Principle Analysis of PHP Implementation of Scheduled Tasks

Many people don’t know what php scheduled tasks are, but in our daily development, our php programs often need to execute task plans and execute them regularly, so today we will introduce it to you todayphp Analysis of the implementation principle of planned task !

Based on the php manual briefly introduce some relevant knowledge:

1. Connection processing:

Inside PHP, the system maintains the connection status, and its status has three possible situations:

• 0 - NORMAL (normal)

• 1 - ABORTED (abnormal exit)

• 2 - TIMEOUT (timeout)
  

When PHP The connection is valid when the script runs normally in NORMAL state. When the remote client disconnects, the ABORTED status flag will be turned on. The interruption of the remote client connection is usually caused by the user clicking the STOP button. When the connection time exceeds PHP's time limit, the TIMEOUT status flag will be turned on.

You can decide whether the script needs to exit when the client disconnects. Sometimes it is convenient to have a script run completely, even if no remote browser accepts the script's output. The default is for the script to exit when the remote client connection is lost.

This processing can be done by ignore_user_abort in php.ini or by the corresponding "php_value ignore_user_abort" and in the Apache .conf settings. ignore_user_abort() function to control.

If PHP is not told to ignore user interruptions, the script will be interrupted unless a shutdown trigger function is set via register_shutdown_function(). Through this close trigger function, when the remote user clicks the STOP button and the script tries to output data again, PHP will detect that the connection has been interrupted and call the close trigger function.

Scripts may also be interrupted by the built-in script timer. The default timeout limit is 30 seconds. This value can be set by setting the max_execution_time of php.ini or the corresponding "php_value max_execution_time" parameter in the Apache .conf setting or set_time_limit() function to change.

When the counter times out, the script will exit similar to the above connection interruption situation, and the previously registered shutdown trigger function will also be executed at this time. In the shutdown trigger function, you can check whether the timeout causes the shutdown trigger function to be called by calling the connection_status() function.

If a timeout results in a call to the shutdown trigger function, the function will return 2.

One thing to note is that the ABORTED and TIMEOUT states can be valid at the same time.

This is possible when telling PHP to ignore user exit actions. PHP will still notice that the user has disconnected but the script is still running. If the running time limit is reached, the script will be exited and the set shutdown trigger function will also be executed. At this point you will find that the function connection_status() returns 3.

2. Related functions:

int ignore_user_abort ( [bool setting] ) 
This function sets whether a client disconnect should cause a script to be aborted. 
It will return the previous setting and can be called without an argument to not change the current setting and only return the current setting. 
int connection_aborted ( void ) 
Returns TRUE if client disconnected. 
int connection_status ( void ) 
Returns the connection status bitfield.

In order to update a certain file regularly, the program needs to run automatically, from the Internet Two methods were found: ignore_user_abort() and crontab

##ignore_user_abort()Function collocation set_time_limit(0) and sleep($interval) can realize automatic running and updating of the program. The following is an example.

The code is as follows:

ignore_user_abort(); //即使Client断开(如关掉浏览器)，PHP脚本也可以继续执行. 
set_time_limit(0); // 执行时间为无限制，php默认的执行时间是30秒，通过set_time_limit(0)可以让程序无限制的执行下去 
$interval=60*5; // 每隔5分钟运行 
do{ 
$fp = fopen('test.txt','a'); 
fwrite($fp,'test'); 
fclose($fp); 
sleep($interval); // 等待5分钟 
}while(true);

Just run the above page and then close it, the program will continue to run.

There is a simpler method under Linux, which is the crontab command

The function of the crontab command is certain Schedule the execution of some commands at intervals.

crontab Usage:

crontab [ -e | -l | -r ] File name

• -e: Edit task

  
  

• -l: Display task information

  
  

• -r: Delete scheduled execution task information

  
  

Format of crontab:

* * * * * Command

Command to be run by time, day, month and week

crontab example:

*/5 * * * * lynx http://www.php.cn

Visit www.php.cn every 5 minutes

0 8 * * * lynx http://www.php.cn

Visit www.php.cn at 8 am every day

0 10 6 * 1-5 lynx http://www.php.cn

Every month Visit www.php.cn on the 6th and every Monday to Friday at 10 a.m.

0 5 7 8 * lynx http://www.php.cn

Visit www.php.cn## at 5 a.m. on August 7

#A few special meanings above:

"*" represents all numbers within the value range, "/" represents the meaning of every, "*/ "5" means every 5 units, "-" means from a certain number to a certain number, "," separates several discrete numbers.

Summary:

I believe that through studying this article, many friends should know the implementation principle of PHP scheduled tasks What is it, I hope it will be helpful to your work!

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