Non-reentrant timers

Question

I have a function that I want to invoke every x seconds, but I want it to be thread-safe.

Can I set up this behavior when I am creating the timer? (I don\'t

Answer 1

Complementing Tim Lloyd's solution for System.Timers.Timer, here's a solution to prevent reentrancy for cases where you want to use System.Threading.Timer instead.

TimeSpan DISABLED_TIME_SPAN = TimeSpan.FromMilliseconds(-1);

TimeSpan interval = TimeSpan.FromSeconds(1);
Timer timer = null; // assign null so we can access it inside the lambda

timer = new Timer(callback: state =>
{
  doSomeWork();
  try
  {
    timer.Change(interval, DISABLED_TIME_SPAN);
  }
  catch (ObjectDisposedException timerHasBeenDisposed)
  {
  }
}, state: null, dueTime: interval, period: DISABLED_TIME_SPAN);

I believe you don't want interval to be accessed inside of the callback, but that is be easy to fix, if you want to: Put the above into a NonReentrantTimer class that wraps the BCL's Timer class. You would then pass the doSomeWork callback in as a parameter. An example of such a class:

public class NonReentrantTimer : IDisposable
{
    private readonly TimerCallback _callback;
    private readonly TimeSpan _period;
    private readonly Timer _timer;

    public NonReentrantTimer(TimerCallback callback, object state, TimeSpan dueTime, TimeSpan period)
    {
        _callback = callback;
        _period = period;
        _timer = new Timer(Callback, state, dueTime, DISABLED_TIME_SPAN);
    }

    private void Callback(object state)
    {
        _callback(state);
        try
        {
            _timer.Change(_period, DISABLED_TIME_SPAN);
        }
        catch (ObjectDisposedException timerHasBeenDisposed)
        {
        }
    }


    public void Dispose()
    {
        _timer.Dispose();
    }
}