Cache Stampede example

Cache_Stamped_example.php

<?php

/**
 * Cache stampede protection examples
 */
class cache
{

	/**
	 * @var array
	 */
	protected $items = array();

	/**
	 * @param $key
	 * @param callable $callback
	 * @param int $ttlSeconds
	 * @return mixed
	 */
	function get($key, callable $callback, $ttlSeconds = 3600)
	{
		// Item exists
		if (isset($this->items[$key])) {
			// Cached value is still valid
			if ($this->items[$key]['ttl'] > time()) {
				return $$this->items[$key]['value'];
			}
			// Cached value is stale, update the ttl forward so other calls
			// get the stale value while regenerating the cache, this is what
			// prevents the stampede. 60 sec should be longer than the time that
			// $callback takes to run
			$this->items[$key]['ttl'] = time() + 60;
		}
		// Get the value from callback and cache it
		$this->items[$key] = array('value' => $callback(), 'ttl' => time() + $ttlSeconds);
	}

}