How to create a thread pool using boost in C++?

How do I create a thread pool using boost in C++, and how do I assign tasks to the threadpool?

Starting from boost 1.66.0, there is a thread_pool class:

#include <boost/asio/thread_pool.hpp>
#include <boost/asio/post.hpp>

boost::asio::thread_pool pool(4); // 4 threads
boost::asio::post(pool, [] {});
pool.join();

See the description.