AsyncTraceListener.cs

public abstract class AsyncTraceListener : TraceListener
{
    public AsyncTraceListener()
    {
        _loggingThread = new Thread(new ThreadStart(ProcessQueue))
        {
            // this is performed from a bg thread, to ensure the queue is serviced from a single thread
            IsBackground = true
        };
        _loggingThread.Start();
    }

    public override void Write(string message)
    {
        lock (_queue)
        {
            _queue.Enqueue(() => AsyncWrite(message));
        }

        _hasNewItems.Set();
    }

    public override void WriteLine(string message)
    {
        lock (_queue)
        {
            _queue.Enqueue(() => AsyncWriteLine(message));
        }

        _hasNewItems.Set();
    }

    public override void Flush()
    {
        _waiting.WaitOne();
    }

    protected override void Dispose(bool disposing)
    {
        _terminate.Set();
        _loggingThread.Join();
    }

    protected abstract void AsyncWrite(string message);

    protected abstract void AsyncWriteLine(string message);

    private void ProcessQueue()
    {
        while (true)
        {
            _waiting.Set();

            int i = ManualResetEvent.WaitAny(new WaitHandle[] { _hasNewItems, _terminate });

            // terminate was signaled 
            if (i == 1)
                return;

            _hasNewItems.Reset();
            _waiting.Reset();

            Queue<Action> queueCopy;

            lock (_queue)
            {
                queueCopy = new Queue<Action>(_queue);
                _queue.Clear();
            }

            foreach (Action fn in queueCopy)
            {
                fn();
            }
        }
    }

    private readonly Queue<Action> _queue = new Queue<Action>();

    private readonly ManualResetEvent _hasNewItems = new ManualResetEvent(false);

    private readonly ManualResetEvent _terminate = new ManualResetEvent(false);

    private readonly ManualResetEvent _waiting = new ManualResetEvent(false);

    private readonly Thread _loggingThread;
}