MUPPET: A programming environment for message-based multiprocessors

A problem which confronts the developers of concurrent logic programming (CLP) systems concerns the design of the programming environment, particularly the provision of debugging tools. Debugging tools are useful for many activities besides identifying bugs: they can help in program testing and demonstration, in software experiments, and in teaching the language semantics. For CLP languages the questions of what debugging tools should be provided, and of how they should be used, are still open. Although the languages are closely related to other logic programming and concurrent programming languages, they are sufficiently different that new debugging techniques are required. This paper describes a primarily channel-oriented debugging methodology and a set of debugging tools that we have developed in the light of our experience in using and teaching the CLP language Parlog. With these tools a programmer can test a program by observing communication on channels, opening up a process to examine the activity on internal channels and, if necessary, to check in detail the execution steps of a process. Almost all of the ideas, which are equally applicable to other CLP languages, have been implemented in two commercial Parlog systems. As well as fulfilling the needs of existing users of CLP languages, we believe that the tools emphasise the attractions of CLP as a concurrent programming paradigm, since they are made possible by the unique attributes of CLP.

We address the problem of specifying concurrent processes that can make local nondeterministic decisions without affecting global system behavior—the sequence of events communicated along each inter-process communication channel. Such nondeterminism can be used to cope with unpredictable execution rates and communication delays. Our model resembles Kahn’s, but does not include unbounded buffered communication, so it is much simpler to reason about and implement. After formally characterizing these so-called confluent processes, we propose a collection of operators, including sequencing, parallel, and our own creation, confluent choice, that guarantee confluence by construction. The result is a set of primitive constructs that form the formal basis of a concurrent programming language for both hardware and software systems that gives deterministic behavior regardless of the relative execution rates of the processes. Such a language greatly simplifies the verification task because any correct implementation of such a system is guaranteed to have the same behavior, a property rarely found in concurrent programming environments.

PQE2000 is an Italian project on High Performance Computing (HPC), whose goal is the realization of innovative general purpose systems and programming tools, as well as the development of new strategic HPC applications for industry, commerce and public services. The research activities of PQE2000 include MPP architecture, software tools and programming environments, and applications in technical, transactional and new media areas. The results of these activities are transferred into industrial products. This paper describes the general guidelines, the current products and technologies of PQE2000, and the trends in the area of relationships between programming environments and architectural models for the efficient exploitation of large degree of variable grain parallelism in complex applications.

Data sets in large applications are often too massive to fit completely inside the computers internal memory. The resulting input/output communication (or I/O) between fast internal memory and slower external memory (such as disks) can be a major performance bottleneck. In this article we survey the state of the art in the design and analysis of external memory (or EM) algorithms and data structures, where the goal is to exploit locality in order to reduce the I/O costs. We consider a variety of EM paradigms for solving batched and online problems efficiently in external memory. For the batched problem of sorting and related problems such as permuting and fast Fourier transform, the key paradigms include distribution and merging. The paradigm of disk striping offers an elegant way to use multiple disks in parallel. For sorting, however, disk striping can be nonoptimal with respect to I/O, so to gain further improvements we discuss distribution and merging techniques for using the disks independently. We also consider useful techniques for batched EM problems involving matrices (such as matrix multiplication and transposition), geometric data (such as finding intersections and constructing convex hulls), and graphs (such as list ranking, connected components, topological sorting, and shortest paths). In the online domain, canonical EM applications include dictionary lookup and range searching. The two important classes of indexed data structures are based upon extendible hashing and B-trees. The paradigms of filtering and bootstrapping provide a convenient means in online data structures to make effective use of the data accessed from disk. We also reexamine some of the above EM problems in slightly different settings, such as when the data items are moving, when the data items are variable-length (e.g., text strings), or when the allocated amount of internal memory can change dynamically. Programming tools and environments are available for simplifying the EM programming task. During the course of the survey, we report on some experiments in the domain of spatial databases using the TPIE system (transparent parallel I/O programming environment). The newly developed EM algorithms and data structures that incorporate the paradigms we discuss are significantly faster than methods currently used in practice.

The Smalltalk-80 system is an interactive graphical programming and applications environment. In the system the language, graphical display, editors, programming tools, operating system features, and application programs are integrated by treating each in a consistent object-oriented manner. The object-orientation of the Smalltalk-80 language, in which all information structure is in the form of objects and all processing is in the form of message-sending, greatly facilitates this consistency of the system.

simpA: An agent-oriented approach for programming concurrent applications on top of Java

Research in programming environments for supercomputers covers several broad areas, including the design of very high level specification tools, the development of new programming languages, and supercompilers that transform code written in a sequential programming language into equivalent concurrent code that can be efficiently executed on a target machine. This chapter is concerned with the last of these, which is also known as automatic restructuring. It examines techniques and systems which were mainly developed for the purpose of transforming sequential numerical programs for large-scale scientific and engineering applications into concurrent programs. The chapter discusses programming environments to support the task of automatic restructuring. It outlines the typical phases of program development and describes the basic scheme for an interactive restructuring system. The chapter provides most important requirements for a suitable programming environment for concurrent computers. The chapter considers some requirements that should be met by advanced software environments supporting program development for concurrent computers.

Wireless sensor networks (WSNs) are emerging as powerful platforms for distributed embedded computing supporting a variety of high-impact applications such as disaster/crime prevention and military applications, environmental applications, health applications, and smart spaces. Programming WSNs is a complex task as system level code and application level code are often intertwined. Several programming paradigms have been to date proposed which provide programming abstractions and programming support for the development of WSN applications. In this paper we propose a specification language centered on the concept of lightweight agent based on events and states which distinctively integrates the advantages of three important paradigms and models for WSN programming: agent- based, event-driven and state-based programming. The proposed language is exemplified through a specification of the well-known EnviroTrack application.

Teaching concurrent and parallel programming by patterns: An interactive ICT approach

Background Software developers are increasingly required to write concurrent code. However, most developers find concurrent programming difficult. To better help developers, it is imperative to understand their interest and difficulties in terms of concurrency topics they encounter often when writing concurrent code.Aims In this work, we conduct a large-scale study on the textual content of the entirety of Stack Overflow to understand the interests and difficulties of concurrency developers.Method First, we develop a set of concurrency tags to extract concurrency questions that developers ask. Second, we use latent Dirichlet allocation (LDA) topic modeling and an open card sort to manually determine the topics of these questions. Third, we construct a topic hierarchy by repeated grouping of similar topics into categories and lower level categories into higher level categories. Fourth, we investigate the coincidence of our concurrency topics with findings of previous work. Fifth, we measure the popularity and difficulty of our concurrency topics and analyze their correlation. Finally, we discuss the implications of our findings.Results A few findings of our study are the following. (1) Developers ask questions about a broad spectrum of concurrency topics ranging from multithreading to parallel computing, mobile concurrency to web concurrency and memory consistency to run-time speedup. (2) These questions can be grouped into a hierarchy with eight major categories: concurrency models, programming paradigms, correctness, debugging, basic concepts, persistence, performance and GUI. (3) Developers ask more about correctness of their concurrent programs than performance. (4) Concurrency questions about thread safety and database management systems are among the most popular and the most difficult, respectively. (5) Difficulty and popularity of concurrency topics are negatively correlated.Conclusions The results of our study can not only help concurrency developers but also concurrency educators and researchers to better decide where to focus their efforts, by trading off one concurrency topic against another.

The use of types to deal with access capabilities of program entities is becoming increasingly popular.In concurrent logic programming, the first attempt was made in Moded Flat GHC in 1990, which gave polarity structures (modes) to every variable occurrence and every predicate argument. Strong moding turned out to play fundamental rôles in programming, implementation and the in-depthunderstanding of constraint-based concurrent computation.The moding principle guarantees that each variable is written only once and encourages capability-conscious programming. Furthermore, it gives less generic modes to programs that discard or duplicate data, thus providing the view of “data as resources.” A simple linearity system built upon the mode system distinguishes variables read only once from those read possibly many times, enabling compile-time garbage collection. Compared to linear types studied in other programming paradigms, the primary issue in constraint-based concurrency has been to deal with logical variables and highly non-strict data structures they induce.In this paper, we put our resource-consciousness one step forward and consider a class of ‘ecological’ programs which recycle or return all the resources given to them while allowing concurrent reading of data structures via controlled aliasing. This completely recyclic subset enforces us to think more about resources, but the resulting programs enjoy high symmetry which we believe has more than aesthetic implications to our programming practice in general.The type system supporting recyclic concurrent programming gives a [−1, +1] capability to each occurrence of variable and function symbols (constructors), where positive/negative values mean read/write capabilities, respectively, and fractions mean non-exclusive read/write paths. The capabilities are intended to be statically checked or reconstructed so that one can tell the polarity and exclusiveness of each piece of information handled by concurrent processes. The capability type system refines and integrates the mode system and the linearity system for Moded Flat GHC. Its arithmetic formulation contributes to the simplicity.The execution of a recyclic program proceeds so that every variable has zero-sum capability and the resources (i.e., constructors weighted by their capabilities) a process absorbs match the resources it emits. Constructors accessed by a process withan exclusive read capability can be reused for other purposes.The first half of this paper is devoted to a tutorial introduction to constraint-based concurrency in the hope that it will encourage crossfertilization of different concurrency formalisms.KeywordsLogic ProgramMode GraphLogical VariableMode ConstraintProgram ClauseThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

A number of concurrent computers have been designed, such as [Ametek 1988] and [NCUBE 1986]. Taking advantage of concurrency on these computers will require new languages, operating systems, and environments to support the programming, monitoring and control of applications. The Rosette project at MCC is developing a system architecture for general-purpose concurrent computation based on the Actor model [Agha 1986]. The aim of the Rosette architecture is to support the use of concurrent computers in solving computationally intensive problems whose structure is not statically determined. The architecture will support variable grain size, dynamic resource management, reflection, and heterogeneity. A number of concurrent language proposals have employed computational models that are limited in their applicability because of assumptions such as granularity of concurrency, static process topology, or inherent communications cost. Others, for example, functional programming, cannot be used to model shared, modifiable objects. The Actor model addresses these issues directly. However, the difficulties of using concurrent computers cannot be addressed solely through programming languages. Traditional operating systems treat each process as an independent entity for the purposes of resource management (i.e., for the run-time allocation of processor, storage, and communication resources.) In the context of concurrent applications, effective operation on a concurrent computer requires that communities of processes be managed together, taking into account the ways in which they interact, and providing for the application itself to guide resource management. For example, consider that programming systems often provide only limited support for the control of resource consumption in search problems in the face of combinatorial explosion; further, it is generally recognized that to optimize search performance, it is useful to vary the resources provided depending on how promising intermediate results of a given path are judged to be. The Rosette architecture will allow the programmer to integrate high-level algorithms within the application for dividing resources dynamically among the sub-computations that are spawned. These algorithms will provide an assessment of the progress of the sub-computations, and will be used to make the large number of low-level resource management decisions that are necessary in carrying out the computation. Thus, operating system functionality will be folded into the application. The Rosette architecture has two major components: an interface layer and a system environment . The interface layer provides mechanisms for the monitoring and control of concurrent applications. It supports a uniform view of the system resources and applications through the use of actors and message-passing semantics. The interface layer includes a set of actors that represent the processing, storage and communication resources across the hardware base. The system environment contains actor communities which implement resource management policies , and support for programming concurrent applications. The environment consists of an extensible set of actors that are organized via a class-based object model. These actors provide monitoring, debugging, resource management system simulation, and compilation/transformation facilities. To demonstrate the effectiveness of the Rosette architecture, as well as to drive its development, two classes of applications are being used. The first class is the Rosette system itself: all of the system components necessary for resource management, monitoring, debugging, and program development are being constructed in the Rosette language and will take full advantage of both concurrency and object-oriented programming support. The second category of applications is chosen to be somewhat independent of the Rosette system so as to ensure adequate feed-back concerning applicability to domains other than software engineering. These applications are in the general area of knowledge-based signal interpretation. The Rosette architecture is implemented via a concurrent object-oriented programming language that provides the following features: Inherent concurrency : A declarative approach is needed which allows fine-grained concurrency to arise naturally from the program. If the programmer is forced to express all of the details of the concurrent execution of an application, it becomes difficult to re-map a given program to different concurrent computers which have varying concurrency characteristics. Dynamic creation/modification of objects : This allows the system to be extensible and reconfigurable. Sharing : The language should support mechanisms such as inheritance so that code, structure, and values need not be replicated. Classes : Objects can be organized into classes to permit more effective management of resources, as for example in a very large database. Classes should be first-class objects and hence it should be possible to create classes dynamically. The Rosette language is a high-level language that is translated into a base language that directly expresses concurrent computations in terms of the semantics of the Actor model. The Rosette language extends the base language with data abstraction facilities and a library of classes, and is used to implement the non-built-in actors of the interface layer, components of the system environment, and applications. Using data abstraction extensions to the base language, the Rosette language organizes actors into classes according to common sets of behaviors and local state. Inheritance is used as a means of sharing code and structure that is common among classes. There is considerable evidence, for example [LaLonde 1986] and [Snyder 1987], that a robust class system should support separate hierarchies that represent what is modeled by a class and how some class of objects are actually implemented. Our approach is to use three different kinds of classes to organize the various kinds of actors in a system and information about these actors: abstract classes specify observable requests, responses, and actions; representation classes specify resource management characteristics of implementations; and behavior classes contain the actual implementations. Associated with an abstract class is the set of representations that are available to implement the particular abstraction. Each representation is associated with the behavior class that contains the corresponding implementation. The power of this separation is that each of the three kinds of class may be related to others in a class hierarchy. This means that the relationships between abstract classes are not forced to have the same structure as the relationships among implementations. Sharing via inheritance among behavior classes is related to engineering concerns; relations among abstract classes are dictated by external/observable behavior. As an example, an abstract class might specify the operations available over real-matrices . There are several ways of representing a matrix as a community of actors, and each of these would be specified with appropriate representation and behavior classes. There is a well-defined abstract hierarchy of matrices such as invertible, positive , etc. These abstract kinds of matrices are independent of the various implementations, which may be chosen according to application and hardware resource constraints. The Rosette language embodies a reflective model of the interface layer that is similar to that used in ABCL/R, [Watanabe and Yonezawa 1988]. This model is t

A new programming environment with a multi-display terminal and early experiences with it

This project aimed to develop an effective and efficient GridRPC-based environment for multiple clusters of computers distributed on the Grid. It contains programming and execution environments for GridRPC applications. The programming environment allows users to deploy GridRPC services and develop GridRPC applications to consume the existing services. In order to make the Grid transparent to the users, the GridRPC execution environment is equipped with many mechanisms for resource discovery, resource selection, request scheduling and dispatching. Especially, composite services and request bundling mechanisms are introduced and examined together with the aids of multithreaded programming techniques. They are useful to improve performance for embarrassingly parallel applications.

Electrocatalysis processes play an important role in the research and development of sustainable energy and environmental applications. However, the utilization of a constant voltage in steady-state operations can sometimes limit the current electrocatalysis process due to unsatisfactory efficiency and limited selectivity behaviors. In comparison, dynamically tuneable pulsed electrocatalysis presents a promising alternative for achieving higher process control, enhanced efficiency, and improved selectivity during certain electrochemical processes when compared to its constant current counterpart. This article presents a comprehensive overview of pulsed electrocatalysis as a valuable tool within electrocatalysis. This includes an overview of the mechanistic details along with a thorough discussion regarding the facile process parameter optimization. Moreover, the contemporary catalyst manipulation and unique electrolytic conditions offered by pulsed electrocatalysis are demonstrated in tandem with other considerations such as mass transfer, long-term stability, and system designs. The potential of it is manifested in cutting-edge applications such as CO2 conversion, water splitting, and other environmental and biomedical applications. It appears that we are entering a new era in electrocatalysis, where adjustable pulse patterns can be employed to achieve enhanced efficiency and unmatched selectivity.