How to implement a concurrent circular ticker (counter) in Java?

Question

I want to implement a circular counter in Java. The counter on each request should increment (atomically) and on reaching an upper limit should roll over to 0.

What would be the best way to implement this and are there any existing implementations?

Answer 1

It is easy to implement such a counter atop AtomicInteger:

public class CyclicCounter {

    private final int maxVal;
    private final AtomicInteger ai = new AtomicInteger(0);

    public CyclicCounter(int maxVal) {
        this.maxVal = maxVal;
    }

    public int cyclicallyIncrementAndGet() {
        int curVal, newVal;
        do {
          curVal = this.ai.get();
          newVal = (curVal + 1) % this.maxVal;
        } while (!this.ai.compareAndSet(curVal, newVal));
        return newVal;
    }

}