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1 : /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
2 : /*
3 : * This file is part of the LibreOffice project.
4 : *
5 : * This Source Code Form is subject to the terms of the Mozilla Public
6 : * License, v. 2.0. If a copy of the MPL was not distributed with this
7 : * file, You can obtain one at http://mozilla.org/MPL/2.0/.
8 : *
9 : * This file incorporates work covered by the following license notice:
10 : *
11 : * Licensed to the Apache Software Foundation (ASF) under one or more
12 : * contributor license agreements. See the NOTICE file distributed
13 : * with this work for additional information regarding copyright
14 : * ownership. The ASF licenses this file to you under the Apache
15 : * License, Version 2.0 (the "License"); you may not use this file
16 : * except in compliance with the License. You may obtain a copy of
17 : * the License at http://www.apache.org/licenses/LICENSE-2.0 .
18 : */
19 :
20 : #ifndef INCLUDED_SALHELPER_SINGLETONREF_HXX
21 : #define INCLUDED_SALHELPER_SINGLETONREF_HXX
22 :
23 : #include <osl/mutex.hxx>
24 : #include <rtl/instance.hxx>
25 : #include <osl/diagnose.h>
26 : #include <osl/getglobalmutex.hxx>
27 :
28 :
29 : namespace salhelper{
30 :
31 :
32 : /** @short template for implementing singleton classes.
33 :
34 : Such classes can be instanciated every time they
35 : are needed. But the internal wrapped object will
36 : be created one times only. Of course its used
37 : resources are referenced one times only too.
38 : This template hold it alive till the last
39 : reference is gone. Further all operations
40 : on this reference are threadsafe. Only
41 : calls directly to the internal object (which modify
42 : its state) must be made threadsafe by the object itself
43 : or from outside.
44 :
45 : @attention To prevent the code against race conditions, its not
46 : allowed to start operations inside the ctor
47 : of the internal wrapped object - especialy operations
48 : which needs a reference to the same singleton too.
49 :
50 : The only chance to supress such strange constellations
51 : is a lazy-init mechanism.
52 :
53 : <ul>
54 : <li>a) The singleton class can provide a special init()
55 : method, which must be called as first after creation.</li>
56 : <li>b) The singleton class can call a special impl_init()
57 : method implicit for every called interface method.</li>
58 : </ul>
59 :
60 : Note further that this singleton pattern can work only, if
61 : all user of such singleton are located inside the same library!
62 : Because static values cant be exported - e.g. from windows libraries.
63 : */
64 : template< class SingletonClass >
65 : class SingletonRef
66 : {
67 :
68 : // member
69 :
70 : private :
71 :
72 : /** @short pointer to the internal wrapped singleton. */
73 : static SingletonClass* m_pInstance;
74 :
75 : /** @short ref count, which regulate creation and removing of m_pInstance. */
76 : static sal_Int32 m_nRef;
77 :
78 :
79 : // interface
80 :
81 : public :
82 :
83 :
84 :
85 : /** @short standard ctor.
86 :
87 : The internal wrapped object is created only,
88 : if its ref count was 0. Otherwise this method
89 : does nothing ... except increasing of the internal
90 : ref count!
91 : */
92 1 : SingletonRef()
93 : {
94 : // GLOBAL SAFE ->
95 1 : ::osl::MutexGuard aLock(SingletonRef::ownStaticLock());
96 :
97 : // must be increased before(!) the check is done.
98 : // Otherwise this check can fail inside the same thread ...
99 1 : ++m_nRef;
100 1 : if (m_nRef == 1)
101 1 : m_pInstance = new SingletonClass();
102 :
103 1 : OSL_ENSURE(m_nRef>0 && m_pInstance, "Race? Ref count of singleton >0, but instance is NULL!");
104 : // <- GLOBAL SAFE
105 1 : }
106 :
107 :
108 :
109 : /** @short standard dtor.
110 :
111 : The internal wrapped object is removed only,
112 : if its ref count wil be 0. Otherwise this method
113 : does nothing ... except decreasing of the internal
114 : ref count!
115 : */
116 1 : ~SingletonRef()
117 : {
118 : // GLOBAL SAFE ->
119 1 : ::osl::MutexGuard aLock(SingletonRef::ownStaticLock());
120 :
121 : // must be decreased before(!) the check is done.
122 : // Otherwise this check can fail inside the same thread ...
123 1 : --m_nRef;
124 1 : if (m_nRef == 0)
125 : {
126 1 : delete m_pInstance;
127 1 : m_pInstance = 0;
128 1 : }
129 : // <- GLOBAL SAFE
130 1 : }
131 :
132 :
133 :
134 : /** @short Allows rSingle->someBodyOp().
135 : */
136 1 : SingletonClass* operator->() const
137 : {
138 : // GLOBAL SAFE ->
139 1 : ::osl::MutexGuard aLock(SingletonRef::ownStaticLock());
140 1 : return m_pInstance;
141 : // <- GLOBAL SAFE
142 : }
143 :
144 :
145 :
146 : /** @short Allows (*rSingle).someBodyOp().
147 : */
148 0 : SingletonClass& operator*() const
149 : {
150 : // GLOBAL SAFE ->
151 0 : ::osl::MutexGuard aLock(SingletonRef::ownStaticLock());
152 0 : return *m_pInstance;
153 : // <- GLOBAL SAFE
154 : }
155 :
156 :
157 : // helper
158 :
159 : private :
160 :
161 :
162 :
163 : /** @short creates an own mutex for guarding static contents.
164 :
165 : The global mutex the osl library is used one times
166 : only to create an own static mutex, which can be used
167 : next time to guard own static member operations.
168 : */
169 : struct SingletonLockInit
170 : {
171 1 : ::osl::Mutex* operator()()
172 : {
173 1 : static ::osl::Mutex aInstance;
174 1 : return &aInstance;
175 : }
176 : };
177 :
178 3 : ::osl::Mutex& ownStaticLock() const
179 : {
180 : return *rtl_Instance< ::osl::Mutex,
181 : SingletonLockInit,
182 : ::osl::MutexGuard,
183 3 : ::osl::GetGlobalMutex >::create(SingletonLockInit(), ::osl::GetGlobalMutex());
184 : }
185 : };
186 :
187 : template< class SingletonClass >
188 : SingletonClass* SingletonRef< SingletonClass >::m_pInstance = 0;
189 :
190 : template< class SingletonClass >
191 : sal_Int32 SingletonRef< SingletonClass >::m_nRef = 0;
192 :
193 : } // namespace salhelper
194 :
195 : #endif // INCLUDED_SALHELPER_SINGLETONREF_HXX
196 :
197 : /* vim:set shiftwidth=4 softtabstop=4 expandtab: */
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