Contact emails fdo...@chromium.org, shase...@chromium.org
Explainer None Specification https://wicg.github.io/page-lifecycle Design docs https://docs.google.com/document/d/1uTJifh_erMX4_CTKgKljlj9O4SAmGam5W61FBHeasGI/edit?usp=sharing 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. 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. Blink component Blink>Scheduling TAG review None TAG review status Not applicable Risks Interoperability and Compatibility Interoperability: This feature does not expose new capabilities to the Web, so it has low chances of creating situations in which the same HTML/CSS/Js/... behaves differently in different browsers. That being said, we invite other browsers vendors that already shipped "tab freezing" to share and discuss their opt-out rules, which will help offer consistent behavior for web developers across browsers, avoiding situations where a site's background functionality works correctly in some browsers but not others. Compatibility: This feature may affect existing sites with background functionality. However, breaking some functionality to extend battery life is in line with user expectations when "Energy Saver" is active. We're interested in Web developer feedback to adjust our opt-outs and minimize avoidable breakages. "Energy Saver" can be disabled via the the "BatterySaverModeAvailability" enterprise policy. Gecko: Under consideration (https://github.com/mozilla/standards-positions/issues/87) WebKit: 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 (eg 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 Other signals: Chrome on Android freezes background tabs after 5 minutes (https://groups.google.com/a/chromium.org/g/blink-dev/c/NKtuFxLsKgo/m/brL3bfS5CAAJ). Chrome on desktop and Android freezes pages before putting them in the BFCache. Chrome on desktop freezes tabs in collapsed tab groups. Edge freezes background tabs after a configurable timeout (https://www.microsoft.com/en-us/edge/features/sleeping-tabs-at-work?form=MT00D8). Ergonomics No Ergonomics Risks identified. Activation No action is required to support browsers that don't freeze pages. Security A frame can observe when it is frozen, either directly (via the “freeze” event) or indirectly (timer runs later than expected, server doesn't receive a ping…). When the decision to freeze a frame depends on observations made on other cross-origin frames (crossing CPU usage threshold, using Web API that opt-outs from freezing) there is a risk of leaking information across origins. Multiple solutions were considered to balance security and ergonomy requirements. We finally landed on "freezing a browsing context group based on independent observations made on groups of same-origin/same-page frames in that browsing context group". Pros & cons + All frames on a page are in the same “frozen” state (does not break Web devs assumptions). + All frames that can synchronously script each other are in the same “frozen” state (does not break Web devs assumptions). + Not aggregating CPU usage across origins minimizes leaks, because an attacker can't vary its own CPU usage to precisely measure the CPU usage of another origin. - Leaks Web API usage across cross-origin frames (a frame can learn that a cross-origin frame in the "browsing context group" uses or doesn't use one of the APIs that prevents freezing depending on whether it itself gets frozen). WebView application risks Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications? This is a desktop-only feature which does not affect Webview. Debuggability The frozen state of a tab is displayed in the "Lifecycle state" column of chrome://discards. Whether a page can be frozen and why (eg usage of WebRTC) is displayed in the "Is freezable" column of chrome://discards. The #freezing-on-energy-saver and #freezing-on-energy-saver-testing features at about:flags can be used to test this intervention. It is also possible to manually freeze a tab via chrome://discards to verify how it reacts. Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)? Yes Chrome for Android already freezes pages in the background (not tied to Energy Saver). This proposal brings freezing to desktop. Is this feature fully tested by web-platform-tests? No Flag name on about://flags freezing-on-energy-saver Finch feature name FreezingOnBatterySaver Requires code in //chrome? False Tracking bug https://crbug.com/325954772 Launch bug https://launch.corp.google.com/launch/4282880 Measurement This feature doesn't introduce new APIs that web pages need to adopt. Availability expectation This feature doesn't introduce new APIs that other browsers need to make available. It expands the sets of conditions under which Chrome may freeze tabs (previously, only tabs in collapsed tab groups could be frozen). Adoption expectation This feature doesn't introduce new APIs that web pages need to adopt. Web pages may listen to the freeze/resume events to react to freezing, but it's not an issue if a web page doesn't. These events are already dispatched when a tab in a collapsed tab group is frozen. Adoption plan In collaboration with DevRel, we will publish an article covering the conditions under which freezing is triggered and possible remediations for broken background use cases. Non-OSS dependencies Does the feature depend on any code or APIs outside the Chromium open source repository and its open-source dependencies to function? No Estimated milestones Shipping on desktop 133 DevTrial on desktop 132 Anticipated spec changes Open questions about a feature may be a source of future web compat or interop issues. Please list open issues (eg links to known github issues in the project for the feature specification) whose resolution may introduce web compat/interop risk (eg, changing to naming or structure of the API in a non-backward-compatible way). This feature does not modify the spec. It changes the conditions under which tabs are frozen in Chrome. Those conditions are expected to evolve over time. Link to entry on the Chrome Platform Status https://chromestatus.com/feature/5158599457767424?gate=5076873410772992 Links to previous Intent discussions Intent to Prototype: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAG9b2qVcRLRWXUz61AkRWi%2BkaOJwgUK8bNCRBG6LOpqgOd%2BvSw%40mail.gmail.com Ready for Trial: https://groups.google.com/a/chromium.org/g/blink-dev/c/Xu1C7WhoGm4/m/_9U_kLHDAwAJ This intent message was generated by Chrome Platform Status. -- You received this message because you are subscribed to the Google Groups "blink-dev" group. To unsubscribe from this group and stop receiving emails from it, send an email to blink-dev+unsubscr...@chromium.org. To view this discussion visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/67462b62.2b0a0220.19a388.0546.GAE%40google.com.
