public class CounterService {

    // Channel stack must include COUNTER protocol.
    public CounterService (JChannel ch) { ... }
    public SyncCounter getOrCreateSyncCounter (String name, long initial_value) { ... }
    public CompletionStage<AsyncCounter> getOrCreateAsyncCounter (String name, long initial_value) { ... }
    public void deleteCounter (String name) { ... }
    ...
}

public interface SyncCounter extends BaseCounter {

    long get ();
    void set (long new_value);

    long addAndGet (long delta);
    long incrementAndGet ();
    long decrementAndGet ();

    long compareAndSwap (long expect, long update);
    boolean compareAndSet (long expect, long update);

    // Useful for complex updates under high contention.
    <T extends Streamable> T update (CounterFunction<T> updateFunction);
}

public interface AsyncCounter extends BaseCounter {

    CompletionStage<Long> get ();
    CompletionStage<Void> set (long new_value);

    ...
}