David's Weblog

Lately, I’ve been playing with c# threading again and designing something to shut down my threads gracefully when the thread supervisor decides it’s time to shut one down.

I was reading Joseph Albahari’s site about safe cancellation, which is an excellent resource I often turn to. My focus is on the “Cancellation Tokens” section.

In my testing I noticed that the following

while (true)
{
    cancelationToken.ThrowIfCancellationRequested();
}

obviously needs try/catch blocks. After the supervisor calls the cancel() method the exception is thrown. At that point you can catch the exception and shut the thread down gracefully. Example:

/// <summary>
/// Test to see how the CancellationToken works…
/// </summary>
public void DoWork3()
{
    bool keepGoing = true;

    while (keepGoing)
    {
        try
        {
             mCancellationToken.ThrowIfCancellationRequested();
             Thread.Sleep(1000);
             log.Info(“Awake. Now going back to sleep”);
        }
        catch (Exception e)
        {
            log.Info(“In the catch Exception block. Add your custom code to shut down things gracefully”);
            keepGoing = false;
        }
    }
    log.Info(“DoWork3 is done”);
}

static void Main(string[] args)
{
     CancellationTokenSource aCTS = new CancellationTokenSource();
     threadTest lThreadTest3 = new threadTest(aCTS.Token);
     System.Threading.Thread lThread3 = new System.Threading.Thread(new System.Threading.ThreadStart(lThreadTest3.DoWork3));

     lThread3.Start();

     Thread.Sleep(10000);

     aCTS.Cancel();

     lThread3.Join();
}

OK, so try/catch is a minor detail, but I prefer simple examples that actually work.