Freezing on Energy Saver

Category: Performance
Type: Chromium catches up
Status: In developer trial (Behind a flag) (Chrome 133)
Intent stage: Start prototyping

Summary

When Energy Saver is active, Chrome will freeze a "browsing context group" that has been hidden and silent for >5 minutes if any subgroup of same-origin frames within it exceeds a CPU usage threshold, unless it: - Provides audio- or video-conferencing functionality (detected via microphone, camera or screen/window/tab capture or an RTCPeerConnection with an 'open' RTCDataChannel or a 'live' MediaStreamTrack). - Controls an external device (detected via usage of Web USB, Web Bluetooth, Web HID or Web Serial). - Holds a Web Lock or an IndexedDB connection that blocks a version update or a transaction on a different connection. - Participates in the freezing opt-out origin trial. Freezing consists of pausing execution. It is formally defined in the Page Lifecycle API. The CPU usage threshold will be calibrated to freeze approximately 10% of background tabs when Energy Saver is active. ** Note: The origin trial is to opt-out from freezing, not to activate it. **

Motivation

When users activate "Energy Saver", they expect the browser to adapt its behavior to maximize battery life. Tab freezing on Energy Saver helps meet that expectation by preventing background tabs that aren't actively used from consuming CPU excessively.

Standards & signals

Specification: https://wicg.github.io/page-lifecycle
Firefox: Under consideration
Safari: No signal
Web developers: No signals — In the past, Web developers expressed concerns about freezing, because it made it difficult to implement background functionality that users care about in a reliable way (e.g. notification for calendar event). By freezing only pages that use a lot of CPU and only when Energy Saver is active, breakages that were reported in the past are mitigated. Additionally, we will listen to Web developers feedback on multiple channels (crbug, blink-dev, stack overflow, twitter, github) and make adjustments to heuristics if we find that background functionality that users care about is broken. Users may deactivate Energy Saver or manually opt-out sites at chrome://settings/performance
Tracking bug: https://crbug.com/325954772

Docs: https://docs.google.com/document/d/1uTJifh_erMX4_CTKgKljlj9O4SAmGam5W61FBHeasGI/edit?usp=sharing

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