2016-04-02 ago prefer infix operations;
2014-06-27 ago more tight Mailbox: single list is sufficient for single receiver, reverse outside critical section;
2013-07-10 ago explicit shutdown of message output thread;
2009-01-19 ago removed Ids;
2008-10-14 ago simplified synchronized variable access;
2008-10-13 ago simplified implementation using Synchronized.var;
2008-10-01 ago more robust treatment of Interrupt (cf. exn.ML);
2008-09-08 ago send: broadcast condition while locked!
2008-09-08 ago tuned Mailbox.send;
2008-09-07 ago tuned;
2008-09-07 ago send: broadcast to all waiting threads;
2008-09-04 ago proper header;
2008-09-04 ago added receive_timeout;
2008-09-04 ago Concurrent message exchange via mailbox -- with unbounded queueing.