Why does the NetworkStream.ReadAsync call end the loop

Question

I have a Task that should continuously read from a Tcp stream and place the data into a ConcurrentQueue for processing. Stepping through the function I notice that the ReadAsync Call does not return.

For reference there is no data currently going across the network but I would still like to attempt to read from the stream so long as the loop is active.

Receive Loop

If I step through this loop, I make it to the _stream.ReadAsync line and then the application window pops up skipping the rest of the loop.

        private async Task ReceiveLoop()
        {
            byte[] buffer = new byte[1024];
            while (_isConnected)
            {
                if(_stream != null && _stream.CanRead)
                {
                    try
                    {
                        int bytesRead = await _stream.ReadAsync(buffer, 0, buffer.Length);
                        if (bytesRead > 0)
                        {
                            byte[] receivedData = new byte[bytesRead];
                            Buffer.BlockCopy(buffer, 0, receivedData, 0, bytesRead);
                            if(_receiveQueue != null)
                            {
                                _receiveQueue.Enqueue(receivedData);
                            }
                        }
                    }
                    catch (ObjectDisposedException ex) 
                    {
                        // Log[Error] - ex
                        _isConnected = false;
                    }
                    catch(InvalidOperationException ex)
                    {
                        //Log[Warning] - ex
                    }
                }
                // Console.WriteLine("ReceiveLoop is alive");
            }
        }

What is calling this code? Sounds like something is not awaited somewhere. Side notes: _stream != null is always true. You should break out of the loop with if (bytesRead == 0) break; which will only happen if the socket is closed. Instead of _isConnected just break; out of the loop or throw. — Charlieface
– Charlieface, Commented Sep 17 at 20:46
The answer depends on how you're calling ReceiveLoop(). It's implied it's a console app, and you're simply "falling through" to the end. There is no "standard wait state" for a console app; and since you did not mention yours ... (Try it from a Windows form or other "window" which has a built-in "loop") — Gerry Schmitz
– Gerry Schmitz, Commented Sep 17 at 20:48
Side note; this is not a great way of handling network buffering. If it is low throughout, it'll work, sure, but: it'll struggle beyond fairly basic scenarios. Also, keep in mind that TCP is a streaming protocol, not a message protocol - your receive queue needs to be considered as a whole. — Marc Gravell
– Marc Gravell, Commented Sep 17 at 22:44

Marc Gravell · Accepted Answer · 2025-09-17 22:48:14Z

3

I notice that the ReadAsync Call does not return.

That is normal and expected. ReadAsync has four expected outcomes:

either immediately or after some time (synchronous for Read, asynchronous for ReadAsync) reads some positive amount of data
it returns a non-positive result to indicate an EOF condition
it results in an exception for a non-graceful failure
in a niche zero-length read case (provided a zero-length buffer to populate), it returns zero to indicate that data is now available to be read, or an EOF - perform another read with a non-empty buffer to find out which (this scenario is somewhat OS-dependent)

If no data is available, the stream hasn't terminated, and nothing has exploded: we expect ReadAsync to simply not return (or rather: to return an incomplete awaitable).

edited Sep 17 at 22:48

answered Sep 17 at 22:39

Marc Gravell

1.1m273 gold badges2.6k silver badges3k bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Why does the NetworkStream.ReadAsync call end the loop

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related