WP8中的System.Net.Sockets

Question

Got unknown issue with System.Net.Sockets in WP8. The communication built on next schema - 4 first bytes - for package length, next 4 bytes for package number, and data. So [4][4][{any}] is a TCP package. Reading of incoming data goes by next steps. 1. Read first 8 bytes. 2. Get package length from the first 4 bytes to determine size of incoming data. 3. Resize buffer to a proper size. 4. Read incoming data in buffer with offset 8 bytes. I am sending a lot of packages to server. Sometimes server's responses in incoming buffer are valid and can be read one by one.

But sometimes it seems the first 8 bytes from incoming data are skipped and with the steps 1-4 I am reading the first 8 bytes from the package's data.

Infinite loop for receiving

while (_channel.Opened)
{
    Debug.WriteLine("Wait for incoming... ");
    Stream responseStream = await _channel.Receive();
    HandleIncomingData(responseStream);
}

Here code for socket:

    public async Task<Stream> Receive()
    {
        byte[] buff = new byte[8];
        ManualResetEventSlim mre = new ManualResetEventSlim();

        var args = new SocketAsyncEventArgs();

        args.SetBuffer(buff, 0, buff.Length);

        EventHandler<SocketAsyncEventArgs> completed = (sender, eventArgs) => mre.Set();

        EventHandler<SocketAsyncEventArgs> removeSubscription = (sender, eventArgs) => args.Completed -= completed;

        args.Completed += completed;
        args.Completed += removeSubscription;

        _connectionSocket.ReceiveAsync(args);
        mre.Wait();

        args.Completed -= removeSubscription;

        int len = BitConverter.ToInt32(buff, 0);
        int num = BitConverter.ToInt32(buff, 4);

        if (Math.Abs(_packageNumber - num) < 3)
        {
            Array.Resize(ref buff, len);
            args.SetBuffer(buff, 8, buff.Length - 8);

            args.Completed += completed;
            args.Completed += removeSubscription;
            mre.Reset();
            _connectionSocket.ReceiveAsync(args);
            mre.Wait();
        }
        Debug.WriteLine("Recv TCP package: {0}", args.Buffer.ToDebugString());
        if (args.BytesTransferred == 0)
            throw new SocketException();

        byte[] result = new byte[buff.Length - 8];
        Array.ConstrainedCopy(buff, 8, result, 0, result.Length);
        MemoryStream stream = new MemoryStream(result, false);
        return await Task.FromResult(stream);
    }

Answer 1

It is 100% issue with crossthreading. Did the same in Console app. If here

mre.Reset();
_connectionSocket.ReceiveAsync(args);
mre.Wait();

before mre.Wait() put Thread.Sleep(n), where n > 1 - everything works fine. But this is very rude solution