Runtime Errors Research Articles

Bounded Symbolic Execution for Runtime Error Detection of Erlang Programs

Dynamically typed languages, like Erlang, allow developers to quickly write programs without explicitly providing any type information on expressions or function definitions. However, this feature makes those languages less reliable than statically typed languages, where many runtime errors can be detected at compile time. In this paper, we present a preliminary work on a tool that, by using the well-known techniques of metaprogramming and symbolic execution, can be used to perform bounded verification of Erlang programs. In particular, by using Constraint Logic Programming, we develop an interpreter that, given an Erlang program and a symbolic input for that program, returns answer constraints that represent sets of concrete data for which the Erlang program generates a runtime error.

AACVOX: mobile application for augmentative alternative communication to help people with speech disorder and motor impairment

AbstractIntroduction: Communication is a fundamental element for the development of human beings, promoting their coexistence in society. However, changes in muscle tone, associated with cerebral palsy (CP), among other conditions, cause phono-articulatory dysfunctions hindering speech capabilities. Although there are resources for augmentative and alternative communication (AAC), most of them do not completely satisfy the needs of individuals with motor impairment. Therefore, this study proposes a tool based on mobile technology for AAC, which can be adapted to the characteristics of the motor limitations of CP users. Methods Mobile system development was conducted employing user-centered design and development methods. Functions were developed allowing the communication of phrases through pictographic resources and a mechanism of speech synthesis, that can be customized according to specific communication needs. To validate this system, 20 CP volunteers with speech difficulties and motor impairment were recruited from two institutions in the State of Sao Paulo, Brazil. They operated the system following a pre-defined test protocol, and they answered a system usability scale (SUS) questionnaire, to rate the ease of learning, memorization, efficiency, occurrence of runtime errors, and the level of user satisfaction. Results The results showed a score of 85.85 ± 2.28 above the average SUS scale, for each one of the quality components assessed by the volunteers. Conclusion The developed software is user-friendly, representing a new option for AAC, and is customized according to the communication needs of people with speech disorder and motor impairment.

Improving Verification Accuracy of CPS by Modeling and Calibrating Interaction Uncertainty

Cyber-Physical Systems (CPS) intrinsically combine hardware and physical systems with software and network, which are together creating complex and correlated interactions. CPS applications often experience uncertainty in interacting with environment through unreliable sensors. They can be faulty and exhibit runtime errors if developers have not considered environmental interaction uncertainty adequately. Existing work in verifying CPS applications ignores interaction uncertainty and thus may overlook uncertainty-related faults. To improve verification accuracy, in this article we propose a novel approach to verifying CPS applications with explicit modeling of uncertainty arisen in the interaction between them and the environment. Our approach builds an Interactive State Machine network for a CPS application and models interaction uncertainty by error ranges and distributions. Then it encodes both the application and uncertainty models to Satisfiability Modulo Theories (SMT) formula to leverage SMT solvers searching for counterexamples that represent application failures. The precision of uncertainty model can affect the verification results. However, it may be difficult to model interaction uncertainty precisely enough at the beginning, because of the uncontrollable noise of sensors and insufficient data sample size. To further improve the accuracy of the verification results, we propose an approach to identifying and calibrating imprecise uncertainty models. We exploit the inconsistency between the counterexamples’ estimate and actual occurrence probabilities to identify possible imprecision in uncertainty models, and the calibration of imprecise models is to minimize the inconsistency, which is reduced to a Search-Based Software Engineering problem. We experimentally evaluated our verification and calibration approaches with real-world CPS applications, and the experimental results confirmed their effectiveness and efficiency.

Identification and Refactoring of Exception Handling Code Smells in JavaScript

Avoid making bad smells is very important in writing exception handling code for dealing with unexpected runtime errors. The task however is challenging and demands proficient programming skills and experience. This is particularly true in developing JavaScript applications because JavaScript is very rich in features as being dynamic, interpreted and object-oriented with first-class functions. What further complicates the situation is the use of event-driven and non-blocking I/O model in Node.js, which is a runtime environment written in server-side JavaScript. Extended from our previous work on exception handling code smells in Java, this study aims at identifying exception handling code smells that can occur in a JavaScript application at either the client side or the server side. The impact to software quality that each smell has is demonstrated with examples. Refactorings corresponding to the identified smells are proposed; their effects to the application, including the robustness level achieved and other benefits gained, are illustrated. The work is intended to serve as a guide in helping JavaScript developers avoid or discover exception handling code smells.

Practical aspects of the DesignDEVS simulation environment

DesignDEVS is a simulation development environment based on the Discrete Event System Specification (DEVS) formalism. This paper provides an in-depth overview of the software while focusing on the practical considerations influencing its design. Practitioners who stand to benefit from systems engineering will approach formalism-based simulation tools with little knowledge of the underlying theory. It is therefore important that theoretical principles, such as the separation of model and simulator, be emphasized by the user interface. Other practical aspects of DesignDEVS include the simplicity of atomic model code, a focus on coupling for collaboration purposes, the enforcement of essential modeling constraints, and a reliance on best practices in cases where strict enforcement might inconvenience users. In DesignDEVS, an issue we refer to as the Insidious Pointer Problem is aggressively tackled through run-time error handling. By contrast, the separation of output values from state transitions is left as a best practice for the sake of user convenience. The design decisions explained in this paper are relevant to developers of other formalism-based tools seeking widespread adoption of scalable modeling and simulation practices.

Optimal production run time and inspection errors in an imperfect production system with warranty

This paper considers an imperfect production system to obtain the optimal production run time and inspection policy. Contrary to the existing literature this model considerers that product inspection performs at any arbitrary time of the production cycle and after the inspection, all defective products produced until the end of the production run are fully reworked. Due to some misclassification during inspection, from the inspector's side two types of inspection errors as Type Ⅰ and Type Ⅱ are considered to make the model more realistic rather than existing models. Defective items, found by the inspector, are salvaged at some cost before being shipped. Non-inspected defective items are passed to customers with free minimal repair warranty. The model gives three special cases, where it is found that this model converges over the exiting literature. Some numerical examples along with graphical representations are provided to illustrate the proposed model with comparison with the existing models. Sensitivity analysis of the optimal solution with respect to key parameters of the model has been carried out and the implications are discussed.

Edit Transactions: Dynamically Scoped Change Sets for Controlled Updates in Live Programming

Live programming environments enable programmers to edit a running program and obtain immediate feedback on each individual change. The liveness quality is valued by programmers to help work in small steps and continuously add or correct small functionality while maintaining the impression of a direct connection between each edit and its manifestation at run-time. Such immediacy may conflict with the desire to perform a combined set of intermediate steps, such as a refactoring, without immediately taking effect after each individual edit. This becomes important when an incomplete sequence of small-scale changes can easily break the running program. State-of-the-art solutions focus on retroactive recovery mechanisms, such as debugging or version control. In contrast, we propose a proactive approach: Multiple individual changes to the program are collected in an Edit Transaction, which can be made effective if deemed complete. Upon activation, the combined steps become visible together. Edit Transactions are capable of dynamic scoping, allowing a set of changes to be tested in isolation before being extended to the running application. This enables a live programming workflow with full control over change granularity, immediate feedback on tests, delayed effect on the running application, and coarse-grained undos. We present an implementation of Edit Transactions along with Edit-Transaction-aware tools in Squeak/Smalltalk. We asses this implementation by conducting a case study with and without the new tool support, comparing programming activities, errors, and detours for implementing new functionality in a running simulation. We conclude that workflows using Edit Transactions have the potential to increase confidence in a change, reduce potential for run-time errors, and eventually make live programming more predictable and engaging.

Analysis and Diagnosis of SLA Violations in a Production SaaS Cloud

A software-as-a-service (SaaS) needs to provide its intended service as per its stated service-level agreements (SLAs). While SLA violations in a SaaS platform have been reported, not much work has been done to empirically characterize failures of SaaS. In this paper, we study SLA violations of a production SaaS platform, diagnose the causes, unearth several critical failure modes, and then, suggest various solution approaches to increase the availability of the platform as perceived by the end user. Our approach combines field failure data analysis (FFDA) and fault injection. Our study is based on 283 days of operational logs of the platform. During this time, the platform received business workload from 42 customers spread over 22 countries. We have first developed a set of home-grown FFDA tools to analyze the log, and second implemented a fault injector to automatically inject several runtime errors in the application code written in .NET/C#, and then, collate the injection results. We summarize our finding as: first, system failures have caused 93% of all SLA violations; second, our fault injector has been able to recreate a few cases of bursts of SLA violations that could not be diagnosed from the logs; and third, the fault injection mechanism could recreate several error propagation paths leading to data corruptions that the failure data analysis could not reveal. Finally, the paper presents some system-level implication of this study and how the joint use of fault injection and log analysis may help in improving the reliability of the measured platform.

Static Analysis of Embedded Real-Time Concurrent Software with Dynamic Priorities

In previous work, we developed a sound static analysis by abstract interpretation to check the absence of run-time errors in concurrent programs, focusing on embedded C programs composed of a fixed set of threads in a shared memory. The method is thread-modular: it considers each thread independently, analyzing them with respect to an abstraction of the effect of the other threads, so-called interference, which are also inferred automatically as part of analyzing the threads. The analysis thus proceeds in a series of rounds that reanalyze all threads, gathering an increasing set of interference, until stabilization. We proved that this method is sound and covers all possible thread interleavings. This analysis was integrated into the Astrée industrial-scale static analyzer, deployed in avionics and automotive industries.In this article, we consider the more specific case of programs running under a priority-based real-time scheduler, as is often the case in embedded systems. In such programs, higher priority threads cannot be preempted by lower priority ones (except when waiting explicitly for some resource). The programmer exploits this property to reduce the reliance on locks when protecting critical sections. We show how our analysis can be refined through partitioning in order to take into account the real-time hypothesis, remove spurious interleavings, and gain precision on programs that rely on priorities. Our analysis supports in particular dynamic priorities: we handle explicit modifications of the priorities by the program, as well as implicit ones through the priority ceiling protocol.We illustrate our construction formally on an idealized language. Following previous work, we first provide a concrete semantics in thread-modular denotational form that is complete for safety properties, and then show how to apply classic abstractions to obtain an effective static analyzer, able to detect all run-time errors, data-races, as well as deadlocks. Finally, we briefly discuss our implementation inside the Astrée analyzer and on-going experimentation, with results limited for now to small programs.

Incremental bounded model checking for embedded software

Program analysis is on the brink of mainstream usage in embedded systems development. Formal verification of behavioural requirements, finding runtime errors and test case generation are some of the most common applications of automated verification tools based on bounded model checking (BMC). Existing industrial tools for embedded software use an off-the-shelf bounded model checker and apply it iteratively to verify the program with an increasing number of unwindings. This approach unnecessarily wastes time repeating work that has already been done and fails to exploit the power of incremental SAT solving. This article reports on the extension of the software model checker CBMC to support incremental BMC and its successful integration with the industrial embedded software verification tool BTC EMBEDDEDTESTER. We present an extensive evaluation over large industrial embedded programs, mainly from the automotive industry. We show that incremental BMC cuts runtimes by one order of magnitude in comparison to the standard non-incremental approach, enabling the application of formal verification to large and complex embedded software. We furthermore report promising results on analysing programs with arbitrary loop structure using incremental BMC, demonstrating its applicability and potential to verify general software beyond the embedded domain.

Numerical Simulation of Hydrodynamic for Abrupt Bathymetry in Palu River Estuary

The failure of numerical simulation for hydrodynamic model in abrupt bathymetry zone is one of the obstacles in solving environmental problems in coastal zone. The research aims to make three dimensional hydrodynamic model in Palu river estuary that has abrubt bathymetry using ECOMSED. The simulation was conducted on horizontal and vertical cross section with the boundary condition of model, i.e. the depth data was used at the bottom of the river and the sea, river discharge at upstream and tide constituents at downstream. Input data and interpolation program was made in solving error problem. Run time error occurred during simulation, therefore, experimental method was used by modifying input data and increasing the number of grid and time step resolution to make calculation became stable. The results revealed that the influence of tidal current in Palu river estuary is smaller than the influence of river discharge and the temperature is mainly distributed westward on the horizontal cross section. While on the vertical cross section, the direction of temperature distribution follows the current movement pattern based on the overlay between current and temperature distribution. The calculated surface elevation and current velocity on the vertical cross section well suits with the secondary data obtained from hydro oceanographic office and observed current velocity.

The Optimization of a Symbolic Execution Engine for Detecting Runtime Errors

In a software system, most of the runtime failures may come to light only during test execution, and this may have a very high cost. To help address this problem, a symbolic execution engine called RTEHunter, which has been developed at the Department of Software Engineering at the University of Szeged, is able to detect runtime errors (such as null pointer dereference, bad array indexing, division by zero) in Java programs without actually running the program in a real-life environment. Applying the theory of symbolic execution, RTEHunter builds a tree, called a symbolic execution tree, composed of all the possible execution paths of the program. RTEHunter detects runtime issues by traversing the symbolic execution tree and if a certain condition is fulfilled the engine reports an issue. However, as the number of execution paths increases exponentially with the number of branching points, the exploration of the whole symbolic execution tree becomes impossible in practice. To overcome this problem, different kinds of constraints can be set up over the tree. E.g. the number of symbolic states, the depth of the execution tree, or the time consumption could be restricted. Our goal in this study is to find the optimal parametrization of RTEHunter in terms of the maximum number of states, maximum depth of the symbolic execution tree and search strategy in order to find more runtime issues in a shorter time. Results on three open-source Java systems demonstrate that more runtime issues can be detected in the 0 to 60 basic block-depth levels than in deeper ones within the same time frame. We also developed two novel search strategies for traversing the tree based on the number of null pointer references in the program and on linear regression that performs better than the default depth-first search strategy.

Jolie Static Type Checker: a Prototype

Static verification of a program source code correctness is an important element of software reliability. Formal verification of software programs involves proving that a program satisfies a formal specification of its behavior. Many languages use both static and dynamic type checking. With such approach, the static type checker verifies everything possible at compile time, and the dynamic one checks the remaining. The current state of the Jolie programming language includes a dynamic type system. Consequently, it allows avoidable run-time errors. A static type system for the language has been formally defined on paper but lacks an implementation yet. In this paper, we describe a prototype of Jolie Static Type Checker (JSTC), which employs a technique based on a SMT solver. We describe the theory behind and the implementation, and the process of static analysis. The article is published in the authors’ wording.

Gradual refinement types

Refinement types are an effective language-based verification technique. However, as any expressive typing discipline, its strength is its weakness, imposing sometimes undesired rigidity. Guided by abstract interpretation, we extend the gradual typing agenda and develop the notion of gradual refinement types, allowing smooth evolution and interoperability between simple types and logically-refined types. In doing so, we address two challenges unexplored in the gradual typing literature: dealing with imprecise logical information, and with dependent function types. The first challenge leads to a crucial notion of locality for refinement formulas, and the second yields novel operators related to type- and term-level substitution, identifying new opportunity for runtime errors in gradual dependently-typed languages. The gradual language we present is type safe, type sound, and satisfies the refined criteria for gradually-typed languages of Siek et al. We also explain how to extend our approach to richer refinement logics, anticipating key challenges to consider.

A Typeful Integration of SQL into Curry

We present an extension of the declarative programming language Curry to support the access to data stored in relational databases via SQL. Since Curry is statically typed, our emphasis on this SQL integration is on type safety. Our extension respects the type system of Curry so that run-time errors due to ill-typed data are avoided. This is obtained by preprocessing SQL statements at compile time and translating them into type-safe database access operations. As a consequence, the type checker of the Curry system can spot type errors in SQL statements at compile time. To generate appropriately typed access operations, the preprocessor uses an entity-relationship (ER) model describing the structure of the relational data. In addition to standard SQL, SQL statements embedded in Curry can include program expressions and also relationships specified in the ER model. The latter feature is useful to avoid the error-prone use of foreign keys. As a result, our SQL integration supports a high-level and type-safe access to databases in Curry programs.

Static Analysis of Runtime Errors in Interrupt-Driven Programs via Sequentialization

Embedded software often involves intensive numerical computations and suffers from a number of runtime errors. The technique of numerical static analysis is of practical importance for checking the correctness of embedded software. However, most of the existing approaches of numerical static analysis consider sequential programs, while interrupts are a commonly used facility that introduces concurrency in embedded systems. Therefore, a numerical static analysis approach is highly desired for embedded software with interrupts. In this article, we propose a static analysis approach specifically for interrupt-driven programs based on sequentialization techniques. We present a method to sequentialize interrupt-driven programs into nondeterministic sequential programs according to the semantics of interrupts. The key benefit of using sequentialization is the ability to leverage the power of state-of-the-art analysis and verification techniques for sequential programs to analyze interrupt-driven programs, for example, the power of numerical abstract interpretation to analyze numerical properties of the sequentialized programs. Furthermore, to improve the analysis precision and scalability, we design specific abstract domains to analyze sequentialized interrupt-driven programs by considering their specific features. Finally, we present encouraging experimental results obtained by our prototype implementation.

Effectuation, Not Being Pragmatic or Process Theorizing, Remains Ineffectual: Responding to the Commentaries

Effectuation, Not Being Pragmatic or Process Theorizing, Remains Ineffectual: Responding to the Commentaries

Event-based run-time adaptation in communication-centric systems

Abstract Communication-centric systems are software systems built as assemblies of distributed artifacts that interact following predefined communication protocols. Session-based concurrency is a type-based approach to ensure the conformance of communication-centric systems to such protocols. This paper presents a model of session-based concurrency with mechanisms for run-time adaptation . Our model allows us to specify communication-centric systems whose session behavior can be dynamically updated at run-time. We improve on previous work by proposing an event-based approach: adaptation requests, issued by the system itself or by its context, are assimilated to events which may trigger adaptation routines. These routines exploit type-directed checks to enable the reconfiguration of processes with active protocols. We equip our model with a type system that ensures communication safety and consistency properties: while safety guarantees absence of run-time communication errors, consistency ensures that update actions do not disrupt already established session protocols. We provide soundness results for binary and multiparty protocols.

A safe-by-design programming language for wireless sensor networks

Wireless sensor networks are notoriously difficult to program and debug. This fact not only stems from the nature of the hardware, but also from the current approaches for developing programming languages and runtime systems for these platforms. In particular, current systems do not place enough stress on providing formal descriptions of the language and its runtime system, and on proving static properties, like type-safety and soundness. In this paper, we present the design, specification, and implementation of a programming language and a runtime system for wireless sensor networks that are safe by design. We say this in the sense that we can statically detect a large set of would-be runtime errors, and that the runtime system will not incorrectly execute an application, once the latter is deployed. We have a full prototype implementation of the system that supports SunSPOT devices, the simulation tool VisualSense, and local computer networks for fast deployment and testing of applications. Development is supported by an IDE implemented on top of the Eclipse tool that embeds both the compiler and the virtual machine seamlessly, and is used to produce software releases.

Principal type inference for GADTs

We present a new method for GADT type inference that improves the precision of previous approaches. In particular, our approach accepts more type-correct programs than previous approaches when they do not employ type annotations. A side benefit of our approach is that it can detect a wide range of runtime errors that are missed by previous approaches. Our method is based on the idea to represent type refinements in pattern-matching branches by choice types, which facilitate a separation of the typing and reconciliation phases and thus support case expressions. This idea is formalized in a type system, which is both sound and a conservative extension of the classical Hindley-Milner system. We present the results of an empirical evaluation that compares our algorithm with previous approaches.