1*cdf0e10cSrcweir /************************************************************************* 2*cdf0e10cSrcweir * 3*cdf0e10cSrcweir * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4*cdf0e10cSrcweir * 5*cdf0e10cSrcweir * Copyright 2000, 2010 Oracle and/or its affiliates. 6*cdf0e10cSrcweir * 7*cdf0e10cSrcweir * OpenOffice.org - a multi-platform office productivity suite 8*cdf0e10cSrcweir * 9*cdf0e10cSrcweir * This file is part of OpenOffice.org. 10*cdf0e10cSrcweir * 11*cdf0e10cSrcweir * OpenOffice.org is free software: you can redistribute it and/or modify 12*cdf0e10cSrcweir * it under the terms of the GNU Lesser General Public License version 3 13*cdf0e10cSrcweir * only, as published by the Free Software Foundation. 14*cdf0e10cSrcweir * 15*cdf0e10cSrcweir * OpenOffice.org is distributed in the hope that it will be useful, 16*cdf0e10cSrcweir * but WITHOUT ANY WARRANTY; without even the implied warranty of 17*cdf0e10cSrcweir * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 18*cdf0e10cSrcweir * GNU Lesser General Public License version 3 for more details 19*cdf0e10cSrcweir * (a copy is included in the LICENSE file that accompanied this code). 20*cdf0e10cSrcweir * 21*cdf0e10cSrcweir * You should have received a copy of the GNU Lesser General Public License 22*cdf0e10cSrcweir * version 3 along with OpenOffice.org. If not, see 23*cdf0e10cSrcweir * <http://www.openoffice.org/license.html> 24*cdf0e10cSrcweir * for a copy of the LGPLv3 License. 25*cdf0e10cSrcweir * 26*cdf0e10cSrcweir ************************************************************************/ 27*cdf0e10cSrcweir 28*cdf0e10cSrcweir #if !defined INCLUDED_OSL_DOUBLECHECKEDLOCKING_H 29*cdf0e10cSrcweir #define INCLUDED_OSL_DOUBLECHECKEDLOCKING_H 30*cdf0e10cSrcweir 31*cdf0e10cSrcweir #if defined __cplusplus 32*cdf0e10cSrcweir extern "C" { 33*cdf0e10cSrcweir #endif /* __cplusplus */ 34*cdf0e10cSrcweir 35*cdf0e10cSrcweir /** A platform specific macro needed to make double-checked locking work. 36*cdf0e10cSrcweir 37*cdf0e10cSrcweir See 38*cdf0e10cSrcweir <http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html> 39*cdf0e10cSrcweir for a description of double-checked locking, why it is broken, and how it 40*cdf0e10cSrcweir can be fixed. On platforms where it is necessary, this macro will expand 41*cdf0e10cSrcweir to some memory barrier instruction. On many platforms, double-checked 42*cdf0e10cSrcweir locking works as it is, though, so on those platforms this macro will be 43*cdf0e10cSrcweir empty. This is a macro instead of a (C++ inline) function to allow for 44*cdf0e10cSrcweir maximum performance in both C and C++. 45*cdf0e10cSrcweir 46*cdf0e10cSrcweir If possible, use the rtl_Instance template instead of explicitly spelling 47*cdf0e10cSrcweir out the double-checked locking pattern. There are few cases where you 48*cdf0e10cSrcweir will have to spell it out explicitly (e.g., the logic of a certain 49*cdf0e10cSrcweir instance of the pattern is too complex to be mapped to the template, or 50*cdf0e10cSrcweir some compiler refuses to compile a template instantiation due to internal 51*cdf0e10cSrcweir compiler errors), though, and you should always call this macro at the 52*cdf0e10cSrcweir right places then: 53*cdf0e10cSrcweir 54*cdf0e10cSrcweir static T * pInstance = 0; 55*cdf0e10cSrcweir 56*cdf0e10cSrcweir T * p = pInstance; 57*cdf0e10cSrcweir if (!p) 58*cdf0e10cSrcweir { 59*cdf0e10cSrcweir Guard aGuard(aMutex); 60*cdf0e10cSrcweir p = pInstance; 61*cdf0e10cSrcweir if (!p) 62*cdf0e10cSrcweir { 63*cdf0e10cSrcweir p = ...; 64*cdf0e10cSrcweir OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER(); 65*cdf0e10cSrcweir pInstance = p; 66*cdf0e10cSrcweir } 67*cdf0e10cSrcweir } 68*cdf0e10cSrcweir else 69*cdf0e10cSrcweir OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER(); 70*cdf0e10cSrcweir return p; 71*cdf0e10cSrcweir 72*cdf0e10cSrcweir One extra advantage of this macro is that it makes it easier to find all 73*cdf0e10cSrcweir places where double-checked locking is used. 74*cdf0e10cSrcweir */ 75*cdf0e10cSrcweir #define OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER() /* empty */ 76*cdf0e10cSrcweir 77*cdf0e10cSrcweir #if defined __cplusplus 78*cdf0e10cSrcweir } 79*cdf0e10cSrcweir #endif /* __cplusplus */ 80*cdf0e10cSrcweir 81*cdf0e10cSrcweir #endif /* INCLUDED_OSL_DOUBLECHECKEDLOCKING_H */ 82