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// Copyright 2022 Huawei Cloud Computing Technology Co., Ltd.
//
// 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.
#ifndef INCLUDED_SRC_UTILS_CPP_ATOMIC_HPP
#define INCLUDED_SRC_UTILS_CPP_ATOMIC_HPP
#include <atomic>
#include <condition_variable>
#include <shared_mutex>
#include <type_traits>
#include <utility> // std::move
// Atomic wrapper with notify/wait capabilities.
// TODO(modernize): Replace any use this class by C++20's std::atomic<T>, once
// libcxx adds support for notify_*() and wait().
// [https://libcxx.llvm.org/docs/Cxx2aStatus.html]
template <class T>
class atomic {
public:
atomic() = default;
explicit atomic(T value) : value_{std::move(value)} {}
atomic(atomic const& other) = delete;
atomic(atomic&& other) = delete;
~atomic() = default;
auto operator=(atomic const& other) -> atomic& = delete;
auto operator=(atomic&& other) -> atomic& = delete;
auto operator=(T desired) -> T { // NOLINT
std::shared_lock lock(mutex_);
value_ = desired;
return desired;
}
operator T() const { return static_cast<T>(value_); } // NOLINT
void store(T desired, std::memory_order order = std::memory_order_seq_cst) {
std::shared_lock lock(mutex_);
value_.store(std::move(desired), order);
}
[[nodiscard]] auto load(
std::memory_order order = std::memory_order_seq_cst) const -> T {
return value_.load(order);
}
template <class U = T>
requires(std::is_integral_v<U>)
auto operator++() -> T {
std::shared_lock lock(mutex_);
return ++value_;
}
template <class U = T>
requires(std::is_integral_v<U>)
[[nodiscard]] auto operator++(int) -> T {
std::shared_lock lock(mutex_);
return value_++;
}
template <class U = T>
requires(std::is_integral_v<U>)
auto operator--() -> T {
std::shared_lock lock(mutex_);
return --value_;
}
template <class U = T>
requires(std::is_integral_v<U>)
[[nodiscard]] auto operator--(int) -> T {
std::shared_lock lock(mutex_);
return value_--;
}
void notify_one() { cv_.notify_one(); }
void notify_all() { cv_.notify_all(); }
void wait(T old,
std::memory_order order = std::memory_order::seq_cst) const {
std::unique_lock lock(mutex_);
cv_.wait(lock,
[this, &old, order]() { return value_.load(order) != old; });
}
private:
std::atomic<T> value_{};
mutable std::shared_mutex mutex_;
mutable std::condition_variable_any cv_;
};
// Atomic shared_pointer with notify/wait capabilities.
// TODO(modernize): Replace any use this class by C++20's
// std::atomic<std::shared_ptr<T>>, once libcxx adds support for it.
// [https://libcxx.llvm.org/docs/Cxx2aStatus.html]
template <class T>
class atomic_shared_ptr {
using ptr_t = std::shared_ptr<T>;
public:
atomic_shared_ptr() = default;
explicit atomic_shared_ptr(ptr_t value) : value_{std::move(value)} {}
atomic_shared_ptr(atomic_shared_ptr const& other) = delete;
atomic_shared_ptr(atomic_shared_ptr&& other) = delete;
~atomic_shared_ptr() = default;
auto operator=(atomic_shared_ptr const& other) -> atomic_shared_ptr& =
delete;
auto operator=(atomic_shared_ptr&& other) -> atomic_shared_ptr& = delete;
auto operator=(ptr_t desired) -> ptr_t { // NOLINT
std::shared_lock lock(mutex_);
std::atomic_store(&value_, desired);
return desired;
}
operator ptr_t() const { return std::atomic_load(&value_); } // NOLINT
void store(ptr_t desired) {
std::shared_lock lock(mutex_);
std::atomic_store(&value_, std::move(desired));
}
[[nodiscard]] auto load() const -> ptr_t {
return std::atomic_load(&value_);
}
void notify_one() { cv_.notify_one(); }
void notify_all() { cv_.notify_all(); }
void wait(ptr_t old) const {
std::unique_lock lock(mutex_);
cv_.wait(lock, [this, &old]() { return value_ != old; });
}
private:
ptr_t value_{};
mutable std::shared_mutex mutex_;
mutable std::condition_variable_any cv_;
};
#endif // INCLUDED_SRC_UTILS_CPP_ATOMIC_HPP
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