c# - 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 mind which .NET timer I use, I just want it to be thread-safe).

I know I can implement locks inside my callback function, but I think it would be more elegant if it were in the timer level.

My callback function, and environment are not related to a UI.

[Edit 1] I just don't want there to be more than one thread inside my callback function.

[Edit 2] I want to keep the locking inside the timer level, because the timer is responsible for when to call my callback, and here there is a particular situation when I don't want to call my callback function. So I think when to call is the responsibility of the timer.

Answer 1

I'm guessing, as your question is not entirely clear, that you want to ensure that your timer cannot re-enter your callback whilst you are processing a callback, and you want to do this without locking. You can achieve this using a System.Timers.Timer and ensuring that the AutoReset property is set to false. This will ensure that you have to trigger the timer on each interval manually, thus preventing any reentrancy:

public class NoLockTimer : IDisposable
{
    private readonly Timer _timer;

    public NoLockTimer()
    {
        _timer = new Timer { AutoReset = false, Interval = 1000 };

        _timer.Elapsed += delegate
        {
            //Do some stuff

            _timer.Start(); // <- Manual restart.
        };

        _timer.Start();
    }

    public void Dispose()
    {
        if (_timer != null)
        {
            _timer.Dispose();
        }
    }
}