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POC# or Python Pipe Blocked
 

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    <p>I'm trying to simply be able to pipe the standard output of my program (written in C#) to another program (e.g. python script). My code simply writes to standard output using Console.Write(), and that works just fine when I'm not piping. The listen command just uses Console.Write() to write data from a separate Thread when it comes in from a socket that is setup.</p> <p><em>[Works - writes data to console as it is received]</em></p> <pre><code>myProgram.exe listen </code></pre> <p><em>[Does Not Work - nothing is written to console]</em></p> <pre><code>myProgram.exe listen | python filter.py </code></pre> <p>I'm not entirely sure what is going wrong, and haven't thought of a way to even troubleshoot this problem. My guess is that the problem has to do with the receiving Thread somehow blocking the standard output from piping data to another process, but I don't know how to test this. I'm looking for anyone who has an idea(s) on what the problem might actually be, or a way to further troubleshoot this. If you need code to help, I'd be willing to post snippets.</p> <p>How do I tell if the problem lies in C# or in Python?</p> <p><strong>EDIT:</strong> Note that the redirection operator (<strong>></strong>) does work though. So, <em>myProgram.exe listen > log.txt</em> does in fact write the data being written to standard out to the <em>log.txt</em> file. I've also tried following the example at <a href="http://linux.byexamples.com/archives/343/python-handle-string-from-pipelines-and-list-of-param/" rel="nofollow">http://linux.byexamples.com/archives/343/python-handle-string-from-pipelines-and-list-of-param/</a>.</p> <p><em><strong>[filter.py]</em></strong></p> <pre><code>import sys for line in sys.stdin: sys.stdout.write(line) </code></pre> <p><strong>EDIT:</strong> Console feedback</p> <p>I figured this is worth mentioning. The python script is getting called, but after waiting for 30 seconds (it should start outputting to standard out right away) I press <em>Ctrl + C</em> to stop the process and get the following.</p> <pre> >> myProgram.exe listen | python filter.py Traceback (most recent call last): File "filter.py", line 2, in for line in sys.stdin: KeyboardInterrupt ^C </pre> <p><strong>EDIT: @Aaronaught</strong></p> <pre><code>using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading; namespace echo { class Program { static void Main(string[] args) { if (args.Length &gt; 0) { foreach (string arg in args) { Console.Out.WriteLine(arg); } } else { Thread thread = new Thread(new ThreadStart(Receive)); thread.Start(); thread.Join(); } } static void Receive() { for (int i = 0; i &lt; 10; i++) { Console.Out.WriteLine(i); } } } } </code></pre>
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    1. USblastthisinferno
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    1. COYou should try to narrow down the problem; for starters, write a simple C# program that does nothing but write to the standard output stream. If that works, then set breakpoints in your existing program to see if it's ever actually reaching the console methods.
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      1. USAaronaught
    2. COI made a very simple program to test two things. 1. That echoing passed arguments will work. 2. That the separate thread writing to standard out wasn't an issue. I then piped it to filter.py, and both worked. I'll post the simple program I used as an edit. The issue with setting breakpoints is that I cannot figure out a way to debug the program with piping in VS 2008.
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    3. COYou should do a thread.Join() after you start the worker thread so it can complete its work before the program exits.
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      1. USDarryl Braaten
 

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