Threading Question - New to Thread !!!

[msnews.microsoft.com]

Hi All,

I have the following code. If the MessageBox.Show statement is enabled then
the "GetDataTableThread" is being started or else its state remains as
unstarted.

What should I do to start the GetDataTableThread Thread and make sure it is
started?

Any suggestions please?

Thanks for your time

Regards
Anand Ganesh

//////// Code Starts //////////////

this.richTextBoxMessage.Text = "" ;
Thread GetDataTableThread = new Thread(new
ThreadStart(InvokeGetDataTableThread)) ;
GetDataTableThread.Start() ;
//MessageBox.Show("This is main Thread!");
while(!GetDataTableThread.IsAlive) ;
this.richTextBoxMessage.Text = this.richTextBoxMessage.Text + "\n" + "Main
Thread State = " + Thread.CurrentThread.ThreadState.ToString() ;
this.richTextBoxMessage.Text = this.richTextBoxMessage.Text + "\n" +
"GetDataTableThread State = " + GetDataTableThread.ThreadState.ToString() ;
GetDataTableThread.Abort() ;
this.richTextBoxMessage.Text = this.richTextBoxMessage.Text + "\n" + "Thread
aborted!" ;
GetDataTableThread.Join() ;

//////// Code Ends //////////////

 

[Pete Davis]

You probably want to replace this:

while(!GetDataTableThread.IsAlive) ;

with:

while(!GetDataTableThread.IsAlive)
{
Thread.Sleep(50);
}

Otherwise your main thread is going to hog the CPU, and that may be keeping
the other thread from getting started. Just a possibility.

Pete

or something.

 

[Jon Skeet [C# MVP]]

I have the following code. If the MessageBox.Show statement is enabled then
the "GetDataTableThread" is being started or else its state remains as
unstarted.

What should I do to start the GetDataTableThread Thread and make sure it is
started?

For one thing, get rid of your tight loop (the while loop). Tight loops
are never a good idea.

 

[msnews.microsoft.com]

Hi Pete / Jon,

Thanks a lot for sparing your time to help me out.

I added a sleep(1000) without the while loop and it works as expected.

The Child Thread is always getting started.

Now in the same code I am getting another difficulty which is not clear for
me.

GetDataTableThread.Join() ;

This line is throwing an exception which I am not able to understand.

Does it mean I should not call Join at all?

Is it enough if I simply abort the thread?

Can you please explain what this exception means?

Thanks
Anand Ganesh

 

[msnews.microsoft.com]

Hi Pete / Jon,

Thanks a lot for sparing your time to help me out.

I added a sleep(1000) without the while loop and it works as expected.

The Child Thread is always getting started.

Now in the same code I am getting another difficulty which is not clear for
me.

GetDataTableThread.Join() ;

This line is throwing an exception which I am not able to understand.

Does it mean I should not call Join at all?

Is it enough if I simply abort the thread?

Can you please explain what this exception means?

Thanks
Anand Ganesh

For one thing, get rid of your tight loop (the while loop). Tight loops
are never a good idea.

 

[msnews.microsoft.com]

Hi All,

Actually I am getting the following Exception

"Object reference not set to an instance of an object."

Is it beacuse the GetDataTableThread was aborted this is causing the error?

I am actaully following a Micrsoft Sample. Here is the link

http://msdn.microsoft.com/library/d...y/en-us/csref/html/vcwlkThreadingTutorial.asp

Here you can see how the oThread.Join() is called after oThread.Abort().

Is it possible there is a typo in the Sample? Should it be Thread.Join() ?

Can someone please explain?

Thanks for your time.

Regards
Anand Ganesh

Hi Pete / Jon,

Thanks a lot for sparing your time to help me out.

I added a sleep(1000) without the while loop and it works as expected.

The Child Thread is always getting started.

Now in the same code I am getting another difficulty which is not clear
for
me.

GetDataTableThread.Join() ;

This line is throwing an exception which I am not able to understand.

Does it mean I should not call Join at all?

Is it enough if I simply abort the thread?

Can you please explain what this exception means?

Thanks
Anand Ganesh

For one thing, get rid of your tight loop (the while loop). Tight loops
are never a good idea.

 

[Jon Skeet [C# MVP]]

Actually I am getting the following Exception

"Object reference not set to an instance of an object."

Is it beacuse the GetDataTableThread was aborted this is causing the error?

I am actaully following a Micrsoft Sample. Here is the link

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/csre
f/html/vcwlkThreadingTutorial.asp

Here you can see how the oThread.Join() is called after oThread.Abort().

Are you sure the exception is happening in that thread, and not in
GetDataTableThread?

Could you post a short but complete program which demonstrates the
problem?

See http://www.pobox.com/~skeet/csharp/complete.html for details of
what I mean by that.

Is it possible there is a typo in the Sample? Should it be Thread.Join() ?

No - Thread.Join isn't a static method.

 

[msnews.microsoft.com]

Hi Jon,

I created a simple program and I am back to the same initial problem.
The child Thread is not at all starting. Any suggestions Please?


//////////// Sample Starts ////////////////////

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.Threading ;
namespace ThreadTest

{
/// <summary>
/// Summary description for Form1.
/// </summary>
public class Form1 : System.Windows.Forms.Form
{
private System.Windows.Forms.Button button1;
private System.Windows.Forms.Label label1;
private System.Windows.Forms.Label label2;
/// <summary>
/// Required designer variable.
/// </summary>
private System.ComponentModel.Container components = null;

public Form1()
{
//
// Required for Windows Form Designer support
//
InitializeComponent();
//
// TODO: Add any constructor code after InitializeComponent call
//
}

/// <summary>
/// Clean up any resources being used.
/// </summary>
protected override void Dispose( bool disposing )
{
if( disposing )
{
if (components != null)
{
components.Dispose();
}
}
base.Dispose( disposing );
}

#region Windows Form Designer generated code

/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.button1 = new System.Windows.Forms.Button();
this.label1 = new System.Windows.Forms.Label();
this.label2 = new System.Windows.Forms.Label();
this.SuspendLayout();
//
// button1
//
this.button1.Location = new System.Drawing.Point(224, 16);
this.button1.Name = "button1";
this.button1.Size = new System.Drawing.Size(216, 23);
this.button1.TabIndex = 0;
this.button1.Text = "Click button to start the Child Thread";
this.button1.Click += new System.EventHandler(this.button1_Click);
//
// label1
//
this.label1.Location = new System.Drawing.Point(24, 56);
this.label1.Name = "label1";
this.label1.Size = new System.Drawing.Size(624, 23);
this.label1.TabIndex = 1;
this.label1.Text = "label1";
//
// label2
//
this.label2.Location = new System.Drawing.Point(24, 104);
this.label2.Name = "label2";
this.label2.Size = new System.Drawing.Size(624, 23);
this.label2.TabIndex = 2;
this.label2.Text = "label2";
//
// Form1
//
this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
this.ClientSize = new System.Drawing.Size(672, 149);
this.Controls.Add(this.label2);
this.Controls.Add(this.label1);
this.Controls.Add(this.button1);
this.Name = "Form1";
this.Text = "Form1";
this.ResumeLayout(false);
}
#endregion
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]

static void Main()
{
Application.Run(new Form1());
}
private void button1_Click(object sender, System.EventArgs e)
{
try
{
this.label1.Text = "" ;
Thread GetDataTableThread = new Thread(new
ThreadStart(InvokeGetDataTableThread)) ;
GetDataTableThread.Start() ;
Thread.Sleep(1000) ;
this.label1.Text = "This is main Thread is going to Sleep !";
this.label1.Refresh() ;
//MessageBox.Show("ok") ;
GetDataTableThread.Abort() ;
this.label1.Text = this.label1.Text + "Again going to Sleep !";
this.label1.Refresh() ;
Thread.Sleep(1000) ;
GetDataTableThread.Join() ;
}

catch(Exception ex)
{
MessageBox.Show(ex.ToString()," Error in function DisplayDataValues") ;
}
}


void InvokeGetDataTableThread()
{
this.label2.Text = "Control is in the Child Thread !" ;
this.label2.Refresh() ;
}
}
}

//////////// Sample Ends ////////////////////


Thanks for your time.

Regards
Anand Ganesh

 

[Jon Skeet [C# MVP]]

I created a simple program and I am back to the same initial problem.
The child Thread is not at all starting. Any suggestions Please?

I haven't tried the code, because I can see one problem immediately -
you're changing the UI from within a non-UI thread, which is a big "no-
no" in Windows Forms.

See http://www.pobox.com/~skeet/csharp/threads/winforms.shtml

 

[msnews.microsoft.com]

Thanks Jon,

I think at this point let me tell my core problem and I hope you can provide
a solution.

I have a windows form which displays a DataTable but it will only show first
500 records.

There is a button called "Complete List". If the user clicks it, it will
fetch all the records. But if the database is too big it takes a long time.

So if the user changes the mind I want him to hit another button and cancel
the record fetching process.

So to fetch the record I will be running one thread and when the user clicks
on the cancel button I want to abort that thread.

So I guess my design was wrong or I cannot do this with threads in the
Windows Form.

Can you please suggest something to resolve this problem?

Thanks for being so kind and spending time in resolving my issue.

Regards
Anand Ganesh

 

[Jon Skeet [C# MVP]]

I think at this point let me tell my core problem and I hope you can provide
a solution.

I have a windows form which displays a DataTable but it will only show first
500 records.

There is a button called "Complete List". If the user clicks it, it will
fetch all the records. But if the database is too big it takes a long time.

So if the user changes the mind I want him to hit another button and cancel
the record fetching process.

So to fetch the record I will be running one thread and when the user clicks
on the cancel button I want to abort that thread.

I wouldn't use Abort myself - I'm pretty much against calling
Thread.Abort, as it can leave threads in unexpected states.

So I guess my design was wrong or I cannot do this with threads in the
Windows Form.

Can you please suggest something to resolve this problem?

Thanks for being so kind and spending time in resolving my issue.

I suggest you do the database access in another thread, periodically
polling a flag to see whether or not the action has been cancelled by
the user. You also then use the techniques described in the link in my
previous post to make sure you only change the UI in the UI thread.

 

[msnews.microsoft.com]

Hi Jon,

I wouldn't use Abort myself - I'm pretty much against calling
Thread.Abort, as it can leave threads in unexpected states.

What is the right way to cancel the Thread, If I don't use Abort? For
example in my case the user wants to cancel the data fetch?

Thanks
Anand Ganesh

 

[Jon Skeet [C# MVP]]

What is the right way to cancel the Thread, If I don't use Abort? For
example in my case the user wants to cancel the data fetch?

As I said, periodically test a flag and just stop fetching if the flag
indicates that the user has cancelled the operation.

Now, if you're using DataAdapter.Fill, there is indeed a problem - you
need a way of exiting during that call. One way you *could* do this,
although it's not very nice, is to add a row handler to the DataTable
which will be fired every time a row is added. Within that handler, you
could test the flag and then throw an exception (nasty, i know) if the
flag is set. It's a shame MS don't provide (as far as I know, anyway) a
way of cancelling a call to DataAdapter.Fill.

 

[msnews.microsoft.com]

Hi Jon,

Thanks for the help and suggestions.

Discussing with you was very good.

Also your article on Threading was good.

Even though you claim you are not master in this subject but I look you as
the MASTER.

Thanks again and happy holidays.

Regards
Anand Ganesh

 

[Josh Ross]

You can cancel a DataAdapter.Fill by killing its SPID serverside on
another thread. Just make sure that your app is logged in as an admin,
on the sql server, and that you handle the exception from the fill.

 

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