Five ways to implement scheduled tasks in PHP

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 the implementation decision of PHP 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 being called, it will automatically exit the memory and has no resident memory.

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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{
  $run = include 'config.php';
  if(!$run) die('process abort');
   
  //ToDo
  sleep($interval);// 等待5分钟
}
while(true);

Stop the program by changing return 0 in config.php. 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: It takes up system resources, and if it runs for a long time, there will be some unexpected hidden dangers. For example, memory management issues.

3. Simple improved

<?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 continues to execute by accessing itself after a period of time. Just like a relay race ..This will 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 time_out limit is exceeded. But it is best to add the control code. cofig.php as above, so that the process can be terminated.

4. Server scheduled tasks

UnixPlatform

If you use a Unix system, you need to add a special line of code at the beginning of your PHP script so that it can be executed, so that the system can know what kind of The program wants 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 a normal shell script in Crontab (specific Crontab usage), use the PHP program to call PHP The script executes myscript.php every hour as follows:

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

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

2. Use URL to execute scripts in Crontab

If your PHP script can be triggered by URL, you can use lynx or curl or wget to configure your Crontab .

The following example uses a Lynx text browser to access a URL to execute a PHP script every hour. Lynx text browser uses conversational mode to open URLs by default. However, as shown below, we use the -dump option on the lynx command line to convert the URL output to standard output.

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

The following example uses WGET to access the URL to execute a PHP script every 10 minutes. The -q option indicates quiet mode. "-O temp.txt" means output will be sent to a temporary file.

*/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 to set the value of php.ini, which 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.

Function format:

string ini_set(string $varname, string $newvalue)

Not all parameters can be configured, you can view the list in the manual.

Common settings:

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

menory_limit: Set the maximum number of memory bytes that a script can apply for, which helps poorly written scripts consume the 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 session processing. When set to 1, you do not need to manually open the session with session_start() in the program. You can also use session.

If the parameter is 0, there is no If you open the session manually, an error will be reported.

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

session.cache_expire: Specifies the limited period (minutes) of the 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: Whether to use cookies to save the session ID on the client;

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

session.use_trans_sid: Whether to use clear code to display the SID (session ID) in the URL,

The default is prohibited because it will bring security risks to your users:

Users may tell other people the URL containing a valid sid through email/irc/QQ/MSN, etc.

URLs containing valid SIDs may be saved on public computers.

Users may save URLs with fixed SIDs in their favorites or browsing history. URL-based session management always carries more risks than cookie-based session management and should be disabled.

PHP scheduled tasks are a very interesting thing. The above are some of the solutions provided in this article. You can also develop your own solution through the ideas of this article. Hope it helps everyone in need.

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