Thanks! Maybe we should also consider setting the maximum size to 64 (but at least number of processors) by default. (It's the default parallelism number for Kotlin's IO scheduler.)

Hi! I like the idea of having sane default limit to number of threads in pool.
I've tried to implement it. I've set default value to small value like4 and launched unit-tests.
I've started gettingRejectedExecutionException, which is not I wanted.
RejectedExecutionException had happen due to usage ofSynchronousQueue.
I've tried to use unboundedLinkedBlockingQueue, but with unbounded queue the onlycorePoolSize make sense.
Basically the meaning ofThreadPoolExecutor withcorePoolSize=X and unboundedLinkedBlockingQueue is an executor service which at maximum can runX tasks in parallel.
This is whatForkJoinPool does naturally, so I've decided to rather switch to it and only provide configuration to override maximum degree of parallelism.
There is one drawback is thatForkJoinPool allow changing keep alive thread timeout only on the very recent API level. I think this is acceptable for now to use default, while having sane limit to number of threads.

@mstyura Oh sorry, I didn't mean for you to implement this. With "we" I meant the ObjectBox team. But thanks for the investigation!