67 lines
1.7 KiB
C++
67 lines
1.7 KiB
C++
/*
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* Copyright (C) 2016 The Android Open Source Project
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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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#ifndef TNT_UTILS_LINUX_MUTEX_H
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#define TNT_UTILS_LINUX_MUTEX_H
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#include <utils/compiler.h>
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#include <atomic>
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#include <stdint.h>
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namespace utils {
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/*
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* A very simple mutex class that can be used as an (almost) drop-in replacement
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* for std::mutex.
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* It is very low overhead as most of it is inlined.
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*/
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class Mutex {
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public:
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constexpr Mutex() noexcept = default;
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Mutex(const Mutex&) = delete;
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Mutex& operator=(const Mutex&) = delete;
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void lock() noexcept {
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uint32_t old_state = UNLOCKED;
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if (UTILS_UNLIKELY(!mState.compare_exchange_strong(old_state,
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LOCKED, std::memory_order_acquire, std::memory_order_relaxed))) {
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wait();
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}
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}
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void unlock() noexcept {
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if (UTILS_UNLIKELY(mState.exchange(UNLOCKED, std::memory_order_release) == LOCKED_CONTENDED)) {
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wake();
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}
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}
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private:
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enum {
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UNLOCKED = 0, LOCKED = 1, LOCKED_CONTENDED = 2
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};
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std::atomic<uint32_t> mState = { UNLOCKED };
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void wait() noexcept;
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void wake() noexcept;
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};
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} // namespace utils
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#endif // TNT_UTILS_LINUX_MUTEX_H
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