Question

static readonly System.Timers.Timer _timer = new System.Timers.Timer();

static void Main(string[] args)
{
    _timer.Interval = 1000;
    _timer.Elapsed += new System.Timers.ElapsedEventHandler(Timer_Elapsed);
    _timer.Start();

    Console.WriteLine("Press any key to exit...");
    Console.ReadKey();
}

static void Timer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
{
    Console.WriteLine(DateTime.Now);
    Thread.Sleep(600000); // 10 minutes
    Console.WriteLine(DateTime.Now);
}

What happens to the timer thread with such a long sleep? Does it get back to thread pool or we end up many sleeping threads?

Answer 1

The sleeping threads will return to the thread pool, but only after the sleep ends. A thread pool has a maximum number of threads, that means you could run out of threads to use, because all of them will be sleeping.

EDIT:

ThreadPool docs:

http://msdn.microsoft.com/en-us/library/system.threading.threadpool.getmaxthreads.aspx