Coding Horror

programming and human factors

Just Say No to Finalization!

I am working with some classes that wrap unmanaged APIs, so I have to be concerned with releasing the resources associated with these APIs-- eg, the IDisposable interface. I was a little confused about the distinction between Dispose() and Finalize(), and in my research I found this article by Brent Rector of Wintellect:

In a worst-case scenario, your object's Finalize method won't run until your process terminates gracefully. (Actually, the real worst case is that it never runs at all because the process terminates abnormally.) Shortly thereafter, non-memory resources will be released anyway, so the Finalize method served no real purpose other than to keep the application from running as fast as it otherwise could.

Just say No to Finalize methods!

It's a good point. In a true worst case scenario-- unhandled exception time-- you won't get any benefit from Finalize. So, given the (evidently) large performance penalty of Finalize, why bother? I tend to agree. However, the best practice according to Microsoft is, if you implement IDispose, you should also implement a Finalizer:

  
Private _IsDisposed as Boolean = False  
''' <summary>
''' public Dispose method intended for client use
''' </summary>
Public Overloads Sub Dispose() Implements IDisposable.Dispose  
Dispose(False)  
GC.SuppressFinalize(Me)  
End Sub  
''' <summary>
''' common Dispose method; can be called by client or the runtime
''' </summary>
Protected Overridable Overloads Sub Dispose(ByVal IsFinalizer As Boolean)  
If Not _IsDisposed Then  
If IsFinalizer Then  
'-- dispose unmanaged resources
End If  
'-- disposed managed resources
End If  
_IsDisposed = True  
End Sub  
''' <summary>
''' called by the runtime only, at garbage collection time
''' this protects us if the client "forgets" to call myObject.Dispose()
''' </summary>
Protected Overrides Sub Finalize()  
Dispose(True)  
End Sub  

It's all rather contradictory.

Written by Jeff Atwood

Indoor enthusiast. Co-founder of Stack Exchange and Discourse. Disclaimer: I have no idea what I'm talking about. Find me here: http://twitter.com/codinghorror