How can a finalize method be suppressed in .NET?

The finalize method can be suppressed in .NET by calling the method GC.SuppressFinalize(). By suppressing, you mean that the finalize method will not be triggered for that particular object by the garbage collector




Why is this suppression required? Normally releasing of unmanaged resources can happen in two ways. One being the finalize method and other being the dispose method. If you are releasing unmanaged resources using dispose method, then you have to ensure that garbage collector does not call finalize method.

If it triggers finalize method, then it is redundant and unnecessary call since the resources are already cleaned up using dispose method. Hence while implementing dispose method you will use this method GC.SuppressFinalize() to suppress the finalize method. This is demonstrated with an example which is shown below:

public class sampleClass {
public class sampleDisposeClass: IDisposable {
public System.IO.StreamReader sampleReader;
System.ComponentModel.Component sampleComponent =
new System.ComponentModel.Component();

bool disposeFlag = false;

public void Dispose() {
DisposeResources(true);
GC.SuppressFinalize(this);
}

private void DisposeResources(bool disposeManagedRes) {
if(!this.disposeFlag) {
if(disposeManagedRes) {
sampleComponent.Dispose();
}
if (sampleReader != null) {
sampleReader.Close();
}
}
disposeFlag = true;
}

~sampleDisposeClass() {
DisposeResources(false);
}
}

public static void Main() {
sampleDisposeClass obj = new sampleDisposeClass();
obj.sampleReader = new System.IO.StreamReader("sample.txt");
string eachLine;
while ((eachLine = obj.sampleReader.ReadLine()) != null) {
Console.WriteLine(eachLine);
}
Console.ReadLine();
}
}

Output of this example will contain the contents of sample.txt file.

In this example, you do the following:

• Created a class called sampleClass which has a nested class called sampleDisposeClass

• The nested class has implemented the IDisposable interface in order to implement the Dispose method.

• The nested class sampleDisposeClass has two resources as its members. The StreamReader object sampleReader is an unmanaged resource and the component sampleComponent is a managed resource. Both these resources have to be cleaned up using Dispose method.

• Define Dispose method such that it calls your newly created method DisposeResources. Pass the Boolean value true while triggering the later method. True signifies that managed resources have to be cleaned up.

• Inside Dispose method, you have to make a call to GC.SuppressFinalize to prevent finalization being done by the garbage collector using finalize method.

• Define the method DisposeResources such that it cleans up both managed resources and unmanaged resources used by the current object. Managed resource will be disposed only if the Boolean flag disposeManagedRes passed as a parameter to the method has its value to be true.

• Define the destructor for the sampleDisposeClass which will be triggered only if the Dispose method is not triggered. The destructor should clean up only unmanaged resources and not managed resources. Hence you call DisposeResources from inside the destructor with the parameter value as false to ensure that managed resources are not cleaned up explicitly through destructors.

• Outside the nested class and inside the sampleClass you define the Main method which creates an instance of the nested class sampleDisposeClass and accesses the unmanaged resource – the StreamReader instance.

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