Event-driven Programs Research Articles

Generating summaries for methods of event-driven programs: An Android case study

The lack of proper documentation makes program comprehension a cumbersome process for developers. Source code summarization is one of the existing solutions to this problem. Many approaches have been proposed to summarize source code in recent years. A prevalent weakness of these solutions is that they do not pay much attention to interactions among elements of software. An element is simply a callable code snippet such as a method or even a clickable button. As a result, these approaches cannot be applied to event-driven programs, such as Android applications, because they have specific features such as numerous interactions between their elements. To tackle this problem, we propose a novel approach based on deep neural networks and dynamic call graphs to generate summaries for methods of event-driven programs. First, we collect a set of comment/code pairs from Github and train a deep neural network on the set. Afterward, by exploiting a dynamic call graph, the Pagerank algorithm, and the pre-trained deep neural network, we generate summaries. An empirical evaluation with 14 real-world Android applications and 42 participants indicates 32.3% BLEU4 which is a definite improvement compared to the existing state-of-the-art techniques. We also assessed the informativeness and naturalness of our generated summaries from developers’ perspectives and showed they are sufficiently understandable and informative.

Event Loops as First-Class Values: A Case Study in Pedagogic Language Design

The World model is an existing functional input-output mechanism for event-driven programming. It is used in numerous popular textbooks and curricular settings. The World model conflates two different tasks -- the definition of an event processor and its execution -- into one. This conflation imposes a significant (even unacceptable) burden on student users in several educational settings where we have tried to use it, e.g., for teaching physics. While it was tempting to pile on features to address these issues, we instead used the Scheme language design dictum of removing weaknesses that made them seem necessary. By separating the two tasks above, we arrived at a slightly different primitive, the reactor, as our basis. This only defines the event processor, and a variety of execution operators dictate how it runs. The new design enables programmatic control over event-driven programs. This simplifies reflecting on program behavior, and eliminates many unnecessary curricular dependencies imposed by the old design. This work has been implemented in the Pyret programming language. The separation of concerns has enabled new curricula, such as the Bootstrap:Physics curriculum, to take flight. Thousands of students use this new mechanism every year. We believe that reducing impedance mismatches improves their educational experience.

Supporting asynchronization in OpenMP for event-driven programming

Abstract The event-driven programming pattern is pervasive in a wide range of modern software applications. Unfortunately, it is not easy to achieve good performance and responsiveness when developing event-driven applications. Traditional approaches require a great amount of programmer effort to restructure and refactor code, to achieve the performance speedup from parallelism and asynchronization. Not only does this restructuring require a lot of development time, it also makes the code harder to debug and understand. We propose an asynchronous programming model based on the philosophy of OpenMP, which does not require code restructuring of the original sequential code. This asynchronous programming model is complementary to the existing OpenMP fork-join model. The coexistence of the two models has potential to decrease developing time for parallel event-driven programs, since it avoids major code refactoring. In addition to its programming simplicity, evaluations show that this approach achieves good performance improvements consistent with more traditional event-driven parallelization.

Static Detection of Event-based Races in Android Apps

Event-based races are the main source of concurrency errors in Android apps. Prior approaches for scalable detection of event-based races have been dynamic. Due to their dynamic nature, these approaches suffer from coverage and false negative issues. We introduce a precise and scalable static approach and tool, named SIERRA, for detecting Android event-based races. SIERRA is centered around a new concept of "concurrency action" (that reifies threads, events/messages, system and user actions) and statically-derived order (happens-before relation) between actions. Establishing action order is complicated in Android, and event-based systems in general, because of externally-orchestrated control flow, use of callbacks, asynchronous tasks, and ad-hoc synchronization. We introduce several novel approaches that enable us to infer order relations statically: auto-generated code models which impose order among lifecycle and GUI events; a novel context abstraction for event-driven programs named action-sensitivity and finally, on-demand path sensitivity via backward symbolic execution to further rule out false positives. We have evaluated SIERRA on 194 Android apps. Of these, we chose 20 apps for manual analysis and comparison with a state-of-the-art dynamic race detector. Experimental results show that SIERRA is effective and efficient, typically taking 960 seconds to analyze an app and revealing 43 potential races. Compared with the dynamic race detector, SIERRA discovered an average 29.5 true races with 3.5 false positives, where the dynamic detector only discovered 4 races (hence missing 25.5 races per app) -- this demonstrates the advantage of a precise static approach. We believe that our approach opens the way for precise analysis and static event race detection in other event-driven systems beyond Android.

Synthesizing Event-driven Network Programs from Scenarios

Synthesizing Event-driven Network Programs from Scenarios

EventHealer: Bypassing data races in event-driven programs

Data races represent a serious threat to the reliability of shared-memory concurrent programs including event-driven programs which handle asynchronous events. Despite the important number of existing testing and detection tools, data races often remain undetectable until the exploitation phase leading the application into unpredictable executions sometimes with disastrous consequences. To heal data races, current approaches which focus only on multithreaded programs are not directly applicable to event-driven programs since they are still incomplete or incur a high runtime overhead which makes them also inappropriate for the exploitation phase. Thus, this paper proposes a hybrid technique that statically disassembles a program binary to collect information about critical sections and event handlers accessing each shared variable, to dynamically prevent data races from occurring by injecting a disabling and an enabling instruction respectively before and after every critical section, in order to enforce the synchronization property of the potentially harmful events. We implemented a prototype of this technique for sequential programs with signal handlers on top of the Pin instrumentation framework. An evaluation of this prototype proved its effectiveness and showed that our technique incurs only a negligible overhead to the monitored program.

Natural proofs for asynchronous programs using almost-synchronous reductions

We consider the problem of provably verifying that an asynchronous message-passing system satisfies its local assertions. We present a novel reduction scheme for asynchronous event-driven programs that finds almost-synchronous invariants - invariants consisting of global states where message buffers are close to empty. The reduction finds almost-synchronous invariants and simultaneously argues that they cover all local states. We show that asynchronous programs often have almost-synchronous invariants and that we can exploit this to build natural proofs that they are correct. We implement our reduction strategy, which is sound and complete, and show that it is more effective in proving programs correct as well as more efficient in finding bugs in several programs, compared to current search strategies which almost always diverge. The high point of our experiments is that our technique can prove the Windows Phone USB Driver written in P [9]correct for the responsiveness property, which was hitherto not provable using state-of-the-art model-checkers.

Race detection for Android applications

Programming environments for smartphones expose a concurrency model that combines multi-threading and asynchronous event-based dispatch. While this enables the development of efficient and feature-rich applications, unforeseen thread interleavings coupled with non-deterministic reorderings of asynchronous tasks can lead to subtle concurrency errors in the applications. In this paper, we formalize the concurrency semantics of the Android programming model. We further define the happens-before relation for Android applications, and develop a dynamic race detection technique based on this relation. Our relation generalizes the so far independently studied happens-before relations for multi-threaded programs and single-threaded event-driven programs. Additionally, our race detection technique uses a model of the Android runtime environment to reduce false positives. We have implemented a tool called DroidRacer. It generates execution traces by systematically testing Android applications and detects data races by computing the happens-before relation on the traces. We analyzed 15 Android applications including popular applications such as Facebook, Twitter and K-9 Mail. Our results indicate that data races are prevalent in Android applications, and that DroidRacer is an effective tool to identify data races.

Effective race detection for event-driven programs

Like shared-memory multi-threaded programs, event-driven programs such as client-side web applications are susceptible to data races that are hard to reproduce and debug. Race detection for such programs is hampered by their pervasive use of ad hoc synchronization, which can lead to a prohibitive number of false positives. Race detection also faces a scalability challenge, as a large number of short-running event handlers can quickly overwhelm standard vector-clock-based techniques. This paper presents several novel contributions that address both of these challenges. First, we introduce race coverage , a systematic method for exposing ad hoc synchronization and other (potentially harmful) races to the user, significantly reducing false positives. Second, we present an efficient connectivity algorithm for computing race coverage. The algorithm is based on chain decomposition and leverages the structure of event-driven programs to dramatically decrease the overhead of vector clocks. We implemented our techniques in a tool called EventRacer and evaluated it on a number of public web sites. The results indicate substantial performance and precision improvements of our approach over the state-of-the-art. Using EventRacer , we found many harmful races, most of which are beyond the reach of current techniques.

Python programming fundamentals

Computer programming is a skill that can bring great enjoyment from the creativity involved in designing and implementing a solution to a problem. This classroom-tested and easy-to-follow textbook teaches the reader how to program using Python, an accessible language which can be learned incrementally. Through an extensive use of examples and practical exercises, students will learn to recognize and apply abstract patterns in programming, as well as how to inspect the state of a program using a debugger tool. Features: contains numerous examples and solved practice exercises designed for an interactive classroom environment; highlights several patterns which commonly appear in programs, and presents exercises that reinforce recognition and application of these patterns; introduces the use of a debugger, and includes supporting material that reveals how programs work; presents the Tkinter framework for building graphical user interface applications and event-driven programs; provides helpful additional resources for instructors at the associated website: http://cs.luther.edu/~leekent/CS1. This hands-on textbook for active learning in the classroom will enable undergraduates in computer science to develop the necessary skills to begin developing their own programs. It employs Python as the introductory language due to the wealth of support available for programmers.

A universal fast graphical user interface building tool for arbitrary interpreters

We consider the issue of implementing graphical user interfaces (GUIs): we present an easy-to-use and fast GUI building tool, specially designed to be used with interpreters. It supports a variety of communication methods and interaction models, therefore being able to collaborate with a huge diversity of interpreters in a natural way, in POSIX compliant (or similar) environment. Thus it enables the programmer to easily create a GUI, no matter what kind of language or model the actual interpreter implements. Event-driven programs in UNIX shells and graphical user interfaces in a data oriented language are presented as example applications.

Software design guidelines for event-driven programming

This paper deals with software design principles and guidelines to improve the reusability and maintainability of event-driven (E-D) programs. The paper examines how well the principles of structured software design from the procedural programming field can be applied to the event-driven environment. Taking into account the unique characteristics of event-driven programming (E-DP), additional guidelines that are specific to this field are proposed. The guidelines presented here deal with modularizing event procedures, graphical representation of E-D programs, sharing data between event/general procedures, using user-defined objects, and developing cohesive procedures and forms.

An inexpensive experiment controller for stand-alone applications or distributed processing networks

An inexpensive microprocessor-based experiment controller available as a commercially produced bare printed circuit board is described. It provides for up to 8 inputs and 40 outputs. An 8K Experiment Control BASIC (ECBASIC) and a compiled Experiment Control Language (ECL) are also available. Both languages have internal structures that enable time and responses to be dealt with in a very convenient and error-free manner. Time and response count are automatically incrementing variables that need only to be tested by the user program. ECBASIC provides a 10-msec accuracy, whereas ECL provides a l-msec accuracy. ECL provides extensive support for event-driven programs. The board and software are designed to provide an orderly migration from a stand-alone controller running ECBASIC as a relay-rack replacement, to a network of ECBASIC machines on a small computer, to a true error-checking network of ECL machines on a time-sharing operating system of a large computer. Network communication is over the three wires of a single unmodified RS232 asynchronous serial communication line.