Practical AJAX race detection for JavaScript web applications

Abstract

Asynchronous client-server communication is a common source of errors in JavaScript web applications. Such errors are difficult to detect using ordinary testing because of the nondeterministic scheduling of AJAX events. Existing automated event race detectors are generally too imprecise or too inefficient to be practically useful. To address this problem, we present a new approach based on a lightweight combination of dynamic analysis and controlled execution that directly targets identification of harmful AJAX event races. We experimentally demonstrate using our implementation, Ajax-Racer, that this approach is capable of automatically detecting harmful AJAX event races in many websites, and producing informative error messages that support diagnosis and debugging. Among 20 widely used web pages that use AJAX, AjaxRacer discovers harmful AJAX races in 12 of them, with a total of 72 error reports, and with very few false positives. CCS CONCEPTS • Software and its engineering → Software testing and debugging;

NodeRacer: Event Race Detection for Node.js Applications

“…In particular, R 4 employs a technique called conflict-reversal bounding to minimize the event reordering; this has inspired the diagnosis mode of NODERACER. RClassify [4], InitRacer [5], EventRaceCommander [8], and AjaxRacer [6] diverge from previous tools in the implementation design. Instead of adopting some kind of browser modification, they instrument the client-side JavaScript code.…”

“…For this reason, Node.fz does not find the bug even after 1 000 runs. 6 III. BACKGROUND Node.js is a JavaScript-based runtime environment that integrates three main components [16]: (i) the V8 highperformance JavaScript engine developed by Google; (ii) the libuv I/O library that implements the event loop, the worker thread mechanism, and all of the asynchronous behavior; and (iii) native libraries that abstract the functionalities for highlevel use by developers.…”

“…Their authors argue that this platform-agnostic design is more robust to changes and updates than platform-specific solutions. The idea of postponing events in NODERACER is also used by EventRaceCommander [8] and AjaxRacer [6], for repairing event race errors and for identify harmful races between AJAX events, respectively.…”

“…The key idea is to explore alternative schedules entirely by selectively postponing events, without interfering with the internal event queues in Node.js. This approach is inspired by EventRaceCommander [8] and AjaxRacer [6]. To avoid postponing events in ways that are impossible in ordinary executions, and to avoid postponing events needlessly, the exploration is guided by a happens-before relation that captures causal relationships of events.…”

“…The happens-before relation is inferred from an initial execution of the application, driven either by a regression test or by a manual interaction with the application. Unlike traditional race detectors [2], we follow the approach of AjaxRacer [6] by completely ignoring the low-level data races on individual memory locations and instead detecting race errors by looking for the observable effects, such as crashes or regression test failures. To support debugging after a race error has been detected, NODERACER can be run in a diagnosis mode where it systematically looks for the smallest number of changes to the original schedule that exposes the error, inspired by the conflict-reversal bounding technique of R 4 [7].…”