Rename 'kohana' to 'system' to conform to the Kohana filesystem layout. I'm comfortable with us not clearly drawing the distinction about the fact that it's Kohana.

system/libraries/drivers/Cache/Memcache.php

@@ -0,0 +1,191 @@
+<?php defined('SYSPATH') OR die('No direct access allowed.');
+/**
+ * Memcache-based Cache driver.
+ *
+ * $Id: Memcache.php 4102 2009-03-19 12:55:54Z Shadowhand $
+ *
+ * @package    Cache
+ * @author     Kohana Team
+ * @copyright  (c) 2007-2008 Kohana Team
+ * @license    http://kohanaphp.com/license.html
+ */
+class Cache_Memcache_Driver implements Cache_Driver {
+
+	const TAGS_KEY = 'memcache_tags_array';
+
+	// Cache backend object and flags
+	protected $backend;
+	protected $flags;
+
+	// Tags array
+	protected static $tags;
+
+	// Have the tags been changed?
+	protected static $tags_changed = FALSE;
+
+	public function __construct()
+	{
+		if ( ! extension_loaded('memcache'))
+			throw new Kohana_Exception('cache.extension_not_loaded', 'memcache');
+
+		$this->backend = new Memcache;
+		$this->flags = Kohana::config('cache_memcache.compression') ? MEMCACHE_COMPRESSED : FALSE;
+
+		$servers = Kohana::config('cache_memcache.servers');
+
+		foreach ($servers as $server)
+		{
+			// Make sure all required keys are set
+			$server += array('host' => '127.0.0.1', 'port' => 11211, 'persistent' => FALSE);
+
+			// Add the server to the pool
+			$this->backend->addServer($server['host'], $server['port'], (bool) $server['persistent'])
+				or Kohana::log('error', 'Cache: Connection failed: '.$server['host']);
+		}
+
+		// Load tags
+		self::$tags = $this->backend->get(self::TAGS_KEY);
+
+		if ( ! is_array(self::$tags))
+		{
+			// Create a new tags array
+			self::$tags = array();
+
+			// Tags have been created
+			self::$tags_changed = TRUE;
+		}
+	}
+
+	public function __destruct()
+	{
+		if (self::$tags_changed === TRUE)
+		{
+			// Save the tags
+			$this->backend->set(self::TAGS_KEY, self::$tags, $this->flags, 0);
+
+			// Tags are now unchanged
+			self::$tags_changed = FALSE;
+		}
+	}
+
+	public function find($tag)
+	{
+		if (isset(self::$tags[$tag]) AND $results = $this->backend->get(self::$tags[$tag]))
+		{
+				// Return all the found caches
+				return $results;
+		}
+		else
+		{
+			// No matching tags
+			return array();
+		}
+	}
+
+	public function get($id)
+	{
+		return (($return = $this->backend->get($id)) === FALSE) ? NULL : $return;
+	}
+
+	public function set($id, $data, array $tags = NULL, $lifetime)
+	{
+		if ( ! empty($tags))
+		{
+			// Tags will be changed
+			self::$tags_changed = TRUE;
+
+			foreach ($tags as $tag)
+			{
+				// Add the id to each tag
+				self::$tags[$tag][$id] = $id;
+			}
+		}
+
+		if ($lifetime !== 0)
+		{
+			// Memcache driver expects unix timestamp
+			$lifetime += time();
+		}
+
+		// Set a new value
+		return $this->backend->set($id, $data, $this->flags, $lifetime);
+	}
+
+	public function delete($id, $tag = FALSE)
+	{
+		// Tags will be changed
+		self::$tags_changed = TRUE;
+
+		if ($id === TRUE)
+		{
+			if ($status = $this->backend->flush())
+			{
+				// Remove all tags, all items have been deleted
+				self::$tags = array();
+
+				// We must sleep after flushing, or overwriting will not work!
+				// @see http://php.net/manual/en/function.memcache-flush.php#81420
+				sleep(1);
+			}
+
+			return $status;
+		}
+		elseif ($tag === TRUE)
+		{
+			if (isset(self::$tags[$id]))
+			{
+				foreach (self::$tags[$id] as $_id)
+				{
+					// Delete each id in the tag
+					$this->backend->delete($_id);
+				}
+
+				// Delete the tag
+				unset(self::$tags[$id]);
+			}
+
+			return TRUE;
+		}
+		else
+		{
+			foreach (self::$tags as $tag => $_ids)
+			{
+				if (isset(self::$tags[$tag][$id]))
+				{
+					// Remove the id from the tags
+					unset(self::$tags[$tag][$id]);
+				}
+			}
+
+			return $this->backend->delete($id);
+		}
+	}
+
+	public function delete_expired()
+	{
+		// Tags will be changed
+		self::$tags_changed = TRUE;
+
+		foreach (self::$tags as $tag => $_ids)
+		{
+			foreach ($_ids as $id)
+			{
+				if ( ! $this->backend->get($id))
+				{
+					// This id has disappeared, delete it from the tags
+					unset(self::$tags[$tag][$id]);
+				}
+			}
+
+			if (empty(self::$tags[$tag]))
+			{
+				// The tag no longer has any valid ids
+				unset(self::$tags[$tag]);
+			}
+		}
+
+		// Memcache handles garbage collection internally
+		return TRUE;
+	}
+
+} // End Cache Memcache Driver