WebDelta: Lightweight Migration of Web Applications with Modified Execution State

摘要

Web applications (apps) can play an important role for the era of ubiquitous computing since they can run on any smart or IoT devices equipped with a browser. This advantage of portability and simplicity can be extended further to allow an interesting user experience called app migration. That is, we can save the execution state of a running web app into a file named snapshot, transmit it to another device, and continue the execution by loading the snapshot. One issue is that saving the whole execution state of a running app including all objects in the runtime heap will be inefficient, since most of the current states are unchanged from the initial state. To reduce this inefficiency, we propose WebDelta which selectively saves only those that are modified from the initial state. This selective snapshot is saved as a patch file so that after migration, once the original app is launched, the current state can be restored by applying the patch file. We model the relationship between the JavaScript objects as a directed graph to efficiently and completely save the delta of the JavaScript state. We solve the challenging issues related to modified closure variables or modified event handlers attached to the DOM objects. Our framework could successfully migrate five real web apps, and we could speed up the total migration time as much as by 2.7x.