇总（欢迎补充）