libevent之bufferevent事件学习

原创

已于 2023-05-11 22:52:42 修改 · 412 阅读

1 ·

CC 4.0 BY-SA版权

文章标签：

#学习

于 2023-05-10 22:41:36 首次发布

本文详细介绍了libevent中的bufferevent事件，包括其结构体详情、创建新节点、连接服务器、连接监听器evconnlistener的使用，以及设置回调函数和数据的发送与接收。重点讨论了evconnlistener_new_bind和evconnlistener_new的内部实现，以及如何通过bufferevent_setcb启用或禁用事件回调。

bufferevent事件

1. 介绍

封装了listen、accept, bind, socket等
应用层有两个缓冲区（读/写缓冲区），每个缓冲区对应一个回调函数，此外还有一个事件的回调函数，总共3个回调函数。

bufferevent内部调用简图
下面介绍bufferevent结构体的详情。

struct bufferevent {
   
   
	/** Event base for which this bufferevent was created. */
	struct event_base *ev_base;
	/** Pointer to a table of function pointers to set up how this
	    bufferevent behaves. */
	const struct bufferevent_ops *be_ops;

	/** A read event that triggers when a timeout has happened or a socket
	    is ready to read data.  Only used by some subtypes of
	    bufferevent. */
	struct event ev_read;
	/** A write event that triggers when a timeout has happened or a socket
	    is ready to write data.  Only used by some subtypes of
	    bufferevent. */
	struct event ev_write;

	/** An input buffer. Only the bufferevent is allowed to add data to
	    this buffer, though the user is allowed to drain it. */
	struct evbuffer *input;

	/** An output buffer. Only the bufferevent is allowed to drain data
	    from this buffer, though the user is allowed to add it. */
	struct evbuffer *output;

	struct event_watermark wm_read;
	struct event_watermark wm_write;

	bufferevent_data_cb readcb;
	bufferevent_data_cb writecb;
	/* This should be called 'eventcb', but renaming it would break
	 * backward compatibility */
	bufferevent_event_cb errorcb;
	void *cbarg;

	struct timeval timeout_read;
	struct timeval timeout_write;

	/** Events that are currently enabled: currently EV_READ and EV_WRITE
	    are supported. */
	short enabled;
};

2. 创建新的节点

struct bufferevent *
bufferevent_socket_new(struct event_base *base, evutil_socket_t fd,
    int options)
parameters: 
    base  : event_base 根节点
    fd    : 要初始化上树的文件描述符,如果想后面设置文件描述符可以先设置为-1
bufferevent_options : 
         BEV_OPT_CLOSE_ON_FREE   -- If set, we close the underlying file descriptor/bufferevent/whatever when this bufferevent is freed.   
         BEV_OPT_THREADSAFE      -- If set, and threading is enabled, operations on this bufferevent are protected by a lock
         BEV_OPT_DEFER_CALLBACKS --If set, callbacks are run deferred in the event loop
         BEV_OPT_UNLOCK_CALLBACKS -- If set, callbacks are executed without locks being held on the bufferevent.  This option currently requires that BEV_OPT_DEFER_CALLBACKS also be set; a future version of Libevent might remove the requirement
       
return value:
   新建节点的地址

descript: 
	创建基于套接字的 bufferevent(初始化bufferevent事件,创建读写缓冲区，读写事件，以及异常事件,设置输出缓冲区回调)

3. 连接服务器

连接远程服务器,当fd=-1 ,创建socket。

int
bufferevent_socket_connect(struct bufferevent *bev,
    const struct sockaddr *sa, int socklen)
parameters: 
    bev  :  bufferevent节点
    sa   :  服务器的地址信息
  socklen:  地址信息长度
  
return value:
   0  ---成功
   -1 ----失败

descript: 
	address 和 addrlen 参数跟标准调用 connect()的参数相同。如果还没有为 bufferevent 设置套接字,调