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Initialize useMemoCache with sentinel values #25465
Initialize useMemoCache with sentinel values #25465
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@kassens @poteto @gsathya Thinking about how we use the cache: const c_x = !cache.has(0) || cache.get(0) !== x;
cache.set(0, x); We'd probably be better off with a single function
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export function createMemoCache(data: Array<any>): MemoCache { | ||
const cache: {data: Array<any>} = (Object.create(MemoCachePrototype): any); | ||
cache.data = data; |
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not sure how much we care about perf/memory here, but one trick is to just use the cache
object as an array and index into it directly rather than creating a separate data
array
I'm pretty concerned about the overhead here. The only thing that made me comfortable about the idea of memoizing everything in first place was the very low overhead that we could get by specializing the code and guarantee inlined operations. If this is a temporary state, what's the plausible next step to getting it back? |
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@sebmarkbage I've completed revised this to just fill the cache with a sentinel value, can you take another look? |
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Thanks for the update!
data = memoCache.data[memoCache.index] = new Array(size).fill( | ||
MEMO_CACHE_UNSET_SENTINEL, | ||
); |
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I was curious about the performance of fill
and ran a microbenchmark: https://jsbench.me/7ol98ws520/1
Looks like the fastest way is:
data = memoCache.data[memoCache.index] = new Array(size);
for (let i = 0; i < size; ++i) data[i] = MEMO_CACHE_UNSET_SENTINEL;
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good call, i updated to use this implementation
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Yea I agree that for the production scenario we should do things as low-level as possible.
I forget about how we do guardMemoCacheRead
for the patched implementation. I guess we switched the implementation of useMemoCache
hooks?
Maybe we can also fork the implementation for React dev build, or actually may be only the debug build.
data = memoCache.data[memoCache.index] = new Array(size).fill( | ||
MEMO_CACHE_UNSET_SENTINEL, | ||
); | ||
// Attach sentinel to the array, eventually we can make the sentinel a public | ||
// export from React and avoid modifying the array | ||
(data: any)._ = MEMO_CACHE_UNSET_SENTINEL; |
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Yea, I originally chose the $._
approach merely to ease the implementation of codegen and patching. It's likely to be faster if we can directly export this symbol to not only save one hidden class transition/modification of array but also one property lookup in the runtime.
The only caveat I had thought about is that we need to deal with potential name clashes everywhere which is hairy:
import { MEMO_CACHE_UNSET_SENTINEL as _ } from "react"
function Foo() {
// ok
}
function Bar() {
let _ = otherThing;
// well
}
const MEMO_CACHE_UNSET_SENTINEL: symbol = Symbol.for( | ||
'react.usememocache_sentinel', | ||
); |
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I originally thought of putting this to https://github.com/facebook/react/blob/main/packages/shared/ReactSymbols.js
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Summary: - **[9fb581c7c](facebook/react@9fb581c7c )**: Refactor: merge duplicate imports ([#25489](facebook/react#25489)) //<c0dedance>// - **[bc358362a](facebook/react@bc358362a )**: [Flight] Improve Error Messages when Invalid Object is Passed to Client/Host Components ([#25492](facebook/react#25492)) //<Sebastian Markbåge>// - **[780eacd40](facebook/react@780eacd40 )**: Flow upgrade to 0.190 ([#25483](facebook/react#25483)) //<Jan Kassens>// - **[54f0e0f73](facebook/react@54f0e0f73 )**: Scaffolding for react-dom/unstable_external-server-runtime ([#25482](facebook/react#25482)) //<Andrew Clark>// - **[0eaca3756](facebook/react@0eaca3756 )**: Add script to generate inline Fizz runtime ([#25481](facebook/react#25481)) //<Andrew Clark>// - **[69c7246d9](facebook/react@69c7246d9 )**: Initialize useMemoCache with sentinel values ([#25465](facebook/react#25465)) //<Joseph Savona>// - **[3b814327e](facebook/react@3b814327e )**: Allow Async Functions to be used in Server Components ([#25479](facebook/react#25479)) //<Sebastian Markbåge>// - **[a6bf46689](facebook/react@a6bf46689 )**: Extract Fizz instruction set to build macro ([#25457](facebook/react#25457)) //<Andrew Clark>// - **[ea5bc6bac](facebook/react@ea5bc6bac )**: [React Native FB] dynamic feature flag for ref access warning ([#25471](facebook/react#25471)) //<Jan Kassens>// - **[08d035bc8](facebook/react@08d035bc8 )**: Remove Shallow Renderer Tests ([#25475](facebook/react#25475)) //<Sebastian Markbåge>// - **[a8c16a004](facebook/react@a8c16a004 )**: Split Cache into its own Dispatcher ([#25474](facebook/react#25474)) //<Sebastian Markbåge>// - **[2cf4352e1](facebook/react@2cf4352e1 )**: Implement HostSingleton Fiber type ([#25426](facebook/react#25426)) //<Josh Story>// - **[aa9988e5e](facebook/react@aa9988e5e )**: Server render fork for react-dom ([#25436](facebook/react#25436)) //<Josh Story>// - **[513417d69](facebook/react@513417d69 )**: Return lastNonHostInstance in getInspectorDataForInstance for devtools ([#25441](facebook/react#25441)) //<Tianyu Yao>// - **[5d60a0b84](facebook/react@5d60a0b84 )**: Bugfix: LegacyHidden shouldn't defer effects ([#25442](facebook/react#25442)) //<Andrew Clark>// - **[618388bc3](facebook/react@618388bc3 )**: [Float] Support script preloads ([#25432](facebook/react#25432)) //<Josh Story>// - **[2872a26e1](facebook/react@2872a26e1 )**: track resources in different roots separately ([#25388](facebook/react#25388)) //<Josh Story>// - **[ea04a486a](facebook/react@ea04a486a )**: Flow: remove unused suppressions ([#25424](facebook/react#25424)) //<Jan Kassens>// - **[9813edef2](facebook/react@9813edef2 )**: Flow upgrade to 0.188 //<Jan Kassens>// - **[3b6826ed9](facebook/react@3b6826ed9 )**: Flow: inference_mode=constrain_writes //<Jan Kassens>// - **[aed33a49c](facebook/react@aed33a49c )**: Flow upgrade to 0.185 //<Jan Kassens>// - **[f02a5f5c7](facebook/react@f02a5f5c7 )**: Flow upgrade to 0.182 //<Jan Kassens>// - **[72593f008](facebook/react@72593f008 )**: Flow upgrade to 0.176 //<Jan Kassens>// - **[46d40f306](facebook/react@46d40f306 )**: Flow upgrade to 0.175 //<Jan Kassens>// - **[1089faf0d](facebook/react@1089faf0d )**: Flow: run codemod to remove existential type //<Jan Kassens>// - **[3fd9bd8e7](facebook/react@3fd9bd8e7 )**: Add RulesOfHooks support for `use` //<Lauren Tan>// - **[338e6a967](facebook/react@338e6a967 )**: Flow upgrade to 0.155 //<Jan Kassens>// - **[8bc95bb3c](facebook/react@8bc95bb3c )**: Flow upgrade to 0.154 //<Jan Kassens>// - **[9f8a98a39](facebook/react@9f8a98a39 )**: Flow upgrade to 0.153 //<Jan Kassens>// - **[64fe791be](facebook/react@64fe791be )**: Flow upgrade to 0.146 //<Jan Kassens>// - **[d3c6c16a0](facebook/react@d3c6c16a0 )**: Flow upgrade to 0.145 //<Jan Kassens>// - **[00a2f8150](facebook/react@00a2f8150 )**: Flow upgrade to 0.143 //<Jan Kassens>// - **[0a3072278](facebook/react@0a3072278 )**: Flow: complete types first migration ([#25389](facebook/react#25389)) //<Jan Kassens>// - **[bcc05671f](facebook/react@bcc05671f )**: Flow: types first in shared ([#25343](facebook/react#25343)) //<Jan Kassens>// - **[b1f34aa30](facebook/react@b1f34aa30 )**: Flow: types first in react-native-renderer ([#25363](facebook/react#25363)) //<Jan Kassens>// - **[9143864ae](facebook/react@9143864ae )**: Flow: well formed exports for smaller packages ([#25361](facebook/react#25361)) //<Jan Kassens>// - **[21a851e03](facebook/react@21a851e03 )**: Fix devtools typos and grammar ([#24587](facebook/react#24587)) //<Alexandru Tasica>// - **[cfafeb685](facebook/react@cfafeb685 )**: Remove extra space in Wedge.js ([#24611](facebook/react#24611)) //<Kerim Büyükakyüz>// - **[9c3de25e1](facebook/react@9c3de25e1 )**: Flow: types first in reconciler ([#25362](facebook/react#25362)) //<Jan Kassens>// - **[7b25b961d](facebook/react@7b25b961d )**: [Fizz/Float] Float for stylesheet resources ([#25243](facebook/react#25243)) //<Josh Story>// - **[4c016e7aa](facebook/react@4c016e7aa )**: Refactor: use property shorthand ([#25366](facebook/react#25366)) //<zhangrenyang>// - **[06066c1a5](facebook/react@06066c1a5 )**: Make RulesOfHooks-test more consistent with ExhaustiveDeps-test //<Lauren Tan>// - **[49ae0fad8](facebook/react@49ae0fad8 )**: Fix RulesOfHooks test case indentation //<Lauren Tan>// - **[abbbdf4ce](facebook/react@abbbdf4ce )**: Put modern StrictMode behind a feature flag ([#25365](facebook/react#25365)) //<Samuel Susla>// - **[434110390](facebook/react@434110390 )**: ReactHooks.js - delete emptyObject ([#25031](facebook/react#25031)) //<Igor Berlenko>// - **[31400ce29](facebook/react@31400ce29 )**: Refactor: merge duplicate imports ([#25364](facebook/react#25364)) //<jerry-lllman>// - **[3517bd9f7](facebook/react@3517bd9f7 )**: Refactor useEvent ([#25336](facebook/react#25336)) //<Lauren Tan>// - **[6cf06a929](facebook/react@6cf06a929 )**: Remove outdated comments. ([#24464](facebook/react#24464)) //<zhangenming>// - **[20a257c25](facebook/react@20a257c25 )**: Refactor: more word doubles removed ([#25352](facebook/react#25352)) //<Vic Graf>// - **[8cadcffd5](facebook/react@8cadcffd5 )**: Fix typo: reconcilation -> reconciliation ([#25355](facebook/react#25355)) //<zhangrenyang>// - **[ebbe599a2](facebook/react@ebbe599a2 )**: Fix EventListener fork ([#25347](facebook/react#25347)) //<Sebastian Markbåge>// - **[97d75c9c8](facebook/react@97d75c9c8 )**: Move react-dom implementation files to react-dom-bindings ([#25345](facebook/react#25345)) //<Sebastian Markbåge>// - **[3de926449](facebook/react@3de926449 )**: [Fizz] experimental_useEvent ([#25325](facebook/react#25325)) //<dan>// - **[5b59dd640](facebook/react@5b59dd640 )**: Fix duplicate words tests ([#25333](facebook/react#25333)) //<Vic Graf>// - **[cb5084d1c](facebook/react@cb5084d1c )**: [ESLint] Check useEvent references instead ([#25319](facebook/react#25319)) //<Lauren Tan>// - **[c89a83695](facebook/react@c89a83695 )**: Update RulesOfHooks with useEvent rules ([#25285](facebook/react#25285)) //<Lauren Tan>// - **[efc6a08e9](facebook/react@efc6a08e9 )**: [Flight] Implement error digests for Flight runtime and expose errorInfo in getDerivedStateFromError ([#25302](facebook/react#25302)) //<Josh Story>// - **[c1d414d75](facebook/react@c1d414d75 )**: Add ref to Offscreen component ([#25254](facebook/react#25254)) //<Samuel Susla>// - **[135e33c95](facebook/react@135e33c95 )**: Flow: typing of Scheduler ([#25317](facebook/react#25317)) //<Jan Kassens>// - **[cc8cb145f](facebook/react@cc8cb145f )**: Flow: add some missing types in react-reconciler ([#25316](facebook/react#25316)) //<Jan Kassens>// - **[112d0498c](facebook/react@112d0498c )**: [Fizz] Move digest from errorInfo to Error instance ([#25313](facebook/react#25313)) //<Josh Story>// - **[d1bb1c586](facebook/react@d1bb1c586 )**: Fix memory leak after repeated setState bailouts ([#25309](facebook/react#25309)) //<Andrew Clark>// Changelog: [General][Changed] - React Native sync for revisions 0cac4d5...9fb581c jest_e2e[run_all_tests] Reviewed By: yungsters Differential Revision: D40383219 fbshipit-source-id: dc2a44bd05df041e0c7f2e1060640b1d2c372187
* Flush out useMemoCache API * rename symbol * rename symbol.for string name * workaround symbol export not working in unit tests
Summary: - **[9fb581c7c](facebook/react@9fb581c7c )**: Refactor: merge duplicate imports ([facebook#25489](facebook/react#25489)) //<c0dedance>// - **[bc358362a](facebook/react@bc358362a )**: [Flight] Improve Error Messages when Invalid Object is Passed to Client/Host Components ([facebook#25492](facebook/react#25492)) //<Sebastian Markbåge>// - **[780eacd40](facebook/react@780eacd40 )**: Flow upgrade to 0.190 ([facebook#25483](facebook/react#25483)) //<Jan Kassens>// - **[54f0e0f73](facebook/react@54f0e0f73 )**: Scaffolding for react-dom/unstable_external-server-runtime ([facebook#25482](facebook/react#25482)) //<Andrew Clark>// - **[0eaca3756](facebook/react@0eaca3756 )**: Add script to generate inline Fizz runtime ([facebook#25481](facebook/react#25481)) //<Andrew Clark>// - **[69c7246d9](facebook/react@69c7246d9 )**: Initialize useMemoCache with sentinel values ([facebook#25465](facebook/react#25465)) //<Joseph Savona>// - **[3b814327e](facebook/react@3b814327e )**: Allow Async Functions to be used in Server Components ([facebook#25479](facebook/react#25479)) //<Sebastian Markbåge>// - **[a6bf46689](facebook/react@a6bf46689 )**: Extract Fizz instruction set to build macro ([facebook#25457](facebook/react#25457)) //<Andrew Clark>// - **[ea5bc6bac](facebook/react@ea5bc6bac )**: [React Native FB] dynamic feature flag for ref access warning ([facebook#25471](facebook/react#25471)) //<Jan Kassens>// - **[08d035bc8](facebook/react@08d035bc8 )**: Remove Shallow Renderer Tests ([facebook#25475](facebook/react#25475)) //<Sebastian Markbåge>// - **[a8c16a004](facebook/react@a8c16a004 )**: Split Cache into its own Dispatcher ([facebook#25474](facebook/react#25474)) //<Sebastian Markbåge>// - **[2cf4352e1](facebook/react@2cf4352e1 )**: Implement HostSingleton Fiber type ([facebook#25426](facebook/react#25426)) //<Josh Story>// - **[aa9988e5e](facebook/react@aa9988e5e )**: Server render fork for react-dom ([facebook#25436](facebook/react#25436)) //<Josh Story>// - **[513417d69](facebook/react@513417d69 )**: Return lastNonHostInstance in getInspectorDataForInstance for devtools ([facebook#25441](facebook/react#25441)) //<Tianyu Yao>// - **[5d60a0b84](facebook/react@5d60a0b84 )**: Bugfix: LegacyHidden shouldn't defer effects ([facebook#25442](facebook/react#25442)) //<Andrew Clark>// - **[618388bc3](facebook/react@618388bc3 )**: [Float] Support script preloads ([facebook#25432](facebook/react#25432)) //<Josh Story>// - **[2872a26e1](facebook/react@2872a26e1 )**: track resources in different roots separately ([facebook#25388](facebook/react#25388)) //<Josh Story>// - **[ea04a486a](facebook/react@ea04a486a )**: Flow: remove unused suppressions ([facebook#25424](facebook/react#25424)) //<Jan Kassens>// - **[9813edef2](facebook/react@9813edef2 )**: Flow upgrade to 0.188 //<Jan Kassens>// - **[3b6826ed9](facebook/react@3b6826ed9 )**: Flow: inference_mode=constrain_writes //<Jan Kassens>// - **[aed33a49c](facebook/react@aed33a49c )**: Flow upgrade to 0.185 //<Jan Kassens>// - **[f02a5f5c7](facebook/react@f02a5f5c7 )**: Flow upgrade to 0.182 //<Jan Kassens>// - **[72593f008](facebook/react@72593f008 )**: Flow upgrade to 0.176 //<Jan Kassens>// - **[46d40f306](facebook/react@46d40f306 )**: Flow upgrade to 0.175 //<Jan Kassens>// - **[1089faf0d](facebook/react@1089faf0d )**: Flow: run codemod to remove existential type //<Jan Kassens>// - **[3fd9bd8e7](facebook/react@3fd9bd8e7 )**: Add RulesOfHooks support for `use` //<Lauren Tan>// - **[338e6a967](facebook/react@338e6a967 )**: Flow upgrade to 0.155 //<Jan Kassens>// - **[8bc95bb3c](facebook/react@8bc95bb3c )**: Flow upgrade to 0.154 //<Jan Kassens>// - **[9f8a98a39](facebook/react@9f8a98a39 )**: Flow upgrade to 0.153 //<Jan Kassens>// - **[64fe791be](facebook/react@64fe791be )**: Flow upgrade to 0.146 //<Jan Kassens>// - **[d3c6c16a0](facebook/react@d3c6c16a0 )**: Flow upgrade to 0.145 //<Jan Kassens>// - **[00a2f8150](facebook/react@00a2f8150 )**: Flow upgrade to 0.143 //<Jan Kassens>// - **[0a3072278](facebook/react@0a3072278 )**: Flow: complete types first migration ([facebook#25389](facebook/react#25389)) //<Jan Kassens>// - **[bcc05671f](facebook/react@bcc05671f )**: Flow: types first in shared ([facebook#25343](facebook/react#25343)) //<Jan Kassens>// - **[b1f34aa30](facebook/react@b1f34aa30 )**: Flow: types first in react-native-renderer ([facebook#25363](facebook/react#25363)) //<Jan Kassens>// - **[9143864ae](facebook/react@9143864ae )**: Flow: well formed exports for smaller packages ([facebook#25361](facebook/react#25361)) //<Jan Kassens>// - **[21a851e03](facebook/react@21a851e03 )**: Fix devtools typos and grammar ([facebook#24587](facebook/react#24587)) //<Alexandru Tasica>// - **[cfafeb685](facebook/react@cfafeb685 )**: Remove extra space in Wedge.js ([facebook#24611](facebook/react#24611)) //<Kerim Büyükakyüz>// - **[9c3de25e1](facebook/react@9c3de25e1 )**: Flow: types first in reconciler ([facebook#25362](facebook/react#25362)) //<Jan Kassens>// - **[7b25b961d](facebook/react@7b25b961d )**: [Fizz/Float] Float for stylesheet resources ([facebook#25243](facebook/react#25243)) //<Josh Story>// - **[4c016e7aa](facebook/react@4c016e7aa )**: Refactor: use property shorthand ([facebook#25366](facebook/react#25366)) //<zhangrenyang>// - **[06066c1a5](facebook/react@06066c1a5 )**: Make RulesOfHooks-test more consistent with ExhaustiveDeps-test //<Lauren Tan>// - **[49ae0fad8](facebook/react@49ae0fad8 )**: Fix RulesOfHooks test case indentation //<Lauren Tan>// - **[abbbdf4ce](facebook/react@abbbdf4ce )**: Put modern StrictMode behind a feature flag ([facebook#25365](facebook/react#25365)) //<Samuel Susla>// - **[434110390](facebook/react@434110390 )**: ReactHooks.js - delete emptyObject ([facebook#25031](facebook/react#25031)) //<Igor Berlenko>// - **[31400ce29](facebook/react@31400ce29 )**: Refactor: merge duplicate imports ([facebook#25364](facebook/react#25364)) //<jerry-lllman>// - **[3517bd9f7](facebook/react@3517bd9f7 )**: Refactor useEvent ([facebook#25336](facebook/react#25336)) //<Lauren Tan>// - **[6cf06a929](facebook/react@6cf06a929 )**: Remove outdated comments. ([facebook#24464](facebook/react#24464)) //<zhangenming>// - **[20a257c25](facebook/react@20a257c25 )**: Refactor: more word doubles removed ([facebook#25352](facebook/react#25352)) //<Vic Graf>// - **[8cadcffd5](facebook/react@8cadcffd5 )**: Fix typo: reconcilation -> reconciliation ([facebook#25355](facebook/react#25355)) //<zhangrenyang>// - **[ebbe599a2](facebook/react@ebbe599a2 )**: Fix EventListener fork ([facebook#25347](facebook/react#25347)) //<Sebastian Markbåge>// - **[97d75c9c8](facebook/react@97d75c9c8 )**: Move react-dom implementation files to react-dom-bindings ([facebook#25345](facebook/react#25345)) //<Sebastian Markbåge>// - **[3de926449](facebook/react@3de926449 )**: [Fizz] experimental_useEvent ([facebook#25325](facebook/react#25325)) //<dan>// - **[5b59dd640](facebook/react@5b59dd640 )**: Fix duplicate words tests ([facebook#25333](facebook/react#25333)) //<Vic Graf>// - **[cb5084d1c](facebook/react@cb5084d1c )**: [ESLint] Check useEvent references instead ([facebook#25319](facebook/react#25319)) //<Lauren Tan>// - **[c89a83695](facebook/react@c89a83695 )**: Update RulesOfHooks with useEvent rules ([facebook#25285](facebook/react#25285)) //<Lauren Tan>// - **[efc6a08e9](facebook/react@efc6a08e9 )**: [Flight] Implement error digests for Flight runtime and expose errorInfo in getDerivedStateFromError ([facebook#25302](facebook/react#25302)) //<Josh Story>// - **[c1d414d75](facebook/react@c1d414d75 )**: Add ref to Offscreen component ([facebook#25254](facebook/react#25254)) //<Samuel Susla>// - **[135e33c95](facebook/react@135e33c95 )**: Flow: typing of Scheduler ([facebook#25317](facebook/react#25317)) //<Jan Kassens>// - **[cc8cb145f](facebook/react@cc8cb145f )**: Flow: add some missing types in react-reconciler ([facebook#25316](facebook/react#25316)) //<Jan Kassens>// - **[112d0498c](facebook/react@112d0498c )**: [Fizz] Move digest from errorInfo to Error instance ([facebook#25313](facebook/react#25313)) //<Josh Story>// - **[d1bb1c586](facebook/react@d1bb1c586 )**: Fix memory leak after repeated setState bailouts ([facebook#25309](facebook/react#25309)) //<Andrew Clark>// Changelog: [General][Changed] - React Native sync for revisions 0cac4d5...9fb581c jest_e2e[run_all_tests] Reviewed By: yungsters Differential Revision: D40383219 fbshipit-source-id: dc2a44bd05df041e0c7f2e1060640b1d2c372187
Summary
EDIT: We ended up taking a different approach based on feedback, the description reflects the revised version.
The compiler needs to be able to insert checks to see if a given memo slot has been initialized yet. This PR defines a sentinel value as a Symbol, and fills all memo cache arrays with that symbol value. Eventually we can export the symbol, but for now i didn't want to add any public exports to React. We can use Symbol.for with the same key to get the sentinel value.
How did you test this change?
useMemoCache-test