Question

The following program throws an error on “Console.ReadKey()”.

How do I re-enable the console after disabling it?

    using System;
    using System.Threading;
    using System.Runtime.InteropServices;

    namespace ConsoleApplication
    {
        class Program
        {
            static void Main(string[] args)
            {
                ThreadPool.QueueUserWorkItem((o) =>
                {
                    Thread.Sleep(1000);
                    IntPtr stdin = GetStdHandle(StdHandle.Stdin);
                    CloseHandle(stdin);
                });
                Console.ReadLine();
                Console.Write("ReadLine() successfully aborted by background thread.\n");
                Console.Write("[any key to exit]");
                Console.ReadKey(); // Throws an exception "Cannot read keys when either application does not have a console or when console input has been redirected from a file. Try Console.Read."
            }

            // P/Invoke:
            private enum StdHandle { Stdin = -10, Stdout = -11, Stderr = -12 };
            [DllImport("kernel32.dll")]
            private static extern IntPtr GetStdHandle(StdHandle std);
            [DllImport("kernel32.dll")]
            private static extern bool CloseHandle(IntPtr hdl);
        }
    }

Extra for Experts

If you’re wondering, I need to be able to kill a background thread running ReadLine(), within C#. This appears to be the only way (thread.Abort won’t work because ReadLine() runs deep within the bowels of the operating system, in unmanaged code). There is a lot of talk on this topic on StackOverflow, nobody has really discovered (or posted) a satisfactory method of aborting Console.ReadLine() yet. I think this code is on the right track – if only we can re-enable the console after disabling it.

Answer 1

Don’t know if it helps, but when I’ve needed to be able to write to the console in a win form app, I’ve used this class:

public class ConsoleHelper
{
    /// <summary>
    /// Allocates a new console for current process.
    /// </summary>
    [DllImport("kernel32.dll")]
    public static extern Boolean AllocConsole();

    /// <summary>
    /// Frees the console.
    /// </summary>
    [DllImport("kernel32.dll")]
    public static extern Boolean FreeConsole();
}

Call AllocConsole to create a console and then you can write to (and read from) it. Then call FreeConsole when you’re done.