BeginReceive / BeginRead timeouts

Question

I'm using a NetworkStream & TcpClient to asynchronously receive data using BeginRead. I need to apply a time-out to this operation, such that after a specified amount of time the read will be aborted.

As far as I'm able to tell, this isn't supported on NetworkStream or TcpClient - there is a ReceiveTimeout property, but this appears to only apply to the synchronous equivalent - 'Read'.

Even the underlying Socket class doesn't appear to support timeouts in its BeginReceive method.

I've searched on this issue and the only suggested resolution I've seen is to set up another background thread to cancel the operation if it doesn't complete within the timeout period. This seems like a horrible hack. Surely there is a better way?

Answer 1

It's the only way to do it, because when you're using an asynchronous operation, the thread that initiated the operation is off doing something else. The timeout is available with the synchronous version because the execution thread is blocked until the Read operation completes.

If you would have to use a background thread to cancel the operation, though, there wouldn't be much point to continuing to use the asynchronous Begin/End methods. If you're going to spin off a background thread, just perform a synchronous Read operation from the background thread, and then you can use the ReceiveTimeout.

Answer 2

Wait on ManualResetEvent with some timeout value to signal when your task is finished. If it times out before it is signaled, then you know that asynchronous operation never completed.

private ManualResetEvent receiveDone = new ManualResetEvent(false);

receiveDone.Reset();
socket.BeginReceive(...);
if(!receiveDone.WaitOne(new TimeSpan(0, 0, 0, 30))) //wait for 30 sec.
    throw new SocketException((int)SocketError.TimedOut);

Inside BeginReceive callback, use

private void ReceiveCallBack(IAsyncResult ar)
{
    /** Use ar to check if receive is correct and complete */
    receiveDone.Set();
}