The use of actors with mailboxes that annoys the author is:

1. Take a message from the mailbox (that may have been queued for a long time).

2. If the mailbox still has more than N items, then throw away the message.

This is a really dumb way to approximate a fixed size mailbox, and doesn't allow for an immediate refusal.

The questionable Scala code is pulled from recently written O'Reilly book on Scala. I haven't read it myself, but it's probably not as good as "Programming in Scala" (Odersky et al), which covers Actors+Concurrency in Chapter 30.

Needless to say, Scala also has access to all the Java concurrency primitives and libraries. I believe there's a Scala STM library as well.