*   cause if this Future has failed.
       *
       * - And this future *has* failed: This method is called only from handleException (through
       *   getOrInitSeenExceptions). handleException tried to call setException and failed, so
       *   either this Future was cancelled (which we ruled out with the isCancelled check above),

/**
 * Handler for exceptions thrown by event subscribers.
 *
 * @since 16.0
 */
public interface SubscriberExceptionHandler {
  /** Handles exceptions thrown by subscribers. */
  void handleException(Throwable exception, SubscriberExceptionContext context);

       *
       * Fortunately, exceptions rarely contain references to expensive resources.
       */

      //
      seenExceptionsLocal = newConcurrentHashSet();
      /*
       * Other handleException() callers may see this as soon as we publish it. We need to populate
       * it with the initial failure before we do, or else they may think that the initial failure
       * has never been seen before.
       */

 */
package org.apache.maven.exception;

/**
 * Transform an exception into useful end-user message.
 *
 * @since 3.0-alpha-3
 */
public interface ExceptionHandler {
    ExceptionSummary handleException(Throwable e);

    EventBus eventBus =
        new EventBus(
            new SubscriberExceptionHandler() {
              @Override
              public void handleException(Throwable exception, SubscriberExceptionContext context) {
                throw new RuntimeException();
              }
            });
    Object subscriber =
        new Object() {
          @Subscribe

    EventBus eventBus =
        new EventBus(
            new SubscriberExceptionHandler() {
              @Override
              public void handleException(Throwable exception, SubscriberExceptionContext context) {
                throw new RuntimeException();
              }
            });
    Object subscriber =
        new Object() {
          @Subscribe

                throw e;
            } catch (Exception e) {
                // other exceptions (including InvokerException but sans Exit, see above): we need to inform user
                throw handleException(context, e);
            }
        } finally {
            Thread.currentThread().setContextClassLoader(oldCL);
            System.setProperties(oldProps);
        }
    }

/**
 * Transform an exception into useful end-user message.
 */
@Named
@Singleton
public class DefaultExceptionHandler implements ExceptionHandler {
    @Override
    public ExceptionSummary handleException(Throwable exception) {
        return handle("", exception);
    }

    private ExceptionSummary handle(String message, Throwable exception) {

  void handleSubscriberException(Throwable e, SubscriberExceptionContext context) {
    checkNotNull(e);
    checkNotNull(context);
    try {
      exceptionHandler.handleException(e, context);
    } catch (Throwable e2) {
      // if the handler threw an exception... well, just log it
      logger.log(
          Level.SEVERE,

            List<MavenProject> failedProjects = new ArrayList<>();

            for (Throwable exception : result.getExceptions()) {
                ExceptionSummary summary = handler.handleException(exception);
                logSummary(context, summary, references, "");

                if (exception instanceof LifecycleExecutionException lifecycleExecutionException) {