Compiler to interpreter: experiences with a distributed programming language

One interpretive approach for handling concurrency is to provide an interpreter instance for each executing language‐level process. Such an approach has mainly been applied to concurrent implementations of logic and functional languages. This paper describes the use of this approach in constructing an interpreter for an imperative, distributed programming language from an existing compiler and run‐time support system (RTS). Primary design goals were to exploit the existing compiler to the extent possible as well as to have minimal impact on the RTS used to support concurrency. We have been successful in meeting these goals. Additionally, performance results show our interpreter's execution times compare favorably to the times required for compilation, linkage, and execution of small programs or programs with a significant number of calls to the RTS; on such programs, our interpreter's performance also compares favorably to that of the standard Java implementation. However, for larger programs and programs with fewer calls to the underlying RTS, the conventional compiler‐based implementation outperforms the interpreter implementation. For many distributed programs in which network costs dominate, the performances of the two implementations differ little. Copyright © 2001 John Wiley & Sons, Ltd.     

DSML4CP: A Domain-specific Modeling Language for Concurrent Programming

Nowadays, concurrent programs are an inevitable part of many software applications. They can increase the computation performance of the applications by parallelizing their computations. One of the approaches to realize the concurrency is using multi thread programming. However, these systems are structurally complex considering the control of the parallelism (such as thread synchronization and resource control) and also considering the interaction between their components. So, the design of these systems can be difficult and their implementation can be error-prone especially when the addressed system is big and complex. On the other hand, a Domain-specific Modeling Language (DSML) is one of the Model Driven Development (MDD) approaches which tackles this problem. Since DSMLs provide a higher abstraction level, they can lead to reduce the complexities of the concurrent programs. With increasing the abstraction level and generating the artifacts automatically, the performance of developing the software (both in design and implementation phases) is increased, and the efficiency is raised by reducing the probability of occurring errors. Thus, in this paper, a DSML is proposed for concurrent programs, called DSML4CP, to work in a higher level of abstraction than code level. To this end, the concepts of concurrent programs and their relationships are presented in a metamodel. The proposed metamodel provides a context for defining abstract syntax, and concrete syntax of the DSML4CP. This new language is supported by a graphical modeling tool which can visualize different instance models for domain problems. In order to clarify the expressions of the language; the static semantic controls are realized in the form of constraints. Finally, the architectural code generation is fulfilled via model transformation rules using the templates of the concurrent programs. To increase level of the DSML׳s leverage and to demonstrate the general support of concurrent programming by the DSML, the transformation mechanism of the tool supports two well-known and highly used programming languages for code generation; Java and C#. The performed experiments on two case studies indicate a high performance for proposed language. In this regard, the results show automatic generation of 79% of the final code and 86% of the functions/modules on average.     

Concurrent programming in VISO

Concurrent programming is more difficult to use and understand than sequential programming. In order to simplify this type of programming a number of approaches have been developed such as visual programming. Visual Occam (VISO) is a visual programming language for concurrent programming. It has a graphical syntax based on the language Occam and its semantics is represented both in petri net and process calculus. This paper presents a modular visual approach to write concurrent programs using the VISO language. Concurrent programs in VISO are specified graphically at different levels of abstraction. This paper describes this modular visual approach by constructing two examples in VISO. The first example is a simple concurrent program and it is mainly used to show the details of constructing a concurrent program in VISO. The second example is a larger concurrent program with more levels of abstraction. Copyright © 2000 John Wiley & Sons, Ltd.     

Inter-entry selection control mechanisms: Implementation and evaluation

Inter-process communication is achieved in many concurrent programming languages through message entries. Many of these languages contain inter-entry selection constructs allowing a process to selectively choose one of a group of message entries to service. Generally, this selection process is handled non-deterministically. To enable a degree of control over this selection, limited inter-entry selection control mechanisms are available in several of these languages. This paper reviews the need for more expressive inter-entry selection control mechanisms and details the design and implementation of two such control mechanisms—static and dynamic preferences. These implementations of static and dynamic preferences, SRps and SRpd respectively, are extensions of the SR concurrent programming language. In both implementations, the use of preferences is optional, and thus, the overhead associated with their use is incurred only when their use is necessary. Finally, this paper describes the performance of these implementations on several classical synchronization problems. For tests run in a shared memory environment the results show that there is substantial cost associated with the preference implementations. However, the results of the distributed environment tests illustrate that the incremental cost of adding preferences is small and often not discernable when the overhead costs associated with communications across a network are considered.     

The Discourje project: run-time verification of communication protocols in Clojure

To simplify shared-memory concurrent programming, languages have started to offer core support for high-level communications primitives, in the form of message passing though channels, in addition to lower-level synchronisation primitives. Yet, a growing body of evidence suggests that channel-based programming abstractions also have their issues. The Discourje project aims to help programmers cope with channels and concurrency bugs in Clojure programs, based on dynamic analysis. The idea is that programmers write not only implementations of communication protocols in their Clojure programs, but also specifications. Discourje then offers a run-time verification library to ensure that channel actions in implementations are safe relative to specifications. The aim of this paper is to provide a comprehensive overview of the current state of Discourje, including case studies, theoretical foundations, and practical aspects.

     

Studies of a Theory of Specifications with Built-in Program Extraction

We present a Theory of Specifications based on Martin-Löf's type theory, with rules for simultaneously constructing programs and their correctness proofs. The theory contains types for representing specifications whose corresponding notion of implementation is that of a pair formed by a program and a correctness proof. The rules of the theory are such that in implementations the program parts appear mixed together with the proof parts. A confluent and normalizing computational relation performs the task of separating programs from proofs. As a consequence, every implementation computes to a pair composed of a program and a proof of its correctness, and so the program extraction procedure is immediate.     

The Refinement Paradigm: The Interaction of Coding and Efficiency Knowledge in Program Synthesis

A refinement paradigm for implementing a high-level specification in a low-level target language is discussed. In this paradigm, coding and analysis knowledge work together to produce an efficient program in the target language. Since there are many possible implementations for a given specification of a program, searching knowledge is applied to increase the efficiency of the process of finding a good implementation. For example, analysis knowledge is applied to determine upper and lower cost bounds on alternate implementations, and these bounds are used to measure the potential impact of different design decisions and to decide which alternatives should be pursued. In this paper we also describe a particular implementation of this program synthesis paradigm, called PSI/SYN, that has automatically implemented a number of programs in the domain of symbolic processing.     

Relation-based computations in a monadic BSP model

We propose a Haskell monadic model of bulk synchronous parallel programs and apply it to the analysis of relation-based computations.

Relation-based computations are simple but general patterns found in scientific computing applications. They are easy to implement sequentially, but difficult to parallelize.

We use the model to give high-level specifications of distributed relation-based algorithms and outline how to obtain testable parallel implementations from these specifications via equational reasoning.

We sketch the architecture of a C++ library of components for distributed relation-based computations. We argue that the model can be used to provide a concise and consistent library documentation.     

Performance of multi-tasking and synchronization mechanisms in the programming language SR

High-level language primitives for concurrent programming exist in languages such as Ada and Modula-2. However, each of these languages provides only a single means for specifying multitasking and synchronization, essential in the implementation of concurrent systems. The SR language provides several mechanisms for specifying multi-tasking and synchronization, so it can be used to explore the performance of various communication techniques. This paper presents performance results for SR's multi-tasking and synchronization mechanisms and discusses the effects of the generated code, the run-time support and the hardware on these results. These results are compared with those for similar mechanisms in other languages, leading to some general conclusions about the performance of process communication primitives. These performance results can be used by programmers to make design choices that allow systems programs written in high-level languages to meet real-time performance specifications.     

A natural language model for managing TV-Anytime information in mobile environments

The TV-Anytime standard describes the structures of categories of digital TV program metadata, as well as user profile metadata for TV programs. We describe a natural language (NL) model for the users to interact with the TV-Anytime metadata and preview TV programs from their mobile devices. The language utilises completely the TV-Anytime metadata specifications (upper ontologies), as well as domain-specific ontologies. The interaction model does not use clarification dialogues, but it uses the user profiles as well as TV-Anytime metadata information and ontologies to rank the possible responses in case of ambiguities. We describe implementations of the model that run on a PDA and on a mobile phone, and manage the metadata on a remote TV-Anytime-compatible TV set. We present user evaluations of the approach. Finally, we propose a generalised implementation framework that can be used to easily provide NL interfaces for mobile devices for different applications and ontologies.     

Towards Acceptability of Optimizations: An Extended View of Compiler Correctness

The theory of relative program correctness and its preservation allows for elaborate and practically adequate definitions of correct implementation notions as they are established by transformations implemented in a compiler. It generalizes Hoare's and Floyd's partial and total program correctness and correctness preservation by classifying finite and infinite errors to be either acceptable (unavoidable) or unacceptable (chaotic, to be avoided). We will define correct implementation by particular compositional diagram commutativities, and we will further extend this theory also to express correctness of compiling specifications and of compiler programs and their implementations in the same uniform relational setting. Unacceptable error outcomes can semantically model pre-conditions such as well-formedness conditions for compilers or optimization pre-conditions for user programs. Our theory allows to distinguish between different correct implementation requirements, for instance (horizontally) for user programs or (vertically) for the compiler implementation, just as if we would switch on and off compiler options and tune one compiler to appropriately preserve correctness in different application domains.     

An agile approach to language modelling and development

We have developed novel techniques for component-based specification of programming languages. In our approach, the semantics of each fundamental programming construct is specified independently, using an inherently modular framework such that no reformulation is needed when constructs are combined. A language specification consists of an unrestricted context-free grammar for the syntax of programs, together with an analysis of each language construct in terms of fundamental constructs. An open-ended collection of fundamental constructs is currently being developed. When supported by appropriate tools, our techniques allow a more agile approach to the design, modelling, and implementation of programming and domain-specific languages. In particular, our approach encourages language designers to proceed incrementally, using prototype implementations generated from specifications to test tentative designs. The components of our specifications are independent and highly reusable, so initial language specifications can be rapidly produced, and can easily evolve in response to changing design decisions. In this paper, we outline our approach, and relate it to the practices and principles of agile modelling.     

Software merge: Models and methods for combining changes to programs

We outline a model for programs and data and present a formal definition of an ideal change merging operation. This model is used to develop a new semantically based method for combining changes to programs. We also evaluate the appropriateness of the change merging operation and examine some circumstances where the specifications of a program as well as the implementations can be used to guide the change merging process in cases where the implementations conflict but the specifications do not. This work was performed for the Office of Naval Research and funded by the Naval Postgraduate School.     

The Evolution of Concurrent Programs

Process algebra are formal languages used for the rigorous specification and analysis of concurrent systems. By using a process algebra as the target language of a genetic programming system, the derivation of concurrent programs satisfying given problem specifications is possible. A genetic programming system based on Koza's model has been implemented. The target language used is Milner's CCS process algebra, and is chosen for its conciseness and simplicity. The genetic programming environment needs a few adaptations to the computational characteristics of concurrent programs. In particular, means for efficiently controlling the exponentially large computation spaces that are common with process algebra must be addressed. Experimental runs of the system successfully evolved a number of non–iterative CCS systems, hence proving the potential of evolutionary approaches to concurrent system development.     

Rendezvous facilities: Concurrent C and the Ada language

The concurrent programming facilities in both Concurrent C and the Ada language are based on the rendezvous concept. Although these facilities are similar, there are substantial differences. Facilities in Concurrent C were designed keeping in perspective the concurrent programming facilities in the Ada language and their limitations. Concurrent C facilities have also been modified as a result of experience with its initial implementations. The authors compare the concurrent programming facilities in Concurrent C and Ada and show that it is easier to write a variety of concurrent programs in Concurrent C than in Ada     

An implementation of the object-oriented concurrent programming language SINA

SINA is an object-oriented language for distributed and concurrent programming. The primary focus of this paper is on the object-oriented concurrent programming mechanisms of SINA and their implementation. This paper presents the SINA constructs for concurrent programming and inter-object communication, some illustrative examples and a message-based implementation model for SINA that we have used in our current implementation.     

Reproducible testing of monitors

This paper describes a systematic method for testing monitor modules which control process interactions in concurrent programs. A monitor is tested by executing a concurrent program in which the processes are synchronized by a clock to make the sequence of interactions reproducible. The method separates the construction and implementation of test cases and makes the analysis of a concurrent experiment similar to the analysis of a sequential program. The implementation of a test program is almost mechanical. The method, which is illustrated by an example, has been successfully used to test a multicomputer network program written in Concurrent Pascal.     

Verifying Contextual Refinement with Ownership Transfer

Contextual refinement is a compositional approach to compositional verification of concurrent objects.There has been much work designing program logics to prove the contextual refinement between the object implementation and its abstract specification.However,these program logics for contextual refinement verification cannot support objects with resource ownership transfer,which is a common pattern in many concurrent objects,such as the memory management module in OS kernels,which transfers the allocated memory block between the object and clients.In this paper,we propose a new approach to give abstract and implementation independent specifications to concurrent objects with ownership transfer.We also design a program logic to verify contextual refinement of concurrent objects w.r.t.their abstract specifications.We have successfully applied our logic to verifying an implementation of the memory management module,where the implementation is an appropriately simplified version of the original version from a real-world preemptive OS kernel.     

Parallel Implementations of the Selection Problem: A Case Study

The selection problem has been studied extensively on sequential machines. A linear average time solution and a linear worst-case solution are considered as the standard by most researchers. Theoretical work is also available on parallel models, but it has not been widely implemented on parallel machines. This paper presents an in-depth analysis of the implementation of the standard algorithms, on a number of multiprocessors and supercomputers from the entire spectrum of Flynn's classification, using both an imperative (C based languages with vendor specific parallel extensions) and a functional (SISAL) language. Very interesting results were obtained for all of the experiments performed, leading us to the conclusion that the selection problem has very efficient parallel implementations. Hand-tuned C programs with parallel extensions provided good efficiency but were time-consuming in terms of development. On the other hand, the SISAL code is fully portable and the same program was used on all the machines. The performances of SISAL implementations were comparable to the ones of the hand-tuned C implementations. On all the tests, the routines were able to sustain good speed-up and reasonable efficiency, even with a large number of processors. In two cases (one machine using SISAL, and one using a C-based language), we were able to obtain an efficiency higher than 80% with a configuration close or equal to the maximum number of processors.