How to make java.util.Date thread-safe

Question

As far as i know that java.util.Date is mutable, so it\'s not thread-safe if multiple threads tried to accessing and modifying it. How do we use client-side loc

Answer 1

You may use the long value (milliseconds since Epoch) instead of a Date instance. Assigning it will be an atomic operation and it would always be coherent.

But your problem maybe isn't on the Date value itself but on the whole algorithm, meaning the real answer would be based on your real problem.

Here's a example of buggy operation in a multithread context :

long time;
void add(long duration) {
   time += duration; 
}

The problem here is that you may have two additions in parallel resulting in only one effective addition, because time += duration isn't atomic (it's really time=time+duration).

Using a long instead of a mutable object isn't enough. In this case you could solve the problem by setting the function as synchronized but other cases could be more tricky.