ThreadBasedCounter.java

package counter;

import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicIntegerArray;

public class ThreadBasedCounter implements Counter {
    private AtomicIntegerArray atomicArray;
    private AtomicInteger base = new AtomicInteger();
    private int mode;

    public ThreadBasedCounter(int size) {
        int newSize = 1;
        while (newSize < size) {
            newSize = newSize << 1;
        }
        atomicArray = new AtomicIntegerArray(newSize);
        mode = newSize - 1;
    }

    @Override
    public int inc() {
        int id = (int) Thread.currentThread().getId();
        int index = id & mode;
        int fail = 0;
        while (true) {
            int currVal = atomicArray.get(index);
            if (atomicArray.compareAndSet(index, currVal, currVal + 1))
                break;
            fail++;
            currVal = base.get();
            if (base.compareAndSet(currVal, currVal + 1))
                break;
            fail++;
        }
        return fail;

    }

    @Override
    public int get() {
        int sum = base.get();
        for (int i = 0; i < mode + 1; i++) {
            sum += atomicArray.get(i);
        }
        return sum;
    }


}