Cleaning up unmanaged resources

For a majority of the objects that your app creates, you can rely on the .NET garbage collector to handle memory management. However, when you create objects that include unmanaged resources, you must explicitly release those resources when you finish using them. The most common types of unmanaged resources are objects that wrap operating system resources, such as files, windows, network connections, or database connections. Although the garbage collector is able to track the lifetime of an object that encapsulates an unmanaged resource, it doesn't know how to release and clean up the unmanaged resource.

If your types use unmanaged resources, you should do the following:

• Implement the dispose pattern. This requires that you provide an IDisposable.Dispose implementation to enable the deterministic release of unmanaged resources. A consumer of your type calls Dispose when the object (and the resources it uses) are no longer needed. The Dispose method immediately releases the unmanaged resources.

• In the event that a consumer of your type forgets to call Dispose, provide a way for your unmanaged resources to be released. There are two ways to do this:

  • Use a safe handle to wrap your unmanaged resource. This is the recommended technique. Safe handles are derived from the System.Runtime.InteropServices.SafeHandle abstract class and include a robust Finalize method. When you use a safe handle, you simply implement the IDisposable interface and call your safe handle's Dispose method in your IDisposable.Dispose implementation. The safe handle's finalizer is called automatically by the garbage collector if its Dispose method is not called.

    —or—

  • Define a finalizer. Finalization enables the non-deterministic release of unmanaged resources when the consumer of a type fails to call IDisposable.Dispose to dispose of them deterministically.

    Warning

    Object finalization can be a complex and error-prone operation, we recommend that you use a safe handle instead of providing your own finalizer.

Consumers of your type can then call your IDisposable.Dispose implementation directly to free memory used by unmanaged resources. When you properly implement a Dispose method, either your safe handle's Finalize method or your own override of the Object.Finalize method becomes a safeguard to clean up resources in the event that the Dispose method is not called.

In this section

Implementing a Dispose method describes how to implement the dispose pattern for releasing unmanaged resources.

Using objects that implement IDisposable describes how consumers of a type ensure that its Dispose implementation is called. We strongly recommend using the C# using (or the Visual Basic Using) statement to do this.

Reference

Type / Member	Description
System.IDisposable	Defines the Dispose method for releasing unmanaged resources.
Object.Finalize	Provides for object finalization if unmanaged resources are not released by the Dispose method.
GC.SuppressFinalize	Suppresses finalization. This method is customarily called from a Dispose method to prevent a finalizer from executing.