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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_ |