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计划任务，顾名思义，就是将一些将来需要做的事情交给Wordpress自动去处理，就像定时发布。有时候我们需要自定义其他的任务，比如自动清理未使用的媒体库图片，自动将注册时间超过某时段的用户升级为高阶角色。

WordPress提供了很方便的方法帮助我们来实现这些功能，该方法分为两类，一类是可重复执行的计划任务，一类是仅执行一次的计划任务。

可重复执行的计划任务

该方法首先需要一个重复的时段，系统默认提供了三个重复时段，可以通过以下方法获取：

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<?php
wp_get_schedules();
?>
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返回值是：

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Array
(
    [hourly] => Array
        (
            [interval] => 3600
            [display] => Once Hourly
        )
    [twicedaily] => Array
        (
            [interval] => 43200
            [display] => Twice Daily
        )
    [daily] => Array
        (
            [interval] => 86400
            [display] => Once Daily
        )
)
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分别是每小时，每2天，每1天，如果你想增加自定义时间段每分钟：

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<?php
add_filter('cron_schedules', 'new_interval');
function new_interval($interval) {
    $interval['minutely'] = array(
        'interval' => 60,
        'display' => __('minutely', YOURTEXTDOMAIN)
    );
    return $interval;
}
?>
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然后，你就可以在这个时间段上定制计划任务了：

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<?php
if (!wp_next_scheduled('your_cron')) {
    wp_schedule_event( time(), 'minutely', 'your_cron', array($arg1, $arg2));
}
add_action( 'your_cron', 'do_somethings', 10, 2 );
function do_somethings($arg1, $arg2) {
    // 你的计划任务代码
}
?>
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仅执行一次的计划任务

这个就比较简单了，只需要指定一个距离当前时间有多久的时间戳就行，比如我要指定一个距离当前时间1小时执行的计划任务：

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<?php
function do_sonething($arg) {
    //do something here
}
add_action( 'your_schedule', array($this, 'do_sonething') );
wp_schedule_single_event( time() + 3600, 'your_schedule', array($arg) );
?>
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取消还未执行的计划任务

这个方法同时适用于重复执行和仅执行一次，只需要提供指定计划任务的下一个执行时间的时间戳及其参数（没有参数可留空）：

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<?php
$timestamp = wp_next_scheduled( 'your_cron', array($arg1, $arg2) );
wp_unschedule_event( $timestamp, 'your_cron', array($arg1, $arg2) );
?>
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或者更野蛮一点，取消所有的该计划任务的节点，如果指定了参数，就是取消所有包含该参数的计划任务。。

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<?php
wp_clear_scheduled_hook( 'your_cron', array($arg1, $arg2) );
?>
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判断计划任务是否存在

有两种方法：

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<?php
$schedule = wp_get_schedule( 'your_cron', array($arg1, $arg2) );
// $schedule == minutely
$schedule = wp_next_scheduled( 'your_schedule', array($arg) );
// $schedule == 194154874541
?>
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如果不存在，都会返回false。