A Study of Concurrency Bugs and Advanced Development Support for Actor-based Programs

The actor model is an attractive foundation for developing concurrent applications because actors are isolated concurrent entities that communicate through asynchronous messages and do not share state. Thereby, they avoid concurrency bugs such as data races, but are not immune to concurrency bugs in general. This study taxonomizes concurrency bugs in actor-based programs reported in literature. Furthermore, it analyzes the bugs to identify the patterns causing them as well as their observable behavior. Based on this taxonomy, we further analyze the literature and find that current approaches to static analysis and testing focus on communication deadlocks and message protocol violations. However, they do not provide solutions to identify livelocks and behavioral deadlocks. The insights obtained in this study can be used to improve debugging support for actor-based programs with new debugging techniques to identify the root cause of complex concurrency bugs.Comment: - Submitted for review - Removed section 6 "Research Roadmap for Debuggers", its content was summarized in the Future Work section - Added references for section 1, section 3, section 4.3 and section 5.1 - Updated citation

Process Patterns for Component-Based Software Development

Abstract. Component-Based Development (CBD) has been broadly used in software development, as it enhances reusability and flexibility, and reduces the costs and risks involved in systems development. It has therefore spawned many widely-used approaches, such as Commercial Off-The-Shelf (COTS) and software product lines. On the other hand, in order to gain a competitive edge, organizations need to define custom processes tailored to fit their specific de-velopment requirements. This has led to the emergence of process patterns and Method Engineering approaches. We propose a set of process patterns commonly encountered in component-based development methodologies. Seven prominent component-based method-ologies have been selected and reviewed, and a set of high-level process patterns recurring in these methodologies have been identified. A generic process framework for component-based development has been proposed based on these process patterns. The process patterns and the generic framework can be used for developing or tailoring a process for producing component-based systems

Safe sessions of channel actions in Clojure: A tour of the Discourje Project

To simplify shared-memory concurrent programming, in addition to low-level synchronisation primitives, several modern programming languages have started to offer core support for higher-level communication primitives as well, in the guise of message passing through channels. Yet, a growing body of evidence suggests that channel-based programming abstractions for shared memory also have their issues. The Discourje project aims to help programmers cope with message-passing concurrency bugs in Clojure programs, based on run-time verification and dynamic monitoring. The idea is that programmers write not only implementations, but also specifications (of sessions of channel actions). Discourje then offers a library to ensure that implementations run safely relative to specifications (= “bad” channel actions never happen). This paper gives a tour of the current state of Discourje, by example; it is intended to serve both as a general overview for readers who are unfamiliar with previous work on Discourje, and as an introduction to new features for readers who are familiar

Statistical POS tagging experiments on Persian text

Part-Of-Speech (POS) tagging is the process of marking-up the words in a text with their corresponding parts of speech. It is an essential part of text and natural language processing. There are many models and software for POS tagging in English and other European languages. Little work has been done on POS tagging of Persian language which uses Arabic script for writing. In these experiments we want to see how effective would be if we just applied a POS tagger from a language such as English to Persian. Although English and Persian are both Indo-European languages but they have subtle differences. This paper presents creation of a POS tagged corpus for evaluation purposes and evaluation of a statistical tagging method on Persian text. The results show that an overall tagging accuracy between 96.4% and 96.9% is achievable without the need to add any Persian linguistic knowledge to the tagging process. In This study we also looked at the effect of the size of training and test corpora on the accuracy of POS tagging

Evaluation of part of speech tagging on Persian text

One of the fundamental tasks in natural language processing is part of speech (POS) tagging. A POS tagger is a piece of software that reads text in some language and assigns a part of speech tag to each one of the words. Our main interest in this research was to see how easy it is to apply methods used in a language such as English to a new and different language such as Persian (Farsi) and what would be the performance of such approaches. This paper presents evaluation of several part of speech tagging methods on Persian text. These are a statistical tagging method, a memory based tagging approach and two different versions of Maximum Likelihood Estimation (MLE) tagging on Persian text. The two MLE versions differ in the way they handle the unknown words. We also demonstrate the value of simple heuristics and post-processing in improving the accuracy of these methods. These experiments have been conducted on a manually part of speech tagged Persian corpus with over two million tagged words. The results of the experiments are encouraging and comparable with the other languages such as English, German or Spanish

Micro Patterns in Agile Software

In this paper we present a study on micro patterns in different releases of two software systems developed with Object Oriented technologies and Agile process. Micro patterns are design decisions in code that can be easily automatically recognised. Gil and Maman introduced the concept to support providing objective assessment of design decisions [1]. They catalogued 27 micro patterns that capture a variety of programming practices in Java. Micro patterns can be a useful metrics in order to measure the quality of software by showing that certain categories of micro patterns are more fault prone than others, and that the classes that do not correspond to any category of micro patterns are more likely to be faulty. In our study we present some empirical results on two case studies of systems developed with Agile methodologies, and compare them to previous results obtained for non Agile systems. In particular we have verified that the distribution of micro patterns in a software system developed using Agile methodologies does not differ from the distribution studied in other systems, and that the micro patterns fault-proneness is about the same. We also analyzed how the distribution of micro patterns changes in different releases of the same software system. We demonstrate that there is a relationship between the number of faults and the classes that do not match with any micro patterns. We found that these classes are more likely to be fault-prone than the others even in software developed with Agile methodologies

Test Case Generation of Actor Systems

Testing is a vital part of the software development process. It is even more so in the context of concurrent languages, since due to undesired task interleavings and to unexpected behaviours of the underlying task scheduler, errors can go easily undetected. Test case generation (TCG) is the process of automatically generating test inputs for interesting coverage criteria, which are then applied to the system under test. This paper presents a TCG framework for actor systems, which consists of three main elements, which are the original contributions of this work: (1) a symbolic execution calculus, which allows symbolically executing the program (i.e., executing the program for unknown input data), (2) improved techniques to avoid performing redundant computations during symbolic execution, (3) new termination and coverage criteria, which ensure the termination of symbolic execution and guarantee that the test cases provide the desired degree of code coverage. Finally, our framework has been implemented and evaluated within the aPET system