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Diffstat (limited to 'src/third_party/boost-1.69.0/boost/container/detail/singleton.hpp')
-rw-r--r-- | src/third_party/boost-1.69.0/boost/container/detail/singleton.hpp | 121 |
1 files changed, 121 insertions, 0 deletions
diff --git a/src/third_party/boost-1.69.0/boost/container/detail/singleton.hpp b/src/third_party/boost-1.69.0/boost/container/detail/singleton.hpp new file mode 100644 index 00000000000..7601c3ca8c0 --- /dev/null +++ b/src/third_party/boost-1.69.0/boost/container/detail/singleton.hpp @@ -0,0 +1,121 @@ +// Copyright (C) 2000 Stephen Cleary +// Copyright (C) 2008 Ion Gaztanaga +// +// 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) +// +// See http://www.boost.org for updates, documentation, and revision history. +// +// This file is a modified file from Boost.Pool + +////////////////////////////////////////////////////////////////////////////// +// +// (C) Copyright Ion Gaztanaga 2007-2013. 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) +// +// See http://www.boost.org/libs/container for documentation. +// +////////////////////////////////////////////////////////////////////////////// + +#ifndef BOOST_CONTAINER_DETAIL_SINGLETON_DETAIL_HPP +#define BOOST_CONTAINER_DETAIL_SINGLETON_DETAIL_HPP + +#ifndef BOOST_CONFIG_HPP +# include <boost/config.hpp> +#endif + +#if defined(BOOST_HAS_PRAGMA_ONCE) +# pragma once +#endif + +#include <boost/container/detail/config_begin.hpp> +#include <boost/container/detail/workaround.hpp> + +// +// The following helper classes are placeholders for a generic "singleton" +// class. The classes below support usage of singletons, including use in +// program startup/shutdown code, AS LONG AS there is only one thread +// running before main() begins, and only one thread running after main() +// exits. +// +// This class is also limited in that it can only provide singleton usage for +// classes with default constructors. +// + +// The design of this class is somewhat twisted, but can be followed by the +// calling inheritance. Let us assume that there is some user code that +// calls "singleton_default<T>::instance()". The following (convoluted) +// sequence ensures that the same function will be called before main(): +// instance() contains a call to create_object.do_nothing() +// Thus, object_creator is implicitly instantiated, and create_object +// must exist. +// Since create_object is a static member, its constructor must be +// called before main(). +// The constructor contains a call to instance(), thus ensuring that +// instance() will be called before main(). +// The first time instance() is called (i.e., before main()) is the +// latest point in program execution where the object of type T +// can be created. +// Thus, any call to instance() will auto-magically result in a call to +// instance() before main(), unless already present. +// Furthermore, since the instance() function contains the object, instead +// of the singleton_default class containing a static instance of the +// object, that object is guaranteed to be constructed (at the latest) in +// the first call to instance(). This permits calls to instance() from +// static code, even if that code is called before the file-scope objects +// in this file have been initialized. + +namespace boost { +namespace container { +namespace dtl { + +// T must be: no-throw default constructible and no-throw destructible +template <typename T> +struct singleton_default +{ + private: + struct object_creator + { + // This constructor does nothing more than ensure that instance() + // is called before main() begins, thus creating the static + // T object before multithreading race issues can come up. + object_creator() { singleton_default<T>::instance(); } + inline void do_nothing() const { } + }; + static object_creator create_object; + + singleton_default(); + + public: + typedef T object_type; + + // If, at any point (in user code), singleton_default<T>::instance() + // is called, then the following function is instantiated. + static object_type & instance() + { + // This is the object that we return a reference to. + // It is guaranteed to be created before main() begins because of + // the next line. + static object_type obj; + + // The following line does nothing else than force the instantiation + // of singleton_default<T>::create_object, whose constructor is + // called before main() begins. + create_object.do_nothing(); + + return obj; + } +}; +template <typename T> +typename singleton_default<T>::object_creator +singleton_default<T>::create_object; + +} // namespace dtl +} // namespace container +} // namespace boost + +#include <boost/container/detail/config_end.hpp> + +#endif //BOOST_CONTAINER_DETAIL_SINGLETON_DETAIL_HPP |