这一小节继续讲解各个观察器(Watcher).
上一小节已经讲解了ev_io(IO可读可写观察器)，ev_stat(文件属性变化观察器)，ev_signal(信号处理观察器)，ev_timer(定时器)，ev_periodic(周期任务处理)，ev_child(子进程状态变化观察器)。这一小节准备讲ev_fork(创建的进程时的观察器)，ev_async(异步调用观察器)，ev_cleanup(event loop退出时触发事件)，ev_prepare(每次event loop之前事件),ev_check(每次event loop之后事件)，ev_idle(每次event loop空闲触发事件).
ev_async (ev_async当ev_async_send通过watcher调用时调用，触发EV_ASYNC)
1 #include <stdio.h>
2 #include <string.h>
3 #include <unistd.h>
4 #include <stdlib.h>
5 #include <ev.h>
6
7 ev_async async_watcher;
8
9 static void sigint_callback(struct ev_loop *loop,ev_signal * w,int revents)
10 {
11 if(revents & EV_SIGNAL)
12 {
13 printf("Call sigint_callback\n");
14 printf("ev_async_send 调用前 %d\n",ev_async_pending(&async_watcher));
15 ev_async_send(loop,&async_watcher);//这里会调用async_callback
16 printf("ev_async_send 调用后 %d\n",ev_async_pending(&async_watcher));
17 }
18 }
19
20 static void sigquit_callback(struct ev_loop *loop,ev_signal *w,int revetns)
21 {
22 printf("Call sigquit_callback\n");
23 ev_break(loop,EVBREAK_ALL);
24 }
25
26 static void async_callback(struct ev_loop *loop,ev_async *w,int revents)
27 {
28 if(revents & EV_ASYNC)
29 {
30 printf("Call async_callback\n");
31 }
32 }
33
34 int main(int argc, char **args)
35 {
36 struct ev_loop *main_loop=ev_default_loop(0);
37
38 ev_init(&async_watcher,async_callback);
39 ev_async_start(main_loop,&async_watcher);
40
41 ev_signal sigint_watcher;
42 ev_init(&sigint_watcher,sigint_callback);
43 ev_signal_set(&sigint_watcher,SIGINT);
44 ev_signal_start(main_loop,&sigint_watcher);
45
46 ev_signal sigquit_watcher;//这里的ev_signal不能与上面共用,必须在声明一个变量
47 ev_init(&sigquit_watcher,sigquit_callback);
48 ev_signal_set(&sigquit_watcher,SIGQUIT);
49 ev_signal_start(main_loop,&sigquit_watcher);
50
51 ev_run(main_loop,0);
52 return 0;
53 }
下面这个是运行截图
可以看出程序ev_async这个是通过ev_async_send来驱动async_callback这个回调函数执行的。而且ev_async_pending这个也是可以判断ev_async是否处于pending状态。我在第15行处增加了sleep(1)后，运行的结构还是一样，可以看出ev_async所绑定的回调函数是处于pending状态而不是另外开一个线程(进程)来执行的。
从上面的处理机制看，好像就是发送一个信号，然后ev_async就调用回调函数去执行，好像跟ev_signal一样，没有什么特点啊。这里给出官方文档的解释。
This functionality is very similar to ev_signal watchers, as signals, too, are asynchronous in nature, and signals, too, will be compressed (i.e. the number of callback invocations may be less than the number of ev_async_sent calls). Unlike ev_signal watchers, ev_async works with any event loop, not just the default loop.
上面说到，不同与ev_signal watchers的是，ev_async可以在多种event loop，而不是默认的loop。前几小节已经讲到ev_loop 的创建，可以通过ev_loop_new进行创建(创建异步事件什么的)。具体的用法这里还不是很清楚，先跳过。
ev_fork (开辟进程时观察器)
1 #include <stdio.h>
2 #include <string.h>
3 #include <unistd.h>
4 #include <stdlib.h>
5 #include <ev.h>
6
7 static void fork_callback(struct ev_loop *loop,ev_fork *w,int revents)
8 {
9 printf("Call fork_callback\n");
10 }
11
12 static void timeout_callback(struct ev_loop*loop,ev_timer *w,int revents)
13 {
14 printf("Time Out\n");
15 ev_break(loop,EVBREAK_ALL);
16 }
17
18 int main(int argc, char **args)
19 {
20 struct ev_loop *main_loop=ev_default_loop(0);
21
22 ev_fork fork_watcher;
23 ev_init(&fork_watcher,fork_callback);
24 ev_fork_start(main_loop,&fork_watcher);
25
26 ev_timer timer_watcher;
27 ev_init(&timer_watcher,timeout_callback);
28 ev_timer_set(&timer_watcher,3,0);
29 ev_timer_start(main_loop,&timer_watcher);
30
31 switch(fork())
32 {
33 case -1:
34 break;
35 case 0://child
36 //ev_loop_fork(main_loop);
37 break;
38 }
39
40 ev_run(main_loop,0);
41 return 0;
42 }
上面这个代码没有输出Call fork_callback，如果把第36行的注释去掉，就会输出Call fork_callback了，可以说明这个ev_fork不是针对fork函数创建的进程。而是要ev_loop_fork针对ev_loop 创建的loop。具体解释的不是很清楚，下面给出官方文档:
Fork watchers are called when a fork () was detected (usually because whoever is a good citizen cared to tell libev about it by calling ev_default_fork or ev_loop_fork). The invocation is done before the event loop blocks next and before ev_check watchers are being called, and only in the child after the fork. If whoever good citizen calling ev_default_fork cheats and calls it in the wrong process, the fork handlers will be invoked, too, of course.
loop的创建小解
1 struct ev_loop *ev_default_loop (unsigned int flags) 2 struct ev_loop *ev_loop_new (unsigned int flags) 3 //这两个函数都是默认原始化一个loop，区别是第一个不是线程安全的，第二个不能捕捉信号和子进程的watcher。 4 //参数flags可以为下面几种类型： 5 //引用 6 #define EVFLAG_AUTO 0x00000000U /* not quite a mask */ 7 /* flag bits */ 8 #define EVFLAG_NOENV 0x01000000U /* do NOT consult environment */ 9 #define EVFLAG_FORKCHECK 0x02000000U /* check for a fork in each iteration */ 10 /* method bits to be ored together */ 11 #define EVBACKEND_SELECT 0x00000001U /* about anywhere */ 12 #define EVBACKEND_POLL 0x00000002U /* !win */ 13 #define EVBACKEND_EPOLL 0x00000004U /* linux */ 14 #define EVBACKEND_KQUEUE 0x00000008U /* bsd */ 15 #define EVBACKEND_DEVPOLL 0x00000010U /* solaris 8 */ /* NYI */ 16 #define EVBACKEND_PORT 0x00000020U /* solaris 10 */ 17 ev_default_fork () 18 ev_loop_fork (loop) 19 //这两个函数就是当你在子进程里须要 运用 libev的函数的之前必须要调用。他们的区别是第二个函数是当运用 ev_loop_new建立 的loop时，才用第二个函数,也就是说重用父进程建立 的loop。 20 ev_loop (loop, int flags) 21 //开始事件循环。 22 ev_TYPE_init (ev_TYPE *watcher, callback, [args]) 23 //原始化一个watcher。TYPE也就是libev支持的事件类型，比如io，比如time等等。。 24 //第一个参数为一个watcher,第二个回调函数，第三个句柄，第四个事件类型。包含下面几种： 25 //引用 26 #define EV_UNDEF -1 /* guaranteed to be invalid */ 27 #define EV_NONE 0x00 /* no events */ 28 #define EV_READ 0x01 /* ev_io detected read will not block */ 29 #define EV_WRITE 0x02 /* ev_io detected write will not block */ 30 #define EV_IOFDSET 0x80 /* internal use only */ 31 #define EV_TIMEOUT 0x00000100 /* timer timed out */ 32 #define EV_PERIODIC 0x00000200 /* periodic timer timed out */ 33 #define EV_SIGNAL 0x00000400 /* signal was received */ 34 #define EV_CHILD 0x00000800 /* child/pid had status change */ 35 #define EV_STAT 0x00001000 /* stat data changed */ 36 #define EV_IDLE 0x00002000 /* event loop is idling */ 37 #define EV_PREPARE 0x00004000 /* event loop about to poll */ 38 #define EV_CHECK 0x00008000 /* event loop finished poll */ 39 #define EV_EMBED 0x00010000 /* embedded event loop needs sweep */ 40 #define EV_FORK 0x00020000 /* event loop resumed in child */ 41 #define EV_ASYNC 0x00040000 /* async intra-loop signal */ 42 #define EV_ERROR 0x80000000 /* sent when an error occurs */ 43 //引用 44 ev_TYPE_start (loop *, ev_TYPE *watcher) 45 //启动一个watcher。
1 switch(fork())
2 {
3 case -1:
4 break;
5 case 0://child
6 ev_loop_fork(main_loop);//使用父进程main_loop
7 ev_timer timer_watcher1;
8 ev_init(&timer_watcher1,timeout_callback);
9 ev_timer_set(&timer_watcher1,3,0);
10 ev_timer_start(main_loop,&timer_watcher1);
11 break;
12 }
上面代码如果修改如下是可以编译通过的。就是在父进程中的main_loop中再增加一个watcher，这个程序将会输出三次Time Out。注意如果没有第六行的ev_loop_fork是编译不通过的。大概的原因是ev库设计的原因。
下面给出一个例子，用于以后可以参考用
1 #include <ev.h>
2 #include <stdio.h>
3
4 //不同的watcher
5 ev_io stdin_watcher;
6 ev_timer timeout_watcher;
7 ev_timer timeout_watcher_child;
8
9 //标准输入的回调函数
10 static void stdin_cb (EV_P_ ev_io *w, int revents)
11 {
12 puts ("stdin ready");
13 ev_io_stop (EV_A_ w);
14 ev_unloop (EV_A_ EVUNLOOP_ALL);
15 }
16
17 //父进程的定时器回调函数
18 static void timeout_cb (EV_P_ ev_timer *w, int revents)
19 {
20 puts ("timeout");
21 ev_unloop (EV_A_ EVUNLOOP_ONE);
22 }
23 //子进程的定时器回调函数
24 static void timeout_cb_child (EV_P_ ev_timer *w, int revents)
25 {
26 puts ("child timeout");
27 ev_unloop (EV_A_ EVUNLOOP_ONE);
28 }
29
30 static void fork_callback(struct ev_loop *loop,ev_fork *w,int revents)
31 {
32 printf("Call fork_callback\n");
33 }
34
35 int main (void)
36 {
37 //创建一个backend为select的loop
38 struct ev_loop *loop = ev_loop_new(EVBACKEND_SELECT);
39
40 //初始化并启动父进程的watcher
41 ev_timer_init(&timeout_watcher, timeout_cb, 10, 0.);
42 ev_timer_start(loop, &timeout_watcher);
43 switch (fork()) {
44 case -1:
45 return -1;
46 case 0:
47 //使用父进程loop。
48 ev_loop_fork(loop);
49 //子进程的loop
50 struct ev_loop *loop_child = ev_loop_new (EVBACKEND_SELECT);
51 ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
52 ev_io_start (loop, &stdin_watcher);
53 ev_timer_init(&timeout_watcher_child, timeout_cb_child, 5.5, 0.);
54 ev_timer_start(loop_child, &timeout_watcher_child);
55 ev_loop(loop_child,0);
56 }
57
58 //等待事件
59 ev_loop (loop, 0);
60 return 0;
61 }
ev_cleanup event loop 退出触发事件
1 #include <stdio.h>
2 #include <string.h>
3 #include <unistd.h>
4 #include <stdlib.h>
5 #include <ev.h>
6
7 struct ev_loop *main_loop;
8
9 static void program_exits(void)
10 {
11 printf("Call AtExit\n");
12 ev_loop_destroy(EV_DEFAULT);//注释掉43行处代码，该函数在这里没有调用到cleanup_callback，但是却执行没有错误
13 }
14
15 static void cleanup_callback(struct ev_loop *loop,ev_cleanup *w,int revents)
16 {
17 printf("Call cleanup_callback\n");
18 }
19
20 static void timer_callback(struct ev_loop *loop,ev_timer *w,int revents)
21 {
22 printf("Call timer_callback\n");
23 }
24
25 int main(int argc, char **args)
26 {
27 //struct ev_loop *main_loop=ev_default_loop(0);//error 注意ev_loop_destroy与ev_loop_new对应
28 main_loop=ev_loop_new(EVBACKEND_EPOLL);
29
30 ev_cleanup cleanup_watcher;
31 ev_init(&cleanup_watcher,cleanup_callback);
32 ev_cleanup_start(main_loop,&cleanup_watcher);
33
34 ev_timer timer_watcher;
35 ev_init(&timer_watcher,timer_callback);
36 ev_timer_set(&timer_watcher,0.2,0);
37 ev_timer_start(main_loop,&timer_watcher);
38
39 atexit(program_exits);
40
41 ev_run(main_loop,0);
42
43 ev_loop_destroy(main_loop);//在这里就可以调用到cleanup_callback
44 printf("END\n");
45 return 0;
46 }
运行时截图
ev_prepare (每次event loop之前事件)
ev_check (每次event loop之后事件)
1 #include <stdio.h>
2 #include <string.h>
3 #include <unistd.h>
4 #include <stdlib.h>
5 #include <ev.h>
6
7 static void prepare_callback(struct ev_loop *loop,ev_prepare *w,int revents)
8 {
9 printf("Prepare Callback\n");
10 }
11
12 static void check_callback(struct ev_loop *loop,ev_check *w,int revents)
13 {
14 printf("Check Callback\n");
15 }
16
17 static void timer_callback(struct ev_loop *loop,ev_timer *w,int revents)
18 {
19 printf("Timer Callback\n");
20 }
21
22 static void sigint_callback(struct ev_loop *loop,ev_signal *w,int revents)
23 {
24 printf("Sigint Callback\n");
25 ev_break(loop,EVBREAK_ALL);
26 }
27
28 int main(int argc, char **args)
29 {
30 struct ev_loop *main_loop=ev_default_loop(0);
31
32 ev_prepare prepare_watcher;
33 ev_check check_watcher;
34 ev_timer timer_watcher;
35 ev_signal signal_watcher;
36
37 ev_prepare_init(&prepare_watcher,prepare_callback);
38 ev_check_init(&check_watcher,check_callback);
39 ev_timer_init(&timer_watcher,timer_callback,2,0);
40 ev_signal_init(&signal_watcher,sigint_callback,SIGINT);
41
42 ev_prepare_start(main_loop,&prepare_watcher);
43 ev_check_start(main_loop,&check_watcher);
44 ev_timer_start(main_loop,&timer_watcher);
45 ev_signal_start(main_loop,&signal_watcher);
46
47 ev_run(main_loop,0);
48 return 0;
49 }
运行结果
看前三个为一组，我测试了几次都是这样，Timer Callback的输出都是在Check之后，这个不知道为什么不过后面的捕获SIGINT信号就没有这个问题，SIGINT信号的回调函数的输出是处于Prepare和Check之间。这个就符合预想。还有就是我们输入一个Ctrl-C时，也会触发Prepare-Check的回调函数。这个倒是没有想到，应该是一个ev_signal会向ev_loop里放入两个处理过程，一个是Linux默认的捕获SIGINT信号(signal函数)一个是我们的回调函数，大概是在默认的回调函数中调用我们的回调函数，毕竟捕获信号是系统调用。上面这个是我的猜想(理解)，不一定是正确的。
ev_idle (每次event loop空闲触发事件)
1 #include <stdio.h>
2 #include <string.h>
3 #include <unistd.h>
4 #include <stdlib.h>
5 #include <ev.h>
6
7 ev_idle idle_watcher;
8 int count=0;
9
10 static void timer_callback_start(struct ev_loop *loop,ev_timer *w,int revents)
11 {
12 printf("Timer Callback Start\n");
13 ev_idle_start(loop,&idle_watcher);
14 }
15 static void timer_callback_stop(struct ev_loop *loop,ev_timer *w,int revents)
16 {
17 printf("Timer Callback Stop\n");
18 ev_idle_stop(loop,&idle_watcher);
19 }
20
21 static void sigint_callback(struct ev_loop *loop,ev_signal *w,int revents)
22 {
23 printf("Sigint Callback\n");
24 ev_break(loop,EVBREAK_ALL);
25 }
26
27 static void idle_callback(struct ev_loop *loop,ev_idle *w,int revents)
28 {
29 count++;
30 }
31
32 int main(int argc, char **args)
33 {
34 struct ev_loop *main_loop=ev_default_loop(0);
35
36 ev_timer timer_watcher_start;
37 ev_timer timer_watcher_stop;
38 ev_signal signal_watcher;
39
40 ev_idle_init(&idle_watcher,idle_callback);
41 ev_timer_init(&timer_watcher_start,timer_callback_start,1,0);
42 ev_timer_init(&timer_watcher_stop,timer_callback_stop,3,0);
43 ev_signal_init(&signal_watcher,sigint_callback,SIGINT);
44
45 ev_timer_start(main_loop,&timer_watcher_start);
46 ev_timer_start(main_loop,&timer_watcher_stop);
47 ev_signal_start(main_loop,&signal_watcher);
48
49 ev_run(main_loop,0);
50
51 printf("从第1秒到第3秒之间count计数器的累加到 %d\n",count);
52 return 0;
53 }
运行结果
我们的idle是可以控制开始和结束的。而这个idle的作用是但event_loop处于空闲的时候，与其在ev_run阻塞等待，不如利用这时的cpu时间来做其他事。应用的话，就是如果服务器繁忙的话就主要处理请求等，如果服务器请求不多时，可以利用cpu时间来处理备份什么的，这样就可以最大限度的利用cpu了。
观察器watcher差不多就这些了，还有个ev_embed这个还不会用。
参考资料: http://wangjunle23.blog.163.com/blog/static/11783817120124308920321/
: http://simohayha.iteye.com/blog/306712
本文地址: http://www.cnblogs.com/wunaozai/p/3955156.html
来源：https://www.cnblogs.com/wunaozai/p/3955156.html