How to use thread.abort()

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I am simply trying to abort thread by clicking a button to stop the process if user wanted instead of exiting the application
This is original code:

private void Abort_Click(object sender, EventArgs e)
        {
         //   thread1.Abort();
        }

        ///  Runs method 'Copy' in a new thread with passed arguments - on this way we separate it from UI thread otherwise it would freeze
        private void backgroundCopy_DoWork(object sender, System.ComponentModel.DoWorkEventArgs e )
        {

            List<object> genericlist = e.Argument as List<object>;
            Thread thread1 = new Thread(() => Copy(genericlist[0].ToString(), genericlist[1].ToString()));
            thread1.Start();
            thread1.Join(); //Waiting for thread to finish
        }

What I have tried:

I tried Abort() thread from button click event by moving thread field out of method, that way you can get access from your button click event, but it throws many errors

object sender;
     System.ComponentModel.DoWorkEventArgs e;
     List<object> genericlist = e.Argument as List<object>;
     Thread thread1 = new Thread(() => Copy(genericlist[0].ToString(), genericlist[1].ToString()));



     private void Abort_Click(object sender, EventArgs e)
     {
         thread1.Abort();
     }

     ///  Runs method 'Copy' in a new thread with passed arguments - on this way we separate it from UI thread otherwise it would freeze
     private void backgroundCopy_DoWork( )
     {


         thread1.Start();
         thread1.Join(); //Waiting for thread to finish
     }

that's what i did but i get error under e and genericlist : a field initialize can not reference a non static field, method or property.

Posted 19-Dec-19 7:14am

AskalotLearnalot

Updated 19-Dec-19 7:27am

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Richard Deeming · Accepted Answer · 2019-12-19T07:27:00

Solution 1

Aborting a thread is a very dangerous thing to do, and should be avoided at all costs.

You're using a BackgroundWorker, which already runs the work on a background thread. Starting another thread to do the work, and then freezing the initial background thread until your new thread has finished, will only decrease the performance of your code.

Forget the manual threading, and do the work in the DoWork event handler.

Set the WorkerSupportsCancellation property[^] to true. When you want to stop the worker, call the CancelAsync method[^]. Within your loop, check the CancellationPending property[^] to see if the work has been cancelled, and stop if it has.

C#

private void Abort_Click(object sender, EventArgs e)
{
    backgroundCopy.CancelAsync();
}

private void backgroundCopy_DoWork(object sender, System.ComponentModel.DoWorkEventArgs e)
{
    List<object> genericlist = e.Argument as List<object>;
    if (genriclist is null || genericlist.Count < 2) throw new ArgumentException();
    
    string source = Convert.ToString(genericlist[0]);
    string destination = Convert.ToString(genericlist[1]);
    
    // Do your work here, periodically checking the CancellationPending flag:
    if (backgroundCopy.CancellationPending)
    {
        e.Cancel = true;
        return;
    }
}

Posted 19-Dec-19 7:27am

Richard Deeming

Comments

Richard Deeming 19-Dec-19 14:06pm

Why are you defining properties in your class instead of setting the properties on the BackgroundWorker?

Remove the lines:

public bool WorkerSupportsCancellation { get; set; }
[System.ComponentModel.Browsable(false)]
public bool CancellationPending { get; }

Select the BackgroundWorker in the designer, open its properties, and find the WorkerSupportsCancellation property. Set it to true.

Remove the lines:

Thread thread1 = new Thread(() => Copy(genericlist[0].ToString(), genericlist[1].ToString()));
thread1.Start();
thread1.Join();

Either move the code from your Copy method into the backgroundCopy_DoWork method, or just call the Copy method directly, without starting another thread.

Within the code that performs the copy, periodically check the backgroundCopy.CancellationPending property and stop if it returns true.

Richard Deeming 19-Dec-19 14:20pm

Because you don't have a control called cancelButton on your form.

Remove that method; it's not needed, since you're already cancelling the work from the Abort_Click handler.

AskalotLearnalot 19-Dec-19 14:30pm

i am sorry i am still having issues after doing that.

Richard Deeming 19-Dec-19 14:52pm

So you didn't read my answer at all?

Do not use a thread.

Check the backgroundCopy.CancellationPending periodically during the copy, and stop copying if it returns true.

AskalotLearnalot 20-Dec-19 9:33am

Thank you for your time.

  private void Abort_Click(object sender, EventArgs e)
        {
            // Cancel the asynchronous operation.
            this.backgroundCopy.CancelAsync();
            // Disable the Cancel button.
            Abort.Enabled = false;
            cancel = !cancel;
        }


        ///  Runs method 'Copy' in a new thread with passed arguments - on this way we separate it from UI thread otherwise it would freeze
        private void backgroundCopy_DoWork(object sender, System.ComponentModel.DoWorkEventArgs e)
        {

            //List<object> genericlist = e.Argument as List<object>;
            //Thread thread1 = new Thread(() => Copy(genericlist[0].ToString(), genericlist[1].ToString()));
            //thread1.Start();
            //thread1.Join(); //Waiting for thread to finish
            List<object> genericlist = e.Argument as List<object>;
            if (genericlist is null || genericlist.Count < 2) throw new ArgumentException();

            string source = Convert.ToString(genericlist[0]);
            string destination = Convert.ToString(genericlist[1]);
            if (backgroundCopy.CancellationPending)
            {
                e.Cancel = true;
                return;
            }

        }

I have this but I can't figure out how to call the Copy method like its done in:
//Thread thread1 = new Thread(() => Copy(genericlist[0].ToString(), genericlist[1].ToString()));

Richard Deeming 20-Dec-19 9:36am

You can't figure out how to call a method in C#?

Copy(source, destination);

But once again, you'll need to check the backgroundCopy.CancellationPending property periodically inside your Copy method, and stop copying if it returns true.

AskalotLearnalot 20-Dec-19 9:59am

Oh I was intimidated by this line:

 //Thread thread1 = new Thread(() => Copy(genericlist[0].ToString(), genericlist[1].ToString()));

Here is what I did in the copy method but its still not aborting, I am sure i did something wrong.

 public void Copy(string sourceDirectory, string targetDirectory)
        {
            if (backgroundCopy.CancellationPending != true)
            {
              //Do code


               
            }
            else
            {
                MessageBox.Show("Progrss terminated");
                return;
            }
        }

Richard Deeming 20-Dec-19 10:00am

You need to check the flag periodically during the "Do code" part, not just once at the start.

How you do that will depend on what the "Do code" part looks like.

AskalotLearnalot 20-Dec-19 10:04am

this is Copy method:

public void Copy(string sourceDirectory, string targetDirectory)
        {
            if (backgroundCopy.CancellationPending != true)
            {


                DirectoryInfo diSource = new DirectoryInfo(sourceDirectory);
                DirectoryInfo diTarget = new DirectoryInfo(targetDirectory);
                string[] entries = null;

                try
                {
                    if (!diSource.ToString().Contains("System Volume Information") && !diSource.ToString().ToUpper().Contains("$RECYCLE.BIN"))
                    {
                        //Gets list of all files and directories (we need it for progress bar)
                        entries = GetFiles(sourceDirectory, "*").ToArray();
                    }
                }

                catch (UnauthorizedAccessException ex)
                {
                    //ok, so we are not allowed to dig into that directory. Move on.
                }
                int max = 1;
                if (entries != null && entries.Count() != 0)
                {
                    max = entries.Count();
                }
                //Using Invoke to prevent Cross thread exception
                Invoke(new Action(() => progressBar1.Maximum = max));




                Invoke(new Action(() => progressBar1.Step = 1));
                Invoke(new Action(() => progressBar1.Value = 0));



                CopyAll(diSource, diTarget, entries);
                Cursor.Current = Cursors.Default;
            }
            else
            {
                MessageBox.Show("Progrss terminated");
                return;
            }
        }

I have this CopyAll method that I think I should put the cancel checking in it:

  public void CopyAll(DirectoryInfo newsource, DirectoryInfo newtarget, string[] entries)
        {
            //if (cancel == true)
            //{

            //    return;
            //}
            Cursor.Current = Cursors.WaitCursor;
            Application.DoEvents();
            Directory.CreateDirectory(newtarget.FullName);
            //cancel = false;
            //while (cancel != true)
            //{
            // Copy each file into the new directory.

            foreach (FileInfo fi in newsource.GetFiles())
            {
                if (!fi.ToString().Contains("System Volume Information") && !fi.ToString().ToUpper().Contains("$RECYCLE.BIN"))
                {

                    Invoke(new Action(() => lblInfo.Text = "Stopped"));

                    //Using Invoke to prevent Cross thread exception
                    Invoke(new Action(() => this.lblInfo.Text = string.Format("{0}\\{1}", newsource.FullName, fi.Name)));


                    if (File.Exists(Path.Combine(newtarget.FullName, fi.Name)))
                    {
                        File.SetAttributes(Path.Combine(newtarget.FullName, fi.Name), FileAttributes.Normal);
                        File.Delete(Path.Combine(newtarget.FullName, fi.Name));
                    }
                    fi.CopyTo(Path.Combine(newtarget.FullName, fi.Name), true);
                    File.SetAttributes(Path.Combine(newtarget.FullName, fi.Name), FileAttributes.Normal);
                    Application.DoEvents();
                    var prval = Math.Min(progressBar1.Maximum, progressBar1.Value + 1);
                    Invoke(new Action(() => progressBar1.Value = prval));

                }
            }
            // Copy each subdirectory using recursion.

            foreach (DirectoryInfo diSourceSubDir in newsource.GetDirectories())
            {
                try
                {
                    if (!diSourceSubDir.ToString().Contains("System Volume Information") && !diSourceSubDir.ToString().ToUpper().Contains("$RECYCLE.BIN"))
                    {
                        DirectoryInfo ne

Richard Deeming 20-Dec-19 10:17am

Firstly, set backgroundCopy.WorkerReportsProgress to true, and use the ReportProgres method and the ProgressChanged event to update the progress bar. Then you won't need to use Invoke.

private void backgroundCopy_ProgressChanged(object sender, System.ComponentModel.ProgressChangedEventArgs e)
{
    progressBar1.Maximum = (int)e.UserState;
    progressBar1.Step = 1;
    progressBar1.Value = e.ProgressPercentage;
}

public void Copy(string sourceDirectory, string targetDirectory)
{
    DirectoryInfo diSource = new DirectoryInfo(sourceDirectory);
    if (!diSource.Exists) return;
    if (diSource.FullName.Contains("System Volume Information")) return;
    if (diSource.FullName.Contains("$RECYCLE.BIN")) return;
    
    string[] entries;
    try
    {
        entries = Directory.GetFiles(diSource.FullName, "*");
    }
    catch (UnauthorizedAccessException)
    {
        return;
    }
    
    backgroundCopy.ReportProgress(0, entries.Length);
    
    CopyAll(diSource, diTarget, entries);
    Cursor.Current = Cursors.Default;
}

Now you need to check the backgroundCopy.CancellationPending flag periodically within your CopyAll method.

Richard Deeming 20-Dec-19 10:24am

public void CopyAll(DirectoryInfo newsource, DirectoryInfo newtarget, string[] entries)
{
    Cursor.Current = Cursors.WaitCursor;
    newtarget.Create();
    
    foreach (FileInfo fi in newsource.GetFiles())
    {
        // Check whether the copy has been cancelled:
        if (backgroundCopy.CancellationPending) return;
        
        if (fi.FullName.Contains("System Volume Information")) continue;
        if (fi.FullName.Contains("$RECYCLE.BIN")) continue;
        
        // Copy the file
        ...
    }
    
    foreach (DirectoryInfo diSourceSubDir in newsource.GetDirectories())
    {
        // Check whether the copy has been cancelled:
        if (backgroundCopy.CancellationPending) return;
        
        if (diSourceSubDir.FullName.Contains("System Volume Information")) continue;
        if (diSourceSubDir.FullName.Contains("$RECYCLE.BIN")) continue;
        
        try
        {
            string entries = Directory.GetFiles(diSource.FullName, "*");
            DirectoryInfo diTargetSubDir = new DirectoryInfo(Path.Combine(newtarget.FullName, diSourceSubDir.Name));
            CopyAll(diSourceSubDir, diTargetSubDir, entries);
        }
        catch (UnauthorizedAccessException)
        {
        }
    }
}

AskalotLearnalot 20-Dec-19 10:31am

Thank you for Much more efficient code, that shows the difference in experience. Now my issue is in the copy all I only know how to check it the way I showed in previous comment with If{} else{} I don't know how to do it constantly before each file or folder get copied.

Richard Deeming 20-Dec-19 10:48am

Just put the if inside the foreach blocks. That way, it will be executed for each file and directory.

AskalotLearnalot 20-Dec-19 11:06am

Here is what i have. It does terminate the process however the message box show about 6 times then it stops. and progress stops.

  public void CopyAll(DirectoryInfo newsource, DirectoryInfo newtarget, string[] entries)
        {
            //if (cancel == true)
            //{

            //    return;
            //}
            Cursor.Current = Cursors.WaitCursor;
            Application.DoEvents();
            Directory.CreateDirectory(newtarget.FullName);
            //cancel = false;
            //while (cancel != true)
            //{
            // Copy each file into the new directory.

            foreach (FileInfo fi in newsource.GetFiles())
            {
                if (backgroundCopy.CancellationPending != true)
                {
                    if (!fi.ToString().Contains("System Volume Information") && !fi.ToString().ToUpper().Contains("$RECYCLE.BIN"))
                    {

                        Invoke(new Action(() => lblInfo.Text = "Stopped"));

                        //Using Invoke to prevent Cross thread exception
                        Invoke(new Action(() => this.lblInfo.Text = string.Format("{0}\\{1}", newsource.FullName, fi.Name)));


                        if (File.Exists(Path.Combine(newtarget.FullName, fi.Name)))
                        {
                            File.SetAttributes(Path.Combine(newtarget.FullName, fi.Name), FileAttributes.Normal);
                            File.Delete(Path.Combine(newtarget.FullName, fi.Name));
                        }
                        fi.CopyTo(Path.Combine(newtarget.FullName, fi.Name), true);
                        File.SetAttributes(Path.Combine(newtarget.FullName, fi.Name), FileAttributes.Normal);
                        Application.DoEvents();
                        var prval = Math.Min(progressBar1.Maximum, progressBar1.Value + 1);
                        Invoke(new Action(() => progressBar1.Value = prval));

                    }
                }
                else
                {
                    MessageBox.Show("Progress have been cancelled");
                    return;
                }
            }
            // Copy each subdirectory using recursion.

            foreach (DirectoryInfo diSourceSubDir in newsource.GetDirectories())
            {
                if (backgroundCopy.CancellationPending != true)
                {
                    try
                    {
                        if (!diSourceSubDir.ToString().Contains("System Volume Information") && !diSourceSubDir.ToString().ToUpper().Contains("$RECYCLE.BIN"))
                        {
                            DirectoryInfo nextTargetSubDir =
                                newtarget.CreateSubdirectory(diSourceSubDir.Name);
                            CopyAll(diSourceSubDir, nextTargetSubDir, entries);
                            var prval = Math.Min(progressBar1.Maximum, progressBar1.Value + 1);
                            Invoke(new Action(() => progressBar1.Value = prval));

                        }

                        else
                        {
                            var prval = Math.Min(progressBar1.Maximum, progressBar1.Value + 1);
                            Invoke(new Action(() => progressBar1.Value = prval));
                        }
                    }

                    catch (Exception ex) { MessageBox.Show(ex.Message); }
                }
                else
                {
                    MessageBox.Show("Progress have been cancelled");
                    return;
                }
            }

  }

AskalotLearnalot 20-Dec-19 11:11am

Also side note: As far as the new copy method You provided the progress bar for some reason stops in the middle even though the progress is done so I edited it this way:

public void Copy(string sourceDirectory, string targetDirectory)
        {
            DirectoryInfo diSource = new DirectoryInfo(sourceDirectory);
            DirectoryInfo diTarget = new DirectoryInfo(targetDirectory);
            if (!diSource.Exists) return;
            if (diSource.FullName.Contains("System Volume Information")) return;
            if (diSource.FullName.Contains("$RECYCLE.BIN")) return;

            string[] entries;
            try
            {
                entries = Directory.GetFiles(diSource.FullName, "*");
            }
            catch (UnauthorizedAccessException)
            {
                return;
            }
            int max = 1;
            if (entries != null && entries.Count() != 0)
            {
                max = entries.Count();
            }
            Invoke(new Action(() => progressBar1.Maximum = max));
            Invoke(new Action(() => progressBar1.Step = 1));
            Invoke(new Action(() => progressBar1.Value = 0));
            int percent = (int)(((double)progressBar1.Value / (double)progressBar1.Maximum) * 100);
            progressBar1.CreateGraphics().DrawString(percent.ToString() + "%", new Font("Arial", (float)8.25, FontStyle.Regular), Brushes.Black, new PointF(progressBar1.Width / 2 - 10, progressBar1.Height / 2 - 7));
            backgroundCopy.ReportProgress(0, max);

            CopyAll(diSource, diTarget, entries);
            Cursor.Current = Cursors.Default;
        }