Mine

        private ManualResetEvent m_Event = new ManualResetEvent ();
        public void StartThread() {
            ThreadPool.QueueUserWorkItem (new WaitCallback (ThreadRun), ar);
        }

        private void ThreadRun () {
            while(true) {
                // do work, do work
                if(m_Event.WaitOne(0)) {
                    // time to exit
                }
            }
        }

        private void OnButtonClick() {
            m_Event.Set (); // Tell the thread it's time to exit gracefully;
        }