Proper use of the IDisposable interface

Question

I know from reading the Microsoft documentation that the \"primary\" use of the IDisposable interface is to clean up unmanaged resources.

To me, \"unman

Answer 1

The purpose of the Dispose pattern is to provide a mechanism to clean up both managed and unmanaged resources and when that occurs depends on how the Dispose method is being called. In your example, the use of Dispose is not actually doing anything related to dispose, since clearing a list has no impact on that collection being disposed. Likewise, the calls to set the variables to null also have no impact on the GC.

You can take a look at this article for more details on how to implement the Dispose pattern, but it basically looks like this:

public class SimpleCleanup : IDisposable
{
    // some fields that require cleanup
    private SafeHandle handle;
    private bool disposed = false; // to detect redundant calls

    public SimpleCleanup()
    {
        this.handle = /*...*/;
    }

    protected virtual void Dispose(bool disposing)
    {
        if (!disposed)
        {
            if (disposing)
            {
                // Dispose managed resources.
                if (handle != null)
                {
                    handle.Dispose();
                }
            }

            // Dispose unmanaged managed resources.

            disposed = true;
        }
    }

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

The method that is the most important here is the Dispose(bool), which actually runs under two different circumstances:

• disposing == true: the method has been called directly or indirectly by a user's code. Managed and unmanaged resources can be disposed.
• disposing == false: the method has been called by the runtime from inside the finalizer, and you should not reference other objects. Only unmanaged resources can be disposed.

The problem with simply letting the GC take care of doing the cleanup is that you have no real control over when the GC will run a collection cycle (you can call GC.Collect(), but you really shouldn't) so resources may stay around longer than needed. Remember, calling Dispose() doesn't actually cause a collection cycle or in any way cause the GC to collect/free the object; it simply provides the means to more deterministicly cleanup the resources used and tell the GC that this cleanup has already been performed.

The whole point of IDisposable and the dispose pattern isn't about immediately freeing memory. The only time a call to Dispose will actually even have a chance of immediately freeing memory is when it is handling the disposing == false scenario and manipulating unmanaged resources. For managed code, the memory won't actually be reclaimed until the GC runs a collection cycle, which you really have no control over (other than calling GC.Collect(), which I've already mentioned is not a good idea).

Your scenario isn't really valid since strings in .NET don't use any unamanged resources and don't implement IDisposable, there is no way to force them to be "cleaned up."