| /* |
| * |
| * Copyright (c) 2023 Project CHIP Authors |
| * |
| * Licensed 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 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| #pragma once |
| |
| #include <lib/core/CHIPConfig.h> |
| |
| #include <mutex> |
| #include <new> |
| |
| #if CHIP_SYSTEM_CONFIG_USE_DISPATCH |
| #include <dispatch/dispatch.h> |
| #endif // CHIP_SYSTEM_CONFIG_USE_DISPATCH |
| |
| namespace chip { |
| namespace detail { |
| |
| #if CHIP_CONFIG_GLOBALS_LAZY_INIT |
| |
| struct NonAtomicOnce |
| { |
| bool mInitialized = false; |
| void call(void (*func)(void *), void * context) |
| { |
| if (!mInitialized) |
| { |
| mInitialized = true; |
| func(context); |
| } |
| } |
| }; |
| |
| struct AtomicOnce |
| { |
| // dispatch_once (if available) is more efficient than std::call_once because |
| // it takes advantage of the additional assumption that the dispatch_once_t |
| // is allocated within a static / global. |
| #if CHIP_SYSTEM_CONFIG_USE_DISPATCH |
| dispatch_once_t mOnce = 0; |
| void call(void (*func)(void *), void * context) { dispatch_once_f(&mOnce, context, func); } |
| #else // CHIP_SYSTEM_CONFIG_USE_DISPATCH |
| std::once_flag mOnce; |
| void call(void (*func)(void *), void * context) { std::call_once(mOnce, func, context); } |
| #endif |
| }; |
| |
| #endif // CHIP_CONFIG_GLOBALS_LAZY_INIT |
| |
| } // namespace detail |
| |
| /** |
| * A wrapper for global object that enables initialization and destruction to |
| * be configured by the platform via `CHIP_CONFIG_GLOBALS_*` options. |
| * |
| * The contained object of type T is default constructed, possibly lazily. |
| * |
| * Values of this type MUST be globals or static class members. |
| * |
| * This class is not thread-safe; external synchronization is required. |
| * @see AtomicGlobal<T> for a thread-safe variant. |
| */ |
| #if CHIP_CONFIG_GLOBALS_LAZY_INIT |
| template <class T, class OnceStrategy = detail::NonAtomicOnce> |
| #else // CHIP_CONFIG_GLOBALS_LAZY_INIT |
| template <class T> |
| #endif // CHIP_CONFIG_GLOBALS_LAZY_INIT |
| class Global |
| { |
| public: |
| /// Returns the global object, initializing it if necessary. |
| /// NOT thread-safe, external synchronization is required. |
| T & get() { return _get(); } |
| T * operator->() { return &_get(); } |
| |
| // Globals are not copyable or movable |
| Global(const Global &) = delete; |
| Global(const Global &&) = delete; |
| Global & operator=(const Global &) = delete; |
| |
| #if CHIP_CONFIG_GLOBALS_LAZY_INIT |
| public: |
| constexpr Global() = default; |
| ~Global() = default; |
| |
| private: |
| // Zero-initialize everything. We should technically leave mStorage uninitialized, |
| // but that can sometimes cause clang to be unable to constant-initialize the object. |
| alignas(T) unsigned char mStorage[sizeof(T)] = {}; |
| OnceStrategy mOnce; |
| |
| T & _get() |
| { |
| T * value = reinterpret_cast<T *>(mStorage); |
| mOnce.call(&create, value); |
| return *value; |
| } |
| static void create(void * value) |
| { |
| new (value) T(); |
| #if !CHIP_CONFIG_GLOBALS_NO_DESTRUCT |
| CHIP_CXA_ATEXIT(&destroy, value); |
| #endif // CHIP_CONFIG_GLOBALS_NO_DESTRUCT |
| } |
| static void destroy(void * value) { static_cast<T *>(value)->~T(); } |
| |
| #else // CHIP_CONFIG_GLOBALS_LAZY_INIT |
| public: |
| constexpr Global() : mValue() {} |
| |
| private: |
| T & _get() { return mValue; } |
| |
| #if CHIP_CONFIG_GLOBALS_NO_DESTRUCT |
| public: |
| // For not-trivially-destructible T, hiding it inside a union means the destructor |
| // won't get called automatically, however our own default destructor will be implicitly |
| // deleted. So Global<T> is technically not trivially-destructible, however the compiler |
| // tends to be able to optimize away the empty destructor call in practice. Getting around |
| // this cleanly requires using the "storage" approach used in the lazy variant, however |
| // this would require std::construct_at from C++20 to get constexpr initialization. |
| ~Global() {} // not "= default" |
| |
| private: |
| union |
| { |
| T mValue; |
| }; |
| #else // CHIP_CONFIG_GLOBALS_NO_DESTRUCT |
| public: |
| ~Global() = default; |
| |
| private: |
| T mValue; |
| #endif // CHIP_CONFIG_GLOBALS_NO_DESTRUCT |
| #endif // CHIP_CONFIG_GLOBALS_LAZY_INIT |
| }; |
| |
| /** |
| * A variant of Global<T> that is thread-safe. |
| */ |
| template <class T> |
| using AtomicGlobal = |
| #if CHIP_CONFIG_GLOBALS_LAZY_INIT |
| Global<T, detail::AtomicOnce>; |
| #else // CHIP_CONFIG_GLOBALS_LAZY_INIT |
| Global<T>; // eager globals are already thread-safe |
| #endif // CHIP_CONFIG_GLOBALS_LAZY_INIT |
| |
| } // namespace chip |