子系统的启动(Start-Up)和关闭(Shut-Down)

错误的方式一

class RenderManager
{
public:
     RenderManager()
     {
          //start up the manager... 
     }
     ~RenderManager()
     {
          //shut down the manager... 
     }
     //...
};

//singleton instance
static RenderManager gRenderManager;

 错误原因：全局变量在函数入口点调用之间就构造好了，但是这些构造函数的调用顺序不确定。同样的，析构函数的调用顺序也不确定。

 

错误的方式2

class RenderManager
{
public:
     //Get the one and only instance
     static RenderManger* get()
     {
          //This function-static will be constructed on the first call to 
//this function
          static RenderManager sSingleton;
          return sSingletion;
     }
     RenderManager()
     {
           //start up other manager we depend on,by calling their 
//get() function first...
           VideoManager::get();
           TextureManager::get();
           //now start up the render manager.
//...
     }
     ~RenderManager()
     {
          //shut down the manager.
//...
     } 
}；

 

错误的原因：函数中定义的静态变量只会在函数第一次调用时候构建。但是这种方式不能够控制析构的顺序。

 

正确的方式

class RenderManager
{
    RenderManger()
    {
           //do nothing
    }
    ~RenderManager
    {
          //do nothing
    }
  
    void StartUp()
    {
          //start up the manager
    }
    void ShutDown()
    {
         //shut down the manager
    }
    //...
};

class PhysicsManager        {/*similar*/};
class AnimationManager    {/*similar*/};
class MemoryManager       {/*similar*/};
class FileSystemManager   {/*similar*/};

RenderManager          gRM;
PhysicsManager          gPM;
AnimationManager      gAM;
MemoryManager         gMM;
FileSystemManager     gFSM;

int main()
{
     //start up engine systems in the correct order
     gMM.StartUp();
     gFSM.StartUp();
     gRM.StartUp();
     gAM.StartUp();
     gPM.StartUp();
     //...
     
//Run the game
    gSimulationManager.Run();
   
    //shut everything down,in reverse order
//... 

    return 0;    
}