Added thirdparty: boost library

thirdparty/include/boost/histogram/detail/mutex_base.hpp

@@ -0,0 +1,41 @@
+// Copyright 2019 Hans Dembinski
+//
+// 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_HISTOGRAM_DETAIL_NOOP_MUTEX_HPP
+#define BOOST_HISTOGRAM_DETAIL_NOOP_MUTEX_HPP
+
+#include <boost/core/empty_value.hpp>
+#include <boost/histogram/detail/axes.hpp>
+#include <boost/mp11/utility.hpp> // mp_if
+#include <mutex>
+
+namespace boost {
+namespace histogram {
+namespace detail {
+
+struct null_mutex {
+  bool try_lock() noexcept { return true; }
+  void lock() noexcept {}
+  void unlock() noexcept {}
+};
+
+template <class Axes, class Storage,
+          class DetailMutex = mp11::mp_if_c<(Storage::has_threading_support &&
+                                             detail::has_growing_axis<Axes>::value),
+                                            std::mutex, detail::null_mutex>>
+struct mutex_base : empty_value<DetailMutex> {
+  mutex_base() = default;
+  // do not copy or move mutex
+  mutex_base(const mutex_base&) : empty_value<DetailMutex>() {}
+  // do not copy or move mutex
+  mutex_base& operator=(const mutex_base&) { return *this; }
+};
+
+} // namespace detail
+} // namespace histogram
+} // namespace boost
+
+#endif