Monitor.Wait - while or if?

Question

Currently, I'm learning for a multithreading exam. I read the good threading article of albahari. I've got a question at the monitor usage - why is here used a loop in place of an if?

lock (_locker)
{
  while (!_go) //why while and not if?
    Monitor.Wait (_locker);  // _lock is released
  // lock is regained
  ...
}

I think, that an if would be sufficient.

I'm afraid, that I don't understand the article completely.

//Edit Example-Code:

class SimpleWaitPulse
{
  static readonly object _locker = new object();
  static bool _go;

  static void Main()
  {                                // The new thread will block
    new Thread (Work).Start();     // because _go==false.

    Console.ReadLine();            // Wait for user to hit Enter

    lock (_locker)                 // Let's now wake up the thread by
    {                              // setting _go=true and pulsing.
      _go = true;
      Monitor.Pulse (_locker);
    }
  }

  static void Work()
  {
    lock (_locker)
      while (!_go)
        Monitor.Wait (_locker);    // Lock is released while we’re waiting

    Console.WriteLine ("Woken!!!");
  }
}

Answer 1

It just depends on the situation. In this case the code is just waiting for _go to be true.

Every time _locker is pulsed it will check to see if _go has been set to true. If _go is still false, it will wait for the next pulse.

If an if was used instead of a while, it would only wait once (or not at all if _go was already true), and would then continue on after a pulse, regardless of the new state of _go.

So how you use Monitor.Wait() depends entirely on your specific needs.