SingleConsumerOnlyUnboundedMailbox is a high-performance, multiple producer—single consumer, unbounded MailboxType,
with the drawback that you can't have multiple consumers,
which rules out using it with BalancingPool (BalancingDispatcher) for instance.
Currently this queue is slower for some benchmarks than the ConcurrentLinkedQueue from JDK 8 that is used by default,
so be sure to measure the performance in your particular setting in order to determine which one to use.