How to “sleep” until timeout or cancellation is requested in .NET 4.0

Question

What\'s the best way to sleep a certain amount of time, but be able to be interrupted by a IsCancellationRequested from a CancellationToken?

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Answer 1

The CancellationToken.WaitHandle can throw an exception when accessed after the CancellationTokenSource has been disposed:

ObjectDisposedException: The CancellationTokenSource has been disposed.

In some cases, especially when linked cancellation sources are being manually disposed (as they should be), this can be a nuisance.

This extension method allows 'safe cancellation waiting'; however, it should be used on conjunction with checks to, and proper flagging of, the cancellation token's state and/or usage of the return value. This is because it suppresses exceptions access the WaitHandle and may return faster than expected.

internal static class CancellationTokenExtensions
{
    /// 

    /// Wait up to a given duration for a token to be cancelled.
    /// Returns true if the token was cancelled within the duration
    /// or the underlying cancellation token source has been disposed.
    /// 
    public static bool WaitForCancellation(this CancellationToken token, TimeSpan duration)
    {
        WaitHandle handle;
        try
        {
            handle = token.WaitHandle;
        }
        catch
        {
            // eg. CancellationTokenSource is disposed
            return true;
        }

        return handle.WaitOne(duration);
    }
}