Changeable Interfaces and Promised Messages for Concurrent Components

              Franz Puntigam and Christof Peter
    Institut für Computersprachen, Technische Universität Wien
           Argentinierstraße 8, A-1040 Vienna, Austria
             E-mail: franz@complang.tuwien.ac.at

Statically checked process types ensure that a server understands all
messages sent by (concurrent) clients, although the acceptability of
messages may change dynamically. But, as proposed so far, process types
do not ensure that servers return appropriate answers. In this paper an
extension is proposed: Servers must send promised messages (to return
results), possibly after receiving further messages. A type checker
statically ensures that promised messages cannot be involved in deadlocks
and lifelocks. The proposed type concept supports subtyping as well as
separate compilation.