diff --git a/core/lib/Drupal/Core/StreamWrapper/StreamWrapperForCacheStorage.php b/core/lib/Drupal/Core/StreamWrapper/StreamWrapperForCacheStorage.php
index 2e7702a..ba8a743 100644
--- a/core/lib/Drupal/Core/StreamWrapper/StreamWrapperForCacheStorage.php
+++ b/core/lib/Drupal/Core/StreamWrapper/StreamWrapperForCacheStorage.php
@@ -6,6 +6,7 @@
  */
 
 namespace Drupal\Core\StreamWrapper;
+
 use Drupal\Core\PhpStorage\CacheStorage;
 
 /**
@@ -23,19 +24,21 @@ class StreamWrapperForCacheStorage {
   protected static $storage;
 
   /**
+   * The (fake) modified timestamp of the file this class wraps.
+   *
    * @var int
    */
   protected static $mtime;
 
   /**
-   * Stream context resource.
+   * Stream context resource set by PHP and ignored by this class.
    *
    * @var resource
    */
   public $context = NULL;
 
   /**
-   * A generic resource handle.
+   * The file handle of the in-memory stream.
    *
    * @var resource
    */
@@ -55,7 +58,12 @@ public static function init(CacheStorage $storage, $mtime) {
     static::$mtime = $mtime;
   }
 
-  public function stream_close () {
+  public function stream_open($path) {
+    static::$handle = static::$storage->open($path);
+    return (bool) static::$handle;
+  }
+
+  public function stream_close() {
     return fclose(static::$handle);
   }
 
@@ -63,20 +71,23 @@ public function stream_eof() {
     return feof(static::$handle);
   }
 
-  public function stream_flush() {
-    return fflush(static::$handle);
-  }
-
-  public function stream_open($path) {
-    static::$handle = static::$storage->open($path);
-    return (bool) static::$handle;
-  }
-
   public function stream_read($count) {
     return fread(static::$handle, $count);
   }
 
+  public function stream_flush() {
+    // This is called on every file close even if there is nothing to flush
+    // and we do not write anything so we do not actually need to flush
+    // anything.
+    return TRUE;
+  }
+
   public function stream_stat() {
+    // When the file is not yet opcode cached, the mtime is read through
+    // stream_stat() during file compile. The stat() results are not dependent
+    // on the position in the file and we know which file we are working on so
+    // using $handle is not necessary and just calling url_stat() to return the
+    // fake mtime is both correct and necessary.
     return static::url_stat();
   }