PendingUpdater construct, great for 2-key locks

PendingUpdater.java

public class PendingUpdater<T> {
    private final Action<T> updateAction;

    private boolean pendingUpdate;

    private T value;

    public PendingUpdater(Action<T> updateAction) {
        this.updateAction = updateAction;
    }

    public void requestUpdate() {
        if (value != null) {
            updateAction.call(value);
        } else {
            pendingUpdate = true;
        }
    }

    public void setValue(T value) {
        this.value = value;
        if (pendingUpdate) {
            updateAction.call(value);
            pendingUpdate = false;
        }
    }

    public interface Action<T> {
        void call(T t);
    }
}