H. Lieberman, "Concurrent Object Oriented Programming in Act 1", in Object Oriented Concurrent Programming, The MIT Press: Cambridge, MA, 1987. pp. 9-36. 69  Home/Search   Document Not in Database   Summary   Related Articles   Check

....use of shared resources, scheduling their access and providing protection and recovery boundaries. Guardians thus explicitly incorporated the notion of state. Lieberman implemented an actor language, Act1, incorporating guardians, serializers, and rock bottom actors which is best described in (Lieberman, 1987). Will Clinger (Clinger, 1981) developed a semantics of actor systems, showing the consistency of axioms proposed in (Baker and Hewitt, 1977) A key accomplishment of Clinger s work was to show that a powerdomain semantics could be developed despite the fact that the underlying domain was ....

Lieberman, H. (1987). Concurrent object-oriented programming in act-1. In Yonezawa, A.

....integration between the concept of an object and the concept of a process (more generally speaking the concept of an autonomous activity) leads to the concept of an active object. Indeed, an object and a process may both be considered as communicating encapsulated units 6 . Actor languages [Lie 87, Agh 86] are a typical example of programming languages based on the notion of an active object. A second level of integration associates synchronization to object activation, leading to the notion of a synchronized object. Message passing is then considered as an implicit synchronization ....

....[LS 83, GCL 92] 4.3 Active Objects The basic idea leading to the concept of an active object is to consider an object having its own computing resource, i.e. its own private activity. This approach, simple and natural, is quite influent [YT 87] following the way traced by actor languages [Lie 87, Agh 86] The concept of an active object is also a natural foundation for building higher level autonomous agents, for distributed knowledge based systems. The independence of object activities provides what is usually called inter object concurrency. When, for each active object, requests are ....

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H. Lieberman, "Concurrent Object-Oriented Programming in Act 1," [YT 87], pages 9--36.

....syntactical nature (cf. Fig. 5 for the transformation scheme) but as a convention, the receiver of the synchronous message must respond with sending a message with the key return. 4. 3 Complex messages It is often claimed that everything in an actor system is an actor, even messages (cf. e.g. [Lieberman, 1987]) But in common actor languages, there is a difference between user defined and explicitly created actors on the one hand and predefined and implicitly created messages on the other hand. We introduce actor definitions for complex messages that must be explicitly created. Complex messages allow ....

Lieberman, H. (1987). Concurrent object-oriented programming in Act 1. In A.Yonezawa and M.Tokoro (Eds.), Object-Oriented Concurrent Programming. Cambridge/MA: MIT Press. pp.936.

....procedure call for multi threaded systems, but can use interprocess communication in distributed systems. Most practical systems are actually hybrids, comprising elements of both the active and passive models. 2.2. 2 Active Objects In a pure active object language, such as those described in [Agh87, Lie87, Yon87b], every object is an active object. Having a process (or thread) per object is simply not practical on existing hardware or software systems since a program may construct millions of objects. Instead most active object systems take a hybrid approach (for example [Act92, Ame87a, Car90a, Ish87, ....

....systems use mechanisms described by Caromel [Car90a] as wait by necessity the caller proceeds until it needs the result of the invocation. This can be achieved implicitly, as is done in SCOOP [Mey96] and Eiffel [Car90a] or explicitly using the notion of a proxy [Lh92] or future object [Lie87]. In some systems, notably Hybrid [Nie92] and composition filters [Ber94] see Section 2.5.4) the callee can also send an early reply to the caller, which allows the caller to proceed whilst the callee continues with local housekeeping activity that is not relevant to the result of the method. ....

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Lieberman H., "Concurrent Object-Oriented Programming in Act 1", in "Object-Oriented Concurrent Programming", A. Yonezawa and M. Tokoro (Eds.), MIT Press, ISBN 0-262-24026-2, pp9-36, 1987

....procedure call for multi threaded systems, but can use interprocess communication in distributed systems. Most practical systems are actually hybrids, comprising elements of both the active and passive models. 2.2. 2 Active Objects In a pure active object language, such as those described in [Agh87, Lie87, Yon87b], every object is an active object. Having a process (or thread) per object is simply not practical on existing hardware or software systems since a program may construct millions of objects. Instead most active object systems take a hybrid approach (for example [Act92, Ame87a, Car90a, Ish87, ....

....systems use mechanisms described by Caromel [Car90a] as wait by necessity the caller proceeds until it needs the result of the invocation. This can be achieved implicitly, as is done in SCOOP [Mey96] and Eiffel [Car90a] or explicitly using the notion of a proxy [Lh92] or future object [Lie87]. In some systems, notably Hybrid [Nie92] and composition filters [Ber94] see Section 2.5.4) the callee can also send an early reply to the caller, which allows the caller to proceed whilst the callee continues with local housekeeping activity that is not relevant to the result of the method. ....

[Article contains additional citation context not shown here]

Lieberman H., "Concurrent Object-Oriented Programming in Act 1", in "Object-Oriented Concurrent Programming", A. Yonezawa and M. Tokoro (Eds.), MIT Press, ISBN 0-262-24026-2, pp9-36, 1987

....Two universal features (available on any object) provide for explicit synchronization: ffl Wait Wait until obj is no longer awaited. ffl Awaited Return TRUE if obj is awaited. This principle ( summarized in Figure 3) can be related to the future concept found in several languages: Act1 [17] and the primitive Hurry, ConcurrentSmalltalk [21] with the CBox objects, abcl 1 [22] with the future type message passing. However, the important difference is that the mechanism presented here is systematic and automatic, reflected by the absence of any special syntactical construction. This has ....

Lieberman, H. "Concurrent Object-Oriented Programming in Act 1", Object-Oriented Concurrent Computing, The MIT Press, 1987.

....Of course if there are active objects then there must also be passive objects objects without their own thread of control, but whose methods are executed in threads of control that originate from other objects. Concurrent object oriented languages exist which support purely active models [Agh87, Lie87], purely passive [Baq95, Gos96, McH94, Mit95, Str91] or a hybrid combination [Act92, Ame87, Car90a, Jal93, Kar92, Loh92, Mey96, Nie92, Yok87] 2 The pure active models were based on the notion of ACTORS [Agh86] but having a process (or thread) per object is simply not a practical on existing ....

....only coming alive when activated by a thread of control executing one of its methods. Such languages contain only passive objects but allow the creation and destruction of new threads of control. The early languages did not concern themselves with the reuse issues of synchronisation at all [Ame87, Lie87], and even today languages like Smalltalk and Java take no special steps to enable reuse of synchronisation code. But as more and more concurrent object oriented languages were proposed with various features for creating and controlling concurrent interactions, so problems with reuse began to ....

Lieberman H., "Concurrent Object-Oriented Programming in Act 1", in "Object Oriented Concurrent Programming", A. Yonezawa and M. Tokoro (Eds.), MIT Press, pp9-36, 1987

....are functional, i.e. side effect free, and untyped. Implementations of the majority of these approaches have targeted fine grain concurrency on massively parallel architectures, and many were never actually implemented on distributed machines. The earliest languages were Act [51] 63] Act1 [64], Act2 [65] Act3 [51] Sal [51] and ABCL 1 [66] A more recent contribution, with an emphasis on reflection, is MERING IV [67] 3.6.3 HAL Among pure actor languages, of particular note is the HAL language of Houck and Agha [68] which was implemented on top of the Charm programming system [69] ....

H. Lieberman, "Concurrent object-oriented programming in Act1," in ObjectOriented Concurrent Programming, A. Yonezawa and M. Tokoro, Eds., Cambridge, MA: The MIT Press, 1987, pp. 9--36.

....only source of parallelism. Furthermore, in order to compute complex, but well understood and locally determined linguistic conditions and functions, such as unification of feature structures and queries sent to a (conceptual) knowledge base, we establish a synchronous request reply protocol (cf. Lieberman, 1987). The ParseTalk model extends the formal foundations of the basic actor model according to the requirements set up by the natural language processing application. These extensions are expressible by the primitives of the basic model. We distinguish between word actors, relations between word ....

LIEBERMAN, H. (1987). Concurrent object-oriented programming in Act 1. In A. Yonezawa & M. Tokoro, Eds. Object-Oriented Concurrent Programming. pp.9-36. MIT Press.

....use of shared resources, scheduling their access and providing protection and recovery boundaries. Guardians thus explicitly incorporated the notion of state. Lieberman implemented an actor language, Act1, incorporating guardians, serializers, and rock bottom actors which is best described in (Lieberman, 1987). Will Clinger (Clinger, 1981) developed a semantics of actor systems, showing the consistency of axioms proposed in (Baker and Hewitt, 1977) A key accomplishment of Clinger s work was to show that a powerdomain semantics could be developed despite the fact that the underlying domain is ....

Lieberman, H. (1987). Concurrent object-oriented programming in act-1. In Yonezawa, A.

....in the introductory section. local computations: To compute complex, but well understood and locally determined linguistic conditions and functions, such as unification of feature structures and queries sent to a (conceptual) knowledge base, we establish a synchronous request reply protocol (cf. Lieberman (1987) for the specification of synchronous message passing in terms of asynchronous message passing for the actor language Act1) It is used for delivering an actor address to the sender of a request, in syntactic terms: actor : ask actor messageKey (actor ) Furthermore, the selection of an ....

LIEBERMAN, H. (1987). Concurrent object-oriented programming in Act 1. In A.YONEZAWA & M.

....communication and synchronization, but we must make a choice as to what style of message passing to adopt. For example, message passing may be synchronous as in POOL T [4] or buffered, as between top level objects in Hybrid [28] Similarly, wemay permit uni directional message passing as in Act 1 [20], or we may insist on a call return protocol as in Hybrid and ConcurrentSmalltalk [41] We may also find it useful to provide an express mode of message passing for interrupting active objects as in ABCL 1 [42] In either case, it is possible to accommodate the various reusability mechanisms we ....

H. Lieberman, "Concurrent Object-Oriented Programming in Act 1," in Object-Oriented Concurrent Programming, ed. A. Yonezawa, M. Tokoro, pp. 9-36, The MIT Press, Cambridge, Massachusetts, 1987.

....1. Introduction The message passing model of communication in object oriented languages appears to naturally support concurrent execution of autonomous objects. This fact has led many researchers to try to exploit this autonomy in developing concurrent object oriented languages [2] 15] [17], 22] 23] 30] 32] Various forms of active, message passing objects, and passive, lockable objects have been proposed and implemented. Unfortunately none of these approaches has yet succeeded in resolving basic conflicts between concurrency mechanisms and the encapsulation that is needed ....

H. Lieberman, "Concurrent Object-Oriented Programming in Act 1," in Object-Oriented Concurrent Programming, ed. A. Yonezawa, M. Tokoro, pp. 9-36, The MIT Press, Cambridge, Massachusetts, 1987.

....network, but this is not necessarily the case: a processor may just as well be time shared with other processors on a computer.For example a Unix task or a lightweight process may be used as processors. The difference between virtual processors and physical CPUs was clearly expressed by Lieberman [10]: The number of [processors] need not be bounded in advance, and if thereare too many [processors] for the number of real physical [CPUs] you have on your computer system, they areautomatically time shared.Thus the user can pretend that processor resources are practically infinite. ....

Henry Lieberman, "Concurrent Object-Oriented Programming in Act 1", in Object-oriented Concurrent Programming,ed. Akinori Yonezawa and Mario Tokoro, pp. 9-36, MIT Press, Cambridge (Mass.), 1987.

....of integration between the concept of an object and the concept of a process (more generally speaking the concept of an autonomous activity) leads to the concept of an active object. Indeed, an object and a process may both be considered as communicating encapsulated units 2 . Actor languages [Lieberman 1987, Agha 1986] are typical examples of programming languages based on the notion of an active object. Objects that are not active are sometimes called passive. 2. A second dimension of integration associates synchronisation with object activation, leading to the notion of a synchronised object. ....

....3.3 Active Objects The basic idea leading to the concept of an active object is to consider an object having its own computing resource, i.e. its own private activity. This approach, simple and natural, was quite influent [Yonezawa and Tokoro 1987] following the way traced by actor languages [Lieberman 1987, Agha 1986] 3.3.1 Levels of object concurrency The independence of object activities provides what is usually called inter object concurrency. Some languages such as POOL [America and van der Linden 1990] provide only this level of concurrency. In several computation models however (e.g. ....

[Article contains additional citation context not shown here]

Lieberman, H., 1987. Concurrent object-oriented programming in Act 1. In

....modules as to help at partitioning the class code among processors. Some radical approach replaces the inheritance mechanism between classes, by the concept mechanism of delegation between objects. This mechanism has actually been introduced in the Actor concurrent programming language Act 1 [Lie 87] Intuitively, an object which may not 10 As supported by Smalltalk. understand a message will then delegate it (i.e. forward it 11 ) to another object, called its proxy. The proxy will process the message in place of the initial receiver, or it can also itself delegate it further to its ....

H. Lieberman, "Concurrent Object-Oriented Programming in Act 1," [YT 87], pages 9--36.

....(acquaintances) An actor system is dynamic, since new actors can be created and the communication topology is reconfigurable. We assume actors that process a single message at a time, step by step (Hewitt Atkinson, 1979) For convenience, we establish a synchronous request reply protocol (Lieberman, 1987) to compute functions such as unification of feature structures and queries to a (conceptual) knowledge base. In contrast to simple messages which unconditionally trigger the execution of a method at the receiving actor, we define complex word actor messages as full fledged actors with ....

LIEBERMAN, H. (1987). Concurrent object-oriented programming in Act 1. In A.Yonezawa & M. Tokoro, Eds. Object-Oriented Concurrent Programming. pp.9-36. MIT Press.

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H. Lieberman, "Concurrent Object Oriented Programming in Act 1", in Object Oriented Concurrent Programming, The MIT Press: Cambridge, MA, 1987. pp. 9-36. 69

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