在后台更新 WordPress Feed 缓存答案

【问题标题】：Renew WordPress Feed Cache in the Background在后台更新 WordPress Feed 缓存
【发布时间】：2012-09-10 15:31:24
【问题描述】：

我正在寻找一种在后台刷新提要缓存的方法。

为了演示我面临的问题，下面的代码会有所帮助。当页面被访问和加载时，它每 30 秒更新一次缓存。因为它有很多 url 需要一次获取，所以当缓存需要重建时它会变得非常慢。

$urls = array(
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&topic=w&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&topic=n&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&topic=b&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&topic=el&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&topic=tc&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&topic=ir&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&topic=s&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&topic=snc&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&topic=m&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&topic=e&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&q=topic:bagram&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&q=topic:syria&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&q=topic:baghdad&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&q=topic:bernard_arnault&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&q=topic:senkaku_islands&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&q=topic:alps&output=rss'
    );

    $feed = fetch_feed_modified($urls);
    foreach ($feed->get_items() as $item):
    ?>

        <div class="item">
            <h2><a href="<?php echo $item->get_permalink(); ?>"><?php echo $item->get_title(); ?></a></h2>
            <p><?php echo $item->get_description(); ?></p>
            <p><small>Posted on <?php echo $item->get_date('j F Y | g:i a'); ?></small></p>
        </div>

    <?php endforeach; 

function fetch_feed_modified($url) {
    require_once (ABSPATH . WPINC . '/class-feed.php');

    $feed = new SimplePie();
    $feed->set_feed_url($url);
    $feed->set_cache_class('WP_Feed_Cache');
    $feed->set_file_class('WP_SimplePie_File');
    $feed->set_cache_duration(apply_filters('wp_feed_cache_transient_lifetime', 30, $url)); // set the cacne timeout to 30 seconds
    do_action_ref_array( 'wp_feed_options', array( &$feed, $url ) );
    $feed->init();
    $feed->handle_content_type();

    if ( $feed->error() )
        return new WP_Error('simplepie-error', $feed->error());

    return $feed;
}

所以我想知道如何修改它，以便它在超时时默默地在后台更新缓存。我的意思是尽管超时超过了，但它会正常显示页面并保存缓存；另一方面，它在访问后开始在后台建立一个新的缓存。这样访问者就不会看到页面变慢了。

有可能吗？

【问题讨论】：

标签： caching background-process wordpress simplepie

【解决方案1】：

好的，这行得通。

<?php
/* Plugin Name: Sample Feed Cache Renew Crawler */

    $urls = array(
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&topic=w&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&topic=n&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&topic=b&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&topic=el&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&topic=tc&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&topic=ir&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&topic=s&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&topic=snc&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&topic=m&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&topic=e&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&q=topic:bagram&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&q=topic:syria&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&q=topic:baghdad&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&q=topic:bernard_arnault&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&q=topic:senkaku_islands&output=rss',
        'http://news.google.com/news?pz=1&cf=all&ned=us&hl=en&q=topic:alps&output=rss'
    );
    $cache_renew_interval = 30; // every thirty seconds

    // admin page
    add_action('admin_menu', 'sample_feed_cache_renew_crawler_menu');
    function sample_feed_cache_renew_crawler_menu() {
        add_options_page(
            'Sample Feed Cache Renew Crawler', 
            'Sample Feed Cache Renew Crawler', 
            'manage_options',
            'sample_feed_cache_renew_crawler', 
            'sample_feed_cache_renew_crawler_admin');
    }
    function sample_feed_cache_renew_crawler_admin() {
        global $urls, $cache_renew_interval;
        ?>
        <div class="wrap">
        <?php       

            $feed = fetch_feed_with_custom_lifetime($urls, 60*60*24 );  // lifetime for 24 hours

            if ( $feed->error() )
                return new WP_Error('simplepie-error', $feed->error());         

            $feed = fetch_feed($urls);

            $i = 0;
            foreach ($feed->get_items() as $item):  
                if (++$i==20) break;
            ?>

                <div class="item">
                    <h2><a href="<?php echo $item->get_permalink(); ?>"><?php echo $item->get_title(); ?></a></h2>
                    <p><?php echo $item->get_description(); ?></p>
                    <p><small>Posted on <?php echo $item->get_date('j F Y | g:i a'); ?></small></p>
                </div>

            <?php endforeach;    
        ?>
        </div>      
        <?php
        wp_clear_scheduled_hook( 'sample_feed_cache_renew_crawler_event' );
        add_action('sample_feed_cache_renew_crawler_event','sample_feed_cache_renew_crawler_function');
        wp_schedule_single_event(time() + $cache_renew_interval, 'sample_feed_cache_renew_crawler_event');

}
// wp_clear_scheduled_hook( 'sample_feed_cache_renew_crawler_event' );
require_once (ABSPATH . WPINC . '/class-feed.php');
function fetch_feed_with_custom_lifetime($url, $lifetime) {
    $feed = new SimplePie();
    $feed->set_feed_url($url);
    $feed->set_cache_class('WP_Feed_Cache');
    $feed->set_file_class('WP_SimplePie_File');
    $feed->set_cache_duration(apply_filters('wp_feed_cache_transient_lifetime', $lifetime, $url)); // set the cacne timeout to 30 seconds
    do_action_ref_array( 'wp_feed_options', array( &$feed, $url ) );
    $feed->init();
    $feed->handle_content_type();
    if ( $feed->error() ) return new WP_Error('simplepie-error', $feed->error());
    return $feed;
}   

add_action('sample_feed_cache_renew_crawler_event','sample_feed_cache_renew_crawler_function');
function sample_feed_cache_renew_crawler_function() {
    $file = __DIR__ . '/log.txt';
    $current = date('l jS \of F Y h:i:s A') . ": cache cleared" . PHP_EOL;
    file_put_contents($file, $current, FILE_APPEND);

    global $urls, $cache_renew_interval;
    fetch_feed_with_custom_lifetime($urls, 0);  // renew the cache right away
    wp_schedule_single_event(time() + $cache_renew_interval, 'sample_feed_cache_renew_crawler_event');

}

我不清楚的一件事是，即使我将时间间隔设置为 30 秒，它并不总是在正确的时间调用函数 sample_feed_cache_renew_crawler_function()。日志文件显示有时需要 2 分钟，有时需要 4 分钟，尽管我一直按浏览器的重新加载按钮超过这些分钟。

根据 Codex，http://codex.wordpress.org/Function_Reference/wp_schedule_single_event，

请注意，在活动开始后 10 分钟内安排活动相同的名称将被忽略，除非您将 $args 的唯一值传递给每个预定的事件。

但是日志文件告诉函数在 2 分钟左右的时间间隔内被调用。所以这没有意义。

【讨论】：