Correct use of IDisposable pattern when using Managed C++ wrapper in C#

Question

My C# class creates and uses Managed C++ object that wraps (allocates and uses) unmanaged C++ objects and resources. The Managed C++ class correctly implements IDisposable with Destructor and Finalizer. Therefore, it appears that my C# class should also implement IDisposable. I want to follow correct IDisposable pattern in C# as well.

The following is unclear to me:

Within Dispose method of my C# class, should I treat my Managed C++ objects as managed or unmanaged (since they rely on unmanaged resources internally)?

Hans Passant · Accepted Answer · 2011-08-26 09:58:06Z

4

Yes, your C# class should implement IDisposable as well. Its Dispose() method should simply dispose the C++/CLI objects. No need for a finalizer, you already implemented one in your wrappers. Your wrappers are no different from many other .NET classes that wrap an operating system resource.

For example:

class Test : IDisposable {
    private CppWrapper obj;
    //...
    public void Dispose() {
       if (obj != null) { 
           obj.Dispose();
           obj = null;
       }
    }
}

edited Aug 26, 2011 at 9:58

answered Aug 23, 2011 at 1:20

Hans Passant

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5 Comments

Puzzled Over a year ago

Sorry, please clarify. If the following is my C# code, in which section A or B should I dispose of my managed C++ classes? class Test : IDisposable { private bool isDisposed = false; ~Test() {Dispose(false);} protected void Dispose(bool disposing) { if (disposing) { // Section A. Dispose the managed resources } // Section B. Dispose the un-managed resources isDisposed = true; } public void Dispose() { Dispose(true); GC.SuppressFinalize(this); } }

Hans Passant Over a year ago

No, there is no need for this pattern since you don't have a finalizer. Thus no need to call GC.SuppressFinalize() and Dispose can never be called with disposing set to false. Which keeps it simple, I posted a snippet.

Puzzled Over a year ago

Thanks a lot Hans. However, I quote: "Finalize provides a backup to prevent resources from permanently leaking if the programmer fails to call Dispose". If so, why not have a Finalizer?

Hans Passant Over a year ago

Because your C++/CLI class wrappers are the ones that own the unmanaged resource. You gave them a finalizer. That's enough to ensure that the unmanaged resource will always be released, even if the client programmer forgets to call Dispose() on your C# class.

Puzzled Over a year ago

OK, I understand now. Thank you once more Hans. Cheers.

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