libev 简单用法示例

ubuntu下安装libev开发包：

$ sudo apt-get install libev-dev

下面是libev的man page自带的libev用法示例，保存到testlibev.c

// a single header file is required
#include <ev.h>

#include <stdio.h> // for puts

// 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_ 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_run’s to stop iterating
    ev_break (EV_A_ EVBREAK_ALL);
}

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

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

    // 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_run (loop, 0);

    // unloop was called, so exit
    return 0;
}

编译：

gcc testlibev.c -lev -o testlibev

运行：

 ./testlibev
timeout
./testlibev
a
stdin ready
第一个没有输入，所以等到5.5秒后超时。
第二个输入a，所以stdin监测到事件退出。

首先来看ev_io_init中做了些什么操作：

ev.h文件中

#define  ev_io_init(ev,cb,fd,events)         

    do { ev_init ((ev), (cb)); ev_io_set  ((ev),(fd),(events)); } while (0)

   

#define  ev_init(ev,cb_) do {                     \

  ((ev_watcher *)(void  *)(ev))->active  =       \

  ((ev_watcher *)(void *)(ev))->pending =  0;    \

  ev_set_priority ((ev), 0);                    \

  ev_set_cb ((ev), cb_);                        \

} while  (0)

 

#define  ev_io_set(ev,fd_,events_)          

    do { (ev)->fd = (fd_); (ev)->events  = (events_) | EV__IOFDSET; } while (0)

 

#define  ev_set_cb(ev,cb_)                  

    ev_cb (ev) = (cb_)

 

#define  ev_cb(ev)                           

    (ev)->cb /* rw */

 

通过定义可以看出ev_io_init主要操作是：

&stdin_watcher->active=stdin_watcher->pending=0；

&stdin_watcher->priority=0；

&stdin_watcher->cb=stdin_cb(函数)；

&stdin_watcher->fd；

&stdin_watcher->events=EV_READ|EV__IOFDSET

同样,ev_io_start做了一些赋值操作,这里不过多讲解；

 

下面通过一张函数调用图来展libev的函数调用：