HACMony: Automatically Detecting Hopping-related Audio-stream Conflict Issues on HarmonyOS

HarmonyOS is emerging as a popular distributed operating system for diverse mobile devices. One of its standout features is app-hopping, which allows users to seamlessly transition apps across different HarmonyOS devices. However, when apps playing audio streams hop between devices, they can easily trigger Hopping-related Audio-stream Conflict (HAC) scenarios. Improper resolution of HAC will lead to significant HAC issues, which are harder to detect compared to single-device audio-stream conflicts, due to the unclear semantics of HarmonyOS's app-hopping mechanism and the lack of effective multi-app hopping testing methods. To fill the gap, this paper introduces an automated and efficient approach to detecting HAC issues. We formalized the operational semantics of HarmonyOS's app-hopping mechanism for audio streams for the first time. Leveraging this formalization, we designed an Audio Service Transition Graph (ASTG) to model the behaviors of audio-API-related services and proposed a model-based approach to detect HAC issues automatically. Our techniques were implemented in a tool, HACMony, and evaluated on 20 real-world HarmonyOS apps. Experimental results reveal that 11 of the 20 apps exhibit HAC issues. Additionally, we summarized the detected issues into two typical types, namely MoD and MoR, and analyzed their characteristics to assist and guide both app and OS developers.