[bad_user]

The dangers of mutability in the context of concurrency are well known and people would do well to read "Java Concurrency in Practice", a book that recommends for all classes to be defined as immutable (with final fields to get the JMM benefits), unless you have really good reasons for not doing it.

Not sure what threading primitives you're talking of, but it depends. In general Scala has very sane abstractions for dealing with concurrency.