Akinori Yonezawa. ABCL, an Object Oriented Concurrent System. MIT Press, 1990. 22  Home/Search   Document Not in Database   Summary   Related Articles   Check

.... the concept of actors [3, 4] with the associated computational model, and; encodings of objects into Milner, Parrow and Walker s calculus or an equivalent asynchronous formulation due to Honda and Tokoro [8] Some actor languages have been implemented with some success such as the ABCL family [26, 25]. Moreover, most existing concurrent object oriented languages incorporate aspects of the actors model in their specifications. 18 In recent years researchers have devoted a lot of effort in providing semantics for objects within the asynchronous calculus [8, 24, 16, 12] variations [20, 6] and ....

Akinori Yonezawa. ABCL, an Object Oriented Concurrent System. MIT Press, 1990. 22

....in order to cope with this new requirement. And what happens if a fourth object to be coordinated appear Should the video object need to be recodified again 3 Whatever a model where the coordination algorithms express explicitly the involved objects fails in extensibility and reusability [Hol92, Luc93, Yon90] Then, what kind of requirements should the model provide for dealing with this kind of coordination algorithms without lost of expressiveness, reusability and extensibility The solution we provide relies on having the responsability of coordination these objects to be delegated transparently ....

.... that clearly cut across groups of components, increases the dependencies between these components which become less reusable because the following important observations: any model where the coordination algorithms express explicitly the involved objects fails in extensibility and reusability [Hol92, Luc93, Yon90]. any model where coordination is based exclusively on message interception fails in reusability [Cal94, Muk95, Bou93] In order to provide a common discussion forum in this regard, we suggest the following questions to be analized and discussed during the workshop: What kind of requirements ....

A. Yonezawa, editor. ABCL. An Object-Oriented Concurrent System. MIT Press, 1990.

....an important element in the achievement of the goals of applications. Many programming languages and formalisms have been proposed so far for the description of software based on communication. As programming languages, we have CSP [9] Ada [33] languages based on Actors [2] POOL [4] ABCL [39], Concurrent Smalltalk [38] or more recently Pict and other # calculus based languages [7, 27, 34, 13] As formalisms, we have CCS [19] Theoretical CSP [10] # calculus [22] and other process algebras. In another vein, we have functional programming languages augmented with communication ....

A. Yonezawa, editor. ABCL, an Object-Oriented Concurrent System. MIT Press, 1990.

....in that is not present in TyCO. TyCO provides a very clean model for an object oriented language which combines the bene ts of the formal framework of process calculi with the characteristics of actor systems. Actor languages have been implemented with some success as in the ABCL family [78, 79]. Moreover, most existing concurrent object oriented languages incorporate aspects of the actor model in their speci cations. TyCO objects are reminiscent of actors [4, 5, 34] in several ways as in response to a method invocation they may: initiate communications with other objects or even to ....

A. Yonezawa. ABCL, an Object Oriented Concurrent System. The MIT Press, 1990.

....message acceptance. An object may accept certain messages only when particular conditions (defined in terms of the values of the instance variables) are met. Amongst other things, this allows non strict or lazy data structures to be programmed if required. Unlike most actor languages, e.g. ABCL [Yone90], HAL[HoAg92] UFO has a static type system which provides type safety but with considerable flexibility. Overloading, subtyping via inheritance, and genericity are all supported. In addition, the type system provides important static protection from some of the problems associated with the ....

A. Yonezawa (ed.): ABCL, an Object-oriented Concurrent System, MIT press Computer Systems Series, 1990.

....At any moment of its execution, the actor can specify (with the become instruction) a new script which will be used for the next message. The model is suitable for concurrent programming. It allows a structuring of application data. Many languages use the actor model. The ABCL 1 language [13 14] and Act language [7,8] are extensions of actor model on distributed architectures. In this paper, we present an active structure of low level for the multicomputers programming: we call it Cac (Communicating Active Component) A Cac is an entity which includes an activity (a thread in the ....

....But the execution model of Cac must be explicitly described. 1.3. Example To illustrate the Cac model, we will now present an example of behavioral function for a binary search tree node Cac. The binary search tree is a data structure storing a key set. The tree is sorted by the nodes values [14]. The operations on the tree are: 1 store a value in the tree. The insertion searches for a leaf from the root of the tree. It then changes the node value through the inside message key and creates two void sub nodes. 2 search a value in the tree. The search starts from the root of the ....

A. Yonezawa ABCL, An Object-Oriented Concurrent System, The MIT Press, 11

....or an equivalent asynchronous formulation due to Honda and Tokoro [6] Despite extensive theoretical research on the subject, abstract machine specifications and implementations of actual models are still scarce. Some actor languages have been implemented with some success such as the ABCL family [27]. Moreover, most existing concurrent object oriented languages incorporate aspects of the actors model in their specifications. A few programming languages based on process calculi have been purposed. Some, such as Pict [22] and Oz [12] have gained some prominence. Pict [22] is a programming ....

Akinori Yonezawa. ABCL, an Object Oriented Concurrent System. MIT Press, 1990.

....programming language, in which this mapping is done by the compiler and runtime system, and is not the responsibility of the application programmer. However, the various forms of implicit parallelism explored during the 80s (functional, And Or parallel logic, concurrent object oriented etc. [1, 2, 3, 4, 5, 6]) have, by and large, made little impact on real use of parallel machines. Fortran is enjoying a resurgence. One problem has been lack of convincing demonstrations of performance. Efficient large scale implicit parallelism is hard to achieve, but the UFO project will be able to build on a ....

....incrementally adding implementation down the hierarchy is not possible. This is very restrictive and UFO has a more conventional inheritance mechanism. 1. 4 Concurrent object based languages, particularly ABCL In concurrent object based 3 languages, such as actor languages [3] POOL [5] or ABCL [4], a computation is expressed as a network of communicating objects, each of which manages its own local state. ABCL seemed the best developed of these. There are considerable similarities between UFO (stateful) objects and ABCL objects; they provide mutual exclusion on method accesses, so ensuring ....

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A. Yonezawa (ed.): ABCL, an Object-Oriented Concurrent System, MIT Press Computer Systems Series, 1990.

....[Agha 1986] are defined by a script which describes the different behaviors of the actor when a message is received.The model is suitable for concurrent programming. It allows a structuring of application data. Several languages use the actor model. The ABCL 1 language [Yonezawa et al. 1986, Yonezawa 1990] and Act language [Kafura1990] are extensions of actor model on distributed architectures. In this paper, we present an active structure of low level for the distributed programming: we call it Cac (Communicating Active Component) Courtrai et al. 1992 a, 1992 b] A Cac is an entity which ....

A. Yonezawa ABCL, An Object-Oriented Concurrent System, The MIT Press,

....message acceptance. An object may accept certain messages only when particular conditions (defined in terms of the values of the instance variables) are met. Amongst other things, this allows non strict or lazy data structures to be programmed if required. Unlike most actor languages, e.g. ABCL [Yone90], HAL[HoAg92] UFO has a static type system which provides type safety but with considerable flexibility. Overloading, subtyping via inheritance, and genericity are all supported. In addition, the type system provides important static protection from some of the problems associated with the ....

A. Yonezawa (ed.): ABCL, an Object-oriented Concurrent System, MIT press Computer Systems Series, 1990.

....(similar to the conditional statement of example 2.5(3) and class and subclass declarations. See reference [63] for details. 7.5. Semantics and Type Systems for Concurrent Languages One of the goals of this thesis is to provide for semantics and type systems for existing (e.g. ABCL [72], and POOL [4] and future concurrent object oriented programming languages. To test the calculus of objects and its typing system, I picked the language ABCL 1. Operational semantics for ABCL were given via a systematic translation of the ABCL program constructors into processes; a type system ....

Akinori Yonezawa, editor. ABCL, an Object-Oriented Concurrent System. MIT Press, 1990.

....an important element in the achievement of the goals of applications. Many programming languages and formalisms have been proposed so far for the description of software based on communication. As programming languages, we have CSP [8] Ada [29] languages based on Actors [2] POOL [4] ABCL [34], Concurrent Smalltalk [33] or more recently Pict and other calculus based languages [7, 12, 24, 30] As formalisms, we have CCS [16] Theoretical CSP [9] calculus [19] and other process algebras. In another vein, we have functional programming languages augmented with communication ....

A. Yonezawa, editor. ABCL, an Object-Oriented Concurrent System. MIT Press, 1990.

....of object oriented languages to concurrent languages by considering objects to be processes and method invocations to be messages. Multiple objects may then be active simultaneously. In order to develop a concurrent object oriented language, sometimes new languages are invented, such as ABCL [31]. Alternatively, compiler extensions can be created such as in C [4] which extends C . Another approach is to provide concurrency abstractions through libraries as in Concurrent Eiffel [12] There are benefits of each approach. Creating a new language provides the most flexibility, while ....

Akinori Yonezawa, editor. ABCL, An Object--Oriented Concurrent System. The MIT Press, Cambridge, Massachusetts, 1990.

....may only be performed by exchanging messages. As a consequence, languages supporting this model offer constructs for sending and receiving messages. Variations occur in synchronous vs. asynchronous messages and in different priorities. Well known languages supporting this model are ABCL 1 [18] and POOL T [2] Shared memory model Here, the cooperating processors may (or may not) have private memory communication is performed via a shared (or global ) memory area. Because the shared memory model comes very close to the single memory of a uniprocessor system, it is much easier to ....

Akinori Yonezawa, editor. ABCL, An Object--Oriented Concurrent System. The MIT Press, Cambridge, Mass., 1990.

....Inference : 24 3.6 Comparison With Other Type Systems : 24 1. Introduction ABCL 1 is a concurrent object oriented programming language. The language itself is part of a more general project, the compilation edited by Yonezawa [9] providing a good source of information on the ABCL project. The semantics of ABCL 1 is often given by transition systems that focus on interobject behaviour, abstracting intra object computations [4] similarly to semantics developed for the actor model of computation [1] As such, the execution ....

....of the form let X(x ) P in Q behaves as Q with occurrences of X(v ) replaced by P [v =x ] that is, by P with occurrences of names x replaced by v . 2. 3 Simple Examples This section presents examples of the encoding of some simple ABCL 1 objects taken from the book on ABCL [9]. Our first example is the greeting object on page 239, which, by expanding the notation, can be written as follows. object greeting (script ( hello reply to] reply to = hi) 1 To avoid renaming variable names in form we assume that v is the sequence of temporary variables ....

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Akinori Yonezawa, editor. ABCL, an Object-Oriented Concurrent System. The MIT Press, 1990.

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A. Yonezawa and M. Tokoro (eds.), Object oriented concurrent systems, MIT Press (1987)

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