81 lines
2.5 KiB
C
81 lines
2.5 KiB
C
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/*
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* Copyright 2016-present Facebook, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#pragma once
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#include <typeinfo>
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#include <folly/CPortability.h>
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namespace folly {
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namespace detail {
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// This internal-use-only class is used to create all leaked Meyers singletons.
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// It guarantees that only one instance of every such singleton will ever be
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// created, even when requested from different compilation units linked
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// dynamically.
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class StaticSingletonManager {
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public:
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template <typename T, typename Tag, typename F>
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FOLLY_ALWAYS_INLINE FOLLY_ATTR_VISIBILITY_HIDDEN static T* create(
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F&& creator) {
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return static_cast<T*>(create_<T, Tag>(creator));
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}
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private:
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template <typename A, typename B>
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struct TypePair {};
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using Key = std::type_info;
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using Make = void*(void*);
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template <typename F>
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struct Creator {
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static void* create(void* f) {
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return static_cast<void*>((*static_cast<F*>(f))());
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}
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};
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template <typename T, typename Tag, typename F>
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FOLLY_ALWAYS_INLINE FOLLY_ATTR_VISIBILITY_HIDDEN static void* create_(
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F& creator) {
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auto const& key = typeid(TypePair<T, Tag>);
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return create_(key, &Creator<F>::create, &creator);
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}
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template <typename T, typename Tag, typename F>
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FOLLY_ALWAYS_INLINE FOLLY_ATTR_VISIBILITY_HIDDEN static void* create_(
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F const& creator) {
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auto const& key = typeid(TypePair<T, Tag>);
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return create_(key, &Creator<F const>::create, const_cast<F*>(&creator));
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}
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FOLLY_NOINLINE static void* create_(Key const& key, Make* make, void* ctx);
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};
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template <typename T, typename Tag, typename F>
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FOLLY_ALWAYS_INLINE FOLLY_ATTR_VISIBILITY_HIDDEN T* createGlobal(F&& creator) {
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return StaticSingletonManager::create<T, Tag>(static_cast<F&&>(creator));
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}
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template <typename T, typename Tag>
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FOLLY_ALWAYS_INLINE FOLLY_ATTR_VISIBILITY_HIDDEN T* createGlobal() {
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return StaticSingletonManager::create<T, Tag>([]() { return new T(); });
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}
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} // namespace detail
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} // namespace folly
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