本文主要研究libevent中用來存儲事件的兩個結構體。

尾隊列

具體定義位於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)

從定義可以看出，尾隊列是一個雙向鏈表，具體表現為：

一個小DEMO:

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

#define LIST_SIZE 5

// 聲明頭結點
TAILQ_HEAD(event_list, event);
// 聲明元素結點
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("當前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("尾部插入結點: 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("當前list: ");
    for (item = list->tqh_first; item; item = item->field.tqe_next) {
        printf("%d ", item->value);
    }
    printf("\n");
    
    printf("頭部插入結點: 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("當前list: ");
    for (item = list->tqh_first; item; item = item->field.tqe_next) {
        printf("%d ", item->value);
    }
    printf("\n");
    
    printf("在值為3的結點之後插入結點: 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("當前list: ");
    for (item = list->tqh_first; item; item = item->field.tqe_next) {
        printf("%d ", item->value);
    }
    printf("\n");
    
    printf("在值為1的結點之前插入結點: 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("當前list: ");
    for (item = list->tqh_first; item; item = item->field.tqe_next) {
        printf("%d ", item->value);
    }
    printf("\n");
    
    printf("刪除值為3的結點\n");
    for (item = list->tqh_first; item; item = item->field.tqe_next) {
        if (item->value == 3) {
            TAILQ_REMOVE(list, item, field);
        }
    }
    
    printf("當前list: ");
    for (item = list->tqh_first; item; item = item->field.tqe_next) {
        printf("%d ", item->value);
    }
    printf("\n");
    
    printf("Done\n");
}

最小堆

typedef struct min_heap
{
    struct event** p;
    unsigned n, a;
} min_heap_t;

暫時不表。

參考資料:

do {...} while (0) 的用途匯總（歡迎補充）

libevent(二)尾隊列 && 最小堆