Ah right - I'd missed that! So my comments about non-deterministic finalisation weren't relevant. Providing every object just cleans up after itself then you never have to worry about delegated/wrapped objects, as their finalisers will just clean up after themselves too. Which was Ian's point (hence why finalisation is non-deterministic - lightbulb switches on!). thanks
Julian -----Original Message----- From: Unmoderated discussion of advanced .NET topics. [mailto:[EMAIL PROTECTED] Behalf Of Eric Gunnerson Sent: 26 January 2005 17:19 To: [email protected] Subject: Re: [ADVANCED-DOTNET] Disposing of objects I disagree that you would always want a finalizer. There are some cases - rare, perhaps - where your object contains an object that is disposable and finalizable, and in these cases, you might want to be disposable, but you would not want to be finalizable, since the finalizer on the contained object would handle that cleanup. The difference is that finalization can happen on any object, but dispose can only happen on the user-visible object. Eric -----Original Message----- From: Unmoderated discussion of advanced .NET topics. [mailto:[EMAIL PROTECTED] On Behalf Of Julian Everett Sent: Wednesday, January 26, 2005 4:12 AM To: [email protected] Subject: Re: [ADVANCED-DOTNET] Disposing of objects If I understand what you say correctly, I think there's a non-obvious point to expand on here. Common sense would suggest that if you need a Dispose() method then you should implement a finaliser too, to perform the same clean-up in the instance that Dispose() is not called explicitly. In other words you should always choose (2) over (3). However, the problem arises because Finalizable objects are finalised in a non-deterministic manner. As a result, if you try to call a method on a non-static Finalizable type (e.g. sqlConnection.Dispose()) from within a finaliser and there is any chance the referenced object could be in the same finalisation object graph, then the referenced object might well have been finalised already - which would result in an exception being thrown. That's why you can do nothing useful to wrapped resources from within a finaliser, at least as I understand it. cheers Julian -----Original Message----- From: Unmoderated discussion of advanced .NET topics. [mailto:[EMAIL PROTECTED] Behalf Of Ian Griffiths Sent: 26 January 2005 11:43 To: [email protected] Subject: Re: [ADVANCED-DOTNET] Disposing of objects One thing that's worth making clear is that for any given class you have three choices: (1) Don't implement IDisposable at all (2) Implement the Dispose pattern you've shown here (or something like it) (3) Implement IDisposable, but don't have a finalizer Because the docs focus so heavily on the dispose pattern (option 2), it's not uncommon for people who are new to this not to realise the (3) is even an option. This is unfortunate because, as it happens, it's often the most important option. It's certainly appropriate more often than (2). The fact is that very few classes need the full dispose pattern. Specifically, the finalization stuff is only required if your class *directly* manages raw handles, or handle-like things. (E.g., anything represented as an IntPtr.) Most classes don't actually wrap raw handles directly. But *lots* of classes wrap them indirectly. If you're wrapping other objects that implement IDisposable (such as a SqlConnection), then you too should implement IDisposable, but there's no need to have a finalizer. (So that would be option 3 above.) You seem to be proposing option 2 on *all* classes. Option 2 should in fact be the least common - for most classes, either 1 or 3 will be more appropriate. So I'd say definitely *don't* implement that pattern you've shown on all classes. Microsoft seem to push 2 too heavily. For example, as someone else pointed out, they say: "Implement the dispose design pattern on a type that encapsulates resources that explicitly need to be freed. Users can free external resources by calling the public Dispose method." If you take this literally, it includes things like SqlConnection and FileStream - those need to be freed explicitly with a call to Close or Dispose. You really don't need the full Dispose pattern (i.e., with a finalizer and two Dispose methods) in that case. And that's the most common case, so it's a shame they tell you to use the full Dispose pattern... The fact is that there's nothing useful you can do to such resources in your finalizer. -- Ian Griffiths - DevelopMentor http://www.interact-sw.co.uk/iangblog/ > -----Original Message----- > From: Knowlton, Gerald F. > > Greetings: > > We are having somewhat of a lengthy discussion going on here regarding the > disposing of objects. > > One camp wants to put the following code into all classes: > > Private Disposed as Boolean > . > . > . > Public sub Dispose() Implements IDisposable.Dispose > Dispose(True) > GC.Suppressfinalize(me) > End sub > > Protected Sub Dispose(ByVal Disposing as Boolean) > If Disposed then Exit Sub > If Disposing then DisposeOfObjects > End Sub > > Private Sub Dispose of Objects > <object_name> = nothing > End Sub > > > While the other camp says it is not needed unless the class has unmanaged > resources. > > Our question is; which would be the better practice? > > Best regards, > > > Jerry > > ================================================================== > All BWXT, Inc. 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