[Playground] Change logic with Cancel method.

Now server call method as a goroutine to check cancel flag.

When the Cancel() method is called the cancel flag is set to the cache as a true.

Need:

• Set false flag as a default value before calling the Process method.
• Change the logic of the cancelCheck() method. Now it checks that the flag cancel exists and after that returns from the method and stops goroutine. Need to change this logic and return from the method in case the cancel flag is true.