[ClassLoader] Added an ApcClassLoader

Unlike the ApcUniversalClassLoader, ApcClassLoader uses composition,
meaning it can be used to wrap any object providing a findFile($class)
method. Both the UniversalClassLoader and the new ClassLoader follow
this convention. It can also be used to wrap the Composer autoloader.

src/Symfony/Component/ClassLoader/ApcClassLoader.php

@@ -0,0 +1,112 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\ClassLoader;
+
+/**
+ * ApcClassLoader implements a wrapping autoloader cached in APC for PHP 5.3.
+ *
+ * It expects an object implementing a findFile method to find the file. This
+ * allow using it as a wrapper around the other loaders of the component (the
+ * ClassLoader and the UniversalClassLoader for instance) but also around any
+ * other autoloader following this convention (the Composer one for instance)
+ *
+ *     $loader = new ClassLoader();
+ *
+ *     // register classes with namespaces
+ *     $loader->add('Symfony\Component', __DIR__.'/component');
+ *     $loader->add('Symfony',           __DIR__.'/framework');
+ *
+ *     $cachedLoader = new ApcClassLoader('my_prefix', $loader);
+ *
+ *     // activate the cached autoloader
+ *     $cachedLoader->register();
+ *
+ *     // eventually deactivate the non-cached loader if it was registered previously
+ *     // to be sure to use the cached one.
+ *     $loader->unregister();
+ *
+ * @author Fabien Potencier <fabien@symfony.com>
+ * @author Kris Wallsmith <kris@symfony.com>
+ *
+ * @api
+ */
+class ApcClassLoader
+{
+    private $prefix;
+    private $classFinder;
+
+    /**
+     * Constructor.
+     *
+     * @param string $prefix A prefix to create a namespace in APC
+     * @param object $classFinder
+     *
+     * @api
+     */
+    public function __construct($prefix, $classFinder)
+    {
+        if (!extension_loaded('apc')) {
+            throw new \RuntimeException('Unable to use ApcUniversalClassLoader as APC is not enabled.');
+        }
+
+        $this->prefix = $prefix;
+        $this->classFinder = $classFinder;
+    }
+
+    /**
+     * Registers this instance as an autoloader.
+     *
+     * @param Boolean $prepend Whether to prepend the autoloader or not
+     */
+    public function register($prepend = false)
+    {
+        spl_autoload_register(array($this, 'loadClass'), true, $prepend);
+    }
+
+    /**
+     * Unregisters this instance as an autoloader.
+     */
+    public function unregister()
+    {
+        spl_autoload_unregister(array($this, 'loadClass'));
+    }
+
+    /**
+     * Loads the given class or interface.
+     *
+     * @param string $class The name of the class
+     * @return Boolean|null True, if loaded
+     */
+    public function loadClass($class)
+    {
+        if ($file = $this->findFile($class)) {
+            require $file;
+            return true;
+        }
+    }
+
+    /**
+     * Finds a file by class name while caching lookups to APC.
+     *
+     * @param string $class A class name to resolve to file
+     *
+     * @return string|null
+     */
+    public function findFile($class)
+    {
+        if (false === $file = apc_fetch($this->prefix.$class)) {
+            apc_store($this->prefix.$class, $file = $this->classFinder->findFile($class));
+        }
+
+        return $file;
+    }
+}