Protection and Synchronization in Actor Systems

Abstract

This paper presents a unified method [called ENCASING] for dealing with the closely related issues of synchronization and protection in actor systems [Hewitt et al. 1973a, 1973b, 1974a; Greif and Hewitt 1975]. Actors are a semantic concept in which no active process is ever allowed to treat anything as an object. Instead a polite request must be extended to accomplish what the activator [process] desires. Actors enable us to define effective and efficient protection schemes. Vulnerable actors can be protected before being passed out by ENCASING their behavior in a guardian which applies appropriate checks before invoking the protected actor. Protected actors can be freely passed out since they work only for actors which have the authority to use them where authority can be decided by an arbitrary procedure. Synchronization can be viewed as a [time-variant] kind of protection in which access is only allowed to the encased actor when it is safe to do so.