public void done(T event) {
        lock.lock();
        try {
            K key = event.key();
            inflightKeys.remove(key);
            if (queues.containsKey(key)) {
                addAvailableKey(key);
            }
        } finally {
            lock.unlock();
        }
    }
Marks the event as processed and releases the next event
with the same key. This unblocks waiting threads.

@param event The event that was processed.
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/runtime/EventAccumulator.java