Libevent Source Code Analysis (i)

The analysis here is libevent-1.4.9.

PS: The front also looked at the source code of the Libev, the mother, the code is too obscene, compared to libevent code written much better.

First, take a look at some of the most important data structures:

The EVENTOP structure is the base class for all event-driven models. All IO multiplexing types will implement various methods in this structure.

struct　eventop　{
const　char　*name;　　　///<事件驱动名称
void　*(*init)(struct　event_base　*);　//<初始化
int　(*add)(void　*,　struct　event　*);　///<加入新的事件监测
int　(*del)(void　*,　struct　event　*);　///<从事件监测中删除某一事件
int　(*dispatch)(struct　event_base　*,　void　*,　struct　timeval　*);///<启动此事件监测
void　(*dealloc)(struct　event_base　*,　void　*);　///<释放此事件驱动的资源
/*　set　if　we　need　to　reinitialize　the　event　base　*/
int　need_reinit;　///<标志位
};

Event_base manages all event objects, including all variables, such as event-driven engine Evsel. All event objects will contain this structure.

struct　event_base　{
const　struct　eventop　*evsel;　　///<事件驱动引擎
void　*evbase;　　　　　　　　　///<事件驱动引擎的全局数据，在每一个事件引擎文件中定义，下面会介绍.
int　event_count;　/*　counts　number　of　total　events　*/
int　event_count_active;　/*　counts　number　of　active　events　*/

int　event_gotterm;　/*　Set　to　terminate　loop　*/
int　event_break;　/*　Set　to　terminate　loop　immediately　*/

/*　active　event　management　*/
struct　event_list　**activequeues;　///<激活队列
int　nactivequeues;　　　　　　　　　///<激活队列数目

/*　signal　handling　info　*/
struct　evsignal_info　sig;　　　　///<信号

struct　event_list　eventqueue;　　///<全部事件队列
struct　timeval　event_tv;

struct　min_heap　timeheap;　　　///<这里libevent将定时器队列实现为一个最小堆，也就是为了每次都把时间最晚的定时器能取出来，然后实现超时。更其实算法很简单，想要详细的了解可以去看下算法导论的第六章的Priority　queues.

struct　timeval　tv_cache;
};

The event structure represents each incident, including some event-private data, such as a callback function. Here the event list it uses the tail queue.

struct　event　{
TAILQ_ENTRY　(event)　ev_next;　　　///<下一个事件
TAILQ_ENTRY　(event)　ev_active_next;　///<下一个激活事件
TAILQ_ENTRY　(event)　ev_signal_next;　///<下一个信号事件列表
unsigned　int　min_heap_idx;　/*　for　managing　timeouts　*/

struct　event_base　*ev_base;　///<全局的base　

int　ev_fd;　　　　　　　　///<所需要监测的事件句柄
short　ev_events;
short　ev_ncalls;
short　*ev_pncalls;　/*　Allows　deletes　in　callback　*/

struct　timeval　ev_timeout;　　///<超时时间

int　ev_pri;　/*　smaller　numbers　are　higher　priority　*/

void　(*ev_callback)(int,　short,　void　*arg);　///<回调函数
void　*ev_arg;　　　　　　　　　　　　　　///<传递给回调函数的参数

int　ev_res;　/*　result　passed　to　event　callback　*/
int　ev_flags;
};