Class Promise

future-java/src/main/java/io/trane/future/Promise.java:26–864

Promise is a Future that provides methods to set its result. They are useful to interact with callback-based APIs like the ones that are typically provided by network libraries. A promise can be created and returned synchronously to the caller, but its completion is deferred until the value is set,

 *          the type of the asynchronous computation result
 */
public abstract class Promise<T> implements Future<T> {

  private static final long STATE_OFFSET = Unsafe.objectFieldOffset(Promise.class, "state");
  private static final Logger LOGGER = Logger.getLogger(Promise.class.getName());

  /**
   * Creates a promise that triggers the provided handlers in case it receives
   * an interrupt.
   * 
   * @param handlers  the list of handlers to be triggered.
   * @return          the new promise instance.
   */
  public static final <T> Promise<T> apply(final List<? extends InterruptHandler> handlers) {
    final Optional<?>[] savedContext = Local.save();
    if (savedContext.length == 0)
      return new Promise<T>() {
        @Override
        protected final Optional<?>[] getSavedContext() {
          return Local.EMPTY;
        }

        @Override
        protected final InterruptHandler getInterruptHandler() {
          return InterruptHandler.apply(handlers);
        }
      };
    else
      return new Promise<T>() {
        @Override
        protected final Optional<?>[] getSavedContext() {
          return savedContext;
        }

        @Override
        protected final InterruptHandler getInterruptHandler() {
          return InterruptHandler.apply(handlers);
        }
      };
  }

  /**
   * Creates a promise that triggers the provided handler in case it receives an
   * interrupt.
   * 
   * @param handler  the handler to be triggered.
   * @return         the new promise instance.
   */
  public static final <T> Promise<T> apply(final InterruptHandler handler) {
    final Optional<?>[] savedContext = Local.save();
    if (savedContext.length == 0)
      return new Promise<T>() {
        @Override
        protected final Optional<?>[] getSavedContext() {
          return Local.EMPTY;
        }

        @Override
        protected final InterruptHandler getInterruptHandler() {