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
27namespace boost {
28
29BOOST_LOG_OPEN_NAMESPACE
30
31namespace aux {
32
33//! A base class for singletons, constructed on-demand
34template< typename DerivedT, typename StorageT = DerivedT >
35class lazy_singleton
36{
37public:
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
59protected:
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
69template< typename DerivedT, typename StorageT = DerivedT >
70class singleton :
71 public lazy_singleton< DerivedT, StorageT >
72{
73public:
74 static StorageT& instance;
75};
76
77template< typename DerivedT, typename StorageT >
78StorageT& singleton< DerivedT, StorageT >::instance =
79 lazy_singleton< DerivedT, StorageT >::get();
80
81} // namespace aux
82
83BOOST_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_
90

source code of boost/libs/log/include/boost/log/detail/singleton.hpp