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[libevent] timer 的原理 (min-heap)

2009-03-21 16:56:39| 分类： net_libevent | 标签： |举报 |字号大中小订阅

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libevent-1.4.12-stable, libevent-2.0.4-alpha

libevent 中，用最小堆(min-heap)来管理所有 timer。

基础知识
min-heap，就是 child node value 一定小于 parent node value 的 binary-tree。因此，获取 min value，只需要 pop root node 即可。

[libevent] min-heap - kasicass - Co<wbr>de@Pig Home

算法实现 (min_heap.h)
对于 libevent，root node 就是最近即将触发的 timer event。node value 就是 timer 触发的时间(秒)。

// p - (struct event *) array
// n - event array count (point to first empty slot)
// a - event array size
typedef struct min_heap
{
    struct event** p;
    unsigned n, a;
} min_heap_t

对于上面的图，n = 9, a = 12，p[] 中存储的值如下：
index   0   1   2    3    4    5 6    7 8   9 10 11
value   1   2   3 17 19 36   7 25 100   ?   ?    ?
而 child/parent 可以构成 parent_index = (child_index - 1) / 2 的关系。

:-) 基本数据便是如此这般，剩下的代码也就比较简单了。

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