Implementation principle of scheduled tasks in PHP_PHP tutorial

A brief introduction to some relevant knowledge according to the PHP manual:

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 the PHP script runs normally in the NORMAL state, the connection is efficient. When the remote client disconnects, the ABORTED status flag will be turned on. 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.

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 controlled by ignore_user_abort in php.ini or by the corresponding "php_value ignore_user_abort" and ignore_user_abort() functions in the Apache .conf settings. If PHP is not told to ignore user interruptions, the script will be interrupted unless a shutdown triggering 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 changed by setting max_execution_time in php.ini or the corresponding "php_value max_execution_time" parameter in the Apache .conf settings or the set_time_limit() function. 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 caused the shutdown trigger function to be called by calling the connection_status() function. If a timeout results in a call to the shutdown triggering function, the function returns 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. I found two methods from the Internet: ignore_user_abort() and crontab

The ignore_user_abort() function can be used with set_time_limit(0) and sleep($interval) to realize the automatic running and updating of the program. The following is an example

Copy code Code As follows:

ignore_user_abort(); //Even if the Client is disconnected (such as closing the browser), the PHP script can continue to execute.
set_time_limit(0); //The execution time is none Limit, the default execution time of PHP is 30 seconds. Through set_time_limit(0), the program can be executed without limit
$interval=60*5; // Run every 5 minutes
do{
$ fp = fopen('test.txt','a');
fwrite($fp,'test');
fclose($fp);
sleep($interval); // Wait 5 minutes
}while(true);

As long as you run the page above 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 to schedule the execution of some commands at a certain time interval.
crontab usage: crontab [ -e | -l | -r ] File name -e: edit task -l: display task information -r: delete scheduled execution task information

crontab format:
* * * * * Command
Command to be run by time, day, month and week

crontab example:

*/5 * * * * lynx http://www. jb51.net
Visit www.jb51.net every 5 minutes

0 8 * * * lynx http://www.jb51.net
Visit www.jb51.net every morning at 8 o'clock

0 10 6 * 1-5 lynx http://www.jb51.net
Visit www.jb51 on the 6th of every month and every Monday to Friday at 10 am. net

0 5 7 8 * lynx http://www.jb51.net
Visit www.jb51.net at 5 am on August 7th

The special meanings of the above :
"*" represents all numbers within the value range, "/" represents every, "*/5" represents every 5 units, "-" represents from a certain number to a certain number," ,"separate several discrete numbers.

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