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Diffstat (limited to '')
-rw-r--r-- | include/osl/doublecheckedlocking.h | 81 |
1 files changed, 81 insertions, 0 deletions
diff --git a/include/osl/doublecheckedlocking.h b/include/osl/doublecheckedlocking.h new file mode 100644 index 0000000000..f89ab36205 --- /dev/null +++ b/include/osl/doublecheckedlocking.h @@ -0,0 +1,81 @@ +/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */ +/* + * This file is part of the LibreOffice project. + * + * This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this + * file, You can obtain one at http://mozilla.org/MPL/2.0/. + * + * This file incorporates work covered by the following license notice: + * + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed + * with this work for additional information regarding copyright + * ownership. The ASF licenses this file to you under the Apache + * License, Version 2.0 (the "License"); you may not use this file + * except in compliance with the License. You may obtain a copy of + * the License at http://www.apache.org/licenses/LICENSE-2.0 . + */ + +/* + * This file is part of LibreOffice published API. + */ + +#ifndef 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: + + @code{.cpp} + 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; + @endcode + + 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: */ |