Google will make the Android Runtime (ART) a Mainline module in Android 12
Project Mainline is one of the biggest changes to Android in recent years. While you as a consumer may not notice this change, it fundamentally alters how Android operates as an open-source operating system, with more power now resting in the hands of Google than ever before. Whether this increase in control is good or bad is a topic for a different debate. Now, Google plans to include the Android Runtime (ART) as an updatable Mainline module in Android 12.
What is Android Runtime (ART)?
Android Runtime, or ART, is the default runtime on Android that was introduced back in 2013 along with Android 4.4 Kitkat. As Google mentions, ART is the “managed runtime used by applications and some system services on Android“. Here is an XDA TV video from 2014 that explains ART with reference to the changes it brings about from the erstwhile Dalvik VM:
Long story short, ART essentially translates an Android app’s bytecode into native instructions. It uses ahead-of-time compilation to compile apps into native machine code directly upon installation. As you can guess, this is a pretty important function that ideally should perform in the same manner across the entire Android ecosystem.
ART as a Mainline Module
By making ART a Mainline module, Google will be able to exercise much more control over it, in line with the overarching theme of mainline modules. As we mention in our primary explainer on Project Mainline:
Project Mainline extends the efforts of Project Treble. While Treble reduced how dependent OEMs were on SoC vendors for every single OS update, Mainline reduces how dependent Google is on OEMs for delivering security updates to key OS components. Project Mainline extends the Treble philosophy to more critical parts of the Android framework, removing OEMs as the dependent middlemen from this equation. The purpose of Project Mainline is for Google to wrest control of framework components and system applications that are critical to security and maintaining development consistency away from OEMs. Project Mainline is rightfully referred to as the biggest change to Android since Project Treble.
ART as a Mainline module would allow Google to update it without needing a system OTA update. If Google makes it mandatory for OEMs to preload a Google-signed ART module (likely delivered in the form of an APEX), then Google will be able to retain control over pushing updates to ART on all Android devices. Google would be able to push updates to ART through the Google Play Store, and OEMs wouldn’t be able to make modifications to ART. This in turn inches towards the behavioural consistency that third-party app developers would expect across the ecosystem.