Argthtjtr

Is ColoredConsoleAppender thread safe?

I have a multi-threaded console application where I use the log4net.Appender.ColoredConsoleAppender to get error messages printed in the console window.

I also use the non blocking console reader that is described here: https://stackoverflow.com/a/18342182/1688642

Occasionally the application blocks and pressing the Return-key (Enter) in the console removes the deadlock. This is always followed by an error from log4net (through the ColoredConsoleAppender). I suspect that there is a deadlock between the Console.ReadLine in the console reader and the writing inside the ColoredConsoleAppender (which is not a simple Console.WriteLine).

I have looked at the source code for ColoredConsoleAppender and it was a lot more involved than I thought and I suspect it is not thread safe.

I have also read about the potential deadlock that can happen between Console.ReadLine and Console.WriteLine described here: http://blogs.microsoft.co.il/dorony/2012/09/12/consolereadkey-net-45-changes-may-deadlock-your-system/ but I have concluded that this is not the same problem.

Update 1:
The code below is an illustration, not the real code. And this code does not deadlock....

using System;

using System.IO;

using System.Reflection;

using System.Threading;

using log4net;

using log4net.Config;

...

class Program

{

    static void Main(string args)

    {

        var exeLocation = new FileInfo(Assembly.GetEntryAssembly().Location);

        var appConfig = new FileInfo(Path.Combine(exeLocation.DirectoryName, Assembly.GetEntryAssembly().GetName().Name + ".exe.config"));

        XmlConfigurator.Configure(appConfig);



        // Start two threads that writes log messages

        Thread t1 = new Thread(ThreadLoop);

        t1.Start("T1");



        Thread t2 = new Thread(ThreadLoop);

        t2.Start("T2");



        ILog log = LogManager.GetLogger("MAIN_LOG");

        Console.Write("$ ");

        while (true)

        {

            string line;

            if (Reader.TryReadLine(out line, 100))

            {

                bool handled = ParseAndExecuteCommand(line);

                if (!handled)

                {

                    Console.WriteLine("Unknown command (type 'h' to get help).");

                }

                Console.Write("$ ");

            }

            log.Info($"Info from main {Environment.TickCount}");

            Console.WriteLine($"Console.WriteLine from main {Environment.TickCount}");

        }

    }



    private static void ThreadLoop(object name)

    {

        while (true)

        {

            Thread.Sleep(1000);

            ILog log = LogManager.GetLogger("THREAD_LOG");

            log.Info($"Info from thread {name} {Environment.TickCount}");

            log.Warn($"Warning from thread {name}  {Environment.TickCount}");

            log.Error($"Error from thread  {name} {Environment.TickCount}");



            Console.WriteLine($"Console.WriteLine from thread {name} {Environment.TickCount}");

        }

    }

Below is the log4net configuration from App.config:

<?xml version="1.0" encoding="utf-8"?>

<configuration>  

  <configSections>

    <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler,log4net" />

  </configSections>

  <log4net>

    <appender name="ConsoleAppender" type="log4net.Appender.ColoredConsoleAppender">

      <mapping>

        <level value="ERROR" />

        <foreColor value="Red, HighIntensity" />

      </mapping>

      <layout type="log4net.Layout.PatternLayout">

        <conversionPattern value="%date [%thread] %-5level %logger [%property{NDC}] - %message%newline" />

      </layout>

      <threshold value="ERROR" />

    </appender>

    <root>

      <level value="INFO" />

      <appender-ref ref="ConsoleAppender" />

    </root>

  </log4net>

  <startup>

    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.6" />

  </startup>

</configuration>