Question

I am trying to fire a method as a result to an asynchronous read operation on a NetworkStream. The read operation is done via BeginRead and EndRead, resulting in the EndRead being called in the callback specified with BeginRead. All pretty basic stuff. Now, as the callback is done in a system generated Thread, the data read from the NetworkStream is no longer owned by my thread, that called the BeginRead. To overcome that, I wrote a method to further process the data read, which I try to call via my Thread’s dispatcher.

// These are created in my Thread
private delegate void ReceiverCallback(IPEndPoint sender, byte[] data);
private Dispatcher dispatcher = Dispatcher.CurrentDispatcher;

With the callback looking like this:

private void DataReceived(IAsyncResult result)
{
    DataReceivedStruct drs = (DataReceivedStruct)result.AsyncState;
    NetworkStream used = drs.stream;
    AutoResetEvent handle = drs.waitHandle;
    used.EndRead(result);
    DispatchRaiseReceived(readBuffer);
    handle.Set();
}

The DataReceivedStruct is a simple struct holding the NetworkStream and an AutoResetEvent.
ReadBuffer is a global private byte[] of 1024 length, as BeginRead and EndRead aren’t called in the same method.

The DispatchRaiseReceive method looks like this:

private void DispatchRaiseReceived(byte[] data)
{
    dispatcher.BeginInvoke((ReceiverCallback)RaiseReceived, socket.Client.RemoteEndPoint, data);
}

Where socket is a TcpClient object.

The disptached method looks like the following bit of code. What this does is simply pass the data along via an event for further processing.

private void RaiseReceived(IPEndPoint sender, byte[] data)
{
    if(IsEnabled){
        if (Received != null)
        {
            Received(this, new TCPDataArgs(sender, data));
        }
    }
}

The actual method that the dispatcher needs to call, is never called. Now from what I’ve been able to find on the web is that it could have something to do with the dispatcher not being created on the correct Thread, and thus it is never invoking the method on the correct Thread. However, the dispatcher is created on my Thread, so that shouldn’t apply.

Answer 1

As an attempt to fix this, I explicitly got the Dispatcher from my UI-Thread, and passed that along to the desired place I wanted to use it. This instead of trying to get it with Dispatcher.CurrentDispatcher. And what do you know, it worked. The delegate is now being called correctly.

Apparently Dispatcher.CurrentDispatcher didn’t get the correct Dispatcher I wanted it to use.