code: public static function readFile($file)
      {
          if (!file_exists($file)) {
              return null;
          }
  
          $handle = fopen($file, 'r');
          if (!self::lockFile($handle, LOCK_SH | LOCK_NB)) {
              $exception = array(
                  "message" => 'exception_file_cannot_be_locked_for_reading',
                  "parameters" => array(
                      "%file%" => basename($file),
                  )
              );
              throw new RuntimeException(json_encode($exception));
          }
  
          $contents = file_get_contents($file);
          self::unlockFile($handle);
  
          return $contents;
      }
docs: Reads and locks a file from the filesystem
  
  @param $file
  
  @return string