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doc/html/boost_asio/example/cpp03/http/server2/io_context_pool.cpp

//
// io_context_pool.cpp
// ~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2021 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/thread/thread.hpp>
#include <boost/bind/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 boost::asio::io_context);
    io_contexts_.push_back(io_context);
    work_.push_back(boost::asio::require(io_context->get_executor(),
          boost::asio::execution::outstanding_work.tracked));
  }
}

void io_context_pool::run()
{
  // Create a pool of threads to run all of the io_contexts.
  std::vector<boost::shared_ptr<boost::thread> > threads;
  for (std::size_t i = 0; i < io_contexts_.size(); ++i)
  {
    boost::shared_ptr<boost::thread> thread(new boost::thread(
          boost::bind(&boost::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();
}

boost::asio::io_context& io_context_pool::get_io_context()
{
  // Use a round-robin scheme to choose the next io_context to use.
  boost::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