[rnadna]

There is no way to know whether a leap second will be used in the future, beyond the half-year "notice period". This can make it tricky to plan for synchronized events past the notice period. The solution, of course, is to use non-leaped time for such planning. As several have pointed out, libraries handle both times. As someone who needs to deal with both types in data processing, I can report that it's definitely not a big deal.