Use native scheduler if defined in global scope

packages/scheduler/index.native.js

@@ -0,0 +1,12 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+'use strict';
+
+export * from './src/forks/SchedulerNative';

packages/scheduler/npm/index.native.js

@@ -0,0 +1,7 @@
+'use strict';
+
+if (process.env.NODE_ENV === 'production') {
+  module.exports = require('./cjs/scheduler.native.production.min.js');
+} else {
+  module.exports = require('./cjs/scheduler.native.development.js');
+}

packages/scheduler/package.json

@@ -2,7 +2,6 @@
   "name": "scheduler",
   "version": "0.23.0",
   "description": "Cooperative scheduler for the browser environment.",
-  "main": "index.js",
   "repository": {
     "type": "git",
     "url": "https://github.com/facebook/react.git",
@@ -23,6 +22,7 @@
     "LICENSE",
     "README.md",
     "index.js",
+    "index.native.js",
     "unstable_mock.js",
     "unstable_post_task.js",
     "cjs/",

packages/scheduler/src/forks/Scheduler.js

@@ -46,7 +46,7 @@ import {
 
 export type Callback = boolean => ?Callback;
 
-type Task = {
+export opaque type Task = {
   id: number,
   callback: Callback | null,
   priorityLevel: PriorityLevel,

packages/scheduler/src/forks/SchedulerNative.js

@@ -0,0 +1,112 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict
+ */
+
+import * as Scheduler from './Scheduler';
+import type {Callback, Task} from './Scheduler';
+import type {PriorityLevel} from '../SchedulerPriorities';
+import typeof * as SchedulerExportsType from './Scheduler';
+import typeof * as SchedulerNativeExportsType from './SchedulerNative';
+
+// This type is supposed to reflect the actual methods and arguments currently supported by the C++ implementation:
+// https://github.com/facebook/react-native/blob/main/packages/react-native/ReactCommon/react/renderer/runtimescheduler/RuntimeSchedulerBinding.cpp
+type NativeSchedulerType = {
+  unstable_ImmediatePriority: PriorityLevel,
+  unstable_UserBlockingPriority: PriorityLevel,
+  unstable_NormalPriority: PriorityLevel,
+  unstable_IdlePriority: PriorityLevel,
+  unstable_LowPriority: PriorityLevel,
+  unstable_scheduleCallback: (
+    priorityLevel: PriorityLevel,
+    callback: Callback,
+  ) => Task,
+  unstable_cancelCallback: (task: Task) => void,
+  unstable_getCurrentPriorityLevel: () => PriorityLevel,
+  unstable_shouldYield: () => boolean,
+  unstable_requestPaint: () => void,
+  unstable_now: () => DOMHighResTimeStamp,
+};
+
+declare var nativeRuntimeScheduler: void | NativeSchedulerType;
+
+export const unstable_UserBlockingPriority: PriorityLevel =
+  typeof nativeRuntimeScheduler !== 'undefined'
+    ? nativeRuntimeScheduler.unstable_UserBlockingPriority
+    : Scheduler.unstable_UserBlockingPriority;
+
+export const unstable_NormalPriority: PriorityLevel =
+  typeof nativeRuntimeScheduler !== 'undefined'
+    ? nativeRuntimeScheduler.unstable_NormalPriority
+    : Scheduler.unstable_NormalPriority;
+
+export const unstable_IdlePriority: PriorityLevel =
+  typeof nativeRuntimeScheduler !== 'undefined'
+    ? nativeRuntimeScheduler.unstable_IdlePriority
+    : Scheduler.unstable_IdlePriority;
+
+export const unstable_LowPriority: PriorityLevel =
+  typeof nativeRuntimeScheduler !== 'undefined'
+    ? nativeRuntimeScheduler.unstable_LowPriority
+    : Scheduler.unstable_LowPriority;
+
+export const unstable_ImmediatePriority: PriorityLevel =
+  typeof nativeRuntimeScheduler !== 'undefined'
+    ? nativeRuntimeScheduler.unstable_ImmediatePriority
+    : Scheduler.unstable_ImmediatePriority;
+
+export const unstable_scheduleCallback: (
+  priorityLevel: PriorityLevel,
+  callback: Callback,
+) => Task =
+  typeof nativeRuntimeScheduler !== 'undefined'
+    ? nativeRuntimeScheduler.unstable_scheduleCallback
+    : Scheduler.unstable_scheduleCallback;
+
+export const unstable_cancelCallback: (task: Task) => void =
+  typeof nativeRuntimeScheduler !== 'undefined'
+    ? nativeRuntimeScheduler.unstable_cancelCallback
+    : Scheduler.unstable_cancelCallback;
+
+export const unstable_getCurrentPriorityLevel: () => PriorityLevel =
+  typeof nativeRuntimeScheduler !== 'undefined'
+    ? nativeRuntimeScheduler.unstable_getCurrentPriorityLevel
+    : Scheduler.unstable_getCurrentPriorityLevel;
+
+export const unstable_shouldYield: () => boolean =
+  typeof nativeRuntimeScheduler !== 'undefined'
+    ? nativeRuntimeScheduler.unstable_shouldYield
+    : Scheduler.unstable_shouldYield;
+
+export const unstable_requestPaint: () => void =
+  typeof nativeRuntimeScheduler !== 'undefined'
+    ? nativeRuntimeScheduler.unstable_requestPaint
+    : Scheduler.unstable_requestPaint;
+
+export const unstable_now: () => number | DOMHighResTimeStamp =
+  typeof nativeRuntimeScheduler !== 'undefined'
+    ? nativeRuntimeScheduler.unstable_now
+    : Scheduler.unstable_now;
+
+// These were never implemented on the native scheduler because React never calls them.
+// For consistency, let's disable them altogether and make them throw.
+export const unstable_next: any = throwNotImplemented;
+export const unstable_runWithPriority: any = throwNotImplemented;
+export const unstable_wrapCallback: any = throwNotImplemented;
+export const unstable_continueExecution: any = throwNotImplemented;
+export const unstable_pauseExecution: any = throwNotImplemented;
+export const unstable_getFirstCallbackNode: any = throwNotImplemented;
+export const unstable_forceFrameRate: any = throwNotImplemented;
+export const unstable_Profiling: any = null;
+
+function throwNotImplemented() {
+  throw Error('Not implemented.');
+}
+
+// Flow magic to verify the exports of this file match the original version.
+export type {Callback, Task};
+((((null: any): SchedulerExportsType): SchedulerNativeExportsType): SchedulerExportsType);

scripts/rollup/bundles.js

@@ -935,6 +935,17 @@ const bundles = [
     externals: ['ReactNativeInternalFeatureFlags'],
   },
 
+  /******* React Scheduler Native *******/
+  {
+    bundleTypes: [NODE_DEV, NODE_PROD],
+    moduleType: ISOMORPHIC,
+    entry: 'scheduler/index.native',
+    global: 'SchedulerNative',
+    minifyWithProdErrorCodes: false,
+    wrapWithModuleBoundaries: false,
+    externals: ['ReactNativeInternalFeatureFlags'],
+  },
+
   /******* React Scheduler Post Task (experimental) *******/
   {
     bundleTypes: [

scripts/rollup/validate/eslintrc.cjs.js

@@ -52,6 +52,9 @@ module.exports = {
 
     // act
     IS_REACT_ACT_ENVIRONMENT: 'readonly',
+
+    // Native Scheduler
+    nativeRuntimeScheduler: 'readonly',
   },
   parserOptions: {
     ecmaVersion: 2020,