diff --git a/setup/src/Magento/Setup/Module/Di/Code/Reader/ClassesScanner.php b/setup/src/Magento/Setup/Module/Di/Code/Reader/ClassesScanner.php
index 972f7570b40ab..a86558ce898ce 100644
--- a/setup/src/Magento/Setup/Module/Di/Code/Reader/ClassesScanner.php
+++ b/setup/src/Magento/Setup/Module/Di/Code/Reader/ClassesScanner.php
@@ -5,8 +5,9 @@
  */
 namespace Magento\Setup\Module\Di\Code\Reader;
 
+use Magento\Framework\App\Filesystem\DirectoryList;
+use Magento\Framework\App\ObjectManager;
 use Magento\Framework\Exception\FileSystemException;
-use Magento\Setup\Module\Di\Code\Reader\FileScanner;
 
 class ClassesScanner implements ClassesScannerInterface
 {
@@ -15,12 +16,27 @@ class ClassesScanner implements ClassesScannerInterface
      */
     protected $excludePatterns = [];
 
+    /**
+     * @var array
+     */
+    private $fileResults = [];
+
+    /**
+     * @var string
+     */
+    private $generationDirectory;
+
     /**
      * @param array $excludePatterns
+     * @param string $generationDirectory
      */
-    public function __construct(array $excludePatterns = [])
+    public function __construct(array $excludePatterns = [], DirectoryList $directoryList = null)
     {
         $this->excludePatterns = $excludePatterns;
+        if ($directoryList === null) {
+            $directoryList = ObjectManager::getInstance()->get(DirectoryList::class);
+        }
+        $this->generationDirectory = $directoryList->getPath(DirectoryList::GENERATION);
     }
 
     /**
@@ -44,7 +60,14 @@ public function addExcludePatterns(array $excludePatterns)
      */
     public function getList($path)
     {
+
         $realPath = realpath($path);
+        $isGeneration = strpos($realPath, $this->generationDirectory) === 0;
+
+        // Generation folders should not have their results cached since they may actually change during compile
+        if (!$isGeneration && isset($this->fileResults[$realPath])) {
+            return $this->fileResults[$realPath];
+        }
         if (!(bool)$realPath) {
             throw new FileSystemException(new \Magento\Framework\Phrase('Invalid path: %1', [$path]));
         }
@@ -53,46 +76,71 @@ public function getList($path)
             \RecursiveIteratorIterator::SELF_FIRST
         );
 
+        $classes = $this->extract($recursiveIterator);
+        if (!$isGeneration) {
+            $this->fileResults[$realPath] = $classes;
+        }
+        return $classes;
+    }
+
+    /**
+     * Extracts all the classes from the recursive iterator
+     *
+     * @param \RecursiveIteratorIterator $recursiveIterator
+     * @return array
+     */
+    private function extract(\RecursiveIteratorIterator $recursiveIterator)
+    {
         $classes = [];
         foreach ($recursiveIterator as $fileItem) {
             /** @var $fileItem \SplFileInfo */
             if ($fileItem->isDir() || $fileItem->getExtension() !== 'php' || $fileItem->getBasename()[0] == '.') {
                 continue;
             }
+            $fileItemPath = $fileItem->getRealPath();
             foreach ($this->excludePatterns as $excludePatterns) {
-                if ($this->isExclude($fileItem, $excludePatterns)) {
+                if ($this->isExclude($fileItemPath, $excludePatterns)) {
                     continue 2;
                 }
             }
-            $fileScanner = new FileScanner($fileItem->getRealPath());
+            $fileScanner = new FileClassScanner($fileItemPath);
             $classNames = $fileScanner->getClassNames();
-            foreach ($classNames as $className) {
-                if (empty($className)) {
-                    continue;
-                }
-                if (!class_exists($className)) {
-                    require_once $fileItem->getRealPath();
-                }
-                $classes[] = $className;
-            }
+            $this->includeClasses($classNames, $fileItemPath);
+            $classes = array_merge($classes, $classNames);
         }
         return $classes;
     }
 
+    /**
+     * @param array $classNames
+     * @param string $fileItemPath
+     * @return bool Whether the clas is included or not
+     */
+    private function includeClasses(array $classNames, $fileItemPath)
+    {
+        foreach ($classNames as $className) {
+            if (!class_exists($className)) {
+                require_once $fileItemPath;
+                return true;
+            }
+        }
+        return false;
+    }
+
     /**
      * Find out if file should be excluded
      *
-     * @param \SplFileInfo $fileItem
+     * @param string $fileItemPath
      * @param string $patterns
      * @return bool
      */
-    private function isExclude(\SplFileInfo $fileItem, $patterns)
+    private function isExclude($fileItemPath, $patterns)
     {
         if (!is_array($patterns)) {
             $patterns = (array)$patterns;
         }
         foreach ($patterns as $pattern) {
-            if (preg_match($pattern, str_replace('\\', '/', $fileItem->getRealPath()))) {
+            if (preg_match($pattern, str_replace('\\', '/', $fileItemPath))) {
                 return true;
             }
         }
diff --git a/setup/src/Magento/Setup/Module/Di/Code/Reader/FileClassScanner.php b/setup/src/Magento/Setup/Module/Di/Code/Reader/FileClassScanner.php
new file mode 100644
index 0000000000000..30dad35a2bcb9
--- /dev/null
+++ b/setup/src/Magento/Setup/Module/Di/Code/Reader/FileClassScanner.php
@@ -0,0 +1,171 @@
+<?php
+
+/**
+ * Copyright © 2013-2017 Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+
+namespace Magento\Setup\Module\Di\Code\Reader;
+
+class FileClassScanner
+{
+    /**
+     * The filename of the file to introspect
+     *
+     * @var string
+     */
+    private $filename;
+
+    /**
+     * The list of classes found in the file.
+     *
+     * @var bool
+     */
+    private $classNames = false;
+
+    /**
+     * @var array
+     */
+    private $tokens;
+
+    /**
+     * Constructor for the file class scanner.  Requires the filename
+     *
+     * @param string $filename
+     */
+    public function __construct($filename)
+    {
+        $filename = realpath($filename);
+        if (!file_exists($filename) || !\is_file($filename)) {
+            throw new InvalidFileException(
+                sprintf(
+                    'The file "%s" does not exist or is not a file',
+                    $filename
+                )
+            );
+        }
+        $this->filename = $filename;
+    }
+
+    /**
+     * Retrieves the contents of a file.  Mostly here for Mock injection
+     *
+     * @return string
+     */
+    public function getFileContents()
+    {
+        return file_get_contents($this->filename);
+    }
+
+    /**
+     * Extracts the fully qualified class name from a file.  It only searches for the first match and stops looking
+     * as soon as it enters the class definition itself.
+     *
+     * Warnings are suppressed for this method due to a micro-optimization that only really shows up when this logic
+     * is called several millions of times, which can happen quite easily with even moderately sized codebases.
+     *
+     * @SuppressWarnings(PHPMD.CyclomaticComplexity)
+     * @SuppressWarnings(PHPMD.NPathComplexity)
+     * @return array
+     */
+    private function extract()
+    {
+        $allowedOpenBraces = [T_CURLY_OPEN, T_DOLLAR_OPEN_CURLY_BRACES, T_STRING_VARNAME];
+        $classes = [];
+        $namespace = '';
+        $class = '';
+        $triggerClass = false;
+        $triggerNamespace = false;
+        $braceLevel = 0;
+        $bracedNamespace = false;
+
+        $this->tokens = token_get_all($this->getFileContents());
+        foreach ($this->tokens as $index => $token) {
+            // Is either a literal brace or an interpolated brace with a variable
+            if ($token == '{' || (is_array($token) && in_array($token[0], $allowedOpenBraces))) {
+                $braceLevel++;
+            } else if ($token == '}') {
+                $braceLevel--;
+            }
+            // The namespace keyword was found in the last loop
+            if ($triggerNamespace) {
+                // A string ; or a discovered namespace that looks like "namespace name { }"
+                if (!is_array($token) || ($namespace && $token[0] == T_WHITESPACE)) {
+                    $triggerNamespace = false;
+                    $namespace .= '\\';
+                    continue;
+                }
+                $namespace .= $token[1];
+
+                // The class keyword was found in the last loop
+            } else if ($triggerClass && $token[0] == T_STRING) {
+                $triggerClass = false;
+                $class = $token[1];
+            }
+
+            switch ($token[0]) {
+                case T_NAMESPACE:
+                    // Current loop contains the namespace keyword.  Between this and the semicolon is the namespace
+                    $triggerNamespace = true;
+                    $namespace = '';
+                    $bracedNamespace = $this->isBracedNamespace($index);
+                    break;
+                case T_CLASS:
+                    // Current loop contains the class keyword.  Next loop will have the class name itself.
+                    if ($braceLevel == 0 || ($bracedNamespace && $braceLevel == 1)) {
+                        $triggerClass = true;
+                    }
+                    break;
+            }
+
+            // We have a class name, let's concatenate and store it!
+            if ($class != '') {
+                $namespace = trim($namespace);
+                $fqClassName = $namespace . trim($class);
+                $classes[] = $fqClassName;
+                $class = '';
+            }
+        }
+        return $classes;
+    }
+
+    /**
+     * Looks forward from the current index to determine if the namespace is nested in {} or terminated with ;
+     *
+     * @param integer $index
+     * @return bool
+     */
+    private function isBracedNamespace($index)
+    {
+        $len = count($this->tokens);
+        while ($index++ < $len) {
+            if (!is_array($this->tokens[$index])) {
+                if ($this->tokens[$index] == ';') {
+                    return false;
+                } else if ($this->tokens[$index] == '{') {
+                    return true;
+                }
+                continue;
+            }
+
+            if (!in_array($this->tokens[$index][0], [T_WHITESPACE, T_STRING, T_NS_SEPARATOR])) {
+                throw new InvalidFileException('Namespace not defined properly');
+            }
+        }
+        throw new InvalidFileException('Could not find namespace termination');
+    }
+
+    /**
+     * Retrieves the first class found in a class file.  The return value is in an array format so it retains the
+     * same usage as the FileScanner.
+     *
+     * @return array
+     */
+    public function getClassNames()
+    {
+        if ($this->classNames === false) {
+            $this->classNames = $this->extract();
+        }
+        return $this->classNames;
+    }
+}
diff --git a/setup/src/Magento/Setup/Module/Di/Code/Reader/InvalidFileException.php b/setup/src/Magento/Setup/Module/Di/Code/Reader/InvalidFileException.php
new file mode 100644
index 0000000000000..049381f907d13
--- /dev/null
+++ b/setup/src/Magento/Setup/Module/Di/Code/Reader/InvalidFileException.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Magento\Setup\Module\Di\Code\Reader;
+
+class InvalidFileException extends \InvalidArgumentException
+{
+
+}
diff --git a/setup/src/Magento/Setup/Test/Unit/Module/Di/Code/Reader/ClassesScannerTest.php b/setup/src/Magento/Setup/Test/Unit/Module/Di/Code/Reader/ClassesScannerTest.php
index 89664d70c4a69..1448a757f669b 100644
--- a/setup/src/Magento/Setup/Test/Unit/Module/Di/Code/Reader/ClassesScannerTest.php
+++ b/setup/src/Magento/Setup/Test/Unit/Module/Di/Code/Reader/ClassesScannerTest.php
@@ -5,6 +5,8 @@
  */
 namespace Magento\Setup\Test\Unit\Module\Di\Code\Reader;
 
+use Magento\Framework\App\Filesystem\DirectoryList;
+
 class ClassesScannerTest extends \PHPUnit_Framework_TestCase
 {
     /**
@@ -12,9 +14,22 @@ class ClassesScannerTest extends \PHPUnit_Framework_TestCase
      */
     private $model;
 
+    /**
+     * the /var/generation directory realpath
+     *
+     * @var string
+     */
+
+    private $generation;
+
     protected function setUp()
     {
-        $this->model = new \Magento\Setup\Module\Di\Code\Reader\ClassesScanner();
+        $this->generation = realpath(__DIR__ . '/../../_files/var/generation');
+        $mock = $this->getMockBuilder(DirectoryList::class)->disableOriginalConstructor()->setMethods(
+            ['getPath']
+        )->getMock();
+        $mock->method('getPath')->willReturn($this->generation);
+        $this->model = new \Magento\Setup\Module\Di\Code\Reader\ClassesScanner([], $mock);
     }
 
     public function testGetList()
diff --git a/setup/src/Magento/Setup/Test/Unit/Module/Di/Code/Reader/FileClassScannerTest.php b/setup/src/Magento/Setup/Test/Unit/Module/Di/Code/Reader/FileClassScannerTest.php
new file mode 100644
index 0000000000000..e9f487c5c3b15
--- /dev/null
+++ b/setup/src/Magento/Setup/Test/Unit/Module/Di/Code/Reader/FileClassScannerTest.php
@@ -0,0 +1,243 @@
+<?php
+
+/**
+ * Copyright © 2013-2017 Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+
+namespace Magento\Setup\Test\Unit\Module\Di\Code\Reader;
+
+use Magento\Setup\Module\Di\Code\Reader\FileClassScanner;
+use Magento\Setup\Module\Di\Code\Reader\InvalidFileException;
+
+class FileClassScannerTest extends \PHPUnit_Framework_TestCase
+{
+
+    public function testInvalidFileThrowsException()
+    {
+        $this->setExpectedException(InvalidFileException::class);
+        new FileClassScanner(false);
+    }
+
+    public function testEmptyArrayForFileWithoutNamespaceOrClass()
+    {
+        $scanner = $this->getMockBuilder(FileClassScanner::class)->disableOriginalConstructor()->setMethods([
+            'getFileContents'
+        ])->getMock();
+        $scanner->expects(self::once())->method('getFileContents')->willReturn(
+            <<<PHP
+<?php
+
+echo 'hello world';
+
+if (class_exists('some_class')) {
+    \$object = new some_class();
+}
+PHP
+        );
+        /** @var $scanner FileClassScanner */
+
+        $result = $scanner->getClassNames();
+        self::assertCount(0, $result);
+    }
+
+    public function testGetClassName()
+    {
+        $scanner = $this->getMockBuilder(FileClassScanner::class)->disableOriginalConstructor()->setMethods([
+            'getFileContents'
+        ])->getMock();
+        $scanner->expects(self::once())->method('getFileContents')->willReturn(
+            <<<PHP
+<?php
+
+class ThisIsATest {
+
+}
+PHP
+        );
+        /** @var $scanner FileClassScanner */
+
+        $result = $scanner->getClassNames();
+
+        self::assertCount(1, $result);
+        self::assertContains('ThisIsATest', $result);
+    }
+
+    public function testGetClassNameAndSingleNamespace()
+    {
+        $scanner = $this->getMockBuilder(FileClassScanner::class)->disableOriginalConstructor()->setMethods([
+            'getFileContents'
+        ])->getMock();
+        $scanner->expects(self::once())->method('getFileContents')->willReturn(
+            <<<PHP
+<?php
+
+namespace NS;
+
+class ThisIsMyTest {
+
+}
+PHP
+        );
+        /** @var $scanner FileClassScanner */
+
+        $result = $scanner->getClassNames();
+
+        self::assertCount(1, $result);
+        self::assertContains('NS\ThisIsMyTest', $result);
+    }
+
+    public function testGetClassNameAndMultiNamespace()
+    {
+        $scanner = $this->getMockBuilder(FileClassScanner::class)->disableOriginalConstructor()->setMethods([
+            'getFileContents'
+        ])->getMock();
+        $scanner->expects(self::once())->method('getFileContents')->willReturn(
+            <<<PHP
+<?php
+
+namespace This\Is\My\Ns;
+
+class ThisIsMyTest {
+
+    public function __construct()
+    {
+        \This\Is\Another\Ns::class;
+    }
+    
+    public function test()
+    {
+        
+    }
+}
+PHP
+        );
+        /** @var $scanner FileClassScanner */
+
+        $result = $scanner->getClassNames();
+
+        self::assertCount(1, $result);
+        self::assertContains('This\Is\My\Ns\ThisIsMyTest', $result);
+    }
+
+    public function testGetMultiClassNameAndMultiNamespace()
+    {
+        $scanner = $this->getMockBuilder(FileClassScanner::class)->disableOriginalConstructor()->setMethods([
+            'getFileContents'
+        ])->getMock();
+        $scanner->expects(self::once())->method('getFileContents')->willReturn(
+            <<<PHP
+<?php
+
+namespace This\Is\My\Ns;
+
+class ThisIsMyTest {
+
+    public function __construct()
+    {
+        \$this->get(\This\Is\Another\Ns::class)->method();
+        self:: class;
+    }
+    
+    public function test()
+    {
+        
+    }
+}
+
+class ThisIsForBreaking {
+
+}
+
+PHP
+        );
+        /** @var $scanner FileClassScanner */
+
+        $result = $scanner->getClassNames();
+
+        self::assertCount(2, $result);
+        self::assertContains('This\Is\My\Ns\ThisIsMyTest', $result);
+        self::assertContains('This\Is\My\Ns\ThisIsForBreaking', $result);
+    }
+
+    public function testBracketedNamespacesAndClasses()
+    {
+        $scanner = $this->getMockBuilder(FileClassScanner::class)->disableOriginalConstructor()->setMethods([
+            'getFileContents'
+        ])->getMock();
+        $scanner->expects(self::once())->method('getFileContents')->willReturn(
+            <<<PHP
+<?php
+
+namespace This\Is\My\Ns {
+
+    class ThisIsMyTest
+    {
+    
+        public function __construct()
+        {
+            \This\Is\Another\Ns::class;
+            self:: class;
+        }
+    
+    }
+    
+    class ThisIsForBreaking
+    {
+    }
+}
+
+namespace This\Is\Not\My\Ns {
+
+    class ThisIsNotMyTest
+    {
+    }   
+}
+
+PHP
+        );
+        /** @var $scanner FileClassScanner */
+
+        $result = $scanner->getClassNames();
+
+        self::assertCount(3, $result);
+        self::assertContains('This\Is\My\Ns\ThisIsMyTest', $result);
+        self::assertContains('This\Is\My\Ns\ThisIsForBreaking', $result);
+        self::assertContains('This\Is\Not\My\Ns\ThisIsNotMyTest', $result);
+    }
+
+    public function testClassKeywordInMiddleOfFile()
+    {
+        $filename = __DIR__
+            . '/../../../../../../../../../..'
+            . '/app/code/Magento/Catalog/Model/ResourceModel/Product/Indexer/Eav/AbstractEav.php';
+        $filename = realpath($filename);
+        $scanner = new FileClassScanner($filename);
+        $result = $scanner->getClassNames();
+
+        self::assertCount(1, $result);
+    }
+
+    public function testInvalidPHPCodeThrowsExceptionWhenCannotDetermineBraceOrSemiColon()
+    {
+        $this->setExpectedException(InvalidFileException::class);
+        $scanner = $this->getMockBuilder(FileClassScanner::class)->disableOriginalConstructor()->setMethods([
+            'getFileContents'
+        ])->getMock();
+        $scanner->expects(self::once())->method('getFileContents')->willReturn(
+            <<<PHP
+            <?php
+
+namespace This\Is\My\Ns 
+
+class ThisIsMyTest
+{
+}
+
+PHP
+        );
+        /** @var $scanner FileClassScanner */
+
+        $scanner->getClassNames();
+    }
+}
diff --git a/setup/src/Magento/Setup/Test/Unit/Module/Di/_files/var/generation/.keep b/setup/src/Magento/Setup/Test/Unit/Module/Di/_files/var/generation/.keep
new file mode 100644
index 0000000000000..e69de29bb2d1d