纯PHP实现定时器任务（Timer）
定时器任务，在WEB应用比较常见，如何使用PHP实现定时器任务，大致有两种方案：1）使用Crontab命令，写一个shell脚本，在脚本中调用PHP文件,然后定期执行该脚本；2）配合使用ignore_user_abort()和set_time_limit()，使脚本脱离浏览器运行。前者是利用Linux的特性，和PHP本身没有多大关系，后者使用场景有限，且只能由一次HTTP请求触发该脚本，执行完后退出。那么我们如何使用纯PHP实现纯粹的定时器任务，且能适应认识任务业务需求？
基础知识
此程序在Linux下开发，以cli模式运行，一下是基本知识的简要介绍。
CLI：PHP的命令行模式，常见的WEB应用使用的是fpm；
进程：进程是程序运行的基本单元，进程之间是独立运行且互不干扰的，有独立的运行空间，每个进程都有一个进程控制块；
进程间通信：既然进程是独立运行，我们需要一种机制保证不同进程信息的交换，进程间通信主要包括：管道，IPC（共享内存，信号，消息队列），套接字；
PCNTL扩展：PHP的一个进程扩展，主要用到pcntl_alarm()函数，详细介绍请查阅官网.
实现原理
用一个三维数组保存所有需要执行的任务，一级索引为时间戳,值为执行任务的方法、回调参数等,具体数组形式如下:
array(
'1438156396' => array(
array(1,array('Class','Func'), array(), true),
)
)
说明:
1438156396 时间戳
array(1,array('Class','Func'), array(), true)
参数依次表示: 执行时间间隔,回调函数,传递给回调函数的参数,是否持久化(ture则一直保存在数据中,否则执行一次后删除)
这些任务可以是任意类的方法。既然是定时任务，我们需要一个类似计时的东东，此方案采用信号量去做，每一秒向当前进程发送SIGALRM信号，并捕获该信号，触发信号处理函数，循环遍历数据，判断是否有当前时间需要执行的任务。如果有则采用回调方式触发，并把参数传递给该方法。
1 <?php
2 /**
3 *定时器
4 */
5 class Timer
6 {
7 //保存所有定时任务
8 public static $task = array();
9
10 //定时间隔
11 public static $time = 1;
12
13 /**
14 *开启服务
15 *@param $time int
16 */
17 public static function run($time = null)
18 {
19 if($time)
20 {
21 self::$time = $time;
22 }
23 self::installHandler();
24 pcntl_alarm(1);
25 }
26 /**
27 *注册信号处理函数
28 */
29 public static function installHandler()
30 {
31 pcntl_signal(SIGALRM, array('Timer','signalHandler'));
32 }
33
34 /**
35 *信号处理函数
36 */
37 public static function signalHandler()
38 {
39 self::task();
40 //一次信号事件执行完成后,再触发下一次
41 pcntl_alarm(self::$time);
42 }
43
44 /**
45 *执行回调
46 */
47 public static function task()
48 {
49 if(empty(self::$task))
50 {//没有任务,返回
51 return ;
52 }
53 foreach(self::$task as $time => $arr)
54 {
55 $current = time();
56
57 foreach($arr as $k => $job)
58 {//遍历每一个任务
59 $func = $job['func']; /*回调函数*/
60 $argv = $job['argv']; /*回调函数参数*/
61 $interval = $job['interval']; /*时间间隔*/
62 $persist = $job['persist']; /*持久化*/
63
64 if($current == $time)
65 {//当前时间有执行任务
66
67 //调用回调函数,并传递参数
68 call_user_func_array($func, $argv);
69
70 //删除该任务
71 unset(self::$task[$time][$k]);
72 }
73 if($persist)
74 {//如果做持久化,则写入数组,等待下次唤醒
75 self::$task[$current+$interval][] = $job;
76 }
77 }
78 if(empty(self::$task[$time]))
79 {
80 unset(self::$task[$time]);
81 }
82 }
83 }
84
85 /**
86 *添加任务
87 */
88 public static function add($interval, $func, $argv = array(), $persist = false)
89 {
90 if(is_null($interval))
91 {
92 return;
93 }
94 $time = time()+$interval;
95 //写入定时任务
96 self::$task[$time][] = array('func'=>$func, 'argv'=>$argv, 'interval'=>$interval, 'persist'=>$persist);
97 }
98
99 /**
100 *删除所有定时器任务
101 */
102 public function dellAll()
103 {
104 self::$task = array();
105 }
106 }
这是定时器类核心部分,有一个静态变量保存有所有需要执行的任务,这里为什么是静态的呢?大家自行思考.当进程接受到 SIGALRM 信号后,触发 signalHandler 函数,随后循序遍历数组查看是否有当前时间需要执行的任务,有则回调,并传递参数,删除当前job,随后检查是否要做持久化任务,是则继续将当前job写入事件数组等待下次触发,最后再为当前进程设置一个闹钟信号.可以看出这个定时器,只要触发一次就会从内部再次触发,得到自循环目的.
1 <?php
2
3 class DoJob
4 {
5 public function job( $param = array() )
6 {
7 $time = time();
8 echo "Time: {$time}, Func: ".get_class()."::".__FUNCTION__."(".json_encode($param).")\n";
9 }
10 }
这是回调类及函数,为方便说明,加入不少调试信息.Timer类及回调都有了,我们看看使用场景是怎么样的.
1 <?php
2
3 require_once(__DIR__."/Timer.php");
4 require_once(__DIR__."/DoJob.php");
5
6
7 Timer::dellAll();
8
9 Timer::add( 1, array('DoJob','job'), array(),true);
10
11 Timer::add( 3, array('DoJob','job'),array('a'=>1), false);
12
13 echo "Time start: ".time()."\n";
14 Timer::run();
15
16 while(1)
17 {
18 sleep(1);
19 pcntl_signal_dispatch();
20 }
代码非常短,这里注册了两个job,随后运行定时器,在一个无限循环里捕捉信号触发动作,如果不捕获将无法触发事先注册的处理函数.这样一个自循环的定时器开发完成.运行结果如下:
如我们场景类添加的任务一样,在90的时候执行了两个任务,一个为持久化的不带参数的job,一个为非持久化带参数的job,随后非持久化job不再执行.
总结
在收到信号前,当前进程不能退出.这里我使用了条件永远为真的循环.在我们实际生产环境中,需要创造这么一个先决条件,比如说,我们有一组服务,这些服务都是一直运行的,不管是IO访问,等待socket链接等等,当前服务都不会终止,即使进程阻塞也不会有问题,这种场景,也就是有一个一直运行的服务中使用.
目前PHP只支持以秒为单位的触发,不支持更小时间单位,对位定时任务而言基本足够
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