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fix(core): ensure change detection runs in a reasonable timeframe wit…
…h zone coalescing (#54578) Zone event and run coalescing now races `requestAnimationFrame` and `setTimeout`. There are tradeoffs to both functions and racing the two gives us the benefits of both. This is explained in more detail in the jsdoc comment. This change also aligns the timing of zone coalescing with what will be used for zoneless. BREAKING CHANGE: The exact timing of change detection execution when using event or run coalescing with `NgZone` is now the first of either `setTimeout` or `requestAnimationFrame`. Code which relies on this timing (usually by accident) will need to be adjusted. If a callback needs to execute after change detection, we recommend `afterNextRender` instead of something like `setTimeout`. fixes #54544 fixes #44314 fixes #39854 (unverified but seems likely) PR Close #54578
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,86 @@ | ||
| /** | ||
| * @license | ||
| * Copyright Google LLC All Rights Reserved. | ||
| * | ||
| * Use of this source code is governed by an MIT-style license that can be | ||
| * found in the LICENSE file at https://angular.io/license | ||
| */ | ||
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| import {global} from './global'; | ||
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| /** | ||
| * Gets a scheduling function that runs the callback after the first of setTimeout and | ||
| * requestAnimationFrame resolves. | ||
| * | ||
| * - `requestAnimationFrame` ensures that change detection runs ahead of a browser repaint. | ||
| * This ensures that the create and update passes of a change detection always happen | ||
| * in the same frame. | ||
| * - When the browser is resource-starved, `rAF` can execute _before_ a `setTimeout` because | ||
| * rendering is a very high priority process. This means that `setTimeout` cannot guarantee | ||
| * same-frame create and update pass, when `setTimeout` is used to schedule the update phase. | ||
| * - While `rAF` gives us the desirable same-frame updates, it has two limitations that | ||
| * prevent it from being used alone. First, it does not run in background tabs, which would | ||
| * prevent Angular from initializing an application when opened in a new tab (for example). | ||
| * Second, repeated calls to requestAnimationFrame will execute at the refresh rate of the | ||
| * hardware (~16ms for a 60Hz display). This would cause significant slowdown of tests that | ||
| * are written with several updates and asserts in the form of "update; await stable; assert;". | ||
| * - Both `setTimeout` and `rAF` are able to "coalesce" several events from a single user | ||
| * interaction into a single change detection. Importantly, this reduces view tree traversals when | ||
| * compared to an alternative timing mechanism like `queueMicrotask`, where change detection would | ||
| * then be interleaves between each event. | ||
| * | ||
| * By running change detection after the first of `setTimeout` and `rAF` to execute, we get the | ||
| * best of both worlds. | ||
| */ | ||
| export function getCallbackScheduler() { | ||
| // Note: the `getNativeRequestAnimationFrame` is used in the `NgZone` class, but we cannot use the | ||
| // `inject` function. The `NgZone` instance may be created manually, and thus the injection | ||
| // context will be unavailable. This might be enough to check whether `requestAnimationFrame` is | ||
| // available because otherwise, we'll fall back to `setTimeout`. | ||
| const hasRequestAnimationFrame = typeof global['requestAnimationFrame'] === 'function'; | ||
| let nativeRequestAnimationFrame = | ||
| hasRequestAnimationFrame ? global['requestAnimationFrame'] : null; | ||
| let nativeSetTimeout = global['setTimeout']; | ||
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| if (typeof Zone !== 'undefined') { | ||
| // Note: zone.js sets original implementations on patched APIs behind the | ||
| // `__zone_symbol__OriginalDelegate` key (see `attachOriginToPatched`). Given the following | ||
| // example: `window.requestAnimationFrame.__zone_symbol__OriginalDelegate`; this would return an | ||
| // unpatched implementation of the `requestAnimationFrame`, which isn't intercepted by the | ||
| // Angular zone. We use the unpatched implementation to avoid another change detection when | ||
| // coalescing tasks. | ||
| const ORIGINAL_DELEGATE_SYMBOL = (Zone as any).__symbol__('OriginalDelegate'); | ||
| if (nativeRequestAnimationFrame) { | ||
| nativeRequestAnimationFrame = | ||
| (nativeRequestAnimationFrame as any)[ORIGINAL_DELEGATE_SYMBOL] ?? | ||
| nativeRequestAnimationFrame; | ||
| } | ||
| nativeSetTimeout = (nativeSetTimeout as any)[ORIGINAL_DELEGATE_SYMBOL] ?? nativeSetTimeout; | ||
| } | ||
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| function scheduleCallback(callback: Function): {cancel: () => void} { | ||
| let executeCallback = true; | ||
| nativeSetTimeout(() => { | ||
| if (!executeCallback) { | ||
| return; | ||
| } | ||
| executeCallback = false; | ||
| callback(); | ||
| }); | ||
| nativeRequestAnimationFrame?.(() => { | ||
| if (!executeCallback) { | ||
| return; | ||
| } | ||
| executeCallback = false; | ||
| callback(); | ||
| }); | ||
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| return { | ||
| cancel: () => { | ||
| executeCallback = false; | ||
| }, | ||
| }; | ||
| } | ||
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| return scheduleCallback; | ||
| } |
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