PHP使用1个crontab管理多个crontab任务

lihu129c

　　http://www.binarytides.com/php-manage-multiple-cronjobs-with-a-single-crontab-entry/
　　
　　In many php applications there are multiple tasks that need to be run via cron at different times. In a typical application you may be doing the following tasks via cronjobs :
　　1. Backup database.
2. Send out email to subscribers.
3. Clear temporary files.
4. Fetch xml feeds from some source and store them in database.
　　So if you had separate php files doing these tasks , and had a cronjob entry for each , your cronjob could look like this :


MAILTO="happy@birthday.com"
0 0 * * * /var/www/my_app/backup_database.php
12 2 * * * /var/www/my_app/email_to_subscribers.php
10 5 * * * /var/www/my_app/clear_temp_files.php
10 7 * * * /var/www/my_app/fetch_xml_feeds.php　　The above is the simplest approach to manage multiple cronjobs for your php application. However this approach has many drawbacks :
　　1. Multiple entries in crontabs means more time and effort needed to edit the crontab and maintain it.
　　- Since this approach involves writing each task separately in the cron list , it becomes difficult to maintain.
　　2. The crontab command has to be used everytime a change is to be made.
　　- You need to either manually do a `crontab -t` in the shell prompt or make your php application do it , everytime there is a change in either the tasks or their timing.
　　3. If the script name changes then have to edit the crontab file again.
4. A log email would be generated for every cron run, creating multiple log emails.
　　- Every task that is running would generate a cronlog and email itself to the email specified
　　5. Inefficient when there are 10s or 100s of tasks to be run via cron.
　　- Do you think it is a good idea if you had many many tasks to do.

An alternative solution
　　How about having only 1 entry in the cronjobs, and that 1 cronjob manages the rest of the cronjobs.
　　1. Add only 1 task to the crontab rule say :

1	* * * * * php /path/to/cronjob.php

　　The cronjob.php file would run all the tasks that need to be run via cron. Its important to note that this cronjob.php will run every minute and forever. Do not be worried about it eating too much of system resources. It is a faily light thing and does not load your CPU or RAM with anything heavy.(注意这个cronjob.php会每分钟执行一次，而且一直会一直这样。不必担心这会消耗太多系统资源，这是一个非常轻量级的东西，它不会额外占用你的CPU和内存)
　　Now the next thing would be to make sure cronjob.php can run all the tasks at the right time.
　　2. Now we need to have different tasks have a different cron schedule. Lets say there are 3 different tasks to run at 3 different times :


0 5 * * * database_backup
0 5 1,15 * * monthly_sales_report
0 10 15 02 * purchase_report

　　
　　The cronjob.php that runs every minute should have an array like this :

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$cronjobs = array(); $cronjobs['database_backup'] = '0 5 * * *'; $cronjobs['monthly_sales_report'] = '0 5 1,15 * *'; $cronjobs['purchase_report'] = '0 10 15 02 *';

　　Now we test each job/task for the timestamp and run it like this :

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foreach($cronjobs as $method => $cron) {     $time = time();         if( is_time_cron($time , $cron) )     {         $result = $method();         echo $result;     } }

　　is_time_cron checks if the current timestamp matches the cron schedule or not. If it matches , then the task is executed. Theis_time_cron method can be found in the previous post here.
　　In this approach the benefits are :
　　1. Only 1 crontab entry.
　　The crontab list is clean and your application does not overload it.
　　2. Easy to maintain , does not need any modification unless the script path/name changes.
　　The crontab once created does not need any change unless the name or path of 'cronjob.php' changes. Meanwhile the jobs inside cronjob.php can change their names , schedules and anything very easily.
　　3. To add/edit/remove tasks or change their time schedules only the cronjob.php needs to be changed.
　　This means easier modification , maintenance and the application can provide simple user interface to make changes anytime without the need to use crontab commands or anything as such.
　　The above mentioned approach can be applied to any language , not just php.
　　
　　
　　附加：判断当前时间蹉是否符合某个cronjob
　　http://www.binarytides.com/php-check-if-a-timestamp-matches-a-given-cron-schedule/



PHP check if a timestamp matches a given cron schedule

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desktop:~$ php -a Interactive shell php > echo time(); 1319362432 php >

　　
　　Above is an example of a given timestamp.
　　And a cron schedule can look like this 0 5 * * * - which means run everyday at 5 hours and 0 minutes.
　　Now in a php application you may need to test if a given timestamp , say 1319362432 matches a given cron schedule like 0 5 * * *.
　　Here is a quick php function that can do this task.

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/**     Test if a timestamp matches a cron format or not     //$cron = '5 0 * * *'; */ function is_time_cron($time , $cron) {     $cron_parts = explode(' ' , $cron);     if(count($cron_parts) != 5)     {         return false;     }           list($min , $hour , $day , $mon , $week) = explode(' ' , $cron);           $to_check = array('min' => 'i' , 'hour' => 'G' , 'day' => 'j' , 'mon' => 'n' , 'week' => 'w');           $ranges = array(         'min' => '0-59' ,         'hour' => '0-23' ,         'day' => '1-31' ,         'mon' => '1-12' ,         'week' => '0-6' ,     );           foreach($to_check as $part => $c)     {         $val = $$part;         $values = array();                   /*             For patters like 0-23/2         */         if(strpos($val , '/') !== false)         {             //Get the range and step             list($range , $steps) = explode('/' , $val);                          //Now get the start and stop             if($range == '*')             {                 $range = $ranges[$part];             }             list($start , $stop) = explode('-' , $range);                               for($i = $start ; $i <= $stop ; $i = $i + $steps)             {                 $values[] = $i;             }         }         /*             For patters like :             2             2,5,8             2-23         */         else         {             $k = explode(',' , $val);                          foreach($k as $v)             {                 if(strpos($v , '-') !== false)                 {                     list($start , $stop) = explode('-' , $v);                                       for($i = $start ; $i <= $stop ; $i++)                     {                         $values[] = $i;                     }                 }                 else                 {                     $values[] = $v;                 }             }         }                   if ( !in_array( date($c , $time) , $values ) and (strval($val) != '*') )         {             return false;         }     }           return true; } var_dump(time() , '0 5 * * *');  //true or false

　　How does it work
　　The above code uses the date format specifiers as follows :
'min' => 'i' ,
'hour' => 'G' ,
'day' => 'j' ,
'mon' => 'n' ,
'week' => 'w'
　　over the timestamp to extract the minute , hour , day , month and week of a timestamp
　　Then it checks the cron format by splitting it into parts like 0 , 5 , * , * , * and then tests each part for the corresponding value from timestamp.