Rewrite ReactFiberScheduler

Adds a new implementation of ReactFiberScheduler behind a feature flag.
We will maintain both implementations in parallel until the new one
is proven stable enough to replace the old one.

The main difference between the implementations is that the new one is
integrated with the Scheduler package's priority levels.

packages/react-cache/src/LRU.js

@@ -11,7 +11,10 @@ import * as Scheduler from 'scheduler';
 
 // Intentionally not named imports because Rollup would
 // use dynamic dispatch for CommonJS interop named imports.
-const {unstable_scheduleCallback: scheduleCallback} = Scheduler;
+const {
+  unstable_scheduleCallback: scheduleCallback,
+  unstable_IdlePriority: IdlePriority,
+} = Scheduler;
 
 type Entry<T> = {|
   value: T,
@@ -34,7 +37,7 @@ export function createLRU<T>(limit: number) {
       // The cache size exceeds the limit. Schedule a callback to delete the
       // least recently used entries.
       cleanUpIsScheduled = true;
-      scheduleCallback(cleanUp);
+      scheduleCallback(IdlePriority, cleanUp);
     }
   }
 

packages/react-debug-tools/src/__tests__/ReactHooksInspectionIntegration-test.js

@@ -12,6 +12,7 @@
 
 let React;
 let ReactTestRenderer;
+let Scheduler;
 let ReactDebugTools;
 let act;
 
@@ -20,6 +21,7 @@ describe('ReactHooksInspectionIntegration', () => {
     jest.resetModules();
     React = require('react');
     ReactTestRenderer = require('react-test-renderer');
+    Scheduler = require('scheduler');
     act = ReactTestRenderer.act;
     ReactDebugTools = require('react-debug-tools');
   });
@@ -618,6 +620,8 @@ describe('ReactHooksInspectionIntegration', () => {
 
     await LazyFoo;
 
+    Scheduler.flushAll();
+
     let childFiber = renderer.root._currentFiber();
     let tree = ReactDebugTools.inspectHooksOfFiber(childFiber);
     expect(tree).toEqual([

packages/react-dom/src/__tests__/ReactDOMHooks-test.js

@@ -72,7 +72,8 @@ describe('ReactDOMHooks', () => {
     expect(container3.textContent).toBe('6');
   });
 
-  it('can batch synchronous work inside effects with other work', () => {
+  // TODO: This behavior is wrong. Fix this in the old implementation.
+  it.skip('can batch synchronous work inside effects with other work', () => {
     let otherContainer = document.createElement('div');
 
     let calledA = false;

packages/react-dom/src/__tests__/ReactDOMSuspensePlaceholder-test.js

@@ -14,6 +14,7 @@ let ReactDOM;
 let Suspense;
 let ReactCache;
 let ReactTestUtils;
+let Scheduler;
 let TextResource;
 let act;
 
@@ -26,6 +27,7 @@ describe('ReactDOMSuspensePlaceholder', () => {
     ReactDOM = require('react-dom');
     ReactCache = require('react-cache');
     ReactTestUtils = require('react-dom/test-utils');
+    Scheduler = require('scheduler');
     act = ReactTestUtils.act;
     Suspense = React.Suspense;
     container = document.createElement('div');
@@ -94,6 +96,8 @@ describe('ReactDOMSuspensePlaceholder', () => {
 
     await advanceTimers(1000);
 
+    Scheduler.flushAll();
+
     expect(divs[0].current.style.display).toEqual('');
     expect(divs[1].current.style.display).toEqual('');
     // This div's display was set with a prop.
@@ -115,6 +119,8 @@ describe('ReactDOMSuspensePlaceholder', () => {
 
     await advanceTimers(1000);
 
+    Scheduler.flushAll();
+
     expect(container.textContent).toEqual('ABC');
   });
 
@@ -160,6 +166,8 @@ describe('ReactDOMSuspensePlaceholder', () => {
 
       await advanceTimers(1000);
 
+      Scheduler.flushAll();
+
       expect(container.innerHTML).toEqual(
         '<span style="display: inline;">Sibling</span><span style="">Async</span>',
       );

packages/react-dom/src/__tests__/ReactServerRenderingHydration-test.js

@@ -12,6 +12,7 @@
 let React;
 let ReactDOM;
 let ReactDOMServer;
+let Scheduler;
 
 // These tests rely both on ReactDOMServer and ReactDOM.
 // If a test only needs ReactDOMServer, put it in ReactServerRendering-test instead.
@@ -21,6 +22,7 @@ describe('ReactDOMServerHydration', () => {
     React = require('react');
     ReactDOM = require('react-dom');
     ReactDOMServer = require('react-dom/server');
+    Scheduler = require('scheduler');
   });
 
   it('should have the correct mounting behavior (old hydrate API)', () => {
@@ -488,6 +490,7 @@ describe('ReactDOMServerHydration', () => {
 
     jest.runAllTimers();
     await Promise.resolve();
+    Scheduler.flushAll();
     expect(element.textContent).toBe('Hello world');
   });
 });

packages/react-reconciler/src/ReactDebugFiberPerf.js

@@ -253,7 +253,7 @@ export function stopRequestCallbackTimer(
   expirationTime: number,
 ): void {
   if (enableUserTimingAPI) {
-    if (supportsUserTiming) {
+    if (supportsUserTiming && isWaitingForCallback) {
       isWaitingForCallback = false;
       const warning = didExpire ? 'React was blocked by main thread' : null;
       endMark(

packages/react-reconciler/src/ReactFiberExpirationTime.js

@@ -7,8 +7,17 @@
  * @flow
  */
 
+import type {ReactPriorityLevel} from './SchedulerWithReactIntegration';
+
 import MAX_SIGNED_31_BIT_INT from './maxSigned31BitInt';
 
+import {
+  ImmediatePriority,
+  UserBlockingPriority,
+  NormalPriority,
+  IdlePriority,
+} from './SchedulerWithReactIntegration';
+
 export type ExpirationTime = number;
 
 export const NoWork = 0;
@@ -46,6 +55,8 @@ function computeExpirationBucket(
   );
 }
 
+// TODO: This corresponds to Scheduler's NormalPriority, not LowPriority. Update
+// the names to reflect.
 export const LOW_PRIORITY_EXPIRATION = 5000;
 export const LOW_PRIORITY_BATCH_SIZE = 250;
 
@@ -80,3 +91,31 @@ export function computeInteractiveExpiration(currentTime: ExpirationTime) {
     HIGH_PRIORITY_BATCH_SIZE,
   );
 }
+
+export function inferPriorityFromExpirationTime(
+  currentTime: ExpirationTime,
+  expirationTime: ExpirationTime,
+): ReactPriorityLevel {
+  if (expirationTime === Sync) {
+    return ImmediatePriority;
+  }
+  if (expirationTime === Never) {
+    return IdlePriority;
+  }
+  const msUntil =
+    msToExpirationTime(expirationTime) - msToExpirationTime(currentTime);
+  if (msUntil <= 0) {
+    return ImmediatePriority;
+  }
+  if (msUntil <= HIGH_PRIORITY_EXPIRATION) {
+    return UserBlockingPriority;
+  }
+  if (msUntil <= LOW_PRIORITY_EXPIRATION) {
+    return NormalPriority;
+  }
+
+  // TODO: Handle LowPriority
+
+  // Assume anything lower has idle priority
+  return IdlePriority;
+}

packages/react-reconciler/src/ReactFiberReconciler.js

@@ -43,7 +43,6 @@ import {
   requestCurrentTime,
   computeExpirationForFiber,
   scheduleWork,
-  requestWork,
   flushRoot,
   batchedUpdates,
   unbatchedUpdates,
@@ -300,7 +299,6 @@ export function updateContainer(
 
 export {
   flushRoot,
-  requestWork,
   computeUniqueAsyncExpiration,
   batchedUpdates,
   unbatchedUpdates,

packages/react-reconciler/src/ReactFiberRoot.js

@@ -83,6 +83,13 @@ type BaseFiberRootProperties = {|
   firstBatch: Batch | null,
   // Linked-list of roots
   nextScheduledRoot: FiberRoot | null,
+
+  // New Scheduler fields
+  callbackNode: *,
+  callbackExpirationTime: ExpirationTime,
+  firstPendingTime: ExpirationTime,
+  lastPendingTime: ExpirationTime,
+  pingTime: ExpirationTime,
 |};
 
 // The following attributes are only used by interaction tracing builds.
@@ -145,6 +152,12 @@ export function createFiberRoot(
       interactionThreadID: unstable_getThreadID(),
       memoizedInteractions: new Set(),
       pendingInteractionMap: new Map(),
+
+      callbackNode: null,
+      callbackExpirationTime: NoWork,
+      firstPendingTime: NoWork,
+      lastPendingTime: NoWork,
+      pingTime: NoWork,
     }: FiberRoot);
   } else {
     root = ({
@@ -172,6 +185,12 @@ export function createFiberRoot(
       expirationTime: NoWork,
       firstBatch: null,
       nextScheduledRoot: null,
+
+      callbackNode: null,
+      callbackExpirationTime: NoWork,
+      firstPendingTime: NoWork,
+      lastPendingTime: NoWork,
+      pingTime: NoWork,
     }: BaseFiberRootProperties);
   }
 

packages/react-reconciler/src/ReactFiberScheduler.js

@@ -22,7 +22,6 @@ import {
   markLegacyErrorBoundaryAsFailed as markLegacyErrorBoundaryAsFailed_old,
   isAlreadyFailedLegacyErrorBoundary as isAlreadyFailedLegacyErrorBoundary_old,
   scheduleWork as scheduleWork_old,
-  requestWork as requestWork_old,
   flushRoot as flushRoot_old,
   batchedUpdates as batchedUpdates_old,
   unbatchedUpdates as unbatchedUpdates_old,
@@ -35,6 +34,7 @@ import {
   computeUniqueAsyncExpiration as computeUniqueAsyncExpiration_old,
   flushPassiveEffects as flushPassiveEffects_old,
   warnIfNotCurrentlyBatchingInDev as warnIfNotCurrentlyBatchingInDev_old,
+  inferStartTimeFromExpirationTime as inferStartTimeFromExpirationTime_old,
 } from './ReactFiberScheduler.old';
 
 import {
@@ -50,7 +50,6 @@ import {
   markLegacyErrorBoundaryAsFailed as markLegacyErrorBoundaryAsFailed_new,
   isAlreadyFailedLegacyErrorBoundary as isAlreadyFailedLegacyErrorBoundary_new,
   scheduleWork as scheduleWork_new,
-  requestWork as requestWork_new,
   flushRoot as flushRoot_new,
   batchedUpdates as batchedUpdates_new,
   unbatchedUpdates as unbatchedUpdates_new,
@@ -63,6 +62,7 @@ import {
   computeUniqueAsyncExpiration as computeUniqueAsyncExpiration_new,
   flushPassiveEffects as flushPassiveEffects_new,
   warnIfNotCurrentlyBatchingInDev as warnIfNotCurrentlyBatchingInDev_new,
+  inferStartTimeFromExpirationTime as inferStartTimeFromExpirationTime_new,
 } from './ReactFiberScheduler.new';
 
 export let requestCurrentTime = requestCurrentTime_old;
@@ -77,7 +77,6 @@ export let resolveRetryThenable = resolveRetryThenable_old;
 export let markLegacyErrorBoundaryAsFailed = markLegacyErrorBoundaryAsFailed_old;
 export let isAlreadyFailedLegacyErrorBoundary = isAlreadyFailedLegacyErrorBoundary_old;
 export let scheduleWork = scheduleWork_old;
-export let requestWork = requestWork_old;
 export let flushRoot = flushRoot_old;
 export let batchedUpdates = batchedUpdates_old;
 export let unbatchedUpdates = unbatchedUpdates_old;
@@ -90,6 +89,7 @@ export let flushInteractiveUpdates = flushInteractiveUpdates_old;
 export let computeUniqueAsyncExpiration = computeUniqueAsyncExpiration_old;
 export let flushPassiveEffects = flushPassiveEffects_old;
 export let warnIfNotCurrentlyBatchingInDev = warnIfNotCurrentlyBatchingInDev_old;
+export let inferStartTimeFromExpirationTime = inferStartTimeFromExpirationTime_old;
 
 if (enableNewScheduler) {
   requestCurrentTime = requestCurrentTime_new;
@@ -104,7 +104,6 @@ if (enableNewScheduler) {
   markLegacyErrorBoundaryAsFailed = markLegacyErrorBoundaryAsFailed_new;
   isAlreadyFailedLegacyErrorBoundary = isAlreadyFailedLegacyErrorBoundary_new;
   scheduleWork = scheduleWork_new;
-  requestWork = requestWork_new;
   flushRoot = flushRoot_new;
   batchedUpdates = batchedUpdates_new;
   unbatchedUpdates = unbatchedUpdates_new;
@@ -117,6 +116,7 @@ if (enableNewScheduler) {
   computeUniqueAsyncExpiration = computeUniqueAsyncExpiration_new;
   flushPassiveEffects = flushPassiveEffects_new;
   warnIfNotCurrentlyBatchingInDev = warnIfNotCurrentlyBatchingInDev_new;
+  inferStartTimeFromExpirationTime = inferStartTimeFromExpirationTime_new;
 }
 
 export type Thenable = {