Question

My question is simple, why GC can’t figure it out that timer object in the main should be garbage collected along with the timer inside TestTimer and associated EventHandler?

Why am I continously getting console.Writeline output?

class Program
{
    public static void Main()
    {       
       TestTimer timer = new  TestTimer();
       timer = null;
       GC.Collect();
       GC.WaitForPendingFinalizers();
       Console.ReadKey();
    }
}

public class TestTimer
{
    private Timer timer;

    public TestTimer()
    {
        timer = new Timer(1000);
        timer.Elapsed += new ElapsedEventHandler(timer_Elapsed);
        timer.Start();
    }

    private void timer_Elapsed(Object sender, ElapsedEventArgs args)
    {
        Console.Write("\n" + DateTime.Now);
    }
}

Answer 1

Don’t depend on the GC, use the Dispose pattern to properly dispose the TestTimer (which then should dispose the Timer).

However, what happens is that the timer keeps itself alive by getting a GC handle on itself. Read this blog post:

http://nitoprograms.blogspot.com/2011/07/systemthreadingtimer-constructor-and.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+blogspot%2FOlZtT+%28Nito+Programming%29