DataContainer.hpp

#ifndef H_EXTENSIONS_CUTEHMI_MODBUS_2_INCLUDE_CUTEHMI_MODBUS_INTERNAL_DATACONTAINER_HPP
#define H_EXTENSIONS_CUTEHMI_MODBUS_2_INCLUDE_CUTEHMI_MODBUS_INTERNAL_DATACONTAINER_HPP
 
#include "common.hpp"
 
#include <QLinkedList>
#include <QReadWriteLock>
 
#include <array>
#include <algorithm>
#include <memory>
 
namespace cutehmi {
namespace modbus {
namespace internal {
 
template <typename T, std::size_t N = 65536>
class DataContainer
{
        typedef std::array<T *, N> InternalContainer;
        friend class KeysIterator;
 
    public:
        typedef T value_type;
        typedef T & reference;
        typedef const T & const_reference;
        typedef T * pointer;
        typedef const T * const_pointer;
        // <Qt-Qt_5_11_2_Reference_Documentation-Qt_Core-Container_Classes-The_Container_Classes-QLinkedList_iterator_semantics.principle>
        // "Iterators pointing to an item in a QLinkedList remain valid as long as the item exists, whereas iterators to a QList can
        //  become invalid after any insertion or removal."
        typedef QLinkedList<std::size_t> KeysContainer;
        // </Qt-Qt_5_11_2_Reference_Documentation-Qt_Core-Container_Classes-The_Container_Classes-QLinkedList_iterator_semantics.principle>
 
        static constexpr std::size_t ADDRESS_SPACE = N;
 
        class KeysIterator
        {
            public:
                KeysIterator(const DataContainer<T, N> * container);
 
                bool hasNext() const;
 
                KeysContainer::value_type next();
 
                KeysContainer::value_type previous();
 
            private:
                mutable QReadWriteLock * m_lock;
                QLinkedListIterator<KeysContainer::value_type> m_it;
        };
 
        DataContainer();
 
        constexpr std::size_t size() const noexcept;
 
        const T * at(std::size_t i) const;
 
        T * at(std::size_t i);
 
        T * value(std::size_t i);
 
        void insert(std::size_t i, T * value);
 
        void clear();
 
        void free();
 
        const KeysContainer & keys() const;
 
    protected:
        QReadWriteLock & lock() const;
 
    private:
        InternalContainer m_array;
        KeysContainer m_keys;
        mutable QReadWriteLock m_lock;
};
 
template <typename T, std::size_t N>
DataContainer<T, N>::KeysIterator::KeysIterator(const DataContainer<T, N> * container):
    m_lock(& container->lock()),
    m_it(container->keys())
{
}
 
template <typename T, std::size_t N>
bool DataContainer<T, N>::KeysIterator::hasNext() const
{
    QReadLocker locker(m_lock);
 
    return m_it.hasNext();
}
 
template <typename T, std::size_t N>
typename DataContainer<T, N>::KeysContainer::value_type DataContainer<T, N>::KeysIterator::next()
{
    QReadLocker locker(m_lock);
 
    return m_it.next();
}
 
template <typename T, std::size_t N>
typename DataContainer<T, N>::KeysContainer::value_type DataContainer<T, N>::KeysIterator::previous()
{
    QReadLocker locker(m_lock);
 
    return m_it.previous();
}
 
template <typename T, std::size_t N>
 
DataContainer<T, N>::DataContainer():
    m_array()
{
}
 
template <typename T, std::size_t N>
constexpr std::size_t DataContainer<T, N>::size() const noexcept
{
    // <cppreference.com-C++-Containers_library-Thread_safety-2.principle>
    // "2. All const member functions can be called concurrently by different threads on the same container."
    //                                                                                -- https://en.cppreference.com/w/cpp/container
    return m_array.size();
    // </cppreference.com-C++-Containers_library-Thread_safety-2.principle>
}
 
template <typename T, std::size_t N>
const T * DataContainer<T, N>::at(std::size_t i) const
{
    QReadLocker locker(& m_lock);
 
    return m_array.at(i);
}
 
template <typename T, std::size_t N>
T * DataContainer<T, N>::at(std::size_t i)
{
    QReadLocker locker(& m_lock);
 
    return m_array.at(i);
}
 
template <typename T, std::size_t N>
T * DataContainer<T, N>::value(std::size_t i)
{
    T * result;
 
    {
        QReadLocker readLocker(& m_lock);
 
        result = m_array.at(i);
    }
 
    if (result == nullptr) {
        QWriteLocker writeLocker(& m_lock);
 
        // In a meanwhile value may have been created from another thread, so perform a lookup again - this time it is serialized by read-write locker.
        result = m_array.at(i);
 
        if (result == nullptr) {
            result = new T;
            m_array[i] = result;
            m_keys.append(i);
        }
    }
 
    return result;
}
 
template <typename T, std::size_t N>
void DataContainer<T, N>::insert(std::size_t i, T * value)
{
    QWriteLocker locker(& m_lock);
 
    m_array[i] = value;
    m_keys.append(i);
}
 
template <typename T, std::size_t N>
void DataContainer<T, N>::clear()
{
    QWriteLocker locker(& m_lock);
 
    m_keys.clear();
 
    std::fill(m_array.begin(), m_array.end(), nullptr);
}
 
template <typename T, std::size_t N>
void DataContainer<T, N>::free()
{
    QWriteLocker locker(& m_lock);
 
    for (typename DataContainer<T, N>::KeysContainer::const_iterator it = keys().begin(); it != keys().end(); ++it)
        delete m_array.at(*it);
 
    m_keys.clear();
 
    std::fill(m_array.begin(), m_array.end(), nullptr);
}
 
template <typename T, std::size_t N>
const typename DataContainer<T, N>::KeysContainer & DataContainer<T, N>::keys() const
{
    return m_keys;
}
 
template <typename T, std::size_t N>
QReadWriteLock & DataContainer<T, N>::lock() const
{
    return m_lock;
}
 
}
}
}
 
#endif
 
//(c)C: Copyright © 2019, Michał Policht <michal@policht.pl>. All rights reserved.
//(c)C: This file is a part of CuteHMI.
//(c)C: CuteHMI is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
//(c)C: CuteHMI 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 GNU Lesser General Public License for more details.
//(c)C: You should have received a copy of the GNU Lesser General Public License along with CuteHMI.  If not, see <https://www.gnu.org/licenses/>.