Incremental Install

Incremental Install is a way of building & deploying an APK that tries to minimize the time it takes to make a change and see that change running on device. They work best with is_component_build=true, and do not require a rooted device.

Building

Add the gn arg:

incremental_install = true

This causes all apks to be built as incremental except for denylisted ones.

Running

It is not enough to adb install them. You must use the generated wrapper script:

out/Debug/bin/your_apk run out/Debug/bin/runchromepublictestapk # Automatically sets --fast-local-dev

How it Works

Overview

The basic idea is to sideload .dex and .so files to /data/local/tmp rather than bundling them in the .apk. Then, when making a change, only the changed .dex / .so needs to be pushed to the device.

Faster Builds:

* No final_dex step (where all .dex files are merged into one) * No need to rebuild .apk for code-only changes (but required for resources) * Apks sign faster because they are smaller.

Faster Installs:

* The .apk is smaller, and so faster to verify. * No need to run adb install for code-only changes. * Only changed .so / .dex files are pushed. MD5s of existing on-device files are cached on host computer.

Slower Initial Runs:

* The first time you run an incremental .apk, the DexOpt needs to run on all .dex files. This step is normally done during adb install, but is done on start-up for incremental apks. * DexOpt results are cached, so subsequent runs are faster. * The slowdown varies significantly based on the Android version. Android O+ has almost no visible slow-down.

Caveats: * Isolated processes (on L+) are incompatible with incremental install. As a work-around, isolated processes are disabled when building incremental apks. * Android resources, assets, and loadable_modules are not sideloaded (they remain in the apk), so builds & installs that modify any of these are not as fast as those that modify only .java / .cc. * Since files are sideloaded to /data/local/tmp, you need to use the wrapper scripts to uninstall them fully. E.g.: `shell out/Default/bin/chromepublicapk uninstall ` * AppComponentFactory.instantiateClassLoader() is not supported.

The Code

All incremental apks have the same classes.dex, which is built from:

//build/android/incrementalinstall:bootstrapjava

They also have a transformed AndroidManifest.xml, which overrides the the main application class and any instrumentation classes so that they instead point to BootstrapApplication. This is built by:

//build/android/incrementalinstall/generateandroid_manifest.py

Wrapper scripts and install logic is contained in:

//build/android/incrementalinstall/createinstall_script.py //build/android/incremental_install/installer.py

Finally, GN logic for incremental apks is sprinkled throughout.