docs: protected LoadBalancer sanitize() {
          final LoadBalancer base = this;
          return new LoadBalancer() {
              @Override
              public Mapping map(Task task, MappingWorksheet worksheet) {
                  if (Queue.isBlockedByShutdown(task)) {
                      // if we are quieting down, don't start anything new so that
                      // all executors will be eventually free.
                      return null;
                  }
                  return base.map(task, worksheet);
              }
  
              /**
               * Double-sanitization is pointless.
               */
              @Override
              protected LoadBalancer sanitize() {
                  return this;
              }
          };
      }