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Diffstat (limited to 'indra/llcommon/llsingleton.h')
| -rw-r--r-- | indra/llcommon/llsingleton.h | 158 |
1 files changed, 158 insertions, 0 deletions
diff --git a/indra/llcommon/llsingleton.h b/indra/llcommon/llsingleton.h new file mode 100644 index 0000000000..dc1457e4f7 --- /dev/null +++ b/indra/llcommon/llsingleton.h @@ -0,0 +1,158 @@ +/** + * @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 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 |