1 /************************************************************************* 2 * 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * Copyright 2000, 2010 Oracle and/or its affiliates. 6 * 7 * OpenOffice.org - a multi-platform office productivity suite 8 * 9 * This file is part of OpenOffice.org. 10 * 11 * OpenOffice.org is free software: you can redistribute it and/or modify 12 * it under the terms of the GNU Lesser General Public License version 3 13 * only, as published by the Free Software Foundation. 14 * 15 * OpenOffice.org is distributed in the hope that it will be useful, 16 * but WITHOUT ANY WARRANTY; without even the implied warranty of 17 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 18 * GNU Lesser General Public License version 3 for more details 19 * (a copy is included in the LICENSE file that accompanied this code). 20 * 21 * You should have received a copy of the GNU Lesser General Public License 22 * version 3 along with OpenOffice.org. If not, see 23 * <http://www.openoffice.org/license.html> 24 * for a copy of the LGPLv3 License. 25 * 26 ************************************************************************/ 27 28 #ifndef _SALHELPER_SINGLETONREF_HXX_ 29 #define _SALHELPER_SINGLETONREF_HXX_ 30 31 //_______________________________________________ 32 // includes 33 34 #include <osl/mutex.hxx> 35 #include "rtl/instance.hxx" 36 #include "osl/diagnose.h" 37 #include "osl/getglobalmutex.hxx" 38 39 //_______________________________________________ 40 // namespace 41 42 namespace salhelper{ 43 44 //_______________________________________________ 45 // definitions 46 47 /** @short template for implementing singleton classes. 48 49 @descr Such classes can be instanciated everytimes they 50 are needed. But the internal wrapped object will 51 be created one times only. Of course its used 52 resources are referenced one times only too. 53 This template hold it alive till the last 54 reference is gone. Further all operations 55 on this reference are threadsafe. Only 56 calls directly to the internal object (which modify 57 its state) must be made threadsafe by the object itself 58 or from outside. 59 60 @attention To prevent the code against race conditions, its not 61 allowed to start operations inside the ctor 62 of the internal wrapped object - especialy operations 63 which needs a reference to the same singleton too. 64 65 The only chance to supress such strange constellations 66 is a lazy-init mechanism. 67 68 <ul> 69 <li>a) The singleton class can provide a special init() 70 method, which must be called as first after creation.</li> 71 <li>b) The singleton class can call a special impl_init() 72 method implicit for every called interface method.</li> 73 </ul> 74 75 Note further that this singleton pattern can work only, if 76 all user of such singleton are located inside the same library! 77 Because static values cant be exported - e.g. from windows libraries. 78 */ 79 template< class SingletonClass > 80 class SingletonRef 81 { 82 //------------------------------------------- 83 // member 84 85 private : 86 87 /** @short pointer to the internal wrapped singleton. */ 88 static SingletonClass* m_pInstance; 89 90 /** @short ref count, which regulate creation and removing of m_pInstance. */ 91 static sal_Int32 m_nRef; 92 93 //------------------------------------------- 94 // interface 95 96 public : 97 98 //--------------------------------------- 99 100 /** @short standard ctor. 101 102 @descr The internal wrapped object is created only, 103 if its ref count was 0. Otherwhise this method 104 does nothing ... except increasing of the internal 105 ref count! 106 */ 107 SingletonRef() 108 { 109 // GLOBAL SAFE -> 110 ::osl::MutexGuard aLock(SingletonRef::ownStaticLock()); 111 112 // must be increased before(!) the check is done. 113 // Otherwhise this check can fail inside the same thread ... 114 ++m_nRef; 115 if (m_nRef == 1) 116 m_pInstance = new SingletonClass(); 117 118 OSL_ENSURE(m_nRef>0 && m_pInstance, "Race? Ref count of singleton >0, but instance is NULL!"); 119 // <- GLOBAL SAFE 120 } 121 122 //--------------------------------------- 123 124 /** @short standard dtor. 125 126 @descr The internal wrapped object is removed only, 127 if its ref count wil be 0. Otherwhise this method 128 does nothing ... except decreasing of the internal 129 ref count! 130 */ 131 ~SingletonRef() 132 { 133 // GLOBAL SAFE -> 134 ::osl::MutexGuard aLock(SingletonRef::ownStaticLock()); 135 136 // must be decreased before(!) the check is done. 137 // Otherwhise this check can fail inside the same thread ... 138 --m_nRef; 139 if (m_nRef == 0) 140 { 141 delete m_pInstance; 142 m_pInstance = 0; 143 } 144 // <- GLOBAL SAFE 145 } 146 147 //--------------------------------------- 148 149 /** @short Allows rSingle->someBodyOp(). 150 */ 151 SingletonClass* operator->() const 152 { 153 // GLOBAL SAFE -> 154 ::osl::MutexGuard aLock(SingletonRef::ownStaticLock()); 155 return m_pInstance; 156 // <- GLOBAL SAFE 157 } 158 159 //--------------------------------------- 160 161 /** @short Allows (*rSingle).someBodyOp(). 162 */ 163 SingletonClass& operator*() const 164 { 165 // GLOBAL SAFE -> 166 ::osl::MutexGuard aLock(SingletonRef::ownStaticLock()); 167 return *m_pInstance; 168 // <- GLOBAL SAFE 169 } 170 171 //------------------------------------------- 172 // helper 173 174 private : 175 176 //--------------------------------------- 177 178 /** @short creates an own mutex for guarding static contents. 179 180 @descr The global mutex the osl library is used one times 181 only to create an own static mutex, which can be used 182 next time to guard own static member operations. 183 */ 184 struct SingletonLockInit 185 { 186 ::osl::Mutex* operator()() 187 { 188 static ::osl::Mutex aInstance; 189 return &aInstance; 190 } 191 }; 192 193 ::osl::Mutex& ownStaticLock() const 194 { 195 return *rtl_Instance< ::osl::Mutex, 196 SingletonLockInit, 197 ::osl::MutexGuard, 198 ::osl::GetGlobalMutex >::create(SingletonLockInit(), ::osl::GetGlobalMutex()); 199 } 200 }; 201 202 template< class SingletonClass > 203 SingletonClass* SingletonRef< SingletonClass >::m_pInstance = 0; 204 205 template< class SingletonClass > 206 sal_Int32 SingletonRef< SingletonClass >::m_nRef = 0; 207 208 } // namespace salhelper 209 210 #endif // _SALHELPER_SINGLETONREF_HXX_ 211