Support for efficient dynamic migration and replication of objects is essential for achieving adequate performance and scalability. Traditional solutions to the problem focused on competitiveness. This means that the algorithm's complexity matches the offline adversary's complexity within an acceptable ratio. We define and study the allocation problem under two new measures: stability and fault tolerance. Stability considers the performance of an object allocation algorithm when the object access patterns at the individual nodes of a distributed system stabilize. We present a new algorithm for uniform networks based on the idea of sliding windows. Besides being optimally competitive, the algorithm also exhibits good stability. For fault-tolerance, we consider the performance of allocation algorithms when at least t copies need to be maintained. We derive a lower bound on the competitiveness of such algorithms. Finally, we modify our earlier solution so that it is also optimally fault-tolerant.

The Chiron-1 user interface system demonstrates key techniques that enable a strict separation of an application from its user interface. These techniques include separating the control-flow aspects of the application and user interface: they are concurrent and may contain many threads. Chiron also separates windowing and look-and-feel issues from dialogue and abstract presentation decisions via mechanisms employing a client-server architecture. To separate application code from user interface code, user interface agents called artists are attached to instances of application abstract data types (ADTs). Operations on ADTs within the application implicitly trigger user interface activities within the artists. Multiple artists can be attached to ADTs, providing multiple views and alternative forms of access and manipulation by either a single user or by multiple users. Each artist and the application run in separate threads of control. Artists maintain the user interface by making remote calls to an abstract depiction hierarchy in the Chiron server, insulting the user interface code from the specifics of particular windowing systems and toolkits. The Chiron server and clients execute in separate processes. The client-server architecture also supports multilingual systems: mechanisms are demonstrated that support clients written in programming languages other than that of the server while nevertheless supporting object-oriented server concepts. The system has been used in several universities and research and development projects. It is available by anonymous ftp.

article Free Access Share on Incremental evaluation for a general class of circular attribute grammars Authors: J. A. Walz Cornell Univ., Ithaca, NY Cornell Univ., Ithaca, NYView Profile , G. F. Johnson Univ. of Maryland, College Park, MD Univ. of Maryland, College Park, MDView Profile Authors Info & Claims ACM SIGPLAN NoticesVolume 23Issue 7July 1988 pp 209–221https://doi.org/10.1145/960116.54011Online:01 June 1988Publication History 6citation247DownloadsMetricsTotal Citations6Total Downloads247Last 12 Months4Last 6 weeks1 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteeReaderPDF

In this paper we describe GL, a language designed to support interactive experimentation with denotational semantics of programming languages, and the novel features of its interpreter. GL is an expressional language that might best be described as an implementation of lambda calculus augmented with several useful basic data types including 1-values.A unique aspect of the GL environment is that it presents a visible, user-accessible implementation of the continuation semantics of GL. The user is expected to understand a denotational definition of GL, and to interact with the system in terms of that definition. In particular, if a computation is temporarily halted the expression continuation extant at that point can be interactively captured and later applied to other values and stores. The implementation of this feature is via a pair of routines called setjmpup and longjmpup that provide what might be called a partial continuation facility. A partial continuation is a function over stores or store/value pairs that represents execution of a partially executed program from its current state to some later state possibly before its half state. The semantics of partial continuations is interesting, and an extension of GL is presented that contains continuations and partial continuations as first-class objects.The GL environment is fairly complete; it has an experimental polymorphic type inference mechanism that supports self-application and report likely sources of user error in a robust manner, and it has a flexible breakpoint and trace facility that permits program execution to be observed and controlled at a variety of levels of granularity. Moreover, it has been used successfully to teach a graduate course in Theory of Programming Languages.

A crucial aspect of a program intended for general use is its behavior in the presence of erroneous inputs. For instance, much attention has been devoted to the problems of error detection, reporting, and correction in compilers1,2. As programming languages and systems based in one way or another on unification3 become more common, it becomes increasingly important to develop a theory of error detection and correction for unification-based systems. We report here on a language-based editor for a variant of ML4 that uses a novel approach to the isolation of likely causes of user errors. As the user edits and manipulates his or her program, unification is incrementally applied to determine its type correctness. If a type inconsistency arises, a maximum flow technique is applied to the set of type equations to determine the most likely source of error. In this way a determination can be made as to the relative strengths with which the set of type equations asserts multiple contradictory hypotheses. In a language such as ML, the type of an object is inferred from patterns of usage. Often it is the case that most uses of a given object are mutually consistent, whereas one or a very small number of uses conflict with the general usage pattern. In MOE (ML-Oriented Editor), if it is possible to discern that such a situation has arisen, likely errors are highlighted at high intensity and all other program components that contributed to the inferred type of the object are highlighted at a lower intensity. In providing error information to the user, two principles are observed:(1) Error indications should be complete but parsimonious; the user should see highlighted on the screen everything that contributed directly to an error, but nothing. more,(2) The user's attention should be drawn to what appear to be the anomalies that are responsible for errors.Language-based editors permit a new level of quality in the process of helping users when inputs are, for one reason or another, invalid. Unification-based type inference in language-based editors appears to have been first considered by Meertens 5. Snelting and Bahlke have more recently also explored this approach.

Article Free Access Share on A meta-language and system for nonlocal incremental attribute evaluation in language-based editors Authors: Gregory F. Johnson Cornell University Cornell UniversityView Profile , C. N. Fischer U. of Wisconsin - Madison U. of Wisconsin - MadisonView Profile Authors Info & Claims POPL '85: Proceedings of the 12th ACM SIGACT-SIGPLAN symposium on Principles of programming languagesJanuary 1985Pages 141–151https://doi.org/10.1145/318593.318627Published:01 January 1985Publication History 42citation149DownloadsMetricsTotal Citations42Total Downloads149Last 12 Months14Last 6 weeks4 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Publisher SiteeReaderPDF

Article Free Access Share on Non-syntactic attribute flow in language based editors Authors: Gregory F. Johnson University of Wisconsin-Madison University of Wisconsin-MadisonView Profile , Charles N. Fischer University of Wisconsin-Madison University of Wisconsin-MadisonView Profile Authors Info & Claims POPL '82: Proceedings of the 9th ACM SIGPLAN-SIGACT symposium on Principles of programming languagesJanuary 1982Pages 185–195https://doi.org/10.1145/582153.582174Published:25 January 1982Publication History 18citation113DownloadsMetricsTotal Citations18Total Downloads113Last 12 Months12Last 6 weeks3 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteeReaderPDF