The following code example is taken from the book
C++20 - The Complete Guide by Nicolai M. Josuttis, Leanpub, 2021
The code is licensed under a Creative Commons Attribution 4.0 International License. Creative Commons License

// raw code

#include "coroasync.hpp"
#include <iostream>

int main()
  // init pool of coroutine threads:
  syncOut() << "**** main() on thread " << std::this_thread::get_id()
            << std::endl;
  CoroPool pool{4};

  // start main coroutine and run it in coroutine pool:
  syncOut() << "runTask(runAsync(1))" << std::endl;
  CoroPoolTask t1 = runAsync("1");

  // wait until all coroutines are done:
  syncOut() << "\n**** waitUntilNoCoros()" << std::endl;

  syncOut() << "\n**** main() done" << std::endl;