public delegate void TestDelegate(object sender, EventArgs e);

    public class ThreadSafeEventsDemo
    {
        // Delegate variable backing the TestEvent event.
        TestDelegate testDelegate;

        // Lock for TestEvent delegate access.
        readonly object eventLock = new object();

        public event TestDelegate TestEvent
        {
            add
            {
                lock (eventLock)
                {
                    testDelegate += value;
                }
            }
            remove
            {
                lock (eventLock)
                {
                    testDelegate -= value;
                }
            }
        }

        /// 

        /// Raises the TestEvent event
        /// 

        protected virtual void OnTestEvent(EventArgs e)
        {
            TestDelegate handler;
            lock (eventLock)
            {
                handler = testDelegate;
            }
            if (handler != null)
            {                
                handler(this, e);
            }
        }
    }