tagged_ptr.hpp

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// SPDX-License-Identifier: BSD-3-Clause
/* Copyright 2021, Intel Corporation */
 
#ifndef LIBPMEMOBJ_CPP_TAGGED_PTR
#define LIBPMEMOBJ_CPP_TAGGED_PTR
 
#include <cassert>
 
#include <libpmemobj++/detail/common.hpp>
#include <libpmemobj++/experimental/atomic_self_relative_ptr.hpp>
#include <libpmemobj++/experimental/self_relative_ptr.hpp>
#include <libpmemobj++/persistent_ptr.hpp>
 
namespace pmem
{
namespace detail
{
 
template <typename P1, typename P2, typename PointerType>
struct tagged_ptr_impl {
    tagged_ptr_impl() = default;
    tagged_ptr_impl(const tagged_ptr_impl &rhs) = default;
 
    tagged_ptr_impl(std::nullptr_t) : ptr(nullptr)
    {
        assert(!(bool)*this);
    }
 
    tagged_ptr_impl(const PointerType &ptr) : ptr(ptr)
    {
    }
 
    tagged_ptr_impl(const obj::persistent_ptr<P1> &ptr)
        : ptr(add_tag(ptr.get()))
    {
        assert(get<P1>() == ptr.get());
    }
 
    tagged_ptr_impl(const obj::persistent_ptr<P2> &ptr) : ptr(ptr.get())
    {
        assert(get<P2>() == ptr.get());
    }
 
    tagged_ptr_impl &operator=(const tagged_ptr_impl &rhs) = default;
 
    tagged_ptr_impl &operator=(std::nullptr_t)
    {
        ptr = nullptr;
        assert(!(bool)*this);
 
        return *this;
    }
    tagged_ptr_impl &
    operator=(const obj::persistent_ptr<P1> &rhs)
    {
        ptr = add_tag(rhs.get());
        assert(get<P1>() == rhs.get());
 
        return *this;
    }
    tagged_ptr_impl &
    operator=(const obj::persistent_ptr<P2> &rhs)
    {
        ptr = rhs.get();
        assert(get<P2>() == rhs.get());
 
        return *this;
    }
 
    bool
    operator==(const tagged_ptr_impl &rhs) const
    {
        return ptr.to_byte_pointer() == rhs.ptr.to_byte_pointer();
    }
    bool
    operator!=(const tagged_ptr_impl &rhs) const
    {
        return !(*this == rhs);
    }
 
    bool
    operator==(const P1 *rhs) const
    {
        return is_tagged() && get<P1>() == rhs;
    }
 
    bool
    operator!=(const P2 *rhs) const
    {
        return !(*this == rhs);
    }
 
    void
    swap(tagged_ptr_impl &rhs)
    {
        ptr.swap(rhs.ptr);
    }
 
    template <typename T>
    typename std::enable_if<std::is_same<T, P1>::value, bool>::type
    is() const
    {
        return is_tagged();
    }
 
    template <typename T>
    typename std::enable_if<!std::is_same<T, P1>::value, bool>::type
    is() const
    {
        return !is_tagged();
    }
 
    template <typename T>
    typename std::enable_if<std::is_same<T, P1>::value, T *>::type
    get() const
    {
        assert(is_tagged());
        return static_cast<P1 *>(remove_tag(ptr.to_void_pointer()));
    }
 
    template <typename T>
    typename std::enable_if<!std::is_same<T, P1>::value, T *>::type
    get() const
    {
        assert(!is_tagged());
        return static_cast<P2 *>(ptr.to_void_pointer());
    }
 
    P2 *operator->() const
    {
        return get<P2>();
    }
 
    explicit operator bool() const noexcept
    {
        return remove_tag(ptr.to_void_pointer()) != nullptr;
    }
 
private:
    static constexpr uintptr_t IS_TAGGED = 1;
    void *
    add_tag(P1 *ptr) const
    {
        auto tagged =
            reinterpret_cast<uintptr_t>(ptr) | uintptr_t(IS_TAGGED);
        return reinterpret_cast<P1 *>(tagged);
    }
 
    void *
    remove_tag(void *ptr) const
    {
        auto untagged = reinterpret_cast<uintptr_t>(ptr) &
            ~uintptr_t(IS_TAGGED);
        return reinterpret_cast<void *>(untagged);
    }
 
    bool
    is_tagged() const
    {
        auto value = reinterpret_cast<uintptr_t>(ptr.to_void_pointer());
        return value & uintptr_t(IS_TAGGED);
    }
 
    PointerType ptr;
 
    friend struct std::atomic<tagged_ptr_impl<
        P1, P2, obj::experimental::self_relative_ptr<void>>>;
};
 
template <typename P1, typename P2>
using tagged_ptr =
    tagged_ptr_impl<P1, P2, obj::experimental::self_relative_ptr<void>>;
 
} /* namespace detail */
} /* namespace pmem */
 
namespace std
{
 
template <typename P1, typename P2>
struct atomic<pmem::detail::tagged_ptr<P1, P2>> {
private:
    using ptr_type = pmem::detail::tagged_ptr_impl<
        P1, P2,
        atomic<pmem::obj::experimental::self_relative_ptr<void>>>;
    using value_type = pmem::detail::tagged_ptr<P1, P2>;
 
public:
    /*
     * Constructors
     */
    constexpr atomic() noexcept = default;
 
    atomic(value_type value) : ptr()
    {
        store(value);
    }
 
    atomic(const atomic &) = delete;
 
    void
    store(value_type desired,
          std::memory_order order = std::memory_order_seq_cst) noexcept
    {
        LIBPMEMOBJ_CPP_ANNOTATE_HAPPENS_BEFORE(order, &ptr.ptr);
        ptr.ptr.store(desired.ptr, order);
    }
 
    void
    store_with_snapshot(value_type desired,
                std::memory_order order = std::memory_order_seq_cst)
    {
        LIBPMEMOBJ_CPP_ANNOTATE_HAPPENS_BEFORE(order, &ptr.ptr);
        pmem::obj::transaction::snapshot(&ptr.ptr);
        ptr.ptr.store(desired.ptr, order);
    }
 
    void
    store_with_snapshot_release(value_type desired)
    {
        store_with_snapshot(desired, std::memory_order_release);
    }
 
    value_type
    load(std::memory_order order = std::memory_order_seq_cst) const noexcept
    {
#if LIBPMEMOBJ_CPP_VG_HELGRIND_ENABLED
        VALGRIND_HG_DISABLE_CHECKING(&ptr.ptr, sizeof(ptr.ptr));
#endif
        auto ret = this->ptr.ptr.load(order);
        LIBPMEMOBJ_CPP_ANNOTATE_HAPPENS_AFTER(order, &ptr.ptr);
        return value_type(ret);
    }
 
    value_type
    load_acquire() const noexcept
    {
        return load(std::memory_order_acquire);
    }
 
    void
    swap(atomic<pmem::detail::tagged_ptr<P1, P2>> &rhs)
    {
        auto tmp = rhs.load();
        rhs.store_with_snapshot(this->load());
        this->store_with_snapshot(tmp);
    }
 
    atomic<pmem::detail::tagged_ptr<P1, P2>> &
    operator=(atomic<pmem::detail::tagged_ptr<P1, P2>> &) = delete;
 
private:
    ptr_type ptr;
};
 
} /* namespace std */
 
#endif /* LIBPMEMOBJ_CPP_TAGGED_PTR */