How can I ensure that I dispose of an object in my singleton before the application closes?

Question

I'm using WatiN for some automated tests and what I found was that creating an IE instance for every test was not scalable. The creation and shutdown time of each IE instance was eating me alive:

    [TestMethod]
    public void Verify_Some_Useful_Thing()
    {
        using (var browser = new IE())
        {
            browser.GoTo("/someurl");
            // etc..
            // some assert() statements
        }
     }

However, the using statement did prove useful in that I can always ensure that my IE instance would have its dispose() method called which would close the IE window.

Anyway, I created a singleton which maintained a single IE instance which all my tests use across all my test classes:

public class BrowserPool
{      
    private static readonly Lazy<BrowserPool> _instance = new Lazy<BrowserPool>(() => new BrowserPool());        

    private IE _browser;
    private string _ieHwnd;
    private int _threadId;

    public IE Browser
    {
        get
        {
            var currentThreadId = GetCurrentThreadId();
            if (currentThreadId != _threadId)
            {
                _browser = IE.AttachTo<IE>(Find.By("hwnd", _ieHwnd));
                _threadId = currentThreadId;
            }
            return _browser;
        }
        set
        {
            _browser = value;
            _ieHwnd = _browser.hWnd.ToString();
            _threadId = GetCurrentThreadId();
        }
    }

    /// <summary>
    /// private to prevent direct instantiation.
    /// </summary>
    private BrowserPool()
    {
        Browser = new IE();
    }

    /// <summary>
    /// Get the current executing thread's id.
    /// </summary>
    /// <returns>Thread Id.</returns>
    private int GetCurrentThreadId()
    {
        return Thread.CurrentThread.GetHashCode();
    }

    /// <summary>
    /// Accessor for instance
    /// </summary>
    public static BrowserPool Instance
    {
        get
        {
            return _instance;
        }
    }
}

And the test now:

  [TestMethod]
  public void Verify_Some_Useful_Thing()
  {
        var browser = BrowserPool.Instance.Browser;
        browser.GoTo("/someurl");
        // some assertions
  }

This works well and my tests run much faster now that I'm not opening and closing IE every test. However, I have this one problem in that when the tests complete my IE instance will still remain open.

I can't figure out an elegant way to ensure that BrowserPool.Browser has dispose() or close() called on it before the application ends. I even tried using a finalizer in the BrowserPool class but that didn't seem to work because the _browser variable had already been reclaimed when my finalizer is called.

How can I ensure that dispose() is called on my IE instance after the test run?

Answer 1

Use the [AssemblyCleanupAttribute()] to clean resources after your tests found in the assembly are finished.

Btw, never rely on the use of destructors in .NET.