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/**
* @file llsingleton.h
*
* $LicenseInfo:firstyear=2002&license=viewergpl$
*
* Copyright (c) 2002-2009, Linden Research, Inc.
*
* Second Life Viewer Source Code
* The source code in this file ("Source Code") is provided by Linden Lab
* to you under the terms of the GNU General Public License, version 2.0
* ("GPL"), unless you have obtained a separate licensing agreement
* ("Other License"), formally executed by you and Linden Lab. Terms of
* the GPL can be found in doc/GPL-license.txt in this distribution, or
* online at http://secondlifegrid.net/programs/open_source/licensing/gplv2
*
* There are special exceptions to the terms and conditions of the GPL as
* it is applied to this Source Code. View the full text of the exception
* in the file doc/FLOSS-exception.txt in this software distribution, or
* online at
* http://secondlifegrid.net/programs/open_source/licensing/flossexception
*
* By copying, modifying or distributing this software, you acknowledge
* that you have read and understood your obligations described above,
* and agree to abide by those obligations.
*
* ALL LINDEN LAB SOURCE CODE IS PROVIDED "AS IS." LINDEN LAB MAKES NO
* WARRANTIES, EXPRESS, IMPLIED OR OTHERWISE, REGARDING ITS ACCURACY,
* COMPLETENESS OR PERFORMANCE.
* $/LicenseInfo$
*/
#ifndef LLSINGLETON_H
#define LLSINGLETON_H
#include "llerror.h" // *TODO: eliminate this
#include <boost/noncopyable.hpp>
// LLSingleton implements the getInstance() method part of the Singleton
// pattern. It can't make the derived class constructors protected, though, so
// you have to do that yourself.
//
// There are two ways to use LLSingleton. The first way is to inherit from it
// while using the typename that you'd like to be static as the template
// parameter, like so:
//
// class Foo: public LLSingleton<Foo>{};
//
// Foo& instance = Foo::instance();
//
// The second way is to use the singleton class directly, without inheritance:
//
// typedef LLSingleton<Foo> FooSingleton;
//
// Foo& instance = FooSingleton::instance();
//
// In this case, the class being managed as a singleton needs to provide an
// initSingleton() method since the LLSingleton virtual method won't be
// available
//
// As currently written, it is not thread-safe.
template <typename DERIVED_TYPE>
class LLSingleton : private boost::noncopyable
{
private:
typedef enum e_init_state
{
UNINITIALIZED,
CONSTRUCTING,
INITIALIZING,
INITIALIZED,
DELETED
} EInitState;
static void deleteSingleton()
{
delete getData().mSingletonInstance;
getData().mSingletonInstance = NULL;
}
// stores pointer to singleton instance
// and tracks initialization state of singleton
struct SingletonInstanceData
{
EInitState mInitState;
DERIVED_TYPE* mSingletonInstance;
SingletonInstanceData()
: mSingletonInstance(NULL),
mInitState(UNINITIALIZED)
{}
~SingletonInstanceData()
{
deleteSingleton();
}
};
public:
virtual ~LLSingleton()
{
SingletonInstanceData& data = getData();
data.mSingletonInstance = NULL;
data.mInitState = DELETED;
}
static SingletonInstanceData& getData()
{
static SingletonInstanceData data;
return data;
}
static DERIVED_TYPE* getInstance()
{
SingletonInstanceData& data = getData();
if (data.mInitState == CONSTRUCTING)
{
llerrs << "Tried to access singleton " << typeid(DERIVED_TYPE).name() << " from singleton constructor!" << llendl;
}
if (data.mInitState == DELETED)
{
llwarns << "Trying to access deleted singleton " << typeid(DERIVED_TYPE).name() << " creating new instance" << llendl;
}
if (!data.mSingletonInstance)
{
data.mInitState = CONSTRUCTING;
data.mSingletonInstance = new DERIVED_TYPE();
data.mInitState = INITIALIZING;
data.mSingletonInstance->initSingleton();
data.mInitState = INITIALIZED;
}
return data.mSingletonInstance;
}
// Reference version of getInstance()
// Preferred over getInstance() as it disallows checking for NULL
static DERIVED_TYPE& instance()
{
return *getInstance();
}
// Has this singleton been created uet?
// Use this to avoid accessing singletons before the can safely be constructed
static bool instanceExists()
{
return getData().mInitState == INITIALIZED;
}
// Has this singleton already been deleted?
// Use this to avoid accessing singletons from a static object's destructor
static bool destroyed()
{
return getData().mInitState == DELETED;
}
private:
virtual void initSingleton() {}
};
#endif
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