C# – Restarting a thread in .NET (using C#)

c++multithreading

I'm looking for a way to restart a thread that has been stopped by Abort()..

public partial class MyProgram : Form
{
  private Thread MyThread = new Thread(MyFunction);
  private System.Windows.Forms.Button startStopBtn = new System.Windows.Forms.Button();
  public MyProgram()
  {
    MyThread.Start();
    startStopBtn += new EventHandler(doStop);
    startStopBtn.Text = "Stop";
  }
  private static void MyFunction()
  {
    // do something
  }
  private void doStop(object sender, EventArgs e)
  {
    MyThread.Abort();
    startStopBtn -= new EventHandler(doStop);
    startStopBtn += new EventHandler(doStart);
    startStopBtn.Text = "Start";
  }
  private void doStart(object sender, EventArgs e)
  {
    MyThread.Start(); // << Error returned when clicking the button for 2nd time
    startStopBtn -= new EventHandler(doStart);
    startStopBtn += new EventHandler(doStop);
    startStopBtn.Text = "Stop";
  }
}

Any idea?

Best Solution

Once you have aborted your thread, you cannot start it again.

But your actual problem is that you are aborting your thread. You should never use Thread.Abort().

If your thread should be paused and continued several times, you should consider using other mechanisms (like AutoResetEvent, for example).

[EDIT]

The simplest solution to abort a thread, as mentioned by Ian Griffiths in the link above, is:

The approach I always recommend is dead simple. Have a volatile bool field that is visible both to your worker thread and your UI thread. If the user clicks cancel, set this flag. Meanwhile, on your worker thread, test the flag from time to time. If you see it get set, stop what you're doing.

The only thing that you need to do to make it work properly, is to rearrange your background method so that it runs in a loop - so that you can periodically check if your flag has been set by a different thread.

If you need to have pause and resume functionality for the same worker thread, instead of the simple volatile bool flag approach, you could go for a slightly more complex approach, a synchronizing construct such as AutoResetEvent. These classes also provide a way to put the worker thread to sleep for a specified (or indefinite) amount of time between signals from the non-worker thread.

This thread contains a concrete example with Start, Pause, Resume and Stop methods. Note how Brannon's example never aborts the thread. It only fires an event, and then waits until the thread finishes gracefully.

Related Solutions

C# – Should ‘using’ directives be inside or outside the namespace

There is actually a (subtle) difference between the two. Imagine you have the following code in File1.cs:

// File1.cs
using System;
namespace Outer.Inner
{
    class Foo
    {
        static void Bar()
        {
            double d = Math.PI;
        }
    }
}

Now imagine that someone adds another file (File2.cs) to the project that looks like this:

// File2.cs
namespace Outer
{
    class Math
    {
    }
}

The compiler searches Outer before looking at those using directives outside the namespace, so it finds Outer.Math instead of System.Math. Unfortunately (or perhaps fortunately?), Outer.Math has no PI member, so File1 is now broken.

This changes if you put the using inside your namespace declaration, as follows:

// File1b.cs
namespace Outer.Inner
{
    using System;
    class Foo
    {
        static void Bar()
        {
            double d = Math.PI;
        }
    }
}

Now the compiler searches System before searching Outer, finds System.Math, and all is well.

Some would argue that Math might be a bad name for a user-defined class, since there's already one in System; the point here is just that there is a difference, and it affects the maintainability of your code.

It's also interesting to note what happens if Foo is in namespace Outer, rather than Outer.Inner. In that case, adding Outer.Math in File2 breaks File1 regardless of where the using goes. This implies that the compiler searches the innermost enclosing namespace before it looks at any using directive.

C# – Cross-thread operation not valid: Control accessed from a thread other than the thread it was created on

As per Prerak K's update comment (since deleted):

I guess I have not presented the question properly.

Situation is this: I want to load data into a global variable based on the value of a control. I don't want to change the value of a control from the child thread. I'm not going to do it ever from a child thread.

So only accessing the value so that corresponding data can be fetched from the database.

The solution you want then should look like:

UserContrl1_LOadDataMethod()
{
    string name = "";
    if(textbox1.InvokeRequired)
    {
        textbox1.Invoke(new MethodInvoker(delegate { name = textbox1.text; }));
    }
    if(name == "MyName")
    {
        // do whatever
    }
}

Do your serious processing in the separate thread before you attempt to switch back to the control's thread. For example:

UserContrl1_LOadDataMethod()
{
    if(textbox1.text=="MyName") //<<======Now it wont give exception**
    {
        //Load data correspondin to "MyName"
        //Populate a globale variable List<string> which will be
        //bound to grid at some later stage
        if(InvokeRequired)
        {
            // after we've done all the processing, 
            this.Invoke(new MethodInvoker(delegate {
                // load the control with the appropriate data
            }));
            return;
        }
    }
}

Best Solution

Related Solutions

C# – Should ‘using’ directives be inside or outside the namespace

C# – Cross-thread operation not valid: Control accessed from a thread other than the thread it was created on

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