Question

I have a System.Timers.Timer that randomly throws a NullReferenceException when I call the Stop() method. This probably occurs probably about 4 times a work day. I’ve seen the problem repeated on multiple computers.

void myTimer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
{
  if (myTimer != null) //trying to stop the exception here
  {
    myTimer.Stop(); //Null Reference Exception occurs here

    DoStuff();

    myTimer.Start();
  }
}

The stack looks like this:

The weirdest part is that I can immediately start the program again from the position of the exception with no problems.

Answer 1

Try this

void myTimer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
{
  lock(this) {
  if (myTimer != null) //trying to stop the exception here
  {
    myTimer.Stop(); //Null Reference Exception occurs here

    DoStuff();

    myTimer.Start();
  }
  }
}