GOTCHA 37 Rules to invoke base.Finalize() aren t consistent

GOTCHA #37 Rules to invoke base.Finalize() aren't consistent

Object.Finalize() is an odd method. It is defined as protected overridable. As mentioned in the introduction to this chapter, in C# you implement your class's Finalize() method with the special syntax ~NameOfClass, where NameOfClass is the actual name of your class. This pseudo-destructor is compiled into the Finalize() method during the MSIL translation.

Furthermore, within the C# destructor, you should not attempt to call Finalize() on the base class. The compiler-generated Finalize() takes care of calling the base class's Finalize(), even if an exception is raised, because the call is safe inside a finally block.

For example, look at this pseudo-destructor:

         ~MyClass()         {             // Whatever cleanup code you write         } 

The C# compiler will translate this into the Finalize() method in your assembly. A look at the generated MSIL using ildasm.exe will clarify this for you (see Figure 5-5).

Figure 5-5. MSIL translation of a C# pseudo-destructor

If a C# programmer ever has to work with VB.NET code, he should remember that the rules are different. In VB.NET, you write Finalize() as a Protected Overrides method, and you must call MyBase.Finalize(), as shown in Example 5-4.

Example 5-4. Writing Finalize() in VB.NET

     Protected Overrides Sub Finalize()         Try             'Whatever cleanup code you write         Finally     MyBase.Finalize()         End Try     End Sub 

However, if you use the Dispose design pattern (refer to Gotcha #40, "Implementing IDisposable isn't enough"), then you most likely will not implement the Finalize() method in your derived classes.

IN A NUTSHELL

In C#, do not invoke the base class's Finalize() method from within the destructor. In VB.NET, do invoke the base class's Finalize() method from within the Finalize() method.

SEE ALSO

Gotcha #35, "Writing Finalize( ) is rarely a good idea," Gotcha #36, "Releasing managed resources in Finalize( ) can wreak havoc," Gotcha #38, "Depending on Finalize() can tie up critical resources," Gotcha #39, "Using Finalize() on disposed objects is costly," Gotcha #40, "Implementing IDisposable isn't enough," and Gotcha #41, "Using the Dispose Design Pattern doesn't guarantee cleanup."