摘要:

AbstractTagging is the augmentation of run‐time data with some form of self‐description for type checking or storage management purposes. We have studied the contribution of automatic tagging by converting two programs written in object‐oriented languages to PL/1. We had thought that much of the apparent superiority of the object‐oriented version came from dynamic binding of operator invocations. However, of several factors contributing to program quality, automatic storage management and the availability of generic abstract data types seem equally important in the examples studied. Tags turned out to be needed for only a few data objects and are used in only a few places. When the obligatory tags are modelled in PL/1, the code becomes particular to the problem at hand and is less elegant. On the other hand, current implementations of object‐oriented languages have considerable overhead in both time and space for tags. This led us to consider combining tagged and non‐tagged objects in a sing

ISSN:0038-0644    

DOI:10.1002/spe.4380150902

出版商:John Wiley&Sons, Ltd.    

年代:1985

数据来源: WILEY

摘要:

AbstractIn this paper we shall discuss concurrency in programming languages, with a view towards designing a process‐oriented language which, by its inherent parallelism, is well suited to exploit the forthcoming generation of distributed processor networks.We shall start by discussing the traditional approach towards managing concurrency, with ‘monitors’ co‐ordinating the interactions of ‘processes’, and shall demonstrate that this approach actually degrades concurrency by imposing sequentiality during interactions because it is based on the premise of co‐ordinating secure access tosharedresources. As a tool for interprocess communication it is felt that the ‘monitor’ is too far removed from the abstract nature of the problem, and so, as a purely engineering solution, it imposes too broad and too prolonged an exclusion to be acceptable in general.Instead we turn to a simpler, and ultimately more powerful notion of ‘message passing’ between parallel processes. We shall show how, if the message system is polymorphic, any data value, however large it is, can pass freely between any pair of processes. By making the processes themselves values in the language we shall discover that message networks can come into being dynamically, and tailor themselves to their applications as and when necessary by ‘short‐circuiting’ extensive communications paths. We shall also see how, if the message system is inherently asynchronous, the degree of the parallelism in a system can be enhanced, not degraded, as more and elaborate communications paths develop, the only sequentiality in the system as a whole being imposed by synchronizing processes, not the message passing system itself.After discussing the various built‐in system facilities that permit processes to dynamically find out about and study one another, thus permitting processes to set up and thereafter supervise whole subsystems, we shall round off by discussing the advantages of introducing the machines themselves into the language, making it possible for processes to become aware of, and then ‘migrate’ within, the topological structure of a multi‐processor distributed network, moving closer to their application, or just to a less‐loaded processor, as the need arises.To conclude we shall contrast this new‐style process‐oriented language with various existing programming languages which have experimented with concurrency, either implicitly or explicitly, in order to see if, and if so how, this new style is any simp

ISSN:0038-0644    

DOI:10.1002/spe.4380150903

出版商:John Wiley&Sons, Ltd.    

年代:1985

数据来源: WILEY

摘要:

AbstractThis paper is concerned with the overall design of the Terabit File Store — a network storage facility based on a Braegen Automated Tape Library. The characteristics of the tape library — in particular its large capacity and slow access — provide both challenges and opportunities for the system designer. The use of disc cache and the optimization of file placement have been used to provide reasonable performance in the face of substantial tape handling times. Catalogue facilities have been tailored to cater for the support of large file holdings and user file back‐up applications. It has been possible to automate the back‐up of essential file‐store information which together with automatic integrity checks, helps to minimize the damage that can be caused by faults. Considerable attention has been given to facilities that automate much of the management of the system in a network environment. Other aspects of the design discussed in the paper include protection, housekeeping and host

ISSN:0038-0644    

DOI:10.1002/spe.4380150904

出版商:John Wiley&Sons, Ltd.    

年代:1985

数据来源: WILEY

摘要:

AbstractThis paper deals with the organization of a distributed load‐balancing policy for a multicomputer system which consists of a cluster of independent computers that are interconnected by a local area communication network. We introduce three algorithms necessary to maintain load balancing in this system: the local load algorithm, used by each processor to monitor its own load; the exchange algorithm, for exchanging load information between the processors, and the process migration algorithm that uses this information to dynamically migrate processes from overloaded to underloaded processors.The policy that we present is distributed, i.e. each processor uses the same policy. It is both dynamic, responding to load changes without using ana prioriknowledge of the resources that each process requires; and stable, unnecessary overloading of a processor is minimized. We give the essential details of the implementation of the policy and initial results on its performance.Our results confirm the feasibility of building distributed systems that are based on network communication for uniform access, resource sharing and improved reliability, as well as the use of workstations without a secondary storage devic

ISSN:0038-0644    

DOI:10.1002/spe.4380150905

出版商:John Wiley&Sons, Ltd.    

年代:1985

数据来源: WILEY

摘要:

AbstractVideo‐Slide is a powerful visual aid for the BBC Microcomputer. It can be used to support a wide variety of talks, ranging from lessons to business presentations. Video‐Slide manipulates screens of coloured information which are referred to as slides. These are compatible with the broadcast teletext standard. Slides are prepared in advance with graphics editor and librarian utilities. During the presentation itself, a display program gives simple, direct control over the sequencing of slides with several important features. Video‐Slide programs are menu‐driven with a simple visual interface, and are designed to be used by non‐computer users. This paper describes the design concepts and implementation of the Video‐S

ISSN:0038-0644    

DOI:10.1002/spe.4380150906

出版商:John Wiley&Sons, Ltd.    

年代:1985

数据来源: WILEY

ISSN:0038-0644    

DOI:10.1002/spe.4380150901

出版商:John Wiley&Sons, Ltd.    

年代:1985

数据来源: WILEY