text: //
  // io_context_pool.cpp
  // ~~~~~~~~~~~~~~~~~~~
  //
  // Copyright (c) 2003-2018 Christopher M. Kohlhoff (chris at kohlhoff dot com)
  //
  // Distributed under the Boost Software License, Version 1.0. (See accompanying
  // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  //
  
  #include "server.hpp"
  #include <stdexcept>
  #include <boost/bind.hpp>
  #include <boost/shared_ptr.hpp>
  
  namespace http {
  namespace server2 {
  
  io_context_pool::io_context_pool(std::size_t pool_size)
    : next_io_context_(0)
  {
    if (pool_size == 0)
      throw std::runtime_error("io_context_pool size is 0");
  
    // Give all the io_contexts work to do so that their run() functions will not
    // exit until they are explicitly stopped.
    for (std::size_t i = 0; i < pool_size; ++i)
    {
      io_context_ptr io_context(new asio::io_context);
      io_contexts_.push_back(io_context);
      work_.push_back(asio::make_work_guard(*io_context));
    }
  }
  
  void io_context_pool::run()
  {
    // Create a pool of threads to run all of the io_contexts.
    std::vector<boost::shared_ptr<asio::thread> > threads;
    for (std::size_t i = 0; i < io_contexts_.size(); ++i)
    {
      boost::shared_ptr<asio::thread> thread(new asio::thread(
            boost::bind(&asio::io_context::run, io_contexts_[i])));
      threads.push_back(thread);
    }
  
    // Wait for all threads in the pool to exit.
    for (std::size_t i = 0; i < threads.size(); ++i)
      threads[i]->join();
  }
  
  void io_context_pool::stop()
  {
    // Explicitly stop all io_contexts.
    for (std::size_t i = 0; i < io_contexts_.size(); ++i)
      io_contexts_[i]->stop();
  }
  
  asio::io_context& io_context_pool::get_io_context()
  {
    // Use a round-robin scheme to choose the next io_context to use.
    asio::io_context& io_context = *io_contexts_[next_io_context_];
    ++next_io_context_;
    if (next_io_context_ == io_contexts_.size())
      next_io_context_ = 0;
    return io_context;
  }
  
  } // namespace server2
  } // namespace http
  