StandardOutput.ReadLine Freezes

Question

5.00/5 (1 vote)

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Hi all,

I am trying to read the output from a process that I have stated, but the Readline() freezes every time it reaches the end of the stream (as marked in bold). How can I get around this? Here is my code:

Process nslookup = new Process()
{
    StartInfo = new ProcessStartInfo("nslookup")
    {
        RedirectStandardInput = true,
        RedirectStandardOutput = true,
        UseShellExecute = false
    }
};
nslookup.Start();

nslookup.StandardInput.WriteLine("set type=srv");
nslookup.StandardInput.WriteLine("_ldap._tcp.domain.local");
nslookup.StandardInput.Flush();
StringBuilder output = new StringBuilder();
while (nslookup.StandardOutput.Peek() > 0)
{
    output.AppendFormat("{0}\n", nslookup.StandardOutput.ReadLine());
}

Many thanks in advance.
Kind regards,

Posted 20-Apr-10 21:34pm

Programm3r

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2 solutions

Solution 2

Hi All,

I have modified your code to get the process output instantly and code is given below.

C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Diagnostics;

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            Process proc = new Process();
            proc.StartInfo.FileName = "test.bat";
            proc.StartInfo.UseShellExecute = false;
           proc.StartInfo.RedirectStandardOutput = true;
            proc.OutputDataReceived += proc_OutputDataReceived;
            proc.Start();
            proc.BeginOutputReadLine();
        }
    }


        void proc_OutputDataReceived(object sender, DataReceivedEventArgs e)
        {
            this.Dispatcher.Invoke((Action)(() =>
                        {
                            txtprogress.Text = txtprogress.Text + "\n" + e.Data;
                            txtprogress.ScrollToEnd();
                        }));
        }
}

Hope this will help you.

Regards,
Ponmalar P

Posted 24-Oct-13 20:35pm

Member 8532719

Updated 24-Oct-13 21:14pm

v4

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Jordy "Kaiwa" Ruiter · Accepted Answer · 2010-04-20T23:38:00

Hey there,

Deadlocks are a common issue when working with RedirectStandardInput & Output. The way to avoid this is to close the RedirectIO. In your example you already flushed it but did not close it.

As for output. Reading line by line is just a waste because ReadToEnd() will also supply the \r\n. And if you want only \n you can do a small:

C#

output = output.Replace("\r\n", "\n");

To avoid deadlocks in your script this should do the trick:

C#

Process nslookup = new Process()
{
   StartInfo = new ProcessStartInfo("nslookup")
   {
      RedirectStandardInput = true,
      RedirectStandardOutput = true,
      UseShellExecute = false,
      CreateNoWindow = true,
      WindowStyle = ProcessWindowStyle.Hidden
   }
};

nslookup.Start();
nslookup.StandardInput.WriteLine("set type=srv");
nslookup.StandardInput.WriteLine("_ldap._tcp.domain.local"); 
            
nslookup.StandardInput.Flush();
nslookup.StandardInput.Close();

string output = nslookup.StandardOutput.ReadToEnd();

nslookup.WaitForExit();
nslookup.Close();