AutoCancellationTokenSource

With the following code you can create a CancellationTokenSource that will signal cancellation on dispose. This provides an alternative to having to wrap a normal CancellationTokenSource in a try finally block.

Code

public class AutoCancellationTokenSource : CancellationTokenSource

{

    private bool _isDisposed;

    public AutoCancellationTokenSource()

    {

    }

    public AutoCancellationTokenSource(params CancellationToken[] linkedTokens)

    {

        foreach (var linkedToken in linkedTokens)

            if (linkedToken.IsCancellationRequested)

                TryCancel();

            else

                linkedToken.Register(TryCancel, false);

    }

    protected override void Dispose(bool disposing)

    {

        if (_isDisposed)

            return;

        TryCancel();

        base.Dispose(disposing);

        _isDisposed = true;

    }

    private void TryCancel()

    {

        if (!_isDisposed && !IsCancellationRequested)

            Cancel();

    }

}

Tests

public class AutoCancellationTokenSourceTests

{

    [Fact]

    public void StandardTest()

    {

        CancellationToken token;

        using (var source = new CancellationTokenSource())

            token = source.Token;

        Assert.False(token.IsCancellationRequested);

    }

    [Fact]

    public void AutoTest()

    {

        CancellationToken token;

        using (var source = new AutoCancellationTokenSource())

            token = source.Token;

        Assert.True(token.IsCancellationRequested);

    }

    [Fact]

    public void LinkedTest()

    {

        using (var standardSource = new CancellationTokenSource())

        using (var autoSource = new AutoCancellationTokenSource(

            standardSource.Token))

        {

            Assert.False(autoSource.IsCancellationRequested);

            standardSource.Cancel();

            Assert.True(autoSource.IsCancellationRequested);

        }

    }

    [Fact]

    public void LinkedPreCancelTest()

    {

        using (var standardSource = new CancellationTokenSource())

        {

            standardSource.Cancel();

            using (var autoSource = new AutoCancellationTokenSource(

                standardSource.Token))

            {

                Assert.True(autoSource.IsCancellationRequested);

            }

        }

    }

    [Fact]

    public void MultipleLinkedTest()

    {

        using (var standardSource1 = new CancellationTokenSource())

        using (var standardSource2 = new CancellationTokenSource())

        using (var autoSource = new AutoCancellationTokenSource(

            standardSource1.Token, 

            standardSource2.Token))

        {

            Assert.False(autoSource.IsCancellationRequested);

            standardSource1.Cancel();

            Assert.True(autoSource.IsCancellationRequested);

            standardSource2.Cancel();

            Assert.True(autoSource.IsCancellationRequested);

        }

    }

}

Enjoy,
Tom