singletonref.hxx

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#pragma once
 
#include <sal/config.h>
#include <osl/diagnose.h>
#include <cstddef>
#include <mutex>
 
namespace comphelper
{
template <class SingletonClass> class SingletonRef
{
    // member
 
private:
    static SingletonClass* m_pInstance;
 
    static sal_Int32 m_nRef;
 
    // interface
 
public:
    SingletonRef()
    {
        // GLOBAL SAFE ->
        std::unique_lock aLock(SingletonRef::ownStaticLock());
 
        // must be increased before(!) the check is done.
        // Otherwise this check can fail inside the same thread ...
        ++m_nRef;
        if (m_nRef == 1)
            m_pInstance = new SingletonClass();
 
        OSL_ENSURE(m_nRef > 0 && m_pInstance,
                   "Race? Ref count of singleton >0, but instance is NULL!");
        // <- GLOBAL SAFE
    }
 
    ~SingletonRef()
    {
        // GLOBAL SAFE ->
        std::unique_lock aLock(SingletonRef::ownStaticLock());
 
        // must be decreased before(!) the check is done.
        // Otherwise this check can fail inside the same thread ...
        --m_nRef;
        if (m_nRef == 0)
        {
            delete m_pInstance;
            m_pInstance = nullptr;
        }
        // <- GLOBAL SAFE
    }
 
    SingletonRef& operator=(SingletonRef const&) = default;
 
    SingletonClass* operator->() const
    {
        // GLOBAL SAFE ->
        return m_pInstance;
        // <- GLOBAL SAFE
    }
 
    SingletonClass& operator*() const
    {
        // GLOBAL SAFE ->
        return *m_pInstance;
        // <- GLOBAL SAFE
    }
 
    // helper
 
private:
    SingletonRef(SingletonRef&) = delete;
 
    static std::mutex& ownStaticLock()
    {
        static std::mutex aInstance;
        return aInstance;
    }
};
 
template <class SingletonClass> SingletonClass* SingletonRef<SingletonClass>::m_pInstance = nullptr;
 
template <class SingletonClass> sal_Int32 SingletonRef<SingletonClass>::m_nRef = 0;
 
} // namespace comphelper
 
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