singletonref.hxx

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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/*
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 *
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 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * This file incorporates work covered by the following license notice:
 *
 *   Licensed to the Apache Software Foundation (ASF) under one or more
 *   contributor license agreements. See the NOTICE file distributed
 *   with this work for additional information regarding copyright
 *   ownership. The ASF licenses this file to you under the Apache
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 *   except in compliance with the License. You may obtain a copy of
 *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
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/*
 * This file is part of LibreOffice published API.
 */

#ifndef INCLUDED_SALHELPER_SINGLETONREF_HXX
#define INCLUDED_SALHELPER_SINGLETONREF_HXX

#include "sal/config.h"

#include <cstddef>

#include "osl/mutex.hxx"
#include "rtl/instance.hxx"
#include "osl/diagnose.h"
#include "osl/getglobalmutex.hxx"


namespace salhelper{


template< class SingletonClass >
class SingletonRef
{

    // member

    private:

        static SingletonClass* m_pInstance;

        static sal_Int32 m_nRef;


    // interface

    public:


        SingletonRef()
        {
            // GLOBAL SAFE ->
            ::osl::MutexGuard 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 ->
            ::osl::MutexGuard 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 = NULL;
            }
            // <- GLOBAL SAFE
        }

#if defined LIBO_INTERNAL_ONLY
        SingletonRef & operator =(SingletonRef const &) = default;
#endif

        SingletonClass* operator->() const
        {
            // GLOBAL SAFE ->
            ::osl::MutexGuard aLock(SingletonRef::ownStaticLock());
            return m_pInstance;
            // <- GLOBAL SAFE
        }


        SingletonClass& operator*() const
        {
            // GLOBAL SAFE ->
            ::osl::MutexGuard aLock(SingletonRef::ownStaticLock());
            return *m_pInstance;
            // <- GLOBAL SAFE
        }


    // helper

    private:
        SingletonRef(SingletonRef &) SAL_DELETED_FUNCTION;

        struct SingletonLockInit
        {
            ::osl::Mutex* operator()()
            {
                static ::osl::Mutex aInstance;
                return &aInstance;
            }
        };

        ::osl::Mutex& ownStaticLock() const
        {
            return *rtl_Instance< ::osl::Mutex,
                                  SingletonLockInit,
                                  ::osl::MutexGuard,
                                  ::osl::GetGlobalMutex >::create(SingletonLockInit(), ::osl::GetGlobalMutex());
        }
};

template< class SingletonClass >
SingletonClass* SingletonRef< SingletonClass >::m_pInstance = NULL;

template< class SingletonClass >
sal_Int32 SingletonRef< SingletonClass >::m_nRef = 0;

} // namespace salhelper

#endif // INCLUDED_SALHELPER_SINGLETONREF_HXX

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