This article records a 2019 issue: animation work continued after the app’s UI was no longer visible. However, some apps continue to run “zombie animations”—animations that are completely invisible to the user yet consume precious CPU cycles and battery. When users discover this, the result is often a manual kill, an OS-level background restriction, or an outright uninstallation.

This issue can be easy to miss. In the original investigation, I used Systrace after opening apps and returning home, capturing traces while swiping between launcher pages. Some departed apps still fired callbacks. A reproduction should record versions, operations, and visibility; opening many apps is not itself a diagnostic requirement or proof.

Here, “zombie animations” means updates that continue when their UI is invisible and the feature no longer needs them. Many paths can schedule animation work through Choreographer. Investigate the actual stack, playback state, and library version. A live process is not necessarily free to consume CPU indefinitely; modern systems can freeze eligible cached processes.

This article introduces Choreographer, a class that app developers rarely encounter but is crucial in the Android Framework rendering pipeline. It covers the background of Choreographer‘s introduction, an overview, source code analysis, its relationship with MessageQueue, its use in APM, and optimization ideas from mobile manufacturers.

Choreographer coordinates animations, some input processing, and View updates with display timing. It requests frame callbacks when work is pending rather than unconditionally waking the app on every physical refresh. A 60Hz display, common in 2019, has an interval of about 16.67ms; 90Hz and 120Hz correspond to about 11.11ms and 8.33ms. Modern devices can also change refresh rates. A timely callback does not mean the image has been presented: RenderThread, GPU, composition, and display work remain. Understanding this flow helps explain Message, Handler, Looper, MessageQueue, Measure, Layout, and Draw.