Welcome

  const int  N = 4;
  std::vector<std::jthread> threads;

  for (int i = 0; i < N; ++i)
    threads.emplace_back([] {
      std::println("work");

      std::println("done");
    });
// work done work done work done work done

  const int  N = 4;
  std::vector<std::jthread> threads;

  for (int i = 0; i < N; ++i)
    threads.emplace_back([] {
      std::println("work");

      std::println("done");
    });
// work work work work done done done done

  const int  N = 4;
  std::vector<std::jthread> threads;
  std::_____ ready{N};
  for (int i = 0; i < N; ++i)
    threads.emplace_back([&ready] {
      std::println("work");
      ready.arrive_and_wait();
      std::println("done");
    });
// work work work work done done done done

  const int  N = 4;
  std::vector<std::jthread> threads;
  std::latch ready{N};
  for (int i = 0; i < N; ++i)
    threads.emplace_back([&ready] {
      std::println("work");
      ready.arrive_and_wait();
      std::println("done");
    });
// work work work work done done done done