ljkiwi/kiwi/shareddata.h

/*-----------------------------------------------------------------------------
| Copyright (c) 2013-2017, Nucleic Development Team.
|
| Distributed under the terms of the Modified BSD License.
|
| The full license is in the file LICENSE, distributed with this software.
|----------------------------------------------------------------------------*/
#pragma once

/*
Implementation note
===================
SharedDataPtr/SharedData offer the same basic functionality as std::shared_ptr,
but do not use atomic counters under the hood.
Since kiwi operates within a single thread context, atomic counters are not necessary,
especially given the extra CPU cost.
Therefore the use of SharedDataPtr/SharedData is preferred over std::shared_ptr.
*/

namespace kiwi
{

class SharedData
{

public:
    SharedData() : m_refcount(0) {}

    SharedData(const SharedData &other) = delete;

    SharedData(SharedData&& other) = delete;

    int m_refcount;

    SharedData &operator=(const SharedData &other) = delete;
    
    SharedData &operator=(SharedData&& other) = delete;
};

template <typename T>
class SharedDataPtr
{

public:
    using Type = T;

    SharedDataPtr() : m_data(nullptr) {}

    explicit SharedDataPtr(T *data) : m_data(data)
    {
        incref(m_data);
    }

    ~SharedDataPtr()
    {
        decref(m_data);
    }

    T *data()
    {
        return m_data;
    }

    const T *data() const
    {
        return m_data;
    }

    operator T *()
    {
        return m_data;
    }

    operator const T *() const
    {
        return m_data;
    }

    T *operator->()
    {
        return m_data;
    }

    const T *operator->() const
    {
        return m_data;
    }

    T &operator*()
    {
        return *m_data;
    }

    const T &operator*() const
    {
        return *m_data;
    }

    bool operator!() const
    {
        return !m_data;
    }

    bool operator<(const SharedDataPtr<T> &other) const
    {
        return m_data < other.m_data;
    }

    bool operator==(const SharedDataPtr<T> &other) const
    {
        return m_data == other.m_data;
    }

    bool operator!=(const SharedDataPtr<T> &other) const
    {
        return m_data != other.m_data;
    }

    SharedDataPtr(const SharedDataPtr<T> &other) : m_data(other.m_data)
    {
        incref(m_data);
    }

    SharedDataPtr(SharedDataPtr&& other) noexcept : m_data(other.m_data)
    {
        other.m_data = nullptr;
    }

    SharedDataPtr<T> &operator=(const SharedDataPtr<T> &other)
    {
        if (m_data != other.m_data)
        {
            T *temp = m_data;
            m_data = other.m_data;
            incref(m_data);
            decref(temp);
        }
        return *this;
    }

    SharedDataPtr<T>& operator=(SharedDataPtr<T>&& other) noexcept
    {
        if (m_data != other.m_data)
        {
            T *temp = m_data;
            m_data = other.m_data;
            other.m_data = nullptr;
            decref(temp);
        }
        return *this;
    }

    SharedDataPtr<T> &operator=(T *other)
    {
        if (m_data != other)
        {
            T *temp = m_data;
            m_data = other;
            incref(m_data);
            decref(temp);
        }
        return *this;
    }

private:
    static void incref(T *data)
    {
        if (data)
            ++data->m_refcount;
    }

    static void decref(T *data)
    {
        if (data && --data->m_refcount == 0)
            delete data;
    }

    T *m_data;
};

} // namespace kiwi