Event Semantics

  The general principle is to finish the execution of a rule as fast as possible. When an event is posted (synchronously or asynchronously), the blocking wait-for predicates are given higher priority than the on-event rules. If there are several threads waiting for an event, then only one of them is picked up nondeterministically to evaluate its wait-for predicate. If no such thread is eligible to continue, then the on-event rules are considered.

Messages are processed in the same way. Predicate accept corresponds to wait-for and on-arrival to on-event.