After watching "The Looper", I could not understand how closing a loop works. What I understood is, If person A is in present as a looper, he would be sent to Past where he would wait for the victim from the present and would kill him so that he can easily dispose of the dead body in the past. Then he would return to present again.
So when a loop is being closed, the looper has to kill his own future-self. But how is it done?
EDIT: After getting a clear answer by @Dforck42 about closing a loop, my question changes a little. So when a contract with a looper comes to an end, the present looper kills his future self in present which is sent from future. Now I am trying to set up an example to clarify what I am trying to ask regarding this concept.
Suppose Abe decides to end the loop of person A in present. Then the future self of A has to be sent from future to present by future Abe. So how can the future Abe know that A should be sent to the particular past say 30yrs back, i.e. present from movies perspective? Somebody should inform the future Abe that A's loops is being closed in present. Then only future Abe can know that A should now be sent to present. But it is not shown anywhere explicitly in the movie.