@Override
        public void scheduleIfAbsent(
            String key,
            long delay,
            TimeUnit unit,
            boolean retry,
            TimeoutOperation<Void, U> operation
        ) {
            if (!tasks.containsKey(key)) {
                schedule(key, delay, unit, retry, 500, operation);
            }
        }
The scheduled timers keyed by their key.
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/runtime/CoordinatorRuntime.java