G. Agha and C. Hewitt. Actors: A Conceptual Foundation for Concurrent Object-Oriented Programming. In B. Shriver and P. Wegner, editors, Research Directions in Object Oriented Programming. MIT Press, Cambridge, Ma, U.S.A., 1987.  Home/Search   Document Not in Database   Summary   Related Articles   Check

.... remark that, since programs are closed X 2 dom(T ) From the above we conclude that no well typed program deadlocks the abstract machine.2 6 Related Work Efforts to provide a framework for concurrent object oriented languages have relied on two fundamental approaches: 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 ....

....language where objects are sets of methods atomically executed (with some state carried by class parameters) 9] Moreover, in a concurrent setting, nondeterminism originates in interactions of threads on shared names. Actually, persistent objects in our abstract machine are reminescent of actors [3, 4, 9]. They may initiate communications with other objects or even to themselves (by sending messages to self ) they may create new objects either by prototyping or instantiation and propagate self channels and; they may change behavior after an incomming communication. This can be achieved by ....

G. Agha and C. Hewitt. Actors: A Conceptual Foundation for Concurrent Object-Oriented Programming. Research Directions on Object-Oriented Programming, 1981. Shiver and Wegner, editors. MIT Press. 20

....Static implementation techniques are ill equipped to handle changes in the class structure. It is thus not surprising that SELF message passing uses dynamic techniques. SELF is not the only language to dispense with classes. Other languages a in the same category are, for instance, Actors [3] and Kevo [52] 2.2 Type Systems Types play an important role in all modern high level programming languages. They give a meaning to values. Without a type, a value would be nothing more than a sequence of bits. A type system describes the typing rules of a programming language. After all, as ....

Agha, G., Hewitt, C.: Actors: A Conceptual Foundation for Concurrent Object-Oriented programming, [51], pp. 49--74.

....were disjunction allowed to appear in the head of a clause; but this case is precisely forbidden. 21 where only the connective is used in goals (but of course, each of these systems also have specific features which are not accounted for in LinLog) It leads to an actors model of computation [2, 32] where multiple independent agents perform concurrent tasks, communicating via a shared blackboard [28] or tuple space [17, 24] In [6] we propose a more refined notion of blackboard (called forum ) which exploits not only the connective , but also , in goals. It provides a notion of ....

G. Agha and C. Hewitt. Actors: a conceptual foundation for concurrent object-oriented programming. In B. Shriver and P. Wegner, editors, Research Directions in Object-Oriented Programming. MIT Press, Cambridge, Ma, U.S.A., 1987.

....basic schedulable and runnable block in the abstract machine. Threads are identi ed as bodies of template de nitions or method implementations; 4. threads cannot be suspended. With this property, our objects are very akin to actors and provide a good model for object oriented concurrent languages [4, 5]. This choice, along with the previous item, also simpli es the treatment of local bindings, introduced with new statements, and the management of environments. The abstract machine is sound, i.e. every state transition in the abstract machine can be viewed as a reduction or a congruence between ....

G. Agha and C. Hewitt. Actors: A Conceptual Foundation for Concurrent ObjectOriented Programming. Research Directions on Object-Oriented Programming, 1981. Shiver and Wegner, editors. MIT Press.

....Such OR concurrency can be nicely characterized with a sociological metaphor as modelling the internal distribution of tasks inside a complex organization; this complements the external cooperation among different entities accounted for by AND concurrency. 1 Introduction Actor languages [1] have been introduced to provide linguistic support for open systems [13] The metaphor programs as societies [16] felicitously characterizes object oriented programming as is possible in such languages: objects (i.e. actors) form a community of interacting, cooperating individuals. The purpose ....

G. Agha and C. Hewitt. Actors: a conceptual foundation for concurrent object-oriented programming. In B. Shriver and P. Wegner, editors, Research Directions in Object-Oriented Programming. MIT Press, Cambridge, Ma, U.S.A., 1987.

....primary form of communication characterizes object oriented concurrent programming: interobject communication, where separate entities exchange information, whether they be structured or not. This is the basic ingredient for object based concurrency, particularly in languages of the Actor family [2], of which LO is an offspring on the side of its logic programming branch [27] communication of such kind reduces procedure calls to exchanges of messages between objects, thus leading to a completely decentralized and truly concurrent model of computation. The computational model for LO ....

G. Agha and C. Hewitt. Actors: a conceptual foundation for concurrent object-oriented programming. In B. Shriver and P. Wegner, editors, Research Directions in Object-Oriented Programming. MIT Press, Cambridge, Ma, U.S.A., 1987.

.... never occurs (and therefore, given the impossibility of partitioning objects into separate proof processes, explicit object identifiers must be used) LO could also be viewed as providing a refinement of the knowledge structuring capabilities of the family of Actor languages (see for instance [1]) as we have shown in [5] One of the main aims of LO is that of providing a more structured notion of goal formula, suitable to represent structured objects with changeable state. In this sense, our effort is complementary with efforts such as [14, 24, 23, 26] which introduce a more structured ....

G. Agha and C. Hewitt. Actors: a conceptual foundation for concurrent object-oriented programming. In B. Shriver and P. Wegner, editors, Research Directions in Object-Oriented Programming. MIT Press, Cambridge, Ma, U.S.A., 1987.

....while hardware complexity is hidden by the visual syntax of the Vorlon programming language. Concurrency Control in Vorlon The next layer down the architecture is the concurrency control layer. In the Vorlon programming language the concurrency control mechanism chosen was the Active Object model [17, 18] with some relaxation to support increased parallel activity. Each object instantiated by method graphs at the language level logically, though for reasons of efficiency not actually, becomes an active object at run time. Under the canonical active object pattern, each object is considered as an ....

Agha, G. and C. Hewitt, Actors: A Conceptual Foundation for Concurrent Object-Oriented Programming.InResearch Directions in ObjectOriented Programming, B. Shriver and P. Wegner, Editors. 1987, MIT Press. p. 49-74.

.... and of control aspects of sequential logic programs [32] type and mode inference in logic programs [44] logical encodings of process calculi formalisms [41] declarative reconstructions of concurrent computational models, such as Linda tuple spaces [26] the Chemical Abstract Machine [9] Actors [2, 48], production systems [14] group communication of the broadcasting and multicasting kind [11] and constraint based programming [45] which have been variously interpreted in terms of a Linear Logic operational semantics based on proof search, as in [7, 5, 12, 35, 46] This flowering of ....

G. Agha and C. Hewitt. Actors: a conceptual foundation for concurrent object-oriented programming. In B. Shriver and P. Wegner, editors, Research Directions in Object-Oriented Programming. MIT Press, Cambridge, Ma, U.S.A., 1987.

....concurrent and distributed. One of the earliest formalisms for concurrent object based programming is based on the actor formalism proposed by Hewitt [21] Hewitt s model uses messagepassing between actors to represent control structures such as request reply and recursion; see also [2] 3] and [4]. The message passing metaphor treats objects as autonomous entities that synchronise and exchange information with one another only by explicitly sending messages. This view has been considered equivalent to stating that each object encapsulates some local state that may be accessed only by ....

Agha, G.A. and C. Hewitt (1987) Actors: A Conceptual Foundation for Concurrent Object-Oriented Programming, in B. Shriver and P. Wegner (eds) Research Directions in Object-Oriented Programming, The MIT Press, Cambridge, MA, pp. 49-74.

....languages. In fact, an object oriented program is already conceived in terms of autonomous objects which could be executed in parallel. However, the classical notion of object is too vague to support large scale concurrency because it limits the amount of parallelism available. The actor model [3, 4] satisfies the double requirements of high level programming and efficiency. Actors combine object oriented and functional programming to make it easier to use the concurrency. Briefly, the actor model can be described as follows: ffl the universe contains computational agents, called actors# ....

Agha, G., Hewitt, A. (1988). Actors: A Conceptual Foundation for Concurrent Object-Oriented Program ming. Research Directions in Object-OrientedProgramming, MIT Press, Cambridge, MA, pp.49-74.

.... to overcoming the design barrier involves mapping the domain analysis directly to a concurrent solution, where each object in the problem specification becomes a concurrent (or active) object in the design (and implementation) For example, the Actor model proposed by Hewitt and defined by Agha [AGHA90, AGHA89, AGHA87, AGHA87a, AGHA86] could be assumed, and a parallel programming environment, such as Regis, MAGE93] could provide a target environment. 61 Unfortunately, an approach such as this can result in excessive concurrency. Generally, as the number of tasks in a solution increases, the amount of overhead associated with ....

G. Agha and C. Hewitt, "Actors: A Conceptual Foundation for Concurrent Object Oriented Programming," in Research Directions in Object Oriented Programming, The MIT Press, Cambridge, Mass., 1987.

....loops that describe the behaviour of the Producer and Consumer. They can be started by way of the asynchronous message send mechanism. However, once again, there is no object corresponding to the Producer or Consumer abstractions. 6. 3 Actors The Actor model [Agha, 1986a, Agha, 1986b, Agha, 1988, Agha and Hewitt, 1987] consists of a set of actors communicating with each other. An actor consists of a mail address and a behaviour. An actor may send communications to any actor it has a mail address for. Communications sent to an actor are buffered in its mailbox, thus providing asynchronous communication. ....

Gul Agha and Carl Hewitt. Actors: A conceptual foundation for concurrent object-oriented programming. In B. Shriver and P. Wegner, editors, Research Directions in Object-Oriented Programming, pages 49--74. The MIT Press, Cambridge, Massachusetts. U. S. A, 1987.

....schedulable and runnable block in the abstract machine. Threads are identified as bodies of template definitions or method implementations; 4. threads cannot be suspended. With this property, our objects are very akin to actors and provide a good model for object oriented concurrent languages [4, 5]. This choice, along with the previous item, also simplifies the treatment of local bindings, introduced with new statements, and the management of environments. The abstract machine is sound, i.e. every state transition in the abstract machine can be viewed as a reduction or a congruence ....

G. Agha and C. Hewitt. Actors: A Conceptual Foundation for Concurrent ObjectOriented Programming. Research Directions on Object-Oriented Programming, 1981. Shiver and Wegner, editors. MIT Press.

....a single distinguished object which is always the last argument to a curried method application, and a visual programming interface providing During the course of this work, Lee Braine was supported by an EPSRC research studentship and a CASE award from Andersen Consulting. the Actor model [AH87] of object identity based on behaviours rather than mutable state. FP is supported through features such as complete (staticallydetermined) type safety, higher order methods, lazy evaluation, curried partial applications, polymorphism and referential transparency. This paper presents the key ....

G. Agha and C. Hewitt. Actors: A Conceptual Foundation for Concurrent Object-Oriented Programming. In B. Shriver and P. Wegner, editors, Research Directions in Object-Oriented Programming, pages 47-- 74, MIT Press, 1986.

....in the comfort of your own workstation. Section 6 discusses some of the basic implementation issues and how they affected the current design. The references ( 7] 8] 6] 21] 10] 29] 11] 38] 28] 17] 19] 22] 27] 30] 1] 18] 40] 43] 39] 3] 4] 5] 50] [2], 53] 52] and [16] constitute a reasonably comprehensive literature of various designs and implementations of parallel object oriented languages. The design of pSather proceeded from several basic considerations. The parallel constructs had to be a natural extension of existing Sather and ....

....the small window between the time the first monitor is released and the second monitor is acquired, losing the original order in the pipeline. The above pipelining can be modeled in the following way: lock monvect[0] then step(0) lock monvect[1] then unlock monvect[0] step(1) lock monvect[2]; unlock monvect[1] step(2) end; end; end; Since one lock is released only AFTER the next one has been acquired, there is no danger of losing the initial sequencing of operations. Other paradigms When locking and signals are put together as monitors , new functionalities become ....

Gul Agha and Carl Hewitt. Actors: A conceptual foundation for concurrent object-oriented programming. In Bruce Shriver and Peter Wegner, editors, Research Directions in ObjectOriented Programming. The MIT Press, Cambridge, Massachusetts, 1987.

....in their common class. In other words, classes serve as templates from which objects can be created. Each created (instantiated) object is an instance of that class. Objects may be either active or passive. An active object is one that encompasses its own thread of control, for example, Actors [Agha,87] or Unix processes, whereas a passive object 42 does not. Active objects can exhibit some behaviour without being operated on by another object, as opposed to passive objects which only undergo states changes when requested by others. In fact Wegner [Wegner,90] further splits the first kind of ....

....with a letter P for a process, a 160 rectangle with a letter A for an activity, an oval shape with a letter R for a resource, and a line for a link. Process It is, in our case, best represented by the concept of the object oriented programming languages such as Simula [Pooley,87] Actors [Agha,87] and in operating systems such as Unix . In these environments objects are not only abstraction of data and methods that access the object private data, but provides further enhancements of the paradigm by allowing objects to behave like lightweight processes. These characteristics capture ....

[Article contains additional citation context not shown here]

Agha, G. and Hewitt, C., "Actors: A Conceptual Foundation for Concurrent Object-Oriented Programming," in Research Directions in Object-Oriented Programming, Shriver, B. and Wegner, P., eds., MIT Press, pp. 49-74, (1987).

....object has a thread that receives and services incoming requests. In this case, a thread is not a first class object and is only associated with an object in the system. There is no way for a programmer to directly manipulate a thread. This is the approach taken by the actor class of languages ([4], 3] For example, in ABCL [231] and POOL2 (Parallel Object Oriented Language [8] when an object is created, it also becomes active 4 As we are preparing for a description of pSather in the next sections, we will try to rephrase ideas in our own terminology when appropriate. 16 with a thread ....

Gul Agha and Carl Hewitt. Actors: A conceptual foundation for concurrent object-oriented programming. In Bruce Shriver and Peter Wegner, editors, Research Directions in ObjectOriented Programming. The MIT Press, Cambridge, Massachusetts, 1987.

....basic schedulable and runnable block in the abstract machine. Threads are identi ed as bodies of template de nitions or method implementations; 4. threads cannot be suspended. With this property, our objects are very akin to actors and provide a good model for object oriented concurrent languages [2, 3]. This choice, along with the previous item, also simpli es the treatment of local bindings, introduced with new statements, and the management of environments. 5 Comparison with Uniform TyCO We have seen that from the programming point of view the use of non uniform types, as opposed to the ....

G. Agha and C. Hewitt. Actors: A Conceptual Foundation for Concurrent Object-Oriented Programming. Research Directions on Object-Oriented Programming, 1981. MIT Press.

....basic schedulable and runnable block in the abstract machine. Threads are identi ed as bodies of template de nitions or method implementations; 4. threads cannot be suspended. With this property, our objects are very akin to actors and provide a good model for object oriented concurrent languages [2, 3]. This choice, along with the previous item, also simpli es the treatment of local bindings, introduced with new statements, and the management of environments. 5 Comparison with Uniform TyCO We have seen that from the programming point of view the use of non uniform types, as opposed to the ....

G. Agha and C. Hewitt. Actors: A Conceptual Foundation for Concurrent Object-Oriented Programming. Research Directions on Object-Oriented Programming, 1981. Shiver and Wegner, editors. MIT Press.

....types to variables and polymorphic types to templates variables. TyCO provides a very clean model for an object oriented language which combines the benefits of the formal framework of process calculi with the characteristics of actor systems. Actually, objects in TyCO are reminiscent of actors [1, 2] in several ways: ffl They may initiate communications with other objects or even to themselves (by sending messages to self ) ffl they may create new objects either by prototyping or instantiation and propagate self channels, and; ffl they may change behavior after an incoming communication. ....

G. Agha and C. Hewitt. Actors: A Conceptual Foundation for Concurrent Object-Oriented Programming. Research Directions on Object-Oriented Programming, 1981. Shiver and Wegner, editors. MIT Press.

....that local variables are private to each thread on only the pool of objects is shared. We make a clear distinction between (active) threads of execution and (passive) objects; and a corresponding distinction between local variables in threads and state variables of objects. In a model like actors [1], where objects are active , the distinction becomes blurred. However, in real systems there are usually many more passive objects than active threads of execution; therefore, the distinction we make is important. When several threads operate on shared data, concurrency control mechanisms are ....

Gul Agha and Carl Hewitt. Actors: A conceptual foundation for concurrent objectoriented programming. In P. Wegner and B. Shriver, editors, Research Directions in Object-Oriented Programming, pages 49--74. MIT Press, 1987.

....and especially the notion of entailment among constraints, offers a flexible and elegant tool for declaratively expressing algorithmic computations, where the real concern is not on coordinating distributed agents, but on desequentializing algorithm execution. 4. 3 Actors The Actors model [1] provides a well defined framework for specifying and reasoning about systems of concurrent communicating processes. Actors are encapsulated entities interacting with each other only via asynchronous message passing. Each actor has a unique system address, to which messages aimed at this actor are ....

G. Agha and C. Hewitt. Actors: a conceptual foundation for concurrent object-oriented programming. In B. Shriver and P. Wegner, editors, Research Directions in Object-Oriented Programming. MIT Press, Cambridge, Ma, U.S.A., 1987.

No context found.

G. Agha and C. Hewitt. Actors: A Conceptual Foundation for Concurrent Object-Oriented Programming. In B. Shriver and P. Wegner, editors, Research Directions in Object Oriented Programming. MIT Press, Cambridge, Ma, U.S.A., 1987.

No context found.

G. Agha and C. Hewitt, "Actors: A Conceptual Foundation for Concurrent Object Oriented Programming", in Research Directions in Object Oriented Programming, The MIT Press: Cambridge, MA, 1987, pp. 49-74.

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