The present invention adds support for concurrency to a mainstream object-oriented language. Language extensions are provided that can enable programs to be developed that can either be run in one address space, distributed across several process on a single computer, or distributed across a local-area or wide-area network, without recoding the program. Central to this aspect is the notion of a service, which can execute its own algorithmic (logical) thread. Services do not share memory or synchronize using explicit synchronization primitives. Rather, both data sharing and synchronization is accomplished via message-passing, e.g., a set of explicitly declared messages are sent between services. Messages can contain data that is shared, and the pattern of message exchange provide the necessary synchronization.