How to check if Thread finished execution

For a thread you have the myThread.IsAlive property. It is false if the thread method returned or the thread was aborted.

Use the Thread.IsAlive flag. This is to give the thread status.

You could fire an event from your thread when it finishes and subscribe to that.

Alternatively you can call Thread.Join() without any arguments:

Blocks the calling thread until a thread terminates, while continuing to perform standard COM and SendMessage pumping.

Thread.Join(1) will:

Blocks the calling thread until a thread terminates or the specified time elapses, while continuing to perform standard COM and SendMessage pumping.

In this case the specified time is 1 millisecond.

If you don't want to block the current thread by waiting/checking for the other running thread completion, you can implement callback method like this.

Action onCompleted = () => 
{  
    //On complete action
};

var thread = new Thread(
  () =>
  {
    try
    {
      // Do your work
    }
    finally
    {
      onCompleted();
    }
  });
thread.Start();

If you are dealing with controls that doesn't support cross-thread operation, then you have to invoke the callback method

this.Invoke(onCompleted);