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

std::mutex cout_mutex;

struct Fork {
   unsigned id;
   std::mutex mutex;
};

class Philosopher {
   public:
      Philosopher(unsigned int id_, Fork& left_fork_, Fork& right_fork_) :
	 id(id_), left_fork(left_fork_), right_fork(right_fork_)
      {
      }
      void operator()() {
	 for (int i = 0; i < 5; ++i) {
	    print_status("sits down at the table");
	    /* which fork has to be taken first? */
	    std::mutex* first; std::mutex* second;
	    std::string first_text; std::string second_text;
	    if (left_fork.id < right_fork.id) {
	       first = &left_fork.mutex; second = &right_fork.mutex;
	       first_text = "left"; second_text = "right";
	    } else {
	       first = &right_fork.mutex; second = &left_fork.mutex;
	       first_text = "right"; second_text = "left";
	    }
	    {
	       std::lock_guard<std::mutex> lock1(*first);
	       print_status("picks up the " + first_text + " fork");
	       {
		  std::lock_guard<std::mutex> lock2(*second);
		  print_status("picks up the " + second_text + " fork");
		  {
		     print_status("is dining");
		  }
	       }
	       print_status("returns the " + second_text + " fork");
	    }
	    print_status("returns the " + first_text + " fork");
	    print_status("leaves the table");
	 }
      }
   private:
      void print_status(const std::string& msg) const {
	 std::lock_guard<std::mutex> lock(cout_mutex);
	 std::cout << "philosopher [" << id << "]: " << msg << std::endl;
      }
      unsigned int id;
      Fork& left_fork;
      Fork& right_fork;
};

int main() {
   constexpr unsigned int PHILOSOPHERS = 5;
   std::thread philosopher[PHILOSOPHERS];
   Fork fork[PHILOSOPHERS];
   for (int i = 0; i < PHILOSOPHERS; ++i) {
      fork[i].id = i;
   }
   for (int i = 0; i < PHILOSOPHERS; ++i) {
      philosopher[i] = std::thread(Philosopher(i+1,
	 fork[i], fork[(i + PHILOSOPHERS - 1) % PHILOSOPHERS]));
   }
   for (int i = 0; i < PHILOSOPHERS; ++i) {
      philosopher[i].join();
   }
}