}
    if (variables[i]->read_only()) {
      VLOG(4) << "Acquiring reader lock for variable "
              << reinterpret_cast<void*>(variable);
      mu->lock_shared();
      variables[i]->set_shared_lock_held();
    } else {
      VLOG(4) << "Acquiring lock for variable "
              << reinterpret_cast<void*>(variable);
      mu->lock();

  // released even on error.  It does not matter in what order we release the
  // locks.
  if (var()) {
    if (lock_held()) {
      var()->mu()->unlock();
    }
    if (shared_lock_held()) {
      var()->mu()->unlock_shared();
    }

    // Unref the variable so it can be released by ResourceManager.
    var()->Unref();
  }
}