Dispose disposing call at the end of its Dispose bool implementation. If we make class A sealed then we can make Dispose bool private.
SuppressFinalize this. However, we should still implement a separate protected Dispose bool method so that derived classes can follow the above pattern. The only case where we can eschew the separate Dispose bool method is if our class is both sealed and has no unmanaged resources.
James Lao Home Posts Contact. So technically IDisposable is not necessary for everything to be freed properly, but it provides us with two things: A consistent way to deterministicly cleanup of unmanaged resources. Avoiding the finalizer queue so the object can be collected in a single GC pass. Dispose true ; GC. James Lao Staff Software Engineer. Copy Download.
Dispose implementation is called by the consumer of a type when the resources owned by an instance are no longer needed, you should either wrap the managed object in a SafeHandle the recommended alternative , or you should override Object. Finalize to free unmanaged resources in the event that the consumer forgets to call Dispose. In the. For a detailed discussion about how this interface and the Object.
If your app simply uses an object that implements the IDisposable interface, you should call the object's IDisposable. Dispose implementation when you are finished using it. Depending on your programming language, you can do this in one of two ways:. By wrapping the call to the IDisposable. Documentation for types that implement IDisposable note that fact and include a reminder to call its Dispose implementation.
If your language supports a construct such as the using statement in C and the Using statement in Visual Basic, you can use it instead of explicitly calling IDisposable. Dispose yourself. The following example uses this approach in defining a WordCount class that preserves information about a file and the number of words in it. The using statement is actually a syntactic convenience. For more information about the using statement, see the Using Statement or using Statement topics.
If your programming language does not support a construct like the using statement in C or Visual Basic, or if you prefer not to use it, you can call the IDisposable. Finally Statement , try-finally , or try-finally Statement. You should implement IDisposable if your type uses unmanaged resources directly or if you wish to use disposable resources yourself. The consumers of your type can call your IDisposable. Dispose implementation to free resources when the instance is no longer needed.
To handle cases in which they fail to call Dispose , you should either use a class derived from SafeHandle to wrap the unmanaged resources, or you should override the Object. Finalize method for a reference type. In either case, you use the Dispose method to perform whatever cleanup is necessary after using the unmanaged resources, such as freeing, releasing, or resetting the unmanaged resources.
Also, what if I am using my Dispose method to clean up event handlers. As Dispose wont automatically get called by the GC, should I implement a Finalizer, to ensure that eventhandlers get unwired? No, you do not need to implement a finalizer if you have a class that implements IDisposable that is if you have implemented the pattern correctly, and that you only have managed resources to dispose of.
If you do, it can actually affect the lifetime of your object, as objects with finalizers get added to the finalization queue in the GC and can live longer than they need to - this can be a problem if your objects are large. A class that owns managed disposable resources but not unmanaged resources should implement the full Dispose pattern, but not have a finalizer. If the class is not sealed , it should call GC. SuppressFinalize this in its Dispose method in case an inherited class adds a finalizer.
No, you are correct, if your object holds an object that holds an unmanaged resource then you should implement IDisposable so that you can call its Dispose on your Dispose, but you don't need a finaliser as its finaliser will deal with that matter. Indeed, trying to do anything with a finalisable member from in a finaliser is fraught, as which order the finalisers will run is not deterministic, so you can get some nasty bugs if you try to do this.
As a rule it's much better to have a class either hold 1 or 0 unmanaged resources. And if it has 1 unmanaged resource, it should have as little other state as needed to deal with it i. SafeHandle is a good way of dealing with this. If a class needs to deal with several unmanaged resources it should do so by handling said resources through these handler classes.
Because having to deal with unmanaged resources directly is relatively rare, the chances are you will never have to write a finaliser I think I have done so once, in real code.
Because sensible people don't do much else in classes that handle unmanaged resources, the whole Dispose bool thing is unnecessary too. If you only have managed resources, then you don't need to implement IDisposable at all. IDisposable is intended for cleaning up things beyond the GC's domain, such as native handles, database connections, etc. If your control contains controls that implement IDisposable and they must release native resources, then you still need to implement the IDisposable pattern and give your child controls a chance to dispose.
The reason for calling Dispose in the finalizer is as a last resort, if the object was not properly disposed, the GC will do it as a last ditch effort.
Yes, if you have only managed resources, they will be cleaned up by the GC when Garbage collection occurs and there isn't any living references pointing to them. But in this case, why do you need to implement IDisposable on your type? I mean, you seem to consider that in your case, not disposing your object is not a big issue, then why would someone dispose them?
You should also note that there is a performance penality with garbage collection while using Finalizers: Any object with a finalizer will escape the first GC pass, which will degrade GC efficiency quite a bit if these objects are short lived. During the first garbage collection during which the object should be cleaned up, it won't, in order to execute the finalizer. The object will then be considered as long lived by the GC, even if it should already be cleaned.
I have never had the need to implement a finalizer. As you know, it gives the object a chance to do whatever it needs prior to GC. All resources should be freed up in the dispose method.
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