Static safety analysis for non-uniform service availability in Actors
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چکیده
Introduction The main purpose of this work is the static detection of orphan messages in actor based languages. An orphan is a message which may not be handled by its target in some execution paths. Two kinds of orphan messages may be encountered : safety ones and liveness ones. Safety orphans occur when all target behaviors on a given execution path do not know how to handle the message. Liveness orphans occur when one of the target behaviors in each execution paths knows how to handle the message but the target is deadlocked and will never assume the corresponding behavior. This paper presents a safe static analysis which detects all safety orphan messages in actor-based programs. This result extends previous work derived from sequential object-oriented languages type systems to non-uniform behaviors. Most of the type systems designed for concurrent objects rely on the uniform behavior assumption : an object is a) always able to handle requests to the same set of methods, and b) always accessible (each method can be handled any number of times). This hypothesis allows the use of type systems designed for sequential object-oriented languages (either kind-based ones as proposed by Vasconcelos and Tokoro VT93] and by Kobayashi and Yonezawa KY94], or subtype-based ones as advocated by the authors in CPS97b]). In the case of objects with non-uniform behavior (i.e. short lifetime objects or behavior changing actors), an object may be able to handle a request to one of its method at a given time and not be able to handle it at some other time. If the request cannot be handled, the associated message is called a \safety orphan". The previous type systems could only detect rather trivial safety orphan messages. The system described in this paper extends our subtype-based previous work in order to catch all potential safety orphans in actor-based programs. 1 In this purpose, a new safe type-based abstraction of an actor possible behaviors is proposed. We extend a Primitive Actor Calculus introduced in the rst section and deened in a previous paper ((CPS96, CPS97b]) in order to give a simple semantic characterisation of safety orphan messages. A sound type system based on the type abstraction is then presented. It rejects all the programs which may produce safety orphan messages. In conclusion, related works and possible extensions are discussed. Type systems for concurrent calculus have been the subject of many recent studies PS95, …
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تاریخ انتشار 1999