Get a value from a Doctrine Cache or compute it using a callback, including stampede protection

cacheGetDefault.php

<?php

/**
 * Get a value from the cache or compute it using a callback
 * Includes cache stampede protection
 * @link http://en.wikipedia.org/wiki/Cache_stampede
 * @link http://blog.lavoie.sl/2014/12/preventing-cache-stampede-using-doctrine-cache.html
 * @global cache Doctrine\Common\Cache\Cache
 *
 * @param  string  $key         Cache key
 * @param  Closure $callback    Computing function
 * @param  float   $ttl         Seconds
 * @param  float   $stampedeTtl Seconds before cache stampede expires
 *                              Should be about 2-3 times the estimated time to build the cache
 * @return mixed
 */
function cacheGetDefault($key, Closure $callback, $ttl = 0, $stampedeTtl = null)
{
    global $cache;

    $data = $cache->fetch($key);

    if (false !== $data) {
        return $data;
    }

    if (null !== $stampede) {
        $stampede = max((double) $stampede, 0.001); // prevention for infinite ttl
        // data is being computed, wait
        while ('__STAMPEDE__' === $data) {
            // wait 1/20th of the stampede TTL, to give the CPU a chance
            sleep($stampede / 20);
            $data = $cache->fetch($key);
        }
    }

    if ($data === false) {
        if (null !== $stampedeTtl) {
            // acquire lock
            $cache->save($key, '__STAMPEDE__', $stampedeTtl);
        }
        // compute the actual data
        $data = $callback();
    }

    $cache->save($key, $data, $ttl);

    return $data;
}

useCache.php

<?php

$cacheTtl = 3600; // an hour
$stampedeTtl = 5; // seconds before releasing lock

cacheGetDefault('recent_tweets', function() {
    return file_get_contents('https://api.twitter.com/1.1/search/tweets.json?q=@lavoiesl');
}, $cacheTtl, $stampedeTtl);