6c7659b584
Change-Id: Ib48a12e902f2311c295b2007f08f44dee28f431d Reviewed-on: https://gerrit.libreoffice.org/3499 Reviewed-by: David Tardon <dtardon@redhat.com> Tested-by: David Tardon <dtardon@redhat.com>
75 lines
2.8 KiB
C
75 lines
2.8 KiB
C
/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
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/*
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* This file is part of the LibreOffice project.
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*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*
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* This file incorporates work covered by the following license notice:
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed
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* with this work for additional information regarding copyright
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* ownership. The ASF licenses this file to you under the Apache
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* License, Version 2.0 (the "License"); you may not use this file
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* except in compliance with the License. You may obtain a copy of
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* the License at http://www.apache.org/licenses/LICENSE-2.0 .
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*/
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#ifndef 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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/* vim:set shiftwidth=4 softtabstop=4 expandtab: */
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