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Diffstat (limited to 'include/comphelper/doublecheckedinit.hxx')
-rw-r--r-- | include/comphelper/doublecheckedinit.hxx | 64 |
1 files changed, 64 insertions, 0 deletions
diff --git a/include/comphelper/doublecheckedinit.hxx b/include/comphelper/doublecheckedinit.hxx new file mode 100644 index 000000000..200a9c88c --- /dev/null +++ b/include/comphelper/doublecheckedinit.hxx @@ -0,0 +1,64 @@ +/* -*- 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 . + */ + +#ifndef INCLUDED_COMPHELPER_DOUBLECHECKEDINIT_HXX +#define INCLUDED_COMPHELPER_DOUBLECHECKEDINIT_HXX + +#include <osl/getglobalmutex.hxx> + +#include <atomic> +// HACK: <atomic> includes <stdbool.h>, which in some Clang versions does '#define bool bool', +// which confuses clang plugins. +#undef bool +#include <functional> + +namespace comphelper +{ +/** + * Thread-safe singleton creation. + * + * It is normally sufficient to create singletons using static variables in a function. + * This function is only for use cases that have a more complex lifetime of the object, + * such as when the object may require specific cleanup or may be created more times + * (e.g. when there is a "singleton" per each instance of another object). + */ +template <typename Type, typename Function = std::function<Type*()>, + typename Guard = osl::MutexGuard, typename GuardCtor = osl::GetGlobalMutex> +static inline Type* doubleCheckedInit(std::atomic<Type*>& pointer, Function function, + GuardCtor guardCtor = osl::GetGlobalMutex()) +{ + Type* p = pointer.load(std::memory_order_acquire); + if (!p) + { + Guard guard(guardCtor()); + p = pointer.load(std::memory_order_relaxed); + if (!p) + { + p = function(); + pointer.store(p, std::memory_order_release); + } + } + return p; +} + +} // namespace + +#endif // INCLUDED_COMPHELPER_DOUBLECHECKEDINIT_HXX + +/* vim:set shiftwidth=4 softtabstop=4 expandtab: */ |