Question

How can we use AtomicInteger for limited sequence generation say the sequence number has to be between 1 to 60. Once the sequence reaches 60 it has to start again from 1. I wrote this code though not quite sure wether this is thread safe or not?

public int getNextValue()
{
 int v;
 do
 {
   v = val.get();
   if ( v == 60)
   {
    val.set(1);
   }
 }
  while (!val.compareAndSet(v , v + 1));
   return v + 1;
  }

Answer 1

As of Java 8, you can use AtomicInteger.updateAndGet:

return val.updateAndGet(n -> (n >= 60) ? 1 : n + 1);

---

Another alternative would be to simply do…

return val.getAndIncrement() % 60;

…unless you’re concerned with exceeding the integer max-value (2147483647). If that is a concern, you could have a look at the getAndIncrement implementation:

public final int getAndIncrement() {
    for (;;) {
        int current = get();
        int next = current + 1;
        if (compareAndSet(current, next))
            return current;
    }
}

All you need to change is the int next... line to something like:

int next = (current + 1) % 60;

---

Oops. This loops through 0->59. You needed 1->60, so add one to the return-value to get the desired result.