Client and Server Synchronization Expressed in Types

Synchronization based on semaphores, monitors, or atomic actions is in general not visible through object types. Often we use unnecessary or even conflicting synchronization in clients and servers because of missing information. Process types – a kind of behavioral types – solve this problem so far only partially: Types specify synchronization required from clients, but they hide the servers’ synchronization. In this paper we propose a solution based on dynamic token management (in addition to static token management already existing in process types). This approach extends conventional object types in a straightforward way, supports subtyping under consideration of synchronization, ensures racefree programs, and still does not expose implementation details to clients.