1.
All parallel streams use a common fork-join thread pool, and if you submit a long-running task, you effectively block all threads in the pool. Consequently, you block all other tasks that are using parallel streams.
2.
The default processing that occurs in such a Stream uses the ForkJoinPool.commonPool(), a Thread Pool shared by the entire application.
3.
This way we essentially force the parallel stream to have a ForkJoin as a parent thread, instead of a regular thread, so
ForkJoinPool.commonPool is not used. Hooray!
