@Override
    public void enqueueFirst(CoordinatorEvent event) throws RejectedExecutionException {
        accumulator.addFirst(event);
    }
Enqueues a new {{@link CoordinatorEvent}} at the front of the processor.

@param event The event.
@throws RejectedExecutionException If the event processor is closed.
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/runtime/MultiThreadedEventProcessor.java