v.hpp

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// SPDX-License-Identifier: BSD-3-Clause
/* Copyright 2018-2021, Intel Corporation */
 
#ifndef LIBPMEMOBJ_CPP_V_HPP
#define LIBPMEMOBJ_CPP_V_HPP
 
#include <memory>
#include <tuple>
 
#include <libpmemobj++/detail/common.hpp>
#include <libpmemobj++/detail/life.hpp>
 
namespace pmem
{
 
namespace obj
{
 
namespace experimental
{
 
template <typename T>
class v {
public:
    static_assert(std::is_default_constructible<T>::value,
              "Type T must be default constructible");
 
    v() noexcept : vlt{0}
    {
    }
 
    ~v()
    {
        /* Destructor of val should NOT be called */
    }
 
    v &
    operator=(const T &rhs)
    {
        /* make sure object is initialized */
        (void)get();
 
        val = rhs;
 
        return *this;
    }
 
    v &
    operator=(v &rhs)
    {
        return *this = rhs.get();
    }
 
    template <typename Y,
          typename = typename std::enable_if<
              std::is_convertible<Y, T>::value>::type>
    v &
    operator=(v<Y> &rhs)
    {
        return *this = rhs.get();
    }
 
    template <typename... Args>
    T &
    get(Args &&... args) noexcept
    {
        auto arg_pack =
            std::forward_as_tuple(std::forward<Args>(args)...);
 
        PMEMobjpool *pop = pmemobj_pool_by_ptr(this);
        if (pop == NULL)
            return this->val;
 
        T *value = static_cast<T *>(pmemobj_volatile(
            pop, &this->vlt, &this->val, sizeof(T),
            pmem::detail::c_style_construct<T, decltype(arg_pack),
                            Args...>,
            static_cast<void *>(&arg_pack)));
 
        return *value;
    }
 
    T &
    unsafe_get()
    {
        return val;
    }
 
    operator T &() noexcept
    {
        return this->get();
    }
 
    void
    swap(v &other)
    {
        std::swap(get(), other.get());
    }
 
private:
    struct pmemvlt vlt;
 
    /*
     * Normally C++ requires all class members to be constructed during
     * enclosing type construction. Holding a value inside of a union allows
     * to bypass this requirement. val is only constructed by call to get().
     */
    union {
        T val;
    };
};
 
template <class T>
inline void
swap(v<T> &a, v<T> &b)
{
    a.swap(b);
}
 
} /* namespace experimental */
 
} /* namespace obj */
 
} /* namespace pmem */
 
#endif /* LIBPMEMOBJ_CPP_V_HPP */