84 lines
3 KiB
C
84 lines
3 KiB
C
/*************************************************************************
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*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* Copyright 2008 by Sun Microsystems, Inc.
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*
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* OpenOffice.org - a multi-platform office productivity suite
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*
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* $RCSfile: doublecheckedlocking.h,v $
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* $Revision: 1.4 $
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*
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* This file is part of OpenOffice.org.
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*
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* OpenOffice.org is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License version 3
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* only, as published by the Free Software Foundation.
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*
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* OpenOffice.org is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Lesser General Public License version 3 for more details
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* (a copy is included in the LICENSE file that accompanied this code).
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*
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* You should have received a copy of the GNU Lesser General Public License
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* version 3 along with OpenOffice.org. If not, see
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* <http://www.openoffice.org/license.html>
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* for a copy of the LGPLv3 License.
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*
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************************************************************************/
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#if !defined INCLUDED_OSL_DOUBLECHECKEDLOCKING_H
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#define INCLUDED_OSL_DOUBLECHECKEDLOCKING_H
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#if defined __cplusplus
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extern "C" {
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#endif /* __cplusplus */
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/** A platform specific macro needed to make double-checked locking work.
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See
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<http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html>
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for a description of double-checked locking, why it is broken, and how it
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can be fixed. On platforms where it is necessary, this macro will expand
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to some memory barrier instruction. On many platforms, double-checked
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locking works as it is, though, so on those platforms this macro will be
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empty. This is a macro instead of a (C++ inline) function to allow for
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maximum performance in both C and C++.
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If possible, use the rtl_Instance template instead of explicitly spelling
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out the double-checked locking pattern. There are few cases where you
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will have to spell it out explicitly (e.g., the logic of a certain
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instance of the pattern is too complex to be mapped to the template, or
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some compiler refuses to compile a template instantiation due to internal
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compiler errors), though, and you should always call this macro at the
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right places then:
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static T * pInstance = 0;
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T * p = pInstance;
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if (!p)
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{
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Guard aGuard(aMutex);
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p = pInstance;
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if (!p)
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{
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p = ...;
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OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER();
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pInstance = p;
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}
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}
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else
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OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER();
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return p;
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One extra advantage of this macro is that it makes it easier to find all
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places where double-checked locking is used.
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*/
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#define OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER() /* empty */
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#if defined __cplusplus
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}
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#endif /* __cplusplus */
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#endif /* INCLUDED_OSL_DOUBLECHECKEDLOCKING_H */
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