As smartphones and tablets have become ubiquitous, there is a growing demand for apps that can enable users to collaboratively use multiple mobile systems. We present Tap, a framework that makes it easy for users to dynamically compose collections of mobile systems and developers to write apps that make use of those impromptu collections. Tap users control the composition by simply tapping systems together for discovery and authentication. The physical interaction mimics and supports ephemeral user interactions without the need for tediously exchanging user contact information such as phone numbers or email addresses. Tapping triggers a simple NFC-based mechanism to exchange connectivity information and security credentials that works across heterogeneous networks and requires no user accounts or cloud infrastructure support. Tap makes it possible for apps to use existing mobile platform APIs across multiple mobile systems by virtualizing data sources so that local and remote data sources can be combined together upon tapping. Virtualized data sources can be hardware or software features, including media, clipboard, calendar events, and devices such as cameras and microphones. Leveraging existing mobile platform APIs makes it easy for developers to write apps that use hardware and software features across dynamically composed collections of mobile systems. We have implemented a Tap prototype that allows apps to make use of both unmodified Android and iOS systems. We have modified and implemented various apps using Tap to demonstrate that it is easy to use and can enable apps to provide powerful new functionality by leveraging multiple mobile systems. Our results show that Tap has good performance, even for high-bandwidth features, and is user and developer friendly.

As smartphones and tablets proliferate, there is a growing demand for multi-mobile computing, the ability to combine multiple mobile systems into more capable ones. We present M2, a system for multi-mobile computing that enables existing unmodified mobile apps to share and combine multiple devices, including cameras, displays, speakers, microphones, sensors, GPS, and input. M2 introduces a new data-centric approach that leverages higher-level device abstractions and hardware acceleration to efficiently share device data, not API calls. To support heterogeneous devices, M2 introduces device transformation, a new technique to mix and match different types of devices. Example transformations include combining multiple displays into a single larger display for better viewing, or substituting accelerometer for touchscreen input to provide a Nintendo Wii-like experience with existing mobile gaming apps. We have implemented M2 and show that it (1) operates across heterogeneous systems, including multiple versions of Android and iOS, (2) can enable unmodified Android apps to use multiple mobile devices in new and powerful ways, including supporting users with disabilities and better audio conferencing, and (3) can run apps across mobile systems with modest overhead and qualitative performance indistinguishable from using local device hardware.

As smartphones and tablets proliferate, there is a growing demand for multi-mobile computing [1, 2], the ability to combine multiple commodity mobile systems into more capable ones, including using multiple hardware devices such as cameras, displays, speakers, microphones, sensors, GPS, and input. However, the tremendous device, hardware, and software heterogeneity of mobile systems makes this difficult. In this demo, we present M2, a system for multi-mobile computing that enables existing unmodified mobile apps to make use of new ways of sharing and combining multiple devices. M2 introduces a new data-centric approach that leverages higher-level device abstractions and encoding/decoding hardware to efficiently share device data as opposed to low-level device-specific APIs.

Mobile apps make extensive use of GPUs on smartphones and tablets to access Web content. To support pervasive Web content, we introduce three key OS techniques for binary graphics compatibility necessary to build a real-world system to run iOS and Android apps together on the same smartphone or tablet. First diplomat usage patterns manage resources to bridge proprietary iOS and Android graphics implementations. Second, thread impersonation allows a single thread-specific context to be shared amongst multiple threads using multiple iOS and Android personas. Third, dynamic library replication allows multiple, independent instances of the same library to be loaded in a single process to support iOS apps on Android while using multiple graphics API versions at the same time. We use these techniques to build a system prototype, and demonstrate that it runs widely-used iOS apps, including apps such as Safari that use the popular GPU-accelerated WebKit framework, using a Google Nexus tablet running Android.

We present Cider, an operating system compatibility architecture that can run applications built for different mobile ecosystems, iOS or Android, together on the same smartphone or tablet. Cider enhances the domestic operating system, Android, of a device with kernel-managed, per-thread personas to mimic the application binary interface of a foreign operating system, iOS, enabling it to run unmodified foreign binaries. This is accomplished using a novel combination of binary compatibility techniques including two new mechanisms: compile-time code adaptation, and diplomatic functions. Compile-time code adaptation enables existing unmodified foreign source code to be reused in the domestic kernel, reducing implementation effort required to support multiple binary interfaces for executing domestic and foreign applications. Diplomatic functions leverage per-thread personas, and allow foreign applications to use domestic libraries to access proprietary software and hardware interfaces. We have built a Cider prototype, and demonstrate that it imposes modest performance overhead and runs unmodified iOS and Android applications together on a Google Nexus tablet running the latest version of Android.