#include <atomic>
#include <thread>

std::vector<int> queue_data;
std::atomic<int> count;

void
populate_queue()
{
  unsigned const number_of_items = 20;
  queue_data.clear();
  for (unsigned i = 0; i < number_of_items; ++i) {
    queue_data.push_back(i);
  }

  count.store(number_of_items, std::memory_order_release);
}

void
consume_queue_items()
{
  while (true) {
    int item_index;
    if ((item_index = count.fetch_sub(1, std::memory_order_acquire)) <= 0) {
      wait_for_more_items();
      continue;
    }
    process(queue_data[item_index - 1]);
  }
}

int
main()
{
  std::thread a(populate_queue);
  std::thread b(consume_queue_items);
  std::thread c(consume_queue_items);
  a.join();
  b.join();
  c.join();
}