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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/run_chrome_public_test_apk  # 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.: 
    out/Default/bin/chrome_public_apk uninstall

The Code

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

//build/android/incremental_install:bootstrap_java

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/incremental_install/generate_android_manifest.py

Wrapper scripts and install logic is contained in:

//build/android/incremental_install/create_install_script.py
//build/android/incremental_install/installer.py

Finally, GN logic for incremental apks is sprinkled throughout.