Stopping timer in its callback method

Question

I have a System.Threading.Timer that calls its appropriate event handler (callback) every 10 ms. The method itself is not reentrant and can sometimes take way longer than 10 ms. Thus, I want to stop the timer during method execution.

Code:

private Timer _creatorTimer;

// BackgroundWorker's work
private void CreatorWork(object sender, DoWorkEventArgs e) {
      _creatorTimer = new Timer(CreatorLoop, null, 0, 10);

      // some other code that worker is doing while the timer is active
      // ...
      // ...
}

private void CreatorLoop(object state) {
      // Stop timer (prevent reentering)
      _creatorTimer.Change(Timeout.Infinite, 0);

      /*
          ... Work here
      */

      // Reenable timer
      _creatorTimer.Change(10, 0);
} 

MSDN states that the callback method is called (every time the timer fires) in separate thread from the thread pool. That means that if I stop the timer the first thing in method it still doesn't neccessarily prevent the timer to fire and run another instance of the method before the first one had a chance to stop the timer.

Should maybe the timer (or even the non-reentrant method itself) be locked? What is the right way to prevent timer from firing during execution of its callback (and non-reentrant) method?

Answer 1

You could let the timer continue firing the callback method but wrap your non-reentrant code in a Monitor.TryEnter/Exit. No need to stop/restart the timer in that case; overlapping calls will not acquire the lock and return immediately.

 private void CreatorLoop(object state) 
 {
   if (Monitor.TryEnter(lockObject))
   {
     try
     {
       // Work here
     }
     finally
     {
       Monitor.Exit(lockObject);
     }
   }
 }