experimental_use(promise) #25084
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experimental_use(promise) #25084
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sebmarkbage
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| }, | ||
| ); | ||
| } | ||
| throw thenable; |
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Should we add ping listeners directly here and instead throw a placeholder value?
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Yeah I can do that
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| if (suspendedThenables === null) { | ||
| suspendedThenables = []; | ||
| } | ||
| suspendedThenables[index] = thenable; |
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So this is a holey array which is pretty deopted. I wonder if it might be worth just setting it to null for every use() call even if nothing suspends. Perhaps reusing the same array every time and filling it with null each time. Maybe that's worse.
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Maybe @gsathya would know which is best
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Looks like this got replaced by expandos? Expandos will cause hidden class transition leading to a potential deopt. Curious if WeakMap works for you? Or is too slow?
I guess, the tradeoff here is between slow lookup in WeakMaps or a deopt in other parts that use this thenable -- I don't know which is the more common workload.
As an aside, if looking up the Promise value synchronously is the common case, then we could champion a Promise.prototype.inspect proposal to add this to the Promise API.
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Promise.prototype.inspect wouldn't help in this particular case because this array is for tracking thenables that aren't cached. We use it when we know two thenables represent the same data even though they are different objects. For example:
const helloPromise = Promise.resolve('Hello');
function HelloWorld() {
// This component uses different promises on every render attempt,
// but if no React state has changed we know that the underlying value
// can be reused.
return
// This promise is the same every time, so we can read the value
// from the expando (a la Promise.prototype.inspect)
use(helloPromise) +
// This promise is new every time, but we know it represents the
// same thing, so we reuse the previous value from the array.
use(Promise.resolve('World');
}In the current implementation, this example would produce a sparse array with a value at index 1 and a hole at index 0.
The reason index 0 is a hole is because if the promise can be inspected, there's no reason to track it. So Seb's suggestion is that it might be better to push to the array even if it's not needed.
There are other solutions to avoid a holey array, like only advancing the thenableIndex if the promise hasn't resolved. I think that would require one additional null check to each read of an inspectable promise, but it might be worth it to prevent a deopt.
| default: { | ||
| // The thenable still hasn't resolved. Suspend with the same | ||
| // thenable as last time to avoid redundant listeners. | ||
| throw prevThenableAtIndex; |
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This seems like it should be an error case - e.g. you used something mutable conditionally.
We shouldn't bother retrying immediately unless lastUsedThenable was pinged. There's no point in retrying due to anything else because that can no longer be blocking. Anything preceding lastUsedThenable must have already been resolved or we wouldn't have gotten that far.
If something else pings maybe we need to reset the suspended thenables anyway - e.g. if we want to treat it as a restart.
So if we have anything in the slot from before, it must've been resolved. Otherwise something went wrong.
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Yeah that seems reasonable. I started a list of a warning cases but maybe this one should be an actual error
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We shouldn't bother retrying immediately unless lastUsedThenable was pinged. There's no point in retrying due to anything else because that can no longer be blocking. Anything preceding lastUsedThenable must have already been resolved or we wouldn't have gotten that far.
Yeah that is how it currently works. It's a different variable though because it also works for ad hoc wakeables (ones that aren't use-d), but the same logic you're describing:
react/packages/react-reconciler/src/ReactFiberWakeable.new.js
Lines 28 to 34 in 796d318
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This update our internal implementation of `act` to support React's new behavior for unwrapping promises. Like we did with Scheduler, when something suspends, it will yield to the main thread so the microtasks can run, then continue in a new task. I need to implement the same behavior in the public version of `act`, but there are some additional considerations so I'll do that in a separate commit.
throwException is the function that finds the nearest boundary and schedules it for a second render pass. We should only call it right before we unwind the stack — not if we receive an immediate ping and render the fiber again. This was an oversight in 8ef3a7c that I didn't notice because it happens to mostly work, anyway. What made me notice the mistake is that throwException also marks the entire render phase as suspended (RootDidSuspend or RootDidSuspendWithDelay), which is only supposed to be happen if we show a fallback. One consequence was that, in the RootDidSuspendWithDelay case, the entire commit phase was blocked, because that's the exit status we use to block a bad fallback from appearing.
Add a `status` expando to a thrown thenable to track when its value has resolved. In a later step, we'll also use `value` and `reason` expandos to track the resolved value. This is not part of the official JavaScript spec — think of it as an extension of the Promise API, or a custom interface that is a superset of Thenable. However, it's inspired by the terminology used by `Promise.allSettled`. The intent is that this will be a public API — Suspense implementations can set these expandos to allow React to unwrap the value synchronously without waiting a microtask.
Sets up a new experimental hook behind a feature flag, but does not implement it yet.
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@acdlite this looks quite exciting actually, what's the target React release to include this changeset? |
|
@nl0 this API is experimental and still in research so there's no target for release yet. |
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* 'main' of ssh://github.com/GrinZero/react: (26 commits) [devtools][easy] Fix flow type (facebook#25147) Remove Symbol Polyfill (again) (facebook#25144) Remove ReactFiberFlags MountLayoutDev and MountPassiveDev (facebook#25091) experimental_use(promise) (facebook#25084) [Transition Tracing] onMarkerIncomplete - Tracing Marker/Suspense Boundary Deletions (facebook#24885) [Flight] Add support for Webpack Async Modules (facebook#25138) Fix typo: supportsMicrotask -> supportsMicrotasks (facebook#25142) Allow functions to be used as module references (facebook#25137) Test the node-register hooks in unit tests (facebook#25132) Return closestInstance in `getInspectorDataForViewAtPoint` (facebook#25118) [DevTools] Highlight RN elements on hover (facebook#25106) Update fixtures/flight to webpack 5 (facebook#25115) Align StrictMode behaviour with production (facebook#25049) Scaffolding for useMemoCache hook (facebook#25123) devtools: Fix typo from directores to directories (facebook#25124) fixture: Fix typo from perfomrance to performance (facebook#25100) [DevTools] Add events necessary for click to inspect on RN (facebook#25111) Add missing createServerContext for experimental shared subset (facebook#25114) support subresource integrity for bootstrapScripts and bootstrapModules (facebook#25104) make preamble and postamble types explicit and fix typo (facebook#25102) ...
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Follow up to facebook#25084. Implements experimental_use(promise) API in the Server Components runtime (Flight). The implementation is much simpler than in Fiber because there is no state. Even the "state" added in this PR — to track the result of each promise across attempts — is reset as soon as a component successfully renders without suspending. There are also fewer caveats around neglecting to cache a promise because the state of the promises is preserved even if we switch to a different task. Server Components is the primary runtime where this API is intended to be used. The last runtime where we need to implement this is the server renderer (Fizz).
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Follow up to facebook#25084. Implements experimental_use(promise) API in the Server Components runtime (Flight). The implementation is much simpler than in Fiber because there is no state. Even the "state" added in this PR — to track the result of each promise across attempts — is reset as soon as a component successfully renders without suspending. There are also fewer caveats around neglecting to cache a promise because the state of the promises is preserved even if we switch to a different task. Server Components is the primary runtime where this API is intended to be used. The last runtime where we need to implement this is the server renderer (Fizz).
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Follow up to facebook#25084. Implements experimental_use(promise) API in the Server Components runtime (Flight). The implementation is much simpler than in Fiber because there is no state. Even the "state" added in this PR — to track the result of each promise across attempts — is reset as soon as a component successfully renders without suspending. There are also fewer caveats around neglecting to cache a promise because the state of the promises is preserved even if we switch to a different task. Server Components is the primary runtime where this API is intended to be used. The last runtime where we need to implement this is the server renderer (Fizz).
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Follow up to facebook#25084. Implements experimental_use(promise) API in the Server Components runtime (Flight). The implementation is much simpler than in Fiber because there is no state. Even the "state" added in this PR — to track the result of each promise across attempts — is reset as soon as a component successfully renders without suspending. There are also fewer caveats around neglecting to cache a promise because the state of the promises is preserved even if we switch to a different task. Server Components is the primary runtime where this API is intended to be used. The last runtime where we need to implement this is the server renderer (Fizz).
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Follow up to #25084. Implements experimental_use(promise) API in the Server Components runtime (Flight). The implementation is much simpler than in Fiber because there is no state. Even the "state" added in this PR — to track the result of each promise across attempts — is reset as soon as a component successfully renders without suspending. There are also fewer caveats around neglecting to cache a promise because the state of the promises is preserved even if we switch to a different task. Server Components is the primary runtime where this API is intended to be used. The last runtime where we need to implement this is the server renderer (Fizz).
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Follow up to facebook#25084. Implements experimental_use(promise) API in the SSR runtime (Fizz). This is largely a copy-paste of the Flight implementation. I have intentionally tried to keep both as close as possible.
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Follow up to facebook#25084 and facebook#25207. Implements experimental_use(promise) API in the SSR runtime (Fizz). This is largely a copy-paste of the Flight implementation. I have intentionally tried to keep both as close as possible.
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Follow up to facebook#25084 and facebook#25207. Implements experimental_use(promise) API in the SSR runtime (Fizz). This is largely a copy-paste of the Flight implementation. I have intentionally tried to keep both as close as possible.
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- [`experimental` entrypoint](https://unpkg.com/browse/react@0.0.0-experimental-c28f313e6-20220908/cjs/react.development.js) - [implementation in `experimental`](https://unpkg.com/browse/react-dom@0.0.0-experimental-c28f313e6-20220908/cjs/react-dom.development.js) - [experimental_use(Thenable)](facebook/react#25084) - [experimental_use(Context)](facebook/react#25202)
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- [`experimental` entrypoint](https://unpkg.com/browse/react@0.0.0-experimental-c28f313e6-20220908/cjs/react.development.js) - [implementation in `experimental`](https://unpkg.com/browse/react-dom@0.0.0-experimental-c28f313e6-20220908/cjs/react-dom.development.js) - [experimental_use(Thenable)](facebook/react#25084) - [experimental_use(Context)](facebook/react#25202)
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- [`experimental` entrypoint](https://unpkg.com/browse/react@0.0.0-experimental-c28f313e6-20220908/cjs/react.development.js) - [implementation in `experimental`](https://unpkg.com/browse/react-dom@0.0.0-experimental-c28f313e6-20220908/cjs/react-dom.development.js) - [experimental_use(Thenable)](facebook/react#25084) - [experimental_use(Context)](facebook/react#25202)
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Follow up to #25084. Implements experimental_use(promise) API in the Server Components runtime (Flight). The implementation is much simpler than in Fiber because there is no state. Even the "state" added in this PR — to track the result of each promise across attempts — is reset as soon as a component successfully renders without suspending. There are also fewer caveats around neglecting to cache a promise because the state of the promises is preserved even if we switch to a different task. Server Components is the primary runtime where this API is intended to be used. The last runtime where we need to implement this is the server renderer (Fizz).
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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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* Internal `act`: Unwrapping resolved promises This update our internal implementation of `act` to support React's new behavior for unwrapping promises. Like we did with Scheduler, when something suspends, it will yield to the main thread so the microtasks can run, then continue in a new task. I need to implement the same behavior in the public version of `act`, but there are some additional considerations so I'll do that in a separate commit. * Move throwException to after work loop resumes throwException is the function that finds the nearest boundary and schedules it for a second render pass. We should only call it right before we unwind the stack — not if we receive an immediate ping and render the fiber again. This was an oversight in 8ef3a7c that I didn't notice because it happens to mostly work, anyway. What made me notice the mistake is that throwException also marks the entire render phase as suspended (RootDidSuspend or RootDidSuspendWithDelay), which is only supposed to be happen if we show a fallback. One consequence was that, in the RootDidSuspendWithDelay case, the entire commit phase was blocked, because that's the exit status we use to block a bad fallback from appearing. * Use expando to check whether promise has resolved Add a `status` expando to a thrown thenable to track when its value has resolved. In a later step, we'll also use `value` and `reason` expandos to track the resolved value. This is not part of the official JavaScript spec — think of it as an extension of the Promise API, or a custom interface that is a superset of Thenable. However, it's inspired by the terminology used by `Promise.allSettled`. The intent is that this will be a public API — Suspense implementations can set these expandos to allow React to unwrap the value synchronously without waiting a microtask. * Scaffolding for `experimental_use` hook Sets up a new experimental hook behind a feature flag, but does not implement it yet. * use(promise) Adds experimental support to Fiber for unwrapping the value of a promise inside a component. It is not yet implemented for Server Components, but that is planned. If promise has already resolved, the value can be unwrapped "immediately" without showing a fallback. The trick we use to implement this is to yield to the main thread (literally suspending the work loop), wait for the microtask queue to drain, then check if the promise resolved in the meantime. If so, we can resume the last attempted fiber without unwinding the stack. This functionality was implemented in previous commits. Another feature is that the promises do not need to be cached between attempts. Because we assume idempotent execution of components, React will track the promises that were used during the previous attempt and reuse the result. You shouldn't rely on this property, but during initial render it mostly just works. Updates are trickier, though, because if you used an uncached promise, we have no way of knowing whether the underlying data has changed, so we have to unwrap the promise every time. It will still work, but it's inefficient and can lead to unnecessary fallbacks if it happens during a discrete update. When we implement this for Server Components, this will be less of an issue because there are no updates in that environment. However, it's still better for performance to cache data requests, so the same principles largely apply. The intention is that this will eventually be the only supported way to suspend on arbitrary promises. Throwing a promise directly will be deprecated.
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Follow up to #25084. Implements experimental_use(promise) API in the Server Components runtime (Flight). The implementation is much simpler than in Fiber because there is no state. Even the "state" added in this PR — to track the result of each promise across attempts — is reset as soon as a component successfully renders without suspending. There are also fewer caveats around neglecting to cache a promise because the state of the promises is preserved even if we switch to a different task. Server Components is the primary runtime where this API is intended to be used. The last runtime where we need to implement this is the server renderer (Fizz).
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This reverts commit c28f313. Follow up to facebook#25084 and facebook#25207. Implements experimental_use(promise) API in the SSR runtime (Fizz). This is largely a copy-paste of the Flight implementation. I have intentionally tried to keep both as close as possible.
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This reverts commit dedfeff. This reverts commit c28f313. Follow up to facebook#25084 and facebook#25207. Implements experimental_use(promise) API in the SSR runtime (Fizz). This is largely a copy-paste of the Flight implementation. I have intentionally tried to keep both as close as possible.
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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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Adds experimental support to Fiber for unwrapping the value of a promise inside a component. It is not yet implemented for Server Components, but that is planned.
If promise has already resolved, the value can be unwrapped "immediately" without showing a fallback. The trick we use to implement this is to yield to the main thread (literally suspending the work loop), wait for the microtask queue to drain, then check if the promise resolved in the meantime. If so, we can resume the last attempted fiber without unwinding the stack. This functionality was implemented in previous commits.
Another feature is that the promises do not need to be cached between attempts. Because we assume idempotent execution of components, React will track the promises that were used during the previous attempt and reuse the result. You shouldn't rely on this property, but during initial render it mostly just works. Updates are trickier, though, because if you used an uncached promise, we have no way of knowing whether the underlying data has changed, so we have to unwrap the promise every time. It will still work, but it's inefficient and can lead to unnecessary fallbacks if it happens during a discrete update.
When we implement this for Server Components, this will be less of an issue because there are no updates in that environment. However, it's still better for performance to cache data requests, so the same principles largely apply.
The intention is that this will eventually be the only supported way to suspend on arbitrary promises. Throwing a promise directly will be deprecated.
Todo