Multi-threading with .Net HttpListener

Question

I have a listener:

listener = new HttpListener();
listener.Prefixes.Add(@\"http://+:8077/\");
listener.Start();
listenerThread = new Thread(HandleRequests);
         


        

Answer 1

Well there are several ways to solve this... This is a simple example that uses a semaphore to track ongoing work, and a signal that is raised when all workers are finished. This should give you a basic idea to work from.

The solution below is not ideal, ideally we should acquire the semaphore before calling BeginGetContext. That makes shutdown more difficult, so I've chosen to use this more simplified approach. If I were doing this for 'real' I'd probably write my own thread management rather than relying on the ThreadPool. This would allow a more dependable shutdown.

Anyway here is the complete example:

class TestHttp
{
    static void Main()
    {
        using (HttpServer srvr = new HttpServer(5))
        {
            srvr.Start(8085);
            Console.WriteLine("Press [Enter] to quit.");
            Console.ReadLine();
        }
    }
}


class HttpServer : IDisposable
{
    private readonly int _maxThreads;
    private readonly HttpListener _listener;
    private readonly Thread _listenerThread;
    private readonly ManualResetEvent _stop, _idle;
    private readonly Semaphore _busy;

    public HttpServer(int maxThreads)
    {
        _maxThreads = maxThreads;
        _stop = new ManualResetEvent(false);
        _idle = new ManualResetEvent(false);
        _busy = new Semaphore(maxThreads, maxThreads);
        _listener = new HttpListener();
        _listenerThread = new Thread(HandleRequests);
    }

    public void Start(int port)
    {
        _listener.Prefixes.Add(String.Format(@"http://+:{0}/", port));
        _listener.Start();
        _listenerThread.Start();
    }

    public void Dispose()
    { Stop(); }

    public void Stop()
    {
        _stop.Set();
        _listenerThread.Join();
        _idle.Reset();

        //aquire and release the semaphore to see if anyone is running, wait for idle if they are.
        _busy.WaitOne();
        if(_maxThreads != 1 + _busy.Release())
            _idle.WaitOne();

        _listener.Stop();
    }

    private void HandleRequests()
    {
        while (_listener.IsListening)
        {
            var context = _listener.BeginGetContext(ListenerCallback, null);

            if (0 == WaitHandle.WaitAny(new[] { _stop, context.AsyncWaitHandle }))
                return;
        }
    }

    private void ListenerCallback(IAsyncResult ar)
    {
        _busy.WaitOne();
        try
        {
            HttpListenerContext context;
            try
            { context = _listener.EndGetContext(ar); }
            catch (HttpListenerException)
            { return; }

            if (_stop.WaitOne(0, false))
                return;

            Console.WriteLine("{0} {1}", context.Request.HttpMethod, context.Request.RawUrl);
            context.Response.SendChunked = true;
            using (TextWriter tw = new StreamWriter(context.Response.OutputStream))
            {
                tw.WriteLine("
Hello World
");
                for (int i = 0; i < 5; i++)
                {
                    tw.WriteLine("
{0} @ {1}
", i, DateTime.Now);
                    tw.Flush();
                    Thread.Sleep(1000);
                }
                tw.WriteLine("");
            }
        }
        finally
        {
            if (_maxThreads == 1 + _busy.Release())
                _idle.Set();
        }
    }
}