Disclosure: Efficient Instrumentation-Based Web App Migration for Liquid Computing

Abstract

Web App migration means capturing a snapshot of the execution state of an web app on a device, and restoring it on another device to continue its execution, for cross-device liquid computing. Although web apps are relatively easy to migrate due to its high portability, there is a JavaScript language feature called closure, which complicates migration since it requires migrating the variable states of already-finished outer functions. One approach of web app migration is to instrument the source code to trace the closure variables, yet it often suffers from performance slowdown, especially for multiple migrations. In this paper, we propose a new instrumentation-based technique called Disclosure, which moves the declarations of closure variables to a managed data structure and replaces closure variables by the corresponding references to the data structure. This can improve the runtime performance while enhancing security. We evaluated our work with eight Octane benchmarks and four real web apps. The runtime performance penalty due to Disclosure is 0%–15%, which is much better than the result of the latest instrumentation-based work that supports deep closures and multiple migrations, as Disclosure. Real web apps are also shown to migrate seamlessly, even multiple times.