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：