子系统的启动(Start-Up)和关闭(Shut-Down)

错误的方式一

wrong solution1

 1 class RenderManager
 2 {
 3 public:
 4      RenderManager()
 5      {
 6           //start up the manager... 
 7      }
 8      ~RenderManager()
 9      {
10           //shut down the manager... 
11      }
12      //...
13 };
14 
15 //singleton instance
16 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

wrong solution2

 1 class RenderManager
 2 {
 3 public:
 4      //Get the one and only instance
 5      static RenderManger* get()
 6      {
 7           //This function-static will be constructed on the first call to 
 8 //this function
 9           static RenderManager sSingleton;
10           return sSingletion;
11      }
12      RenderManager()
13      {
14            //start up other manager we depend on,by calling their 
15 //get() function first...
16            VideoManager::get();
17            TextureManager::get();
18            //now start up the render manager.
19 //...
20      }
21      ~RenderManager()
22      {
23           //shut down the manager.
24 //...
25      } 
26 }；

 

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

right solution

 1 class RenderManager
 2 {
 3     RenderManger()
 4     {
 5            //do nothing
 6     }
 7     ~RenderManager
 8     {
 9           //do nothing
10     }
11   
12     void StartUp()
13     {
14           //start up the manager
15     }
16     void ShutDown()
17     {
18          //shut down the manager
19     }
20     //...
21 };
22 
23 class PhysicsManager        {/*similar*/};
24 class AnimationManager    {/*similar*/};
25 class MemoryManager       {/*similar*/};
26 class FileSystemManager   {/*similar*/};
27 
28 RenderManager          gRM;
29 PhysicsManager          gPM;
30 AnimationManager      gAM;
31 MemoryManager         gMM;
32 FileSystemManager     gFSM;
33 
34 int main()
35 {
36      //start up engine systems in the correct order
37      gMM.StartUp();
38      gFSM.StartUp();
39      gRM.StartUp();
40      gAM.StartUp();
41      gPM.StartUp();
42      //...
43      
44 //Run the game
45     gSimulationManager.Run();
46    
47     //shut everything down,in reverse order
48 //... 
49 
50     return 0;    
51 }