EventLoopThread::startLoop()中为什么需要创建局部变量loop？是否可以返回loop_?

EventLoop* EventLoopThread::startLoop()
{
  assert(!thread_.started());
  thread_.start();

  EventLoop* loop = NULL;
  {
    MutexLockGuard lock(mutex_);
    while (loop_ == NULL)
    {
      cond_.wait();
    }
    loop = loop_;
  }

  return loop;
}

void EventLoopThread::threadFunc()
{
  EventLoop loop;

  if (callback_)
  {
    callback_(&loop);
  }

  {
    MutexLockGuard lock(mutex_);
    loop_ = &loop;
    cond_.notify();
  }

  loop.loop();
  //assert(exiting_);
  MutexLockGuard lock(mutex_);
  loop_ = NULL;
}

EventLoop* EventLoopThread::startLoop() {
  thread_.start();
  std::unique_lock lock(mutex_);
  cv_.wait(lock, [this]() { return loop_ != nullptr; });
  return loop_;
}