### Events with Retries and Follow-Ups

OkHttp is resilient and can automatically recover from some connectivity failures. In this case, the `connectFailed()` event is not terminal and not followed by `callFailed()`. Event listeners will receive multiple events of the same type when retries are attempted.

                WitnessNotificationListener listener = listeners.get(entry.getKey());
                if (listener != null) {
                    try {
                        listener.onWitnessNotification(notification);
                    } catch (Exception e) {
                        log.error("Error in witness notification listener", e);
                    }
                }
            }

FIELD com.google.common.collect.TreeTraverser.PreOrderIterator.stack
FIELD com.google.common.util.concurrent.AbstractFuture.Listener.executor com.google.common.util.concurrent.MoreExecutors.rejectionPropagatingExecutor.$
FIELD com.google.common.util.concurrent.AbstractService.listeners
# NonReentrantExecutor is not exposed to this field

    super(callable);
  }

  ListenableFutureTask(Runnable runnable, @ParametricNullness V result) {
    super(runnable, result);
  }

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

  @CanIgnoreReturnValue
  @Override
  @ParametricNullness
  public V get(long timeout, TimeUnit unit)
      throws TimeoutException, InterruptedException, ExecutionException {

    exec.shutdown();
    exec.awaitTermination(100, MILLISECONDS);
  }

  /**
   * Tests that all listeners complete, even if they were added before or after the future was
   * finishing. Also acts as a concurrency test to make sure the locking is done correctly when a
   * future is finishing so that no listeners can be lost.
   */
  public void testAllListenersCompleteSuccessfully()

    assertEquals(1, listenerLatch.getCount());
    assertFalse(task.isDone());
    assertFalse(task.isCancelled());

    // Finish the task by unblocking the task latch.  Then wait for the
    // listener to be called by blocking on the listener latch.
    taskLatch.countDown();
    assertEquals(25, task.get().intValue());
    assertTrue(listenerLatch.await(5, SECONDS));
    assertTrue(task.isDone());
    assertFalse(task.isCancelled());

    for (int k = 0; k < 50; k++) {
      // For each listener we add a task that submits it to the executor directly for the blocking
      // get use case and another task that adds it as a listener to the future to exercise both
      // racing addListener calls and addListener calls completing after the future completes.
      Runnable listener = k % 2 == 0 ? collectResultsRunnable : collectResultsTimedGetRunnable;

                events.add(transferEvent);
            }
        }

        TransferListener listener = new TransferListener();
        wagonManager.getArtifact(artifact, repos, listener, false);
        assertEquals(1, listener.events.size());
    }

    @Test
    void testGetMissingJar() throws TransferFailedException, UnsupportedProtocolException, IOException {

      RunnableExecutorPair list;
      synchronized (this) {
        if (executed) {
          return;
        }
        executed = true;
        list = runnables;
        runnables = null; // allow GC to free listeners even if this stays around for a while.
      }
      while (list != null) {
        executeListener(list.runnable, list.executor);
        list = list.next;
      }
    }

import org.apache.maven.api.annotations.Experimental;
import org.apache.maven.api.annotations.Nonnull;

/**
 * Event sent by maven during various phases of the build process.
 * Such events can be listened to using {@link Listener}s objects
 * registered in the {@link Session}.
 *
 * @since 4.0.0
 */
@Experimental
public interface Event {

    /**
     * Gets the type of the event.
     *