AppDomainSingleton.hxx

//
//  Copyright PHOENIX CONTACT Electronics GmbH
//
#pragma once
#include "Arp/System/Core/Arp.h"
#include "Arp/System/Core/Singleton.hxx"
#include "Arp/System/Core/AppDomain.hpp"

namespace Arp
{

template <class Derived>
class AppDomainSingleton
{
protected: // typedefs
    typedef AppDomainSingleton<Derived> SingletonBase; // for use in derived classes

private: // typedefs
    typedef Derived     Instance;

protected: // construction/destruction
    AppDomainSingleton(void) = default;
    ~AppDomainSingleton(void) = default;

public: // static operations
    template <class T = Instance, class ...Args>
    static Derived & CreateInstance(Args && ... args);

    static bool     IsCreated(void);

    static Derived& GetInstance(void);

    static Derived* GetInstancePtr(void);

    static void     DisposeInstance(void);

private: // deleted methods to avoid copying
    AppDomainSingleton(const AppDomainSingleton& arg) = delete;
    AppDomainSingleton& operator=(const AppDomainSingleton& arg) = delete;
};

// inline methods of class AppDomainSingleton<T>
template <class Derived>
template <class T, class ...Args>
inline Derived& AppDomainSingleton<Derived>::CreateInstance(Args&& ... args)
{
    Derived* pInstance = GetInstancePtr();
    // create instance first
    if(pInstance != nullptr)
    {
        throw Exception("AppDomain Singleton instance of type '{0}' was created yet!", TypeName<Derived>().Value);
    }
    // else
    pInstance = new T(std::forward<Args>(args)...);
    // and add it to appDomains singleton collection
    AppDomain::GetCurrent().AddSingleton(pInstance);

    return *pInstance;
}

template <class Derived>
inline bool AppDomainSingleton<Derived>::IsCreated(void)
{
    if (!AppDomain::IsCreated())
    {
        return false;
    }
    // else
    return AppDomainSingleton::GetInstancePtr() != nullptr;
}

template <class Derived>
inline Derived& AppDomainSingleton<Derived>::GetInstance()
{
    Derived* pResult = GetInstancePtr();
    if (pResult == nullptr)
    {
        throw Exception("AppDomain Singleton instance of type '{0}' was not created yet!", TypeName<Derived>().Value);
    }
    return *pResult;
}

template <class Derived>
inline Derived* AppDomainSingleton<Derived>::GetInstancePtr()
{
    return AppDomain::GetCurrent().GetSingletonPtr<Derived>(); // might return nullptr
}

template <class Derived>
inline void AppDomainSingleton<Derived>::DisposeInstance()
{
    // destroy instance
    delete GetInstancePtr();
    // and remove singleton from appDomain
    AppDomain::GetCurrent().RemoveSingleton<Derived>();
}

} // end of namesapce Arp