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I have a c# class. Whenever this class is not in use anymore I want to do some things. For example log the current state and so on.

I want to be sure that this method is run everytime when the class is not used anymore. I don't want just use a simple method because I can't be sure that every user is calling it.

I have no resources (like file handles) to clear up.

Is the best way to use a destructor?

"not in use" is when (for example):

  • a user uses my class in a form and the form is closed
  • the class is used in an application and this application is shut down
Chris
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3 Answers3

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No that would not be the best way, a destructor is costly.

The best way would be to add a Close() or maybe the Dispose() (IDiposable interface) method.

But you need to define very carefully what "not in use anymore" means, and if you want the extra trouble to manage and track that.

You can use a destructor to automate it, but it would be better to make that conditional (Debug config only). Also consider that the destuctor implements "non deterministic" finalization.

H H
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  • For Dispose() if you don't already have IDispose implemented (http://msdn.microsoft.com/en-us/library/system.idisposable.aspx) you'll want to make sure you're doing that. – scwagner Jul 28 '11 at 16:48
  • Can I be sure that Dispose() is called every time when the class is not in use anymore? I read in http://stackoverflow.com/questions/1076965/in-c-what-is-the-difference-between-a-destructor-and-a-finalize-method-in-a-clas that Finalize() is used if Dispose() is not called. So it sounds like Dispose() would not be the correct way to do it. – Chris Jul 28 '11 at 17:05
  • Define "not in use" first. It is a vague concept in a GC language. You can guarantee the Dispose() of your objects if you use them in `using(){}` statements. – H H Jul 28 '11 at 17:07
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It depends. C# .NET utilizes a garbage collector that implicitly cleans up objects for you. Normally, you cannot control the clean up of objects - the garbage collector does that. You can implement a destructor in your class if you desire, but you may get a performance hit. MSDN has this to say on destructors:

In general, C# does not require as much memory management as is needed when you develop with a language that does not target a runtime with garbage collection. This is because the .NET Framework garbage collector implicitly manages the allocation and release of memory for your objects. However, when your application encapsulates unmanaged resources such as windows, files, and network connections, you should use destructors to free those resources. When the object is eligible for destruction, the garbage collector runs the Finalize method of the object.

and finally on performance:

When a class contains a destructor, an entry is created in the Finalize queue. When the destructor is called, the garbage collector is invoked to process the queue. If the destructor is empty, this just causes a needless loss of performance.

There are other ways to manage resources besides a destructor:

Cleaning Up Unmanaged Resources

Implementing a Dispose Method

using Statement (C# Reference)

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If you want something to run when it's done, you should implement IDisposable.

Kyle W
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