Resume immediately pinged fiber without unwinding #25074
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Instead of using an imperative method `requestYield` to ask Scheduler to yield to the main thread, we can assume that any time a Scheduler task returns a continuation callback, it's because it wants to yield to the main thread. We can assume the task already checked some condition that caused it to return a continuation, so we don't need to do any additional checks — we can immediately yield and schedule a new task for the continuation. The replaces the `requestYield` API that I added in ca990e9.
I need to be able to yield to the main thread in between when an error is thrown and when the stack is unwound. (This is the motivation behind the refactor, but it isn't implemented in this commit.) Currently the unwind is inlined directly into `handleError`. Instead, I've moved the unwind logic into the main work loop. At the very beginning of the function, we check to see if the work-in-progress is in a "suspended" state — that is, whether it needs to be unwound. If it is, we will enter the unwind phase instead of the begin phase. We only need to perform this check when we first enter the work loop: at the beginning of a Scheduler chunk, or after something throws. We don't need to perform it after every unit of work.
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acdlite
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Aug 10, 2022
| @@ -998,8 +1001,14 @@ describe('ReactSuspenseWithNoopRenderer', () => { | |||
| 'Loading...', | |||
| // Once we've completed the boundary we restarted. | |||
| 'Async', | |||
| 'Sibling', | |||
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These changes are because this test happened to produce a scenario where a fiber is immediately pinged. It's not relevant to the test so I modified it slightly.
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When a fiber suspends, we should yield to the main thread in case the data is already cached, to unblock a potential ping event. By itself, this commit isn't useful because we don't do anything special in the case where to do receive an immediate ping event. I've split this out only to demonstrate that it doesn't break any existing behavior. See the next commit for full context and motivation.
If a fiber suspends, and is pinged immediately in a microtask (or a regular task that fires before React resumes rendering), try rendering the same fiber again without unwinding the stack. This can be super helpful when working with promises and async-await, because even if the outermost promise hasn't been cached before, the underlying data may have been preloaded. In many cases, we can continue rendering immediately without having to show a fallback. This optimization should work during any concurrent (time-sliced) render. It doesn't work during discrete updates because those are semantically required to finish synchronously — those get the current behavior.
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sebmarkbage
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Aug 11, 2022
| @@ -195,10 +195,22 @@ function workLoop(hasTimeRemaining, initialTime) { | |||
| const continuationCallback = callback(didUserCallbackTimeout); | |||
| currentTime = getCurrentTime(); | |||
| if (typeof continuationCallback === 'function') { | |||
| // If a continuation is returned, immediately yield to the main thread | |||
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This heuristic is a bit weird because API wise it's only supposed to yield to higher priority but this makes it yield more to same/lower priority native events than before or if you don't use continuation.
It only makes sense if you assume that React only yields a continuation if it has already used up the allotted time because itself has a timer heuristic but other uses of continuations wouldn't necessarily do that.
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If there were a native way to schedule a continuation, I think how I'd implement it is: inside the reconciler, when exiting the work loop, choose between either native continuation (normal time slice case) or a separate postTask call (explicit yield to microtasks). If Scheduler tasks were 1:1 with native tasks that's how I would have done it in this PR, too — we should probably make that change, anyway, so that microtasks aren't blocked by successive tasks and it aligns more closely with postTask behavior. But that's a bigger change than I wanted to do within the scope of this PR. So for now I'm treating the continuation API as an internal React detail.
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I suppose the previous solution (requestYield) is closer to that supposed end state, it's just slightly more overhead in the meantime if you assume that React is the only thing that uses this API.
| 'Outer: 1', | ||
| 'Suspend! [Async: 1]', | ||
| ]); | ||
| expect(Scheduler).toFlushUntilNextPaint(['Loading...']); |
| @@ -963,33 +963,36 @@ describe('ReactSuspenseWithNoopRenderer', () => { | |||
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| // @gate enableCache | |||
| it('resolves successfully even if fallback render is pending', async () => { | |||
| ReactNoop.render( | |||
| const root = ReactNoop.createRoot(); | |||
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The createRoot method? No it's been there
|
|
||
| // Wait for microtasks to resolve | ||
| // TODO: The async form of `act` should automatically yield to microtasks | ||
| // when a continuation is returned, the way Scheduler does. |
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+1, then we can get rid of all the other await nulls
| expect(Scheduler).toFlushAndYield(['Continuation Task']); | ||
| }); | ||
|
|
||
| it("toFlushAndYield keeps flushing even if there's a continuation", () => { |
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No inherent reason, just that there are a ton of tests that already use this helper. These internal flushing helpers are designed to test implementation details, and in nearly all of the existing uses, whether the work loop yields after a suspend is an irrelevant implementation detail.
The important API to get right is act, though I haven't implemented that in this PR yet.
sebmarkbage
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Aug 11, 2022
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Summary: This sync includes the following changes: - **[c28f313e6](facebook/react@c28f313e6 )**: experimental_use(promise) for SSR ([#25214](facebook/react#25214)) //<Andrew Clark>// - **[d6f9628a8](facebook/react@d6f9628a8 )**: Remove some RSC subset entry points that were removed in the main entry point ([#25209](facebook/react#25209)) //<Sebastian Markbåge>// - **[a473d08fc](facebook/react@a473d08fc )**: Update to Flow from 0.97 to 0.122 ([#25204](facebook/react#25204)) //<Jan Kassens>// - **[7028ce745](facebook/react@7028ce745 )**: experimental_use(promise) for Server Components ([#25207](facebook/react#25207)) //<Andrew Clark>// - **[bfb65681e](facebook/react@bfb65681e )**: experimental_use(context)([#25202](facebook/react#25202)) //<mofeiZ>// - **[f0efa1164](facebook/react@f0efa1164 )**: [flow] remove custom suppress comment config ([#25170](facebook/react#25170)) //<Jan Kassens>// - **[2e7f422fe](facebook/react@2e7f422fe )**: Refactor: its type is Container ([#25153](facebook/react#25153)) //<bubucuo>// - **[2c2d9a1df](facebook/react@2c2d9a1df )**: [eslint-plugin-react-hooks] only allow capitalized component names ([#25162](facebook/react#25162)) //<Jan Kassens>// - **[36c908a6c](facebook/react@36c908a6c )**: Don't use the Flight terminology in public error messages ([#25166](facebook/react#25166)) //<Sebastian Markbåge>// - **[8d1b057ec](facebook/react@8d1b057ec )**: [Flight] Minor error handling fixes ([#25151](facebook/react#25151)) //<Sebastian Markbåge>// - **[9ff738f53](facebook/react@9ff738f53 )**: [devtools][easy] Fix flow type ([#25147](facebook/react#25147)) //<Tianyu Yao>// - **[0de3ddf56](facebook/react@0de3ddf56 )**: Remove Symbol Polyfill (again) ([#25144](facebook/react#25144)) //<Ricky>// - **[b36f72235](facebook/react@b36f72235 )**: Remove ReactFiberFlags MountLayoutDev and MountPassiveDev ([#25091](facebook/react#25091)) //<Samuel Susla>// - **[b6978bc38](facebook/react@b6978bc38 )**: experimental_use(promise) ([#25084](facebook/react#25084)) //<Andrew Clark>// - **[11ed7010c](facebook/react@11ed7010c )**: [Transition Tracing] onMarkerIncomplete - Tracing Marker/Suspense Boundary Deletions ([#24885](facebook/react#24885)) //<Luna Ruan>// - **[b79894259](facebook/react@b79894259 )**: [Flight] Add support for Webpack Async Modules ([#25138](facebook/react#25138)) //<Sebastian Markbåge>// - **[c8b778b7f](facebook/react@c8b778b7f )**: Fix typo: supportsMicrotask -> supportsMicrotasks ([#25142](facebook/react#25142)) //<kwzr>// - **[d0f396651](facebook/react@d0f396651 )**: Allow functions to be used as module references ([#25137](facebook/react#25137)) //<Sebastian Markbåge>// - **[38c5d8a03](facebook/react@38c5d8a03 )**: Test the node-register hooks in unit tests ([#25132](facebook/react#25132)) //<Sebastian Markbåge>// - **[3f70e68ce](facebook/react@3f70e68ce )**: Return closestInstance in `getInspectorDataForViewAtPoint` ([#25118](facebook/react#25118)) //<Tianyu Yao>// - **[3d443cad7](facebook/react@3d443cad7 )**: Update fixtures/flight to webpack 5 ([#25115](facebook/react#25115)) //<Tim Neutkens>// - **[5d1ce6513](facebook/react@5d1ce6513 )**: Align StrictMode behaviour with production ([#25049](facebook/react#25049)) //<Samuel Susla>// - **[9e67e7a31](facebook/react@9e67e7a31 )**: Scaffolding for useMemoCache hook ([#25123](facebook/react#25123)) //<Joseph Savona>// - **[19e9a4c68](facebook/react@19e9a4c68 )**: Add missing createServerContext for experimental shared subset ([#25114](facebook/react#25114)) //<Jiachi Liu>// - **[6ef466c68](facebook/react@6ef466c68 )**: make preamble and postamble types explicit and fix typo ([#25102](facebook/react#25102)) //<Josh Story>// - **[796d31809](facebook/react@796d31809 )**: Implement basic stylesheet Resources for react-dom ([#25060](facebook/react#25060)) //<Josh Story>// - **[32baab38f](facebook/react@32baab38f )**: [Transition Tracing] Add Tag Field to Marker Instance ([#25085](facebook/react#25085)) //<Luna Ruan>// - **[8ef3a7c08](facebook/react@8ef3a7c08 )**: Resume immediately pinged fiber without unwinding ([#25074](facebook/react#25074)) //<Andrew Clark>// - **[7bcc68772](facebook/react@7bcc68772 )**: Remove argument committedLanes from reappearLayoutEffects and recursivelyTraverseReappearLayoutEffects ([#25080](facebook/react#25080)) //<Samuel Susla>// - **[ca990e9a7](facebook/react@ca990e9a7 )**: Add API to force Scheduler to yield for macrotask ([#25044](facebook/react#25044)) //<Andrew Clark>// - **[b4204ede6](facebook/react@b4204ede6 )**: Clean up unused Deletion flag ([#24992](facebook/react#24992)) //<Andrew Clark>// - **[e193be87e](facebook/react@e193be87e )**: [Transition Tracing] Add Offscreen Test ([#25035](facebook/react#25035)) //<Luna Ruan>// - **[9fcaf88d5](facebook/react@9fcaf88d5 )**: Remove rootContainerInstance from unnecessary places ([#25024](facebook/react#25024)) //<Sebastian Markbåge>// - **[80f3d8819](facebook/react@80f3d8819 )**: Mount/unmount passive effects when Offscreen visibility changes ([#24977](facebook/react#24977)) //<Andrew Clark>// Changelog: [General][Changed] - React Native sync for revisions 4ea064e...c28f313 Reviewed By: rickhanlonii Differential Revision: D39384898 fbshipit-source-id: 20b080a53851d6dd9d522c8468dd02aab9ba76db
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* Yield to main thread if continuation is returned Instead of using an imperative method `requestYield` to ask Scheduler to yield to the main thread, we can assume that any time a Scheduler task returns a continuation callback, it's because it wants to yield to the main thread. We can assume the task already checked some condition that caused it to return a continuation, so we don't need to do any additional checks — we can immediately yield and schedule a new task for the continuation. The replaces the `requestYield` API that I added in ca990e9. * Move unwind after error into main work loop I need to be able to yield to the main thread in between when an error is thrown and when the stack is unwound. (This is the motivation behind the refactor, but it isn't implemented in this commit.) Currently the unwind is inlined directly into `handleError`. Instead, I've moved the unwind logic into the main work loop. At the very beginning of the function, we check to see if the work-in-progress is in a "suspended" state — that is, whether it needs to be unwound. If it is, we will enter the unwind phase instead of the begin phase. We only need to perform this check when we first enter the work loop: at the beginning of a Scheduler chunk, or after something throws. We don't need to perform it after every unit of work. * Yield to main thread whenever a fiber suspends When a fiber suspends, we should yield to the main thread in case the data is already cached, to unblock a potential ping event. By itself, this commit isn't useful because we don't do anything special in the case where to do receive an immediate ping event. I've split this out only to demonstrate that it doesn't break any existing behavior. See the next commit for full context and motivation. * Resume immediately pinged fiber without unwinding If a fiber suspends, and is pinged immediately in a microtask (or a regular task that fires before React resumes rendering), try rendering the same fiber again without unwinding the stack. This can be super helpful when working with promises and async-await, because even if the outermost promise hasn't been cached before, the underlying data may have been preloaded. In many cases, we can continue rendering immediately without having to show a fallback. This optimization should work during any concurrent (time-sliced) render. It doesn't work during discrete updates because those are semantically required to finish synchronously — those get the current behavior.
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Summary: This sync includes the following changes: - **[c28f313e6](facebook/react@c28f313e6 )**: experimental_use(promise) for SSR ([facebook#25214](facebook/react#25214)) //<Andrew Clark>// - **[d6f9628a8](facebook/react@d6f9628a8 )**: Remove some RSC subset entry points that were removed in the main entry point ([facebook#25209](facebook/react#25209)) //<Sebastian Markbåge>// - **[a473d08fc](facebook/react@a473d08fc )**: Update to Flow from 0.97 to 0.122 ([facebook#25204](facebook/react#25204)) //<Jan Kassens>// - **[7028ce745](facebook/react@7028ce745 )**: experimental_use(promise) for Server Components ([facebook#25207](facebook/react#25207)) //<Andrew Clark>// - **[bfb65681e](facebook/react@bfb65681e )**: experimental_use(context)([facebook#25202](facebook/react#25202)) //<mofeiZ>// - **[f0efa1164](facebook/react@f0efa1164 )**: [flow] remove custom suppress comment config ([facebook#25170](facebook/react#25170)) //<Jan Kassens>// - **[2e7f422fe](facebook/react@2e7f422fe )**: Refactor: its type is Container ([facebook#25153](facebook/react#25153)) //<bubucuo>// - **[2c2d9a1df](facebook/react@2c2d9a1df )**: [eslint-plugin-react-hooks] only allow capitalized component names ([facebook#25162](facebook/react#25162)) //<Jan Kassens>// - **[36c908a6c](facebook/react@36c908a6c )**: Don't use the Flight terminology in public error messages ([facebook#25166](facebook/react#25166)) //<Sebastian Markbåge>// - **[8d1b057ec](facebook/react@8d1b057ec )**: [Flight] Minor error handling fixes ([facebook#25151](facebook/react#25151)) //<Sebastian Markbåge>// - **[9ff738f53](facebook/react@9ff738f53 )**: [devtools][easy] Fix flow type ([facebook#25147](facebook/react#25147)) //<Tianyu Yao>// - **[0de3ddf56](facebook/react@0de3ddf56 )**: Remove Symbol Polyfill (again) ([facebook#25144](facebook/react#25144)) //<Ricky>// - **[b36f72235](facebook/react@b36f72235 )**: Remove ReactFiberFlags MountLayoutDev and MountPassiveDev ([facebook#25091](facebook/react#25091)) //<Samuel Susla>// - **[b6978bc38](facebook/react@b6978bc38 )**: experimental_use(promise) ([facebook#25084](facebook/react#25084)) //<Andrew Clark>// - **[11ed7010c](facebook/react@11ed7010c )**: [Transition Tracing] onMarkerIncomplete - Tracing Marker/Suspense Boundary Deletions ([facebook#24885](facebook/react#24885)) //<Luna Ruan>// - **[b79894259](facebook/react@b79894259 )**: [Flight] Add support for Webpack Async Modules ([facebook#25138](facebook/react#25138)) //<Sebastian Markbåge>// - **[c8b778b7f](facebook/react@c8b778b7f )**: Fix typo: supportsMicrotask -> supportsMicrotasks ([facebook#25142](facebook/react#25142)) //<kwzr>// - **[d0f396651](facebook/react@d0f396651 )**: Allow functions to be used as module references ([facebook#25137](facebook/react#25137)) //<Sebastian Markbåge>// - **[38c5d8a03](facebook/react@38c5d8a03 )**: Test the node-register hooks in unit tests ([facebook#25132](facebook/react#25132)) //<Sebastian Markbåge>// - **[3f70e68ce](facebook/react@3f70e68ce )**: Return closestInstance in `getInspectorDataForViewAtPoint` ([facebook#25118](facebook/react#25118)) //<Tianyu Yao>// - **[3d443cad7](facebook/react@3d443cad7 )**: Update fixtures/flight to webpack 5 ([facebook#25115](facebook/react#25115)) //<Tim Neutkens>// - **[5d1ce6513](facebook/react@5d1ce6513 )**: Align StrictMode behaviour with production ([facebook#25049](facebook/react#25049)) //<Samuel Susla>// - **[9e67e7a31](facebook/react@9e67e7a31 )**: Scaffolding for useMemoCache hook ([facebook#25123](facebook/react#25123)) //<Joseph Savona>// - **[19e9a4c68](facebook/react@19e9a4c68 )**: Add missing createServerContext for experimental shared subset ([facebook#25114](facebook/react#25114)) //<Jiachi Liu>// - **[6ef466c68](facebook/react@6ef466c68 )**: make preamble and postamble types explicit and fix typo ([facebook#25102](facebook/react#25102)) //<Josh Story>// - **[796d31809](facebook/react@796d31809 )**: Implement basic stylesheet Resources for react-dom ([facebook#25060](facebook/react#25060)) //<Josh Story>// - **[32baab38f](facebook/react@32baab38f )**: [Transition Tracing] Add Tag Field to Marker Instance ([facebook#25085](facebook/react#25085)) //<Luna Ruan>// - **[8ef3a7c08](facebook/react@8ef3a7c08 )**: Resume immediately pinged fiber without unwinding ([facebook#25074](facebook/react#25074)) //<Andrew Clark>// - **[7bcc68772](facebook/react@7bcc68772 )**: Remove argument committedLanes from reappearLayoutEffects and recursivelyTraverseReappearLayoutEffects ([facebook#25080](facebook/react#25080)) //<Samuel Susla>// - **[ca990e9a7](facebook/react@ca990e9a7 )**: Add API to force Scheduler to yield for macrotask ([facebook#25044](facebook/react#25044)) //<Andrew Clark>// - **[b4204ede6](facebook/react@b4204ede6 )**: Clean up unused Deletion flag ([facebook#24992](facebook/react#24992)) //<Andrew Clark>// - **[e193be87e](facebook/react@e193be87e )**: [Transition Tracing] Add Offscreen Test ([facebook#25035](facebook/react#25035)) //<Luna Ruan>// - **[9fcaf88d5](facebook/react@9fcaf88d5 )**: Remove rootContainerInstance from unnecessary places ([facebook#25024](facebook/react#25024)) //<Sebastian Markbåge>// - **[80f3d8819](facebook/react@80f3d8819 )**: Mount/unmount passive effects when Offscreen visibility changes ([facebook#24977](facebook/react#24977)) //<Andrew Clark>// Changelog: [General][Changed] - React Native sync for revisions 4ea064e...c28f313 Reviewed By: rickhanlonii Differential Revision: D39384898 fbshipit-source-id: 20b080a53851d6dd9d522c8468dd02aab9ba76db
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If a fiber suspends, and is pinged immediately in a microtask (or a regular task that fires before React resumes rendering), try rendering the same fiber again without unwinding the stack. This can be super helpful when working with promises and async-await, because even if the outermost promise hasn't been cached before, the underlying data may have been preloaded. In many cases, we can continue rendering immediately without having to show a fallback.
This optimization should work during any concurrent (time-sliced) render. It doesn't work during discrete updates because those are semantically required to finish synchronously — those get the current behavior.