C#

lock(lockObject)
{
    while(jobCount > 0)
    {
        Monitor.Wait(lockObject);
    }
}

private void ThreadJobProcedure(object data)
{
    // Do stuff...

    lock(lockObject)
    {
        jobCount--;

        Monitor.Pulse(lockObject);
    }
}

private static void StartQueue
{
  StringReader sr = new StringReader(rawData);
  string line = string.Empty;
  int jobCount = 0;
  while (((line = sr.ReadLine()) != null) && (this.allowQueuing))
  {
    ThreadPool.QueueUserWorkItem(new WaitCallback(DoMagicalThings), line);
    jobCount++
  }

  lock(lockObject)
  {
    while(jobCount > 0)
    {
      Monitor.Wait(lockObject);
    }
  }

  Console.WriteLine("All done");
}

private static void DoMagicalThings(object data)
{
  Console.WriteLine(data.ToString())

  lock(lockObject)
  {
    jobCount--;
    Monitor.Pulse(lockObject);
  }
}

private readonly object lockObject = new object();

MrEyes wrote:

An additional problem is that externally to this a user could click a Stop button, this should stop all threads and stop any further items being processed. Could I somehow use this Lock and Monitor functionality to do this?

In my original code, I had a simple class var bool that would be checked at the top of the worker method. If the value was false then the worker method would immediately return

private void ThreadMethod(object data)
{
    while(notStopped)
    {
        // Do stuff...
    }
 
    lock(lockObject)
    {
        jobCount--;
        Monitor.Pulse(lockObject);
    }
}