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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/*************************************************************************
*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* Copyright 2000, 2010 Oracle and/or its affiliates.
*
* OpenOffice.org - a multi-platform office productivity suite
*
* This file is part of OpenOffice.org.
*
* OpenOffice.org is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License version 3
* only, as published by the Free Software Foundation.
*
* OpenOffice.org is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License version 3 for more details
* (a copy is included in the LICENSE file that accompanied this code).
*
* You should have received a copy of the GNU Lesser General Public License
* version 3 along with OpenOffice.org. If not, see
* <http://www.openoffice.org/license.html>
* for a copy of the LGPLv3 License.
*
************************************************************************/
#if !defined INCLUDED_OSL_DOUBLECHECKEDLOCKING_H
#define INCLUDED_OSL_DOUBLECHECKEDLOCKING_H
#if defined __cplusplus
extern "C" {
#endif /* __cplusplus */
/** A platform specific macro needed to make double-checked locking work.
See
<http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html>
for a description of double-checked locking, why it is broken, and how it
can be fixed. On platforms where it is necessary, this macro will expand
to some memory barrier instruction. On many platforms, double-checked
locking works as it is, though, so on those platforms this macro will be
empty. This is a macro instead of a (C++ inline) function to allow for
maximum performance in both C and C++.
If possible, use the rtl_Instance template instead of explicitly spelling
out the double-checked locking pattern. There are few cases where you
will have to spell it out explicitly (e.g., the logic of a certain
instance of the pattern is too complex to be mapped to the template, or
some compiler refuses to compile a template instantiation due to internal
compiler errors), though, and you should always call this macro at the
right places then:
static T * pInstance = 0;
T * p = pInstance;
if (!p)
{
Guard aGuard(aMutex);
p = pInstance;
if (!p)
{
p = ...;
OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER();
pInstance = p;
}
}
else
OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER();
return p;
One extra advantage of this macro is that it makes it easier to find all
places where double-checked locking is used.
*/
#define OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER() /* empty */
#if defined __cplusplus
}
#endif /* __cplusplus */
#endif /* INCLUDED_OSL_DOUBLECHECKEDLOCKING_H */
/* vim:set shiftwidth=4 softtabstop=4 expandtab: */
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