Update boost to 1.71 and add asio

boost/asio/impl/thread_pool.ipp

@@ -0,0 +1,89 @@
+//
+// impl/thread_pool.ipp
+// ~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2019 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)
+//
+
+#ifndef BOOST_ASIO_IMPL_THREAD_POOL_IPP
+#define BOOST_ASIO_IMPL_THREAD_POOL_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/thread_pool.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+
+struct thread_pool::thread_function
+{
+  detail::scheduler* scheduler_;
+
+  void operator()()
+  {
+    boost::system::error_code ec;
+    scheduler_->run(ec);
+  }
+};
+
+thread_pool::thread_pool()
+  : scheduler_(add_scheduler(new detail::scheduler(*this, 0, false)))
+{
+  scheduler_.work_started();
+
+  thread_function f = { &scheduler_ };
+  std::size_t num_threads = detail::thread::hardware_concurrency() * 2;
+  threads_.create_threads(f, num_threads ? num_threads : 2);
+}
+
+thread_pool::thread_pool(std::size_t num_threads)
+  : scheduler_(add_scheduler(new detail::scheduler(
+          *this, num_threads == 1 ? 1 : 0, false)))
+{
+  scheduler_.work_started();
+
+  thread_function f = { &scheduler_ };
+  threads_.create_threads(f, num_threads);
+}
+
+thread_pool::~thread_pool()
+{
+  stop();
+  join();
+}
+
+void thread_pool::stop()
+{
+  scheduler_.stop();
+}
+
+void thread_pool::join()
+{
+  if (!threads_.empty())
+  {
+    scheduler_.work_finished();
+    threads_.join();
+  }
+}
+
+detail::scheduler& thread_pool::add_scheduler(detail::scheduler* s)
+{
+  detail::scoped_ptr<detail::scheduler> scoped_impl(s);
+  boost::asio::add_service<detail::scheduler>(*this, scoped_impl.get());
+  return *scoped_impl.release();
+}
+
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_IMPL_THREAD_POOL_IPP