{

// create a thread pool with max. 4 concurrency threads

ThreadPool pool(4);

// create execution results list

std::vector< std::future<std::string> > results;

// start eight thread task

for(int i = 0; i < 8; ++i) {

// add all task to result list

results.emplace_back(

// ass print task to thread pool

pool.enqueue([i] {

std::cout << "hello " << i << std::endl;

// wait a sec when the previous line is out

std::this_thread::sleep_for(std::chrono::seconds(1));

// keep output and return the status of execution

std::cout << "world " << i << std::endl;

return std::string("---thread ") + std::to_string(i) + std::string(" finished.---");

})

);

}

// outputs

for(auto && result: results)

std::cout << result.get() << ' ';

std::cout << std::endl;

return 0;