Question

I have two functions named ChangeText() & ChangeColor(), the first function called ChangeText who will loading a large number of data into memory, it will cost a lot of time, So I run it asynchorously; the other one is called ChangeColor who will change the button’s color when data loading ok, so there is an order to run these two functions: ChangeText first and ChangeColor second. here is my code:

using System;
using System.Text;
using System.Windows;
using System.Windows.Media;
using System.Threading;
using System.IO;

namespace ThreadSynchorous
{
    public partial class Window1 : Window
    {
        public Window1()
        {
        InitializeComponent();
        asyncInvoke = new AsyncInvoke();
    }
    AsyncInvoke asyncInvoke;
    EventWaitHandle waitMeHandle = new EventWaitHandle(false,EventResetMode.ManualReset);

    private void button1_Click(object sender, RoutedEventArgs e)
    {
        ThreadPool.QueueUserWorkItem(new WaitCallback(delegate(object state)
        {
            asyncInvoke.BeginAsync(ChangeText);
        }), null);

        ThreadPool.QueueUserWorkItem(new WaitCallback(delegate(object state)
        {
            asyncInvoke.BeginAsync(ChangeColor);
        }), null);

        label1.Content += " \r\n-------------------------\r\n";
    }

    private bool ChangeText()
    {
        waitMeHandle.Reset();
        this.button1.Dispatcher.Invoke(new Func<bool>(delegate()
        {
            string filename = @"C:\EXO.txt";
            using (StreamReader sr = new StreamReader(filename, Encoding.Default))
            {
                string result;
                while ((result = sr.ReadLine()) != null)
                {
                    //here perform action
                }
            }

            label1.Dispatcher.Invoke(new Func<bool>(delegate
            {
                label1.Content += "Loading finish!(Thread.CurrentThreadName="+Thread.CurrentThread.ManagedThreadId.ToString()+") ";
                waitMeHandle.Set();
                return true;
            }));
            waitMeHandle.Set();
            return true;
        }));
        waitMeHandle.Set();
        return true;
    }

    private bool ChangeColor()
    {
        waitMeHandle.WaitOne();
        this.button1.Dispatcher.Invoke(new Func<bool>(delegate()
        {
            this.button1.Background = Brushes.Red;

            label1.Dispatcher.Invoke(new Func<bool>(delegate()
            {
                label1.Content += "Coloring finish!(Thread.CurrentThreadName="+Thread.CurrentThread.ManagedThreadId+") ";
                return true;
            }));

            return true;
        }));
        return true;
    }
}
}

here is the class of AsyncInvoke:

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

namespace ThreadSynchorous
{
    public  class AsyncInvoke
    {
        public void BeginAsync(Func<bool> MyFunction)
        {
            Func<bool> func = new Func<bool>(MyFunction);
            IAsyncResult iar = func.BeginInvoke(new AsyncCallback(EndAsync), func);
        }

        public void EndAsync(IAsyncResult iar)
        {
            Func<bool> func = (Func<bool>)iar.AsyncState;
            func.EndInvoke(iar);
        }
    }
}

I planed to use EventWaitHandle to sync these two functions, but the result is that these two function will still running in a mess order: sometimes ChangeText() function first, sometimes ChangeColor() first. I just so confused.

And also, I use ThreadPool to start these two function, but why I got the same threadID like below:
Loading finish!(Thread.CurrentThreadName=10) Coloring finish!(Thread.CurrentThreadName=10)

I thought that the Thread.CurrentThreadName will be different because I use the threadpool!!! why? thx for your answer.

Answer 1

public partial class Window1 : Window
{
    public Window1()
    {
        InitializeComponent();
        asyncInvoke = new AsyncInvoke();
    }
    AsyncInvoke asyncInvoke;
    EventWaitHandle waitMeHandle = new EventWaitHandle(false, EventResetMode.ManualReset);

    private void button1_Click(object sender, RoutedEventArgs e)
    {
        ThreadPool.QueueUserWorkItem(new WaitCallback(delegate(object state)
        {
            asyncInvoke.BeginAsync(ChangeText);
        }), null);

        ThreadPool.QueueUserWorkItem(new WaitCallback(delegate(object state)
        {
            asyncInvoke.BeginAsync(ChangeColor);
        }), null);

        label1.Content += " \r\n-------------------------\r\n";
    }

    private bool ChangeText()
    {
        Debug.WriteLine("ChangeText");         

        //do your time-consuming operation here, controls' delegated are for UI updates only

        this.button1.Dispatcher.Invoke((Action)(()=>
        {
            Thread.Sleep(2000);
            Debug.WriteLine("Button invoker");
            //update button here


            //what was bool return type for?
            label1.Dispatcher.Invoke((Action)(() =>
            {
                label1.Content += "Loading finish!(Thread.CurrentThreadName=" + Thread.CurrentThread.ManagedThreadId.ToString() + ") ";
                waitMeHandle.Set();
            }));

        }));


        //waitMeHandle.Set(); - here's your guilty - button delegate runs asynchrounously so you had absolutely no guarantee that it's done as your app reach this line
        return true;
    }

    private bool ChangeColor()
    {
        waitMeHandle.WaitOne();
        Debug.WriteLine("ChangeColor");
        this.button1.Dispatcher.Invoke((Action)(() =>
        {
            this.button1.Background = Brushes.Red;

            label1.Dispatcher.Invoke((Action)(() =>
            {
                label1.Content += "Coloring finish!(Thread.CurrentThreadName=" + Thread.CurrentThread.ManagedThreadId + ") ";
                waitMeHandle.Reset(); //you've consumed your event here so this is the place to reset it
            }));
        }));
        return true;
    }
}

See code snippet above -it should explain you a bit. And of course, you’ve got same thread name because you dispatch label delegate to UI thread – that’s the primary reason you shouldn’t do any lengthy operations there like you did initially