if(argc != 2) {

std::cerr << usage << std::endl;

std::exit(EXIT_FAILURE);

}

std::string_view opt(argv[1]);

if(opt != "detach" && opt != "join") {

std::cerr << usage << std::endl;

std::exit(EXIT_FAILURE);

}

auto detached = (opt == "detach") ? true : false;

// Create a taskflow graph with three regular tasks and one subflow task.

tf::Taskflow tf(std::thread::hardware_concurrency());

auto [A, B, C, D] = tf.emplace(

// Task A

[] () { std::cout << "TaskA\n"; },

// Task B

[cap=std::vector<int>{1,2,3,4,5,6,7,8}, detached] (auto& subflow) {

std::cout << "TaskB is spawning B1, B2, and B3 ...\n";

auto B1 = subflow.emplace([&]() {

printf(" Subtask B1: reduce sum = %d\n",

std::accumulate(cap.begin(), cap.end(), 0, std::plus<int>()));

}).name("B1");

auto B2 = subflow.emplace([&]() {

printf(" Subtask B2: reduce multiply = %d\n",

std::accumulate(cap.begin(), cap.end(), 1, std::multiplies<int>()));

}).name("B2");

auto B3 = subflow.emplace([&]() {

printf(" Subtask B3: reduce minus = %d\n",

std::accumulate(cap.begin(), cap.end(), 0, std::minus<int>()));

}).name("B3");

B1.precede(B3);

B2.precede(B3);

// detach or join the subflow (by default the subflow join at B)

if(detached) subflow.detach();

},

// Task C

[] () { std::cout << "TaskC\n"; },

// Task D

[] () { std::cout << "TaskD\n"; }

);

A.name("A");

B.name("B");

C.name("C");

D.name("D");

A.precede(B); // B runs after A

A.precede(C); // C runs after A

B.precede(D); // D runs after B

C.precede(D); // D runs after C

tf.dispatch().get(); // block until finished

// examine the graph

std::cout << '\n' << tf.dump_topologies();

return 0;