[wp-trac] [WordPress Trac] #17888: Problems with build in Cronjob Schedule - is this a bug?

[WordPress Trac]

#17888: Problems with build in Cronjob Schedule - is this a bug?
--------------------------+-----------------------------
 Reporter:  1manfactory   |      Owner:
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  Cron          |    Version:  3.1.3
 Severity:  normal        |   Keywords:
--------------------------+-----------------------------
 I have programmed a pluging (Emu2 - Email Users 2) to send out mails to
 users/groups. It's still beta but the main functions work.

 Now I added a feature for a digest of the newest posts to be sent out once
 a day controlled by the build in scheduler.

 I do the following:


 {{{
 # plan the scheduler
  add_action('EMU2_task_hook', 'EMU2_send_scheduled');
 }}}


 where EMU2_send_scheduled is the function sending all the mails. This is
 working.


 {{{
 wp_clear_scheduled_hook('EMU2_task_hook');
  wp_schedule_event( strtotime( $schedule_time ) - get_option('gmt_offset')
 * 3600 , 'daily', 'EMU2_task_hook' );
 }}}


 Where $schedule_time is set by the user, e.g. "23:15" for mails to be sent
 at 11:15 pm.

 This works, I checked it with wp-crontrol.

 But now come the problems.

 Some of the users which downloaded my plugin reported strange behaviors
 with the scheduled mails send out every hour instead of only once a day.
 Or with mails send three times in a row.

 I first thought they did something wrong. But after a few days of stable
 work it happened to me as well (Online, less than 10 users, Linux)

 I am using/testing this on 5 installations, online and offline, on
 different hosts and systems (Windows/xampp and Linux). Some work today,
 but they fail the next day with sending two or even three mails at once,
 i.e. starting the job two/three times.

 I have no clue what is going on.

 Is this a bug? Is this caused by interferences with other schedules or
 plugins?

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Ticket URL: <http://core.trac.wordpress.org/ticket/17888>
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