Thread scheduling [modified] - C# Discussion Boards

20-Sep-09 16:58

Hi,

Please help me on the thread scheduling problem described below.

The method Play() plays a sound file using WMPLib and
the method DoSomething() does some kind of time consuming tasks (just for testing).

I wonder why the two cases below showed me different results in spite of using thread for asynchronous processing.
It's been killing me... Confused | :confused:

public void Play()
{
     player.controls.stop();
     player.currentMedia = player.newMedia(path);
     player.controls.play();
}

public void DoSomething()
{
     int z = 1;
     for(int i=0; i<1000000; i++) {
         z = i + 1000;
         z = z - 1000;
         string str = "Test String";
         str = str + " What's up?";
     }
     MessageBox.Show("Something done");
}

// Case 1: Asynchronous processing
// Signature of DoSomething --> public void DoSomething(Object state)
private void button1_Click(object sender, EventArgs e)
{
     // Get full path of sound file here.
     Play();
     ThreadPool.QueueUserWorkItem(new WaitCallback(DoSomething));
}

// Case 2: Synchronous processing
// Signature of Play --> public void Play(Object state)
private void button2_Click(object sender, EventArgs e)
{
     // Get full path of sound file here.
     ThreadPool.QueueUserWorkItem(new WaitCallback(Play));
     DoSomething();
}

Thanks in advance.
Roh

modified on Monday, September 21, 2009 10:37 PM

Dave Kreskowiak20-Sep-09 17:02

20-Sep-09 17:02

Kwonhyung Roh wrote:
showed me different results

And those would be ....??

You've got one major problem that I see. You're launching a MsgBox and touching UI controls from a non-UI thread. Both are not good ideas and can give you screwy results.

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Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007, 2008
But no longer in 2009...

Kwonhyung Roh20-Sep-09 18:15

20-Sep-09 18:15

Thanks.

In case1, it starts playing the sound file and, at the same time, starts DoSomething. And while the sound file is being played, the MessageBox shows up which means end of DoSomething. (Asynchronous)
But in case2, DoSomething starts first. After showing up the MessageBox, it starts playing the sound file. (Synchronous)

I used the MessageBox just to mark the end of DoSomething.
And codes for the method Play() were originally parts of the event handler.
(But it made no difference.)
I rewrote them as the method for convenience' sake.

Thanks again.
Roh

Dave Kreskowiak21-Sep-09 2:11

21-Sep-09 2:11

Like I said, touching a UI control (MessageBox, and the WMP) from anything other than the thread your app started on, will yield very weird results. You cannot call the Play method directly from the background worker thread. You cannot directly touch any UI control from a different thread than it was created on.

Kwonhyung Roh wrote:
I rewrote them as the method for convenience' sake

You can Invoke the Play method from the background thread, which tells the thread that Form1 is on to execute the code. Something like:

    Private Delegate Sub PlayDelegate()
.
.
.
    ' This would be inside the BackgroundWorker target.
    Form1.Invoke(New PlayDelegate(AddressOf Play))

A guide to posting questions on CodeProject[^]

Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007, 2008
But no longer in 2009...

Kwonhyung Roh21-Sep-09 17:31

21-Sep-09 17:31

Thanks.

With your help, I can go back to my original problem.
Please refer to the code snippet below.

private void button2_Click(object sender, EventArgs e)
     {
         filename = listBox1.SelectedItem.ToString();
         path = directory + "\\" + filename;


         // Play()
         player.controls.stop();
         player.currentMedia = player.newMedia(path);
         player.controls.play();


         // DoSomething()
         int z = 1;
         for(int i=0; i<1000000; i++) {
             z = i + 1000;
             z = z - 1000;
             string str = "Test String";
             str = str + " What's up?";
         }
         MessageBox.Show("Iteration Ends");
     }

This code snippet is processed in the order
1. Do for-block first (for about 4 seconds)
2. Show MessageBox
3. And then play sound.

But what I expected and wanted is the order
1. Play sound/Do for-block at the same time
2. Show MessageBox while the sound is being played

If I put another MessageBox just before the for block like

MessageBox.Show("Now Starting...");
int z = 1;
for(int i=0; i<1000000; i++) {
   // do the same as above code block
}
MessageBox.Show("Iteration Ends");

The result order (of processing) is
1. Play sound/Show the first MessageBox at the same time (maybe not exactly the same time but I felt it was Smile | :)

)
2. Do for-block (for about 4 seconds)
3. Show the second MessageBox while the sound is being played

I wanted to know where all of these differences come from.
Thanks.

Dave Kreskowiak22-Sep-09 4:30

22-Sep-09 4:30

First, 1000000 iterations will not take 4 seconds to complete. It'll complete in the blink of an eye.

Next, since you start playing the audio and then immediately block the thread with the loop, the player can't start playing the audio. The player has to do this on the UI thread, so as long as you've got the UI thread blocked doing other thing, the audio won't play. You have to move the loop code to a seperate thread.

A guide to posting questions on CodeProject[^]

Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007, 2008
But no longer in 2009...

Kwonhyung Roh22-Sep-09 16:14

Error using tao framework

22-Sep-09 16:14

Dave, I really appreciate your help.
You guide me to understand the big picture. Wink | ;)

Thanks.

billy_iii20-Sep-09 11:42

billy_iii

20-Sep-09 11:42

Hi forum...

Im trying to use the TaoFramework libraries in c# but I always get this error

Unable to load the DLL file 'freeglut.dll'. (Excepción de HRESULT: 0x8007007E)

when i call the function at this line

Glut.glutInit();

I have this code

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using Tao.FreeGlut;
using Tao.OpenGl;

...
class program
{
static int alto = 512;
static int ancho = 512;
static double imgalfaspect;

static int alto_original = alto;

static void Main(string[] args)
{
Glut.glutInit();
Glut.glutInitWindowSize(ancho, alto);
Glut.glutInitDisplayMode(Glut.GLUT_RGBA | Glut.GLUT_DOUBLE);
Glut.glutCreateWindow("test opengl");
Glut.glutDisplayFunc(display);
Glut.glutReshapeFunc(resize);%

imgalfaspect = ((double)ancho / (double)alto) * 0.5;

Glut.glutMainLoop();
}
...
}

I have added the references to my project, but i don't know what to do to fix this problem.

Thanks in advance

Henry Minute20-Sep-09 12:40

Henry Minute

20-Sep-09 12:40

You are far more likely to get an answer from their site, than here! Confused | :confused:

taoFramework.com[^].

Is Google not working where you are?

Henry Minute

Do not read medical books! You could die of a misprint. - Mark Twain
Girl: (staring) "Why do you need an icy cucumber?"
“I want to report a fraud. The government is lying to us all.”

billy_iii20-Sep-09 13:23

billy_iii

20-Sep-09 13:23

Hello Henry

Thanks for your answer...

Where i am, my google web site is working... I have been looking a lot in google, but i have could not find an answer for this.

for this reason i am here writing, because maybe you have a response for this.

thanks again

Dave Kreskowiak20-Sep-09 16:59

20-Sep-09 16:59

billy_iii wrote:
for this reason i am here writing, because maybe you have a response for this.

Henry gave you the best reponse anyone is going to come up with. Ask the people who wrote the library you're having problems with.

A guide to posting questions on CodeProject[^]

Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007, 2008
But no longer in 2009...

We will either find a way, or make one!
(\ /)
(- .-)
C(''')(''')

carlecomm29-Sep-09 1:25

carlecomm

29-Sep-09 1:25

Have you got the answer already?

You may create a WinForm aplication project,and try it again.

Corsor position

Muammar©

20-Sep-09 10:29

private void Form1_Paint(object sender, PaintEventArgs e)
{
    Graphics gfx = e.Graphics;
    gfx.DrawString("135", new Font("Freestyle Script",
    40f, FontStyle.Bold),
    new SolidBrush(Color.Red),
    new Point(20,20));

How would you know when the mouse cursor is inside a rectangle area of the above drawn text??

Abhishek Sur20-Sep-09 10:32

Abhishek Sur

20-Sep-09 10:32

well.. You need to trap mousemove to get the cursor position.

check value of EventArgs that comes along with the Event Delegate. Wink | ;)

Abhishek Sur

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Luc Pattyn20-Sep-09 11:01

Luc Pattyn

20-Sep-09 11:01

Hi,

there is a sibbling method called MeasureString, when used correctly it provides information about the size a DrawString is going to take. However there are minor deviations, there even is a CP article on that subject.

I expect most text processors (when using a proportional font) would draw only one word at a time, and store all the coordinates; so you would need MeasureString only inside a word, and visual feedback with a caret sufficiently solves inaccuracies.

BTW: the few lines of code you have shown are horrible for performance and memory, as they create new objects (Font, Brush) for every Paint, and don't Dispose of them.

Smile | :)

Luc Pattyn

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We will either find a way, or make one!
(\ /)
(- .-)
C(''')(''')

Muammar©

20-Sep-09 11:18

Thanks Luc, Actually I know about the measureString thing but wanted to hear your opinions.. And don't worry, I just posted the shortest segment I can to show my problem Laugh | :laugh:

Daniel Grunwald20-Sep-09 13:19

Daniel Grunwald

20-Sep-09 13:19

Luc Pattyn wrote:
there is a sibbling method called MeasureString, when used correctly it provides information about the size a DrawString is going to take. However there are minor deviations, there even is a CP article on that subject.

I expect most text processors (when using a proportional font) would draw only one word at a time, and store all the coordinates; so you would need MeasureString only inside a word, and visual feedback with a caret sufficiently solves inaccuracies.

The inaccuracies with MeasureString make it unusable for text processors. When selecting text, you need to be able to draw text in two parts (because the selected part has a different color) at exactly the same position (other text will start to 'jump around' if you select stuff). AFAIK this isn't possible with MeasureString+DrawString - it might work for some fonts (mostly the mono-spaced ones), but the inaccuracies will cause trouble for other fonts.
Use the Measure+Draw methods from the System.Windows.Forms.TextRenderer class instead - those work much better. You might have to specify some TextFormatFlags to keep the TextRenderer from adding padding.