make parallelism:p async returns a new thread pool with parallelism p
(target number of active threads in pool). If async is true, then a
FIFO scheduling is used for tasks.
See ForkJoinPool(...).Java_exception if p is less than 1t (time value
whose unit is u); see
awaitTermination(...).Java_exception if the thread is interruptedwrap obj wraps the reference obj into an option type:Some x if obj is not null;None if obj is null.unwrap obj unwraps the option obj into a bare reference:Some x is mapped to x;None is mapped to null.