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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include <atomic>
#include <cstdint>
#include <cstring>
#include <type_traits>
#include "mongo/base/static_assert.h"
#include "mongo/config.h"
namespace mongo {
/**
* Provides a simple version of an atomic version of T
* that uses std::atomic<BaseWordT> as a backing type;
*/
template <typename T, typename BaseWordT>
class AtomicProxy {
MONGO_STATIC_ASSERT_MSG(sizeof(T) == sizeof(BaseWordT),
"T and BaseWordT must have the same size");
MONGO_STATIC_ASSERT_MSG(std::is_integral<BaseWordT>::value,
"BaseWordT must be an integral type");
#if MONGO_HAVE_STD_IS_TRIVIALLY_COPYABLE
MONGO_STATIC_ASSERT_MSG(std::is_trivially_copyable<T>::value, "T must be trivially copyable");
#endif
public:
using value_type = T;
using base_type = BaseWordT;
explicit AtomicProxy(T value = 0) {
store(value);
}
T operator=(T value) {
store(value);
return value;
}
operator T() const {
return load();
}
T load(std::memory_order order = std::memory_order_seq_cst) const {
const BaseWordT tempInteger = _value.load(order);
T value;
std::memcpy(&value, &tempInteger, sizeof(T));
return value;
}
void store(const T value, std::memory_order order = std::memory_order_seq_cst) {
BaseWordT tempInteger;
std::memcpy(&tempInteger, &value, sizeof(T));
_value.store(tempInteger, order);
}
private:
std::atomic<BaseWordT> _value; // NOLINT
};
using AtomicDouble = AtomicProxy<double, std::uint64_t>;
}
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