Summary Thread‐level speculation can be used to take advantage of multicore architectures for JavaScript in web applications. We extend previous studies with these main contributions; we implement thread‐level speculation in the state‐of‐the art just‐in‐time‐enabled JavaScript engine V8 and make the measurements in the Chromium web browser both from Google instead of using an interpreted JavaScript engine. We evaluate the thread‐level speculation and just‐in‐time compilation combination on 15 very popular web applications, 20 HTML5 demos from the JS1K competition, and 4 Google Maps use cases. The performance is evaluated on two, four, and eight cores. The results clearly show that it is possible to successfully combine thread‐level speculation and just‐in‐time compilation. This makes it possible to take advantage of multicore architectures for web applications while hiding the details of parallel programming from the programmer. Further, our results show an average speedup for the thread‐level speculation and just‐in‐time compilation combination by a factor of almost 3 on four cores and over 4 on eight cores, without changing any of the JavaScript source code. Copyright © 2016 John Wiley & Sons, Ltd.

JavaScript is a sequential programming language that has a large potential for parallel execution in Web applications. Thread-level speculation can take advantage of this, but it has a large memory overhead. In this article, we evaluate the effects of adjusting various parameters for thread-level speculation. Our results clearly show that thread-level speculation is a useful technique for taking advantage of multicore architectures for JavaScript in Web applications, that nested speculation is required in thread-level speculation, and that the execution characteristics of Web applications significantly reduce the needed memory, the number of threads, and the depth of our speculation.