Question

IBM (see Source) wrote on the benefits of Java’s 1.5 java.util.concurrent class, which offers non-blocking queues.

Please explain the weaknesses/disadvantages of the NonBlockingCounter below.

public class NonblockingCounter {
    private AtomicInteger value;

    public int getValue() {
        return value.get();
    }

    public int increment() {
        int v;
        do {
            v = value.get();
        }
         while (!value.compareAndSet(v, v + 1)); // params - (actual, expected)
        return v + 1;
    }
}

Source – http://www.ibm.com/developerworks/java/library/j-jtp04186/index.html

Answer 1

The disadvantage is that it spins while trying to increment the value if there’s contention. That means it’s bad for high-contention locks.

The advantage is that it doesn’t have lock acquistion/semaphore overhead. That’s good for low-contention locks.