c# - Reading from a process, StreamReader.Peek() not working as expected

Question

See the following class below, I use it to read the output from any of the processes that are added to it. At the moment I'm starting up a Jar that acts as a channel adapter between the C# application and a JMS messaging broker. The only problem is, that when reading from the StandardOutput of the process the thread blocks on the reader.Peek() call.

After some debugging I found out that this only happens if no output has been written to the StandardOutput stream of the process. I've played around a bit with the immediate window to figure out if I can find a way to determine whether the underlying stream is empty. But so far all calls to properties like Stream.CanRead or FileStream.Length throw InvalidOperationExceptions or return output that cannot be used to check for this condition.

Furthermore, I also tried using the OutputDataReceived and ErrorDataReceived events, but for some reason they never seem to fire.

So my question is; is there any way that can be used to cleanly read the output from the processes as it becomes available?

The class in which the output is read:

namespace ReparatieSysteem.Lib
{
    internal delegate void NewOutputLineEvent(Process process, int port, string line);

    class ProcessListener
    {
        private static readonly Dictionary<int, Process> processes;
        private static readonly Thread thread;

        static ProcessListener()
        {
            processes = new Dictionary<int, Process>();
            thread = new Thread(RunThread);
            thread.Start();
        }

        private static void PollProcesses()
        {
            foreach (var item in processes.Where(p => p.Value.HasExited).ToList())
            {
                processes.Remove(item.Key);
            }

            foreach (var item in processes)
            {
                SendLines(item.Value, item.Key, ReadReader(item.Value.StandardError));
                SendLines(item.Value, item.Key, ReadReader(item.Value.StandardOutput));
            }

        }

        private static void SendLines(Process process, int port, IEnumerable<String> lines)
        {
            foreach(var line in lines)
            {
                if (OnNewOutput != null)
                {
                    OnNewOutput(process, port, line);
                }
            }
        }

        private static IEnumerable<string> ReadReader(StreamReader reader)
        {
            while (reader.Peek() >= 0)
            {
                yield return reader.ReadLine();
            }
        }

        private static void RunThread()
        {
            while(true)
            {
                if (processes.Count > 0)
                {
                    PollProcesses();
                }

                Thread.Sleep(200);
            }
        }

        public static void AddProcess(int port, Process process)
        {
            processes.Add(port, process);
        }

        public static event NewOutputLineEvent OnNewOutput;
    }
}

The code that creates the process:

var procStartInfo = new ProcessStartInfo("java", 
            string.Format("-jar {0} {1} {2} {3}", JarPath, ConnectionName, _listenQueue, _listenPort))
        {
            RedirectStandardOutput = true,
            RedirectStandardError = true,
            UseShellExecute = false,
            CreateNoWindow = true
        };

        _brokerProcess = new Process { StartInfo = procStartInfo };

        _brokerProcess.Start();

        ShutdownListener.OnApplicationQuit += _brokerProcess.Kill;

        ProcessListener.AddProcess(_listenPort, _brokerProcess);

Answer 1

Seems that this is a known bug in StreamReader implementation, as suggested in this answer. The workaround in your case is to use asynchronous stream methods like StreamReader.ReadAsync or StreamReader.ReadLineAsync.