private void schedulePendingSync(ClassicGroup group) {
        timer.schedule(
            classicGroupSyncKey(group.groupId()),
            group.rebalanceTimeoutMs(),
            TimeUnit.MILLISECONDS,
            false,
            () -> expirePendingSync(group.groupId(), group.generationId()));
    }
Wait for sync requests for the group.

@param group The group.
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/GroupMetadataManager.java