///////////////////////////////////////////////////////////////////////
// MT4Q5.cpp - Thread safe sharing                                   //
//                                                                   //
// Jim Fawcett, CSE687 - Object Oriented Design Midterm, Spring 2018 //
///////////////////////////////////////////////////////////////////////

#include <thread>
#include <future>
#include <string>
#include <iostream>
#include <mutex>

//----< concurrent sharing happens here >------------------------------

void modifyString(const std::string& name, std::string& shared)
{
  static std::mutex mtx;
  std::unique_lock<std::mutex> lck(mtx, std::defer_lock);

  for (size_t i = 0; i < 5; ++i)
  {
    lck.lock();
    shared += name;
    lck.unlock();
    std::this_thread::sleep_for(std::chrono::milliseconds(20));
  }
}
//----< protect shared string from outside access >--------------------

std::string makeCopyOfSharedString(std::string shared)
{
  std::thread t1(modifyString, "Gabe ", std::ref(shared));
  std::thread t2(modifyString, "Ankur ", std::ref(shared));
  std::thread t3(modifyString, "Tianyu ", std::ref(shared));
  // client can't use shared string until threads are done
  // so we might as well join, but even so, sharing is
  // a parallel execution
  t1.join();
  t2.join();
  t3.join();
  return shared;
}

int main()
{
  std::cout << "\n  MT4Q5 - thread safe sharing";
  std::cout << "\n =============================";

  std::string shared;
  std::cout << "\n  " << makeCopyOfSharedString(shared) << "\n\n";
  return 0;
}