if (N < 2) {

return N;

}

size_t res1, res2;

// create a task group

tf::TaskGroup tg = get_executor().task_group();

tg.silent_async([N, &res1](){ res1 = spawn_async(N-1); });

// tail optimization

res2 = spawn_async(N-2);

tg.corun();

return res1 + res2;

if(argc != 2) {

std::cerr << "usage: ./fibonacci N\n";

std::exit(EXIT_FAILURE);

}

size_t N = std::atoi(argv[1]);

auto& executor = get_executor();

auto tbeg = std::chrono::steady_clock::now();

printf("fib[%zu] = %zu\n", N, executor.async([N](){ return spawn_async(N); }).get());

auto tend = std::chrono::steady_clock::now();

std::cout << "elapsed time: "

<< std::chrono::duration_cast<std::chrono::milliseconds>(tend-tbeg).count()

<< " ms\n";

return 0;