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Pointer Management

General and Gameplay Programming Programming

Started by Marz87 December 06, 2010 09:08 PM

12 comments, last by rip-off 13 years, 4 months ago

Marz87

122

Author

December 06, 2010 09:08 PM

Hello helpful readers!

I currently have a class, SDLSubSystem, that inherits from two interfaces: IWindowSystem and ITimerSystem. In my game engine, I have a pointer to a timer system and a pointer to a window system. When SDL is configured, both pointers will end up pointing to SDLSubSystem:

if (m_config.compare("SDL") == 0) {	SDLSubSystem *sdlSystem = new SDLSubSystem();	sdlSystem->init();	m_winSystem = sdlSystem;;	m_timerSystem = sdlSystem;}

The problem comes when the user quits the window and the engine is shutting down. Before I am able to delete either of the pointers, the other one needs to be set to null:

if (m_config.compare("SDL")) {	m_timerSystem = NULL;	delete m_winSystem;}

My problem is... this solution is horrible because it could escalate and cleanup isn't as nice as I'd like it to be. Here's what I've researched:

- I've read up on the Enginuity Engine's method for memory management but I also read some articles on the problems of reference counting with pointers.
- I also read up on auto_ptr and heard that it will be deprecated soon, so I don't want to use it.
- I can't seem to get the new standard, unique_ptr, to work on Visual Studio 2008 (I assume that's because it's not a standard yet...)

I'd appreciate any help/insight you may have. Thank you :)

wqking

778

December 06, 2010 09:53 PM

That's a kind of unclear "ownership" issue.
Your timer and window are "users" of sdl, not the owner. So you should not free sdl via either timer or window.
Instead, you'd better store sdl to an owner, such like sdlSystem, and when cleanup, call,
delete sdlSystem.
And be sure no "users" will use it after the delete. If you can't do that, notify the "users" before the delete.

If you don't mind mess up the ownership, use a shared pointer (shared_ptr from Boost, e.g) and you don't need to worry about freeing the pointer. But I myself will stick to clear ownership way and never want to mess it up.

https://www.kbasm.com -- My personal website

https://github.com/wqking/eventpp eventpp -- C++ library for event dispatcher and callback list

https://github.com/cpgf/cpgf cpgf library -- free C++ open source library for reflection, serialization, script binding, callbacks, and meta data for OpenGL Box2D, SFML and Irrlicht.

Chris_F

3,030

December 07, 2010 01:20 AM

1: You could upgrade to Visual Studio 2010 and use std::shared_ptr which is a rcptr.

2: You can download Boost and use boost::shared_ptr which is virtually identical.

Pomnico

110

December 07, 2010 02:33 AM

Or you could implement simple reference counter on your own inside a SDLSubSystem. After you perform init and assign it to winSystem and timerSystem this counter should equal 2. On deinit you should not call destructor, but rather decrease reference counter (fe. m_timerSystem->Release()). After both timer and win will release this object it will be automatically destroyed.

My current project: 3D jigsaw puzzle game (under development)
My blog: Magic-Ars Blog

Marz87

122

Author

December 07, 2010 12:02 PM

@wqking: I'm not sure I fully understand. I'd like the engine to be configurable. So in one case you could have the m_winSystem pointing to an SFML Window System while the m_soundSystem is pointing to an OpenAL Sound system. However in some cases you may opt to use the same "system" for everything, and that's where it causes problems.

I suppose the way around this is to have the SDLWindowSystem as its own separate class from SDLTimerSystem, but then I think I run into problems with initialization (e.g. who calls SDL_Init and who calls SDL_InitSubSystem). So I decided to lump the entire SDLSubSystem into one class with multiple inheritance.

@Chris_F: Thanks, I'll look into those!

@Pomnico: Thanks! I've seen that idea but was hoping for alternatives.

WavyVirus

885

December 07, 2010 04:10 PM

Quote:Original post by Marz87
@wqking: I'm not sure I fully understand. I'd like the engine to be configurable. So in one case you could have the m_winSystem pointing to an SFML Window System while the m_soundSystem is pointing to an OpenAL Sound system. However in some cases you may opt to use the same "system" for everything, and that's where it causes problems.

I think what he is suggesting is to have a separate piece of code for taking care of specific subsystems implementations and their initialization and destruction. This might handle the mapping via config of functions to subsystems, handing out the appropriate pointers to wherever m_winSystem and m_timerSystem are being used. When it's time to clean up, this "subsystem manager" can stop the subsystems in the correct order, rather than the class which actually uses the subsystems having to worry about it.

Marz87

122

Author

December 07, 2010 05:56 PM

Quote:Original post by WavyVirus

I think what he is suggesting is to have a separate piece of code for taking care of specific subsystems implementations and their initialization and destruction. This might handle the mapping via config of functions to subsystems, handing out the appropriate pointers to wherever m_winSystem and m_timerSystem are being used. When it's time to clean up, this "subsystem manager" can stop the subsystems in the correct order, rather than the class which actually uses the subsystems having to worry about it.

Hm, well I certainly like the idea, but I don't think it solves my problem. I'm just reassigning my problem to another class :P

CzarKirk

100

December 07, 2010 06:04 PM

Like throwing your garbage in the trash hands it over to the professional garbage man xD

wqking

778

December 07, 2010 07:49 PM

Quote:Original post by WavyVirus
I think what he is suggesting is to have a separate piece of code for taking care of specific subsystems implementations and their initialization and destruction. This might handle the mapping via config of functions to subsystems, handing out the appropriate pointers to wherever m_winSystem and m_timerSystem are being used. When it's time to clean up, this "subsystem manager" can stop the subsystems in the correct order, rather than the class which actually uses the subsystems having to worry about it.

Thanks so much, that saves a lot of my words. :-)

https://www.kbasm.com -- My personal website

https://github.com/wqking/eventpp eventpp -- C++ library for event dispatcher and callback list

https://github.com/cpgf/cpgf cpgf library -- free C++ open source library for reflection, serialization, script binding, callbacks, and meta data for OpenGL Box2D, SFML and Irrlicht.

wqking

778

December 07, 2010 07:53 PM

Quote:Original post by Marz87
Hm, well I certainly like the idea, but I don't think it solves my problem. I'm just reassigning my problem to another class :P

That indeed is to solve your problem...
Please re-read mine, WavyVirus, and CzarKirk's replies again.

https://www.kbasm.com -- My personal website

https://github.com/wqking/eventpp eventpp -- C++ library for event dispatcher and callback list

https://github.com/cpgf/cpgf cpgf library -- free C++ open source library for reflection, serialization, script binding, callbacks, and meta data for OpenGL Box2D, SFML and Irrlicht.

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