#include <iostream>

#include <thread>
#include <mutex>

using namespace std;

/* LatexBeginFunc */
void receptionist(mutex& cout_mutex)
{
  cout_mutex.lock();
  cout << "R: Welcome, how can I help you?" << endl;  
  cout_mutex.unlock();
    
  this_thread::yield(); // let other thread run
  
  lock_guard<mutex> lock(cout_mutex); // destructor auto unlock
  cout << "R: Please enter, he's expecting you." << endl;
}
/* LatexEndFunc */

/* LatexBeginClass */
class Visitor
{
public:
  Visitor(mutex& cm) : cout_mutex{cm} {}

  void operator()()
  {
    cout_mutex.lock();
    cout << "V: Hi, I'm here to meet Mr X" << endl;
    cout_mutex.unlock();
    
    this_thread::yield(); // let other thread run
    
    lock_guard<mutex> lock(cout_mutex); // destructor auto unlock
    cout << "V: Thank you" << endl;
  }
private:
  mutex& cout_mutex;
};
/* LatexEndClass */

/* LatexBeginMain */
int main()
{
  // Note: cout is thread safe on character level
  mutex cout_mutex;

  // references parameters have to be specified explicitly
  thread r(receptionist, ref(cout_mutex));
  thread v(Visitor{cout_mutex});

  r.join();
  v.join();

  cout << "Main done" << endl;
  
  return 0;
}
/* LatexEndMain */