#include <atomic>
#include <chrono>
#include <iostream>
#include <thread>
#include <vector>

std::vector<int> data;
std::atomic_bool data_ready(false);

void
reader_thread()
{
  while (!data_ready.load()) {
    std::this_thread::sleep_for(std::chrono::milliseconds(1));
  }
  std::cout << "The answer=" << data[0] << "\n";
}
void
writer_thread()
{
  data.push_back(42);
  data_ready = true;
}