Chapter 12. Disposal and Garbage Collection

Some objects require explicit tear-down code to release resources such as open files, locks, operating system handles, and unmanaged objects. In .NET parlance, this is called disposal, and it is supported through the IDisposable interface. The managed memory occupied by unused objects must also be reclaimed at some point; this function is known as garbage collection and is performed by the CLR.

Disposal differs from garbage collection in that disposal is usually explicitly instigated; garbage collection is totally automatic. In other words, the programmer takes care of such things as releasing file handles, locks, and operating system resources while the CLR takes care of releasing memory.

This chapter discusses both disposal and garbage collection, also describing C# finalizers and the pattern by which they can provide a backup for disposal. Lastly, the intricacies of the garbage collector are explored in detail, and other memory management options are discussed.

IDisposable, Dispose, and Close

The .NET Framework defines a special interface for types requiring a tear-down method:

public interface IDisposable
{
  void Dispose(  );
}

C#’s using statement provides a syntactic shortcut for calling Dispose on objects that implement IDisposable, using a try / finally block. For example:

using (FileStream fs = new FileStream ("myFile.txt", FileMode.Open))
{
  // ... Write to the file ...
}

The compiler converts this to:

FileStream fs = new FileStream ("myFile.txt", ...

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