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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/*************************************************************************
*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* Copyright 2000, 2010 Oracle and/or its affiliates.
*
* OpenOffice.org - a multi-platform office productivity suite
*
* This file is part of OpenOffice.org.
*
* OpenOffice.org is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License version 3
* only, as published by the Free Software Foundation.
*
* OpenOffice.org 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 version 3 for more details
* (a copy is included in the LICENSE file that accompanied this code).
*
* You should have received a copy of the GNU Lesser General Public License
* version 3 along with OpenOffice.org. If not, see
* <http://www.openoffice.org/license.html>
* for a copy of the LGPLv3 License.
*
************************************************************************/
#ifndef _SALHELPER_SINGLETONREF_HXX_
#define _SALHELPER_SINGLETONREF_HXX_
//_______________________________________________
// includes
#include <osl/mutex.hxx>
#include "rtl/instance.hxx"
#include "osl/diagnose.h"
#include "osl/getglobalmutex.hxx"
//_______________________________________________
// namespace
namespace salhelper{
//_______________________________________________
// definitions
/** @short template for implementing singleton classes.
@descr Such classes can be instanciated everytimes they
are needed. But the internal wrapped object will
be created one times only. Of course its used
resources are referenced one times only too.
This template hold it alive till the last
reference is gone. Further all operations
on this reference are threadsafe. Only
calls directly to the internal object (which modify
its state) must be made threadsafe by the object itself
or from outside.
@attention To prevent the code against race conditions, its not
allowed to start operations inside the ctor
of the internal wrapped object - especialy operations
which needs a reference to the same singleton too.
The only chance to supress such strange constellations
is a lazy-init mechanism.
<ul>
<li>a) The singleton class can provide a special init()
method, which must be called as first after creation.</li>
<li>b) The singleton class can call a special impl_init()
method implicit for every called interface method.</li>
</ul>
Note further that this singleton pattern can work only, if
all user of such singleton are located inside the same library!
Because static values cant be exported - e.g. from windows libraries.
*/
template< class SingletonClass >
class SingletonRef
{
//-------------------------------------------
// member
private :
/** @short pointer to the internal wrapped singleton. */
static SingletonClass* m_pInstance;
/** @short ref count, which regulate creation and removing of m_pInstance. */
static sal_Int32 m_nRef;
//-------------------------------------------
// interface
public :
//---------------------------------------
/** @short standard ctor.
@descr The internal wrapped object is created only,
if its ref count was 0. Otherwhise this method
does nothing ... except increasing of the internal
ref count!
*/
SingletonRef()
{
// GLOBAL SAFE ->
::osl::MutexGuard aLock(SingletonRef::ownStaticLock());
// must be increased before(!) the check is done.
// Otherwhise 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
}
//---------------------------------------
/** @short standard dtor.
@descr The internal wrapped object is removed only,
if its ref count wil be 0. Otherwhise this method
does nothing ... except decreasing of the internal
ref count!
*/
~SingletonRef()
{
// GLOBAL SAFE ->
::osl::MutexGuard aLock(SingletonRef::ownStaticLock());
// must be decreased before(!) the check is done.
// Otherwhise this check can fail inside the same thread ...
--m_nRef;
if (m_nRef == 0)
{
delete m_pInstance;
m_pInstance = 0;
}
// <- GLOBAL SAFE
}
//---------------------------------------
/** @short Allows rSingle->someBodyOp().
*/
SingletonClass* operator->() const
{
// GLOBAL SAFE ->
::osl::MutexGuard aLock(SingletonRef::ownStaticLock());
return m_pInstance;
// <- GLOBAL SAFE
}
//---------------------------------------
/** @short Allows (*rSingle).someBodyOp().
*/
SingletonClass& operator*() const
{
// GLOBAL SAFE ->
::osl::MutexGuard aLock(SingletonRef::ownStaticLock());
return *m_pInstance;
// <- GLOBAL SAFE
}
//-------------------------------------------
// helper
private :
//---------------------------------------
/** @short creates an own mutex for guarding static contents.
@descr The global mutex the osl library is used one times
only to create an own static mutex, which can be used
next time to guard own static member operations.
*/
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 = 0;
template< class SingletonClass >
sal_Int32 SingletonRef< SingletonClass >::m_nRef = 0;
} // namespace salhelper
#endif // _SALHELPER_SINGLETONREF_HXX_
/* vim:set shiftwidth=4 softtabstop=4 expandtab: */
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