Infrequent hangs in a multi-threaded C# console ap

Question

I have written a console application that makes use of console.write and console.writeline to provide some logging. The application is a server application that uses asynchronous beginacceptconnection() and beginread() ( Sockets ) for communication. Occasionally i get reports of it hanging and from the limited debug i can do i am able to see the problem being Console.Writeline() or Console.write().

Being multi-threaded I have been careful to have a lock around the logging class so only one thread can log a message at once.....when I've caught a hang all i get are threads blocking on the lock and VS reporting that the control has passed into Console.Write and it is waiting for it to come back....it never does.

A couple of days ago i got another report of a failure but this time during bootup....where no asynch connections have yet been kicked off( the main thread does spawn a thread to bootup though ) and I was sent a picture.....see below.( i added the begin and end critical section lines to prevent this and it did not )

// Logging Class

public class Logging
{
    // Lock to make the logging class thread safe.
    static readonly object _locker = new object();

    public delegate void msgHandlerWriteLineDelegate(string msg, Color col);
    public static event msgHandlerWriteLineDelegate themsgHandlerWriteLineDelegate;

    public delegate void msgHandlerWriteDelegate(string msg, Color col);
    public static event msgHandlerWriteDelegate themsgHandlerWriteDelegate;

    public static void Write(string a, Color Col)
    {
        if (themsgHandlerWriteDelegate != null)
        {
            lock (_locker)
            {
                themsgHandlerWriteDelegate(a, Col);
            }
        }
    }

    public static void Write(string a)
    {
        if (themsgHandlerWriteDelegate != null)
        {
            lock (_locker)
            {
                themsgHandlerWriteDelegate(a, Color.Black);
            }
        }
    }

    public static void WriteLine(string a, Color Col)
    {
        if (themsgHandlerWriteLineDelegate != null)
        {
            lock (_locker)
            {
                themsgHandlerWriteLineDelegate(a, Col);
            }
        }
    }

    public static void WriteLine(string a)
    {
        if (themsgHandlerWriteLineDelegate != null)
        {
            lock (_locker)
            {
                themsgHandlerWriteLineDelegate(a, Color.Black);
            }
        }
    }

    // Console Methods That implement the delegates in my logging class.

    public static void ConsoleWriteLine(string message, Color Col)
    {
        try
        {
            if (Col == Color.Black)
            {
                Console.ForegroundColor = ConsoleColor.Gray;
            }
            else
            {
                Console.ForegroundColor = (ConsoleColor)Enum.Parse(typeof(ConsoleColor), Col.Name);
            }
            Thread.BeginCriticalRegion();
            Console.WriteLine(message);
            Thread.EndCriticalRegion();
            Console.ForegroundColor = ConsoleColor.Gray;
        }
        catch (ThreadAbortException ex)
        {
            Console.WriteLine("ThreadAbortException : " + ex.Message);
        }
        catch (Exception ex)
        {
            Console.WriteLine("Exception : " + ex.Message);
        }
    }

    public static void ConsoleWrite(string message, Color Col)
    {
        try
        {
            if (Col == Color.Black)
            {
                Console.ForegroundColor = ConsoleColor.Gray;
            }
            else
            {
                Console.ForegroundColor = (ConsoleColor)Enum.Parse(typeof(ConsoleColor), Col.Name);
            }
            Thread.BeginCriticalRegion();
            Console.Write(message);//**THIS IS WHERE IS HANGS...IT NEVER RETURNS **
            Thread.EndCriticalRegion();
            Console.ForegroundColor = ConsoleColor.Gray;
        }
        catch (ThreadAbortException ex)
        {
            Console.WriteLine("ThreadAbortException : " + ex.Message);
        }
        catch (Exception ex)
        {
            Console.WriteLine("Exception : " + ex.Message);
        }
    }

    public static void ConsoleUpdate(string message)
    {
        try
        {
            Thread.BeginCriticalRegion();
            Console.WriteLine(message);//**THIS IS WHERE IS HANGS...IT NEVER RETURNS **
            Thread.EndCriticalRegion();
        }
        catch (ThreadAbortException ex)
        {
            Console.WriteLine("ThreadAbortException : " + ex.Message);
        }
        catch (Exception ex)
        {
            Console.WriteLine("Exception : " + ex.Message);
        }
    }

    // The main method...subscribes to delegates and spawns a thread to boot HW..main thread then exits.

    public static void Main()
    {
        Logging.themsgHandlerWriteDelegate += new Logging.msgHandlerWriteDelegate(ConsoleWrite);
        Logging.themsgHandlerWriteLineDelegate += new Logging.msgHandlerWriteLineDelegate(ConsoleWriteLine);
        Logging.themsgHandlerUpdateDelegate += new Logging.msgHandlerUpdateDelegate(ConsoleUpdate);
    }
}

public class ClassOnOtherThread
{
    // In a different class running on a different thread the following line occasionly invokes the error:

    private void BootHw(string Resource, string Resource2)
    {
        Logging.Write("\t\t[");
    }
}

My reading of the MSDN suggests Console.WriteLine and Console.Write are threadsafe and therefore i don't actually need a lock around it....i also can't believe it Microsoft's code is wrong(;-) and so I am guessing it is some interaction my code is doing which creates the error.

Now my question : Should i be doing anything to prevent Console.WriteLine and Console.Write being interrupted?...it is my guess that something it interrupting it...but i don't really know that!!

Any help would me very much appreciated.

Regards,

Gordon.

Answer 1

You should solve your problem by removing the locks around the logging. The logging is done via Console.WriteLine which is synchronized (and thread safe). You are possibly causing a deadlock through your own locking mechanism (though I can't verify without seeing the code).

Answer 2

I guess your application is started by another process which does redirect stderr and stdout. If your "watcher" process uses ReadToEnd() for both streams on the same thread you can deadlock.

Another option to deadlock is to send the child process input via stdin which in turn starts another process which has a console which waits for input indefinitely. This happend once to me with wmic.exe which does block when stdin is redirected.

If you have played with your log class I suspect that you change the underlying Stream of Console.Out with your own one. Please post at least the callstack where your application is hanging so we have something to analyze. There are many ways to shoot yourself in the foot if you replace the console stream with your own one.

Yours, Alois Kraus

Answer 3

I had the same problem.

I was using console.readkey() in main thread to prevent closing application in debug mode.

After I replaced it with an infinite loop my problem was solved.

Answer 4

This is a bit of a long shot, but I wonder if you are calling Console.WriteLine with objects whose ToString() method takes a lock. If so, you can get yourself in a deadlock situation with respect to the lock taken internally by Console.WriteLine.

I once posted this bug report to Microsoft Connect, though sadly they declined to fix it.

Answer 5

Consol.Writeline() is thread-safe. So

I have been careful to have a lock around the logging class

This should not be necessary and could very well be the casue of deadlocks. Without any code samples it's impossible to say if/how/what.

and so I am guessing it is some interaction my code is doing which creates the error.

Quite likely.

it is my guess that something it interrupting it..

No.