请说明条件变量在c ++线程中的用法，以及为什么我们需要与此一起使用`unique_lock`和`mutex`

我指的是这段特定的代码：

该代码基本上具有三个线程1.与服务器进行一些握手2.从XML文件加载数据。3.对从XML加载的数据进行处理。我们可以看到任务1不依赖于任何其他任务，但是任务3依赖于任务2。因此，这意味着任务1和任务2可以由不同的线程并行运行以提高应用程序的性能。因此，应用程序被构建为多线程的。

#include <iostream>
#include <thread>
#include <functional>
#include <mutex>
#include <condition_variable>
using namespace std::placeholders;

class Application
{
  std::mutex m_mutex;
  std::condition_variable m_condVar;
  bool m_bDataLoaded;
public:
  Application()
  {
    m_bDataLoaded = false;
  }
  void loadData()
  {
   // Make This Thread sleep for 1 Second
   std::this_thread::sleep_for(std::chrono::milliseconds(1000));
   std::cout<<"Loading Data from XML"<<std::endl;
   // Lock The Data structure
   std::lock_guard<std::mutex> guard(m_mutex);
   // Set the flag to true, means data is loaded
   m_bDataLoaded = true;
   // Notify the condition variable
   m_condVar.notify_one();
  }
  bool isDataLoaded()
  {
    return m_bDataLoaded;
  }
  void mainTask()
  {
    std::cout<<"Do Some Handshaking"<<std::endl;
    // Acquire the lock
    std::unique_lock<std::mutex> mlock(m_mutex);
    // Start waiting for the Condition Variable to get signaled
    // Wait() will internally release the lock and make the thread to block
    // As soon as condition variable get signaled, resume the thread and
    // again acquire the lock. Then check if condition is met or not
    // If condition is met then continue else again go in wait.
    m_condVar.wait(mlock, std::bind(&Application::isDataLoaded, this));
    std::cout<<"Do Processing On loaded Data"<<std::endl;
  }
};
int main()
{
   Application app;
   std::thread thread_1(&Application::mainTask, &app);
   std::thread thread_2(&Application::loadData, &app);
   thread_2.join();
   thread_1.join();
   return 0;
}

此代码来自http://thispointer.com/c11-multithreading-part-7-condition-variables-explained/

谢谢