Update to drupal 8.0.0-rc1. For more information, see https://www.drupal.org/node/2582663

vendor/symfony/http-foundation/Session/Storage/Handler/WriteCheckSessionHandler.php

@@ -0,0 +1,91 @@
+<?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\HttpFoundation\Session\Storage\Handler;
+
+/**
+ * Wraps another SessionHandlerInterface to only write the session when it has been modified.
+ *
+ * @author Adrien Brault <adrien.brault@gmail.com>
+ */
+class WriteCheckSessionHandler implements \SessionHandlerInterface
+{
+    /**
+     * @var \SessionHandlerInterface
+     */
+    private $wrappedSessionHandler;
+
+    /**
+     * @var array sessionId => session
+     */
+    private $readSessions;
+
+    public function __construct(\SessionHandlerInterface $wrappedSessionHandler)
+    {
+        $this->wrappedSessionHandler = $wrappedSessionHandler;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function close()
+    {
+        return $this->wrappedSessionHandler->close();
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function destroy($sessionId)
+    {
+        return $this->wrappedSessionHandler->destroy($sessionId);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function gc($maxlifetime)
+    {
+        return $this->wrappedSessionHandler->gc($maxlifetime);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function open($savePath, $sessionName)
+    {
+        return $this->wrappedSessionHandler->open($savePath, $sessionName);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function read($sessionId)
+    {
+        $session = $this->wrappedSessionHandler->read($sessionId);
+
+        $this->readSessions[$sessionId] = $session;
+
+        return $session;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function write($sessionId, $data)
+    {
+        if (isset($this->readSessions[$sessionId]) && $data === $this->readSessions[$sessionId]) {
+            return true;
+        }
+
+        return $this->wrappedSessionHandler->write($sessionId, $data);
+    }
+}