Detailed explanation of five ways to implement scheduled tasks in PHP

This article mainly introduces five methods of implementing scheduled tasks in PHP. Now I will share it with you and give you a reference. Let's take a look together

In the past few days, I need to use PHP to write a server application that regularly crawls web pages. I searched the Internet for solutions and found several solutions, which are summarized as follows.

Scheduled running tasks are a relatively important task for a website, such as regularly publishing documents, regularly cleaning up junk information, etc. Most of today’s websites are developed using PHP dynamic language, and for PHP The implementation determines that it does not have the concept of AppServer such as Java and .Net, and the http protocol is a stateless protocol. PHP can only be triggered and called by the user. After the call, it will automatically exit the memory and has no resident memory.

If you have to use PHP to implement scheduled tasks, you can have the following solutions:

1. Simple, direct and reckless type

<?php
ignore_user_abort();//关掉浏览器，PHP脚本也可以继续执行.
set_time_limit(0);// 通过set_time_limit(0)可以让程序无限制的执行下去
ini_set(&#39;memory_limit&#39;,&#39;512M&#39;); // 设置内存限制
$interval=60*30;// 每隔半小时运行
do{
  //ToDo 
  sleep($interval);// 等待5分钟
}
while(true);

Disadvantages: Once started, it cannot be controlled unless the PHP host is terminated. Do not use this method unless you are a hacker.

2. Simple controllable type

config.php

<?php
return 1;
?>
cron.php


  
ignore_user_abort();//关掉浏览器，PHP脚本也可以继续执行.
set_time_limit(0);// 通过set_time_limit(0)可以让程序无限制的执行下去
$interval=60*30;// 每隔半小时运行
do{
  $run = include &#39;config.php&#39;;
  if(!$run) die(&#39;process abort&#39;);
  
  //ToDo
  sleep($interval);// 等待5分钟
}
while(true);

By changing the return 0 of config.php, To stop the program. A feasible way is to interact with the config.php file and a special form, and set some variables through the HTML page for configuration

Disadvantages: Occups system resources, long-running , there will be some unexpected hidden dangers. For example, memory management issues.

3. Simple improved version

<?php
$time=15;
$url="http://".$_SERVER[&#39;HTTP_HOST&#39;].$_SERVER[&#39;REQUEST_URI&#39;];
/*
  function
*/
sleep($time);
file_get_contents($url);
?>

php script sleep section After the time, continue execution by accessing itself. Just like a relay race. This can ensure that the execution time of each PHP script will not be too long. It will not be restricted by time_out.

Because each cycle of the php file is executed independently, this method avoids the restrictions of time_out. But it is best to add the control code. cofig.php as above, so that it can be terminated Process.

4. Server scheduled tasks

Unix platform

If you use a Unix system, you need Add a special line of code at the top of your PHP script to enable it to be executed, so the system knows what program to use to run the script. The first line of code added for Unix systems will not affect the running of the script under Windows, so you can also use this method to write cross-platform scripts.

1. Use PHP to execute the script in Crontab

Just like calling an ordinary shell script in Crontab (specific Crontab usage), use the PHP program To call the PHP script, execute myscript.php every hour as follows:

# crontab -e
00 * * * * /usr/local/bin/php /home/john/myscript.php

##/usr/local/bin/php is the PHP program path of.

2. Use URL to execute the script in Crontab

00 * * * * lynx -dump http://www.sf.net/myscript.php

The following example uses CURL to access the URL to execute a PHP script every 5 minutes. Curl displays output on standard output by default. Using the "curl -o" option, you can also dump the output of the script to a temporary file temp.txt.

*/5 * * * * /usr/bin/curl -o temp.txt http://www.sf.net/myscript.php

*/10 * * * * /usr/bin/wget -q -O temp.txt http://www.sf.net/myscript.php

5. Detailed explanation of ini_set function usage

PHP ini_set is used Setting the value of php.ini takes effect when the function is executed. After the script ends, the setting becomes invalid. You can modify the configuration without opening the php.ini file, which is very convenient for virtual spaces.

string ini_set(string $varname, string $newvalue)

@ ini_set('memory_limit', '64M');

menory_limit:Set the maximum memory bytes that a script can apply for number, which favors poorly written scripts consuming available memory on the server. The @ symbol means no errors are output.

@ini_set('display_errors', 1);

display_errors: Set the category of error messages.

@ini_set('session.auto_start', 0);

session.auto_start: Whether to automatically open the session processing, when set to 1, there is no need to manually open the session with session_start() in the program You can also use session.

@ini_set('session.cache_expire', 180);

session.cache_expire: Specifies the expiration date (minutes) of the specified session page in the client cache. The default is 180 minutes. If session.cache_limiter=nocache is set, the setting here is invalid.

@ini_set('session.use_cookies', 1);

session.use_cookies：是否使用cookie在客户端保存会话ID；

@ini_set('session.use_trans_sid', 0);

session.use_trans_sid：是否使用明码在URL中显示SID（会话ID），

默认是禁止的，因为它会给你用户带来安全危险：

    用户可能将包含有效的sid的URL通过email/irc/QQ/MSN等途径告诉其他人。

    包含有效sid的URL可能会保存在公用电脑上。

    用户可能保存带有固定不变的SID的URL在他们的收藏夹或者浏览历史记录里。 基于URL的会话管理总是比基于Cookie的会话管理有更多的风险，所以应当禁用。

PHP定时任务是一个非常有意思的东西，以上就是本文提供的一些解决方案，你也可以通过本文的思路，开发出自己的一种解决方案。希望能帮助到有需要的大家。

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