ceph/src/boost/libs/log/include/boost/log/detail/singleton.hpp

   1 /*
   2  *          Copyright Andrey Semashev 2007 - 2015.
   3  * Distributed under the Boost Software License, Version 1.0.
   4  *    (See accompanying file LICENSE_1_0.txt or copy at
   5  *          http://www.boost.org/LICENSE_1_0.txt)
   6  */
   7 /*!
   8  * \file   singleton.hpp
   9  * \author Andrey Semashev
  10  * \date   20.04.2008
  11  *
  12  * \brief  This header is the Boost.Log library implementation, see the library documentation
  13  *         at http://www.boost.org/doc/libs/release/libs/log/doc/html/index.html.
  14  */
  15
  16 #ifndef BOOST_LOG_DETAIL_SINGLETON_HPP_INCLUDED_
  17 #define BOOST_LOG_DETAIL_SINGLETON_HPP_INCLUDED_
  18
  19 #include <boost/log/detail/config.hpp>
  20 #include <boost/log/utility/once_block.hpp>
  21 #include <boost/log/detail/header.hpp>
  22
  23 #ifdef BOOST_HAS_PRAGMA_ONCE
  24 #pragma once
  25 #endif
  26
  27 namespace boost {
  28
  29 BOOST_LOG_OPEN_NAMESPACE
  30
  31 namespace aux {
  32
  33 //! A base class for singletons, constructed on-demand
  34 template< typename DerivedT, typename StorageT = DerivedT >
  35 class lazy_singleton
  36 {
  37 public:
  38     BOOST_DEFAULTED_FUNCTION(lazy_singleton(), {})
  39
  40     //! Returns the singleton instance
  41     static StorageT& get()
  42     {
  43         BOOST_LOG_ONCE_BLOCK()
  44         {
  45             DerivedT::init_instance();
  46         }
  47         return get_instance();
  48     }
  49
  50     //! Initializes the singleton instance
  51     static void init_instance()
  52     {
  53         get_instance();
  54     }
  55
  56     BOOST_DELETED_FUNCTION(lazy_singleton(lazy_singleton const&))
  57     BOOST_DELETED_FUNCTION(lazy_singleton& operator= (lazy_singleton const&))
  58
  59 protected:
  60     //! Returns the singleton instance (not thread-safe)
  61     static StorageT& get_instance()
  62     {
  63         static StorageT instance;
  64         return instance;
  65     }
  66 };
  67
  68 //! A base class for singletons, constructed on namespace scope initialization stage
  69 template< typename DerivedT, typename StorageT = DerivedT >
  70 class singleton :
  71     public lazy_singleton< DerivedT, StorageT >
  72 {
  73 public:
  74     static StorageT& instance;
  75 };
  76
  77 template< typename DerivedT, typename StorageT >
  78 StorageT& singleton< DerivedT, StorageT >::instance =
  79     lazy_singleton< DerivedT, StorageT >::get();
  80
  81 } // namespace aux
  82
  83 BOOST_LOG_CLOSE_NAMESPACE // namespace log
  84
  85 } // namespace boost
  86
  87 #include <boost/log/detail/footer.hpp>
  88
  89 #endif // BOOST_LOG_DETAIL_SINGLETON_HPP_INCLUDED_