// threadLocal.cpp
#include <iostream>
#include <string>
#include <mutex>
#include <thread>
std::mutex coutMutex;
thread_local std::string s("hello from ");
void addThreadLocal(std::string const& s2){
  s += s2;
  // protect std::cout
  std::lock_guard<std::mutex> guard(coutMutex);
  std::cout << s << std::endl;
  std::cout << "&s: " << &s << std::endl;
  std::cout << std::endl;
}
int main(){
  std::cout << std::endl;
  std::thread t1(addThreadLocal,"t1"); 
  std::thread t2(addThreadLocal,"t2"); 
  std::thread t3(addThreadLocal,"t3"); 
  std::thread t4(addThreadLocal,"t4"); 
  t1.join();
  t2.join();
  t3.join();
  t4.join();
}