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/*
* Copyright (c) 2020 Samsung Electronics Co., Ltd. All rights reserved.
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#ifndef VCOWPTR_H
#define VCOWPTR_H
#include <cassert>
#include <atomic>
template <typename T>
class vcow_ptr {
struct model {
std::atomic<std::size_t> mRef{1};
model() = default;
template <class... Args>
explicit model(Args&&... args) : mValue(std::forward<Args>(args)...){}
explicit model(const T& other) : mValue(other){}
T mValue;
};
model* mModel;
public:
using element_type = T;
vcow_ptr()
{
static model default_s;
mModel = &default_s;
++mModel->mRef;
}
~vcow_ptr()
{
if (mModel && (--mModel->mRef == 0)) delete mModel;
}
template <class... Args>
explicit vcow_ptr(Args&&... args) : mModel(new model(std::forward<Args>(args)...))
{
}
vcow_ptr(const vcow_ptr& x) noexcept : mModel(x.mModel)
{
assert(mModel);
++mModel->mRef;
}
vcow_ptr(vcow_ptr&& x) noexcept : mModel(x.mModel)
{
assert(mModel);
x.mModel = nullptr;
}
auto operator=(const vcow_ptr& x) noexcept -> vcow_ptr&
{
*this = vcow_ptr(x);
return *this;
}
auto operator=(vcow_ptr&& x) noexcept -> vcow_ptr&
{
auto tmp = std::move(x);
swap(*this, tmp);
return *this;
}
auto operator*() const noexcept -> const element_type& { return read(); }
auto operator-> () const noexcept -> const element_type* { return &read(); }
std::size_t refCount() const noexcept
{
assert(mModel);
return mModel->mRef;
}
bool unique() const noexcept
{
assert(mModel);
return mModel->mRef == 1;
}
auto write() -> element_type&
{
if (!unique()) *this = vcow_ptr(read());
return mModel->mValue;
}
auto read() const noexcept -> const element_type&
{
assert(mModel);
return mModel->mValue;
}
friend inline void swap(vcow_ptr& x, vcow_ptr& y) noexcept
{
std::swap(x.mModel, y.mModel);
}
};
#endif // VCOWPTR_H
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