How to end executing method from outside?

You can use BackgroundWorker class to run time and resource consuming stuff on other thread, and use its CancelAsync method, to request (it's not immediate execution) cancelation of the other thread.

For concrete example on how to implement that, can have a look on accepted answer in this question:

How to wait for a BackgroundWorker to cancel?

First of all, you need to run the time-consuming function in a thread separate from the main thread. Otherwise the UI will stop responding.

Then you need to have a static variable or a shared instance where the UI can set a flag indicating that the time-consuming function should stop.

Finally, the time-consuming function should regular check the flag and stop processing if it is set.

The BackgroundWorker class implements this pattern and solves a few other requirements as well (such as the inter-thread communication and the progress reporting).

Lets say your time-consuming method is called MyTimeConsumingMethod.

void MyTimeConsumingMethod() { //Do stuff } 

Put globally a thread:

Thread t; 

Put in your Form_Load()

t = new Thread(new ThreadStart(MyTimeConsumingMethod)); t.Start(); 

And on button press:

t.Abort(); 

Try running it on a Background Worker.

This Gives a good example of how to use it.

Then you can call

Worker.CancelAsync(); 

when the user wants to cancel the operation

Here's an example

bool _cancel = false; private void count() { _cancel = false; new System.Threading.Thread(delegate() { for (int i = 0; i < 100000; i++) { if (_cancel) break; Console.WriteLine(i); } }).Start(); } private void button1_Click(object sender, EventArgs e) { _cancel = true; }