How do I stop a BackgroundWorker thread?

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Hi all,

Need help to stop the BackgroundWorker thread. I am trying to stop a background worker thread. This is what I am doing:

//On stop button click (UI layer):
if (backgroundWorker.IsBusy == true && backgroundWorker.WorkerSupportsCancellation == true) 
{     
    backgroundWorker.CancelAsync(); 
} 

//On DoWork event (UI layer):
if ((backgroundWorker.CancellationPending == true)) 
{      
    e.Cancel = true; 
} 
else 
{     
    //Function which progresses the progress bar is called      
    //here with its definition in business layer  
}

Once the DoWork event is fired and my program control is in the function defined in Business layer, how do I revert back to the DoWork event to set ‘e.Cancel = true’?

Posted 14-Feb-11 20:21pm

Sam Van

Updated 14-Feb-11 20:38pm

v10

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JF2015 15-Feb-11 2:25am

Edited to add code formatting.

2 solutions

Solution 2

AlbinAbel's solution is correct, I would just change the busyFunction to make it return a bool: true if busyFunction finished normally, false if it was cancelled, so you can get the return value back from the thread function and assign the return value to e.Cancel:

In addition to this solution, I remind you that setting e.Cancel to true will not make your thread function stop. This property is usefull only if you handle the RunWorkerCompleted event. Here you may check whether your thread function finished completely, or was canceled, or was terminated due to an unhandled exception.

Posted 14-Feb-11 22:16pm

Olivier Levrey

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Albin Abel · Accepted Answer · 2011-02-14T21:04:00

I am having an example here. say in this example MyBusyObject class has the business logic.

Follow the example. Ask me if any doubt arises

In the business logic code (in class files)...

C#

public interface IObservable
{
    void notify();
}
public interface IObserver
{
    void executeMessage(bool isStop);
}

public class MyBusyObject:IObserver
{
    int dummyValue;
    public bool isStop;
    public void busyFunction()
    {
        for(int i=0;i<1000000;i++){
            System.Threading.Thread.Sleep(1000);
            if (isStop == true) {
                //just for testing purpose
                System.Windows.Forms.MessageBox.Show("Loop stoped at " + i.ToString());
                //use return null if the function returns or whatever you may need to do
                break;
            }
            dummyValue = i;
        }
     }
    public void executeMessage(bool isStop)
    {
        this.isStop = isStop;
    }
}

In the form code...

C#

public partial class Form1 : Form,IObservable
{

    private IList<IObserver> myObservers = new List<IObserver>();
    public Form1()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        backgroundWorker1.WorkerSupportsCancellation = true;
        backgroundWorker1.RunWorkerAsync();
    }
    private void button2_Click(object sender, EventArgs e)
    {
        backgroundWorker1.CancelAsync();
        notify();
    }

    private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
    {
        MyBusyObject obj = new MyBusyObject();
        myObservers.Add(obj);
        for (int i = 0; i < 5; i++)
        {
            if ((backgroundWorker1.CancellationPending == true))
            {
                e.Cancel = true;
            }
            obj.busyFunction();
        }
    }

    public void notify()
    {
        foreach (IObserver observer in myObservers)
        {
            observer.executeMessage(true);
        }
    }


}

Button1 is for start and button2 for stop. I am calling the busyfunction from 5 objects and stopping it by pressing the button2

Once your busy function returned, background worker stops thread automatically