Question

Doing a course on concurrent programming.

As an example we have

final class Counter {

        private AtomicInteger value;

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

        public long increment() {
            int v;
            do {
                v = value.get();
            }
            while(!value.compareAndSet(v, v+1));
            return v+1;
        }
}

Why would you use compareAndSet in this case and not incrementAndGet ?

Thanks

Answer 1

Here the the implementation of AtomicInteger.incrementAndGet() method from the JDK version I have on my machine:

/**
 * Atomically increments by one the current value.
 *
 * @return the updated value
 */
public final int incrementAndGet() {
    for (;;) {
        int current = get();
        int next = current + 1;
        if (compareAndSet(current, next))
            return next;
    }
}

As you can see, the implementation is very similar to yours.

PS: Why do you compute v+1 twice?