void call(L listener);
  }

  /**
   * Adds a listener that will be called using the given executor when events are later {@link
   * #enqueue enqueued} and {@link #dispatch dispatched}.
   */
  public void addListener(L listener, Executor executor) {
    checkNotNull(listener, "listener");
    checkNotNull(executor, "executor");
    listeners.add(new PerListenerQueue<>(listener, executor));
  }

  /**

        for (ProjectExecutionListener listener : listeners) {
            listener.beforeProjectExecution(event);
        }
    }

    @Override
    public void beforeProjectLifecycleExecution(ProjectExecutionEvent event) throws LifecycleExecutionException {
        for (ProjectExecutionListener listener : listeners) {
            listener.beforeProjectLifecycleExecution(event);
        }
    }

                    InternalMavenSession.from(ee.getSession().getSession());
            Collection<Listener> listeners = session.getListeners();
            if (!listeners.isEmpty()) {
                Event event = new DefaultEvent(session, ee);
                for (Listener listener : listeners) {
                    listener.onEvent(event);
                }
            }
        }
    }

    @Override

    }

    @Override
    public void registerListener(@Nonnull Listener listener) {
        listeners.add(nonNull(listener));
    }

    @Override
    public void unregisterListener(@Nonnull Listener listener) {
        listeners.remove(nonNull(listener));
    }

    @Nonnull
    @Override
    public Collection<Listener> getListeners() {
        return Collections.unmodifiableCollection(listeners);

  }

  @Override
  public final State state() {
    return delegate.state();
  }

  /** @since 13.0 */
  @Override
  public final void addListener(Listener listener, Executor executor) {
    delegate.addListener(listener, executor);
  }

  /** @since 14.0 */
  @Override
  public final Throwable failureCause() {
    return delegate.failureCause();
  }

  /** @since 15.0 */

    }

    @Override
    protected Future<V> delegate() {
      return delegate;
    }

    @Override
    public void addListener(Runnable listener, Executor exec) {
      executionList.add(listener, exec);

      // When a listener is first added, we run a task that will wait for the delegate to finish,
      // and when it is done will run the listeners.
      if (hasListeners.compareAndSet(false, true)) {

    checkNotNull(unit);
    return get();
  }

  @Override
  public void addListener(Runnable runnable, Executor executor) {
    Listener listener = new Listener(runnable, executor);
    if (isDone()) {
      listener.execute();
    } else {
      listeners.add(listener);
    }
  }

  @CanIgnoreReturnValue
  protected boolean setException(Throwable throwable) {
    checkNotNull(throwable);

    compound.addListener(listener, directExecutor());
    assertThat(getDone(compound)).isEmpty();
    assertTrue(listener.wasCalled());
  }

  public void testAllAsList_emptyArray() throws Exception {
    SingleCallListener listener = new SingleCallListener();
    listener.expectCall();
    ListenableFuture<List<String>> compound = allAsList();
    compound.addListener(listener, directExecutor());

       * lets all futures share the same listener.
       *
       * We store `localFutures` inside the listener because `this.futures` might be nulled out by
       * the time the listener runs for the final future -- at which point we need to check all
       * inputs for exceptions *if* we're collecting values. If we're not, then the listener doesn't
       * need access to the futures again, so we can just pass `null`.

    /**
     * Register the given listener which will receive all events.
     *
     * @param listener the listener to register
     * @throws NullPointerException if {@code listener} is null
     */
    void registerListener(@Nonnull Listener listener);

    /**
     * Unregisters a previously registered listener.
     *
     * @param listener the listener to unregister