Click test plan add a new variable with name = count and value =15

Then in the thread group Add a while controller.And two requests to this controller. In while controller in Condition type

 $(__javaScript(${count}>10)}

And a new Debug sampler to the thread group as well.

Then the above condition will execute the two reqs continously in a infinite loop if the value of count is greater than 10.

If in the while controller we put the condition equal to blank then the loop will execute continously.

If after two java reqs we put a http req with no server name defined in a while loop with conditon blank then after execution of two java reqs the http req fails and loop stops.

While controller with condition LAST-If we put the condition in while loop equal to LAST and then put few reqs in while loop controller but put a condition just before the while contoller that is bound to fail like a http req without a server name then the reqs in while loop will never be executed at all.