Provides a method for yielding control to the browser, which can be used to break up long tasks. Awaiting the promise returned by scheduler.yield() causes the current task to yield, continuing in a new browser task. This can be used to improve responsiveness issues caused by long tasks. Continuations are prioritized to mitigate performance problems of existing alternatives.
TAG review statusPending
Interoperability and Compatibility
This is a new feature and will not change existing event loop task scheduling, so the main risk is that other browsers might not implement the feature.
There is an interop challenge, however, that comes with prioritization: we want to be specific enough to provide developers guarantees and interoperable implementations, but provide enough scheduling flexibility for UAs (like the HTML specification does with task sources/task queues), which we'll keep in mind while drafting the spec (see also https://github.com/WICG/scheduling-apis/issues/67).Gecko
: No signalWebKit
: No signalWeb developers
: No signalsOther signals
The default use (inserting yield points in long tasks) should enable Chrome to maintain better performance (responsiveness). There is a risk of continuations starving other work, but there are reasonable mitigations, e.g. bounding total of prioritized continuations (see also https://github.com/WICG/scheduling-apis/blob/main/explainers/yield-and-continuation.md#preventing-task-starvation-by-continuations).
The feature would benefit from a polyfill so that tasks still yield in the case the feature is unavailable. The behavior can be approximated by awaiting `scheduler.postTask()` or wrapping `setTimeout(0)` in a promise.
The signal inheritance bit , however, would need transpilation support to propagate the current signal across async (Promise) boundaries. But developers can alternatively pass the appropriate priority/signal if necessary on browsers that don't support the feature.
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?
Goals for experimentation
The main goal is to evaluate yielding with prioritized continuations on site-specific metrics. More frequent yielding is known to improve responsiveness (should also be measured in experiments), but there's often a cost (latency) to regaining control of the thread. This API prioritizes continuations to mitigate this, and we want to measure the impact on site-specific metrics to evaluate the scheduling behavior.
Ongoing technical constraints
This has basic new-API devtools support. We plan to work with the devtools team to see if we can integrate continuations into the performance panel in some way.
Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, Chrome OS, Android, and Android WebView)?YesYes
Requires code in //chrome?False
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|OriginTrial webView last||118|
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Link to entry on the Chrome Platform Statushttps://chromestatus.com/feature/6266249336586240
Links to previous Intent discussionsIntent to prototype: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAKXGoJ1SBQP-ABM3%2BsDtKzUZiPoSCWqW2mLOjMrUfFBx4TomSw%40mail.gmail.com