VB/C#：将一次性对象放置在全局范围内：这样可以吗？
作为一项优化，我决定将一个我经常需要的对象 - 带有整个关卡预渲染图像的 SDL 表面（称为 S_AreaBMP） - 放在全局范围内。
现在不必在每一帧的 DrawScreen 函数中创建和销毁它。我只需要在加载新关卡或 GFX 表时处理和更改它，这是通过以下函数完成的：
Public Sub PrepareAreaImage()
''#dispose old image before it becomes unreferenced
If AreaBMPExists
S_AreaBMP.Dispose()
End If
AreaBMPExists = True
''#declare an appropriately sized bitmap w/ a GDI Graphics object
Dim AreaBMP As Bitmap = New Bitmap(Area.W * TLDIM, Area.H * TLDIM)
Dim AreaGrph As Graphics = Graphics.FromImage(AreaBMP)
''#...(omitted: iterate through Area and draw each tile to AreaBMP)
''#Store to the SDL surface
S_AreaBMP = New SdlDotNet.Graphics.Surface(AreaBMP)
''#Dispose
AreaBMP.Dispose()
AreaGrph.Dispose()
End Sub
（AreaBMPExists 和 S_AreaBMP 是全局范围）
问题：这从根本上来说合理吗？
它工作得很好，但我不禁觉得这种事情是不鼓励的......
As an optimization, I decided to put an object I frequently need - an SDL surface with a prerendered image of the entire level (called S_AreaBMP) - at global scope.
Now it doesn't have to be created and destroyed in the DrawScreen function every frame. I only need to dispose and change it when a new level or GFX sheet is loaded, which I do via this function:
Public Sub PrepareAreaImage()
''#dispose old image before it becomes unreferenced
If AreaBMPExists
S_AreaBMP.Dispose()
End If
AreaBMPExists = True
''#declare an appropriately sized bitmap w/ a GDI Graphics object
Dim AreaBMP As Bitmap = New Bitmap(Area.W * TLDIM, Area.H * TLDIM)
Dim AreaGrph As Graphics = Graphics.FromImage(AreaBMP)
''#...(omitted: iterate through Area and draw each tile to AreaBMP)
''#Store to the SDL surface
S_AreaBMP = New SdlDotNet.Graphics.Surface(AreaBMP)
''#Dispose
AreaBMP.Dispose()
AreaGrph.Dispose()
End Sub
(AreaBMPExists and S_AreaBMP are global scope)
Question: Is this fundamentally sound?
It works fine, but I can't help but feel that this sort of thing is discouraged...
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评论（2）
您基本上是在全局范围内创建静态变量。这样做在技术上没有任何错误，但通常更好的选择是使用 之类的东西来包装它单例模式。这将使控制对此的访问变得更容易，并且可能更容易以提供更好的线程安全性、此逻辑的封装等的方式包装资源。
You're basically making a static variable at a global scope. There isn't anything technically incorrect in doing this, but it's usually a better option to wrap this using something like the Singleton pattern. This would make it easier to control access to this, and potentially easier to wrap the resource in a way to provide better thread safety, encapsulation of this logic, etc.
线程安全将是我最关心的问题。特别是，如果在PrepareAreaImage()执行期间调用PrepareAreaImage，或者在PrepareAreaImage()执行期间访问S_AreaBMP，会发生什么情况。
Thread safety would be my biggest concern. Particularly, what happens if PrepareAreaImage is called when it is already executing, or S_AreaBMP is accessed sometime during PrepareAreaImage()'s execution.