libev库解剖（1）

libev的安装

（注意，libev仅支持linux）

从github下载源码 源码

进入源码目录，安装指令三连：

./configure
make
make install

这样就安装完成了，默认安装在/usr/local/lib

在编写程序时，引用<ev.h>， 并在编译时，指定 -lev 选项就可以了

从示例程序看架构

// a single header file is required
#include <ev.h>
#include <cstdio>
#include <cstdlib>
// every watcher type has its own typedef'd struct
// with the name ev_<type>;

ev_io stdin_watcher;
ev_timer timeout_watcher;

// all watcher callbacks have a similar signature
// this callback is called when data is readable on stdin

static void
stdin_cb (EV_P_ struct ev_io *w, int revents)
{
  puts ("stdin ready");
  // for one-shot events, one must manually stop the watcher
  // with its corresponding stop function.

  ev_io_stop (EV_A_ w);


  // this causes all nested ev_loop's to stop iterating
  ev_unloop (EV_A_ EVUNLOOP_ALL);
}

// another callback, this time for a time-out
static void
timeout_cb (EV_P_ struct ev_timer *w, int revents)
{
  puts ("timeout");
  // this causes the innermost ev_loop to stop iterating
  ev_unloop (EV_A_ EVUNLOOP_ONE);
}

int
main (void)
{
  // use the default event loop unless you have special needs
  struct ev_loop *loop = ev_default_loop (0);

  // initialise an io watcher, then start it
  // this one will watch for stdin to become readable

  ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
  ev_io_start (loop, &stdin_watcher);


  // initialise a timer watcher, then start it
  // simple non-repeating 5.5 second timeout
  ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
  ev_timer_start (loop, &timeout_watcher);


  // now wait for events to arrive
  ev_loop (loop, 0);

  // unloop was called, so exit

  return 0;
}

上述代码为官方提供的一段示例程序，从中我们可以一窥使用libev的基本框架

1. 定义事件监听结构和回调函数

   libev提供了多种事件类型，每种事件类型有其相应的事件监听结构，官方称其为watcher

   ev_io stdin_watcher;
   ev_timer timeout_watcher;
   

   代码中先是声明了ev_io 和 ev_timer两种事件监听结构，io即io事件，timer即定时器事件

   static void
   stdin_cb (EV_P_ struct ev_io *w, int revents)
   {
     puts ("stdin ready");
     // for one-shot events, one must manually stop the watcher
     // with its corresponding stop function.
   
     ev_io_stop (EV_A_ w);
   
   
     // this causes all nested ev_loop's to stop iterating
     ev_unloop (EV_A_ EVUNLOOP_ALL);
   }
   
   // another callback, this time for a time-out
   static void
   timeout_cb (EV_P_ struct ev_timer *w, int revents)
   {
     puts ("timeout");
     // this causes the innermost ev_loop to stop iterating
     ev_unloop (EV_A_ EVUNLOOP_ONE);
   }
   

   继而是两种事件的回调函数，即发生事件后调用的函数。

   回调函数的结构：

   void cb_name(struct ev_loop *loop, xx_watcher *w, int revents);
   

   有三个参数，xx_watcher指的是某种事件监听结构，那种事件的回调就用那种事件的监听结构，比如

   void stdin_cb(struct ev_loop *loop, ev_io *w, int revents);
   

   基本io的回调函数，就用ev_io

   示例中的EV_P_其实就是 struct ev_loop* 的宏

2. 初始化事件循环

   // use the default event loop unless you have special needs
   struct ev_loop *loop = ev_default_loop (0);
   

3. 初始化事件并绑定回调函数

   // initialise an io watcher, then start it
   // this one will watch for stdin to become readable
   ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
   ev_io_start (loop, &stdin_watcher);
   
   
   // initialise a timer watcher, then start it
   // simple non-repeating 5.5 second timeout
   ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
   ev_timer_start (loop, &timeout_watcher);
   

4. 开始事件循环，等待事件

   // now wait for events to arrive
   ev_loop (loop, 0);
   

所以，总体来看，libev的整体架构就是，将事件和事件回调函数相绑定，然后开启事件循环，等待事件到来，事件到来后调用相应的回调函数，然后继续循环。

这是一个典型的异步非阻塞框架，接下来我们深入源码，分析下libev的实现