[scheduler] Deadline object -> shouldYield (facebook#14025)

* [scheduler] Deadline object -> shouldYield

Instead of using a requestIdleCallback-style deadline object, expose a
method Scheduler.shouldYield that returns true if there's a higher
priority event in the queue.

* Nits

packages/react-art/src/ReactARTHostConfig.js

@@ -8,6 +8,7 @@
 export {
   unstable_now as now,
   unstable_scheduleCallback as scheduleDeferredCallback,
+  unstable_shouldYield as shouldYield,
   unstable_cancelCallback as cancelDeferredCallback,
 } from 'scheduler';
 import Transform from 'art/core/transform';

packages/react-dom/src/client/ReactDOMHostConfig.js

@@ -68,6 +68,7 @@ export type NoTimeout = -1;
 export {
   unstable_now as now,
   unstable_scheduleCallback as scheduleDeferredCallback,
+  unstable_shouldYield as shouldYield,
   unstable_cancelCallback as cancelDeferredCallback,
 } from 'scheduler';
 

packages/react-native-renderer/src/ReactFabricHostConfig.js

@@ -332,6 +332,7 @@ export const scheduleDeferredCallback =
   ReactNativeFrameScheduling.scheduleDeferredCallback;
 export const cancelDeferredCallback =
   ReactNativeFrameScheduling.cancelDeferredCallback;
+export const shouldYield = ReactNativeFrameScheduling.shouldYield;
 
 export const scheduleTimeout = setTimeout;
 export const cancelTimeout = clearTimeout;

packages/react-native-renderer/src/ReactNativeFrameScheduling.js

@@ -7,25 +7,16 @@
  * @flow
  */
 
-import type {Deadline} from 'react-reconciler/src/ReactFiberScheduler';
-
 const hasNativePerformanceNow =
   typeof performance === 'object' && typeof performance.now === 'function';
 
 const now = hasNativePerformanceNow
   ? () => performance.now()
   : () => Date.now();
 
-type Callback = (deadline: Deadline) => void;
-
-let scheduledCallback: Callback | null = null;
+let scheduledCallback: (() => mixed) | null = null;
 let frameDeadline: number = 0;
 
-const frameDeadlineObject: Deadline = {
-  timeRemaining: () => frameDeadline - now(),
-  didTimeout: false,
-};
-
 function setTimeoutCallback() {
   // TODO (bvaughn) Hard-coded 5ms unblocks initial async testing.
   // React API probably changing to boolean rather than time remaining.
@@ -36,15 +27,15 @@ function setTimeoutCallback() {
   const callback = scheduledCallback;
   scheduledCallback = null;
   if (callback !== null) {
-    callback(frameDeadlineObject);
+    callback();
   }
 }
 
 // RN has a poor polyfill for requestIdleCallback so we aren't using it.
 // This implementation is only intended for short-term use anyway.
 // We also don't implement cancel functionality b'c Fiber doesn't currently need it.
 function scheduleDeferredCallback(
-  callback: Callback,
+  callback: () => mixed,
   options?: {timeout: number},
 ): number {
   // We assume only one callback is scheduled at a time b'c that's how Fiber works.
@@ -58,4 +49,8 @@ function cancelDeferredCallback(callbackID: number) {
   clearTimeout((callbackID: any)); // Timeouts are always numbers on RN
 }
 
-export {now, scheduleDeferredCallback, cancelDeferredCallback};
+function shouldYield() {
+  return frameDeadline <= now();
+}
+
+export {now, scheduleDeferredCallback, cancelDeferredCallback, shouldYield};

packages/react-native-renderer/src/ReactNativeHostConfig.js

@@ -238,6 +238,7 @@ export const scheduleDeferredCallback =
   ReactNativeFrameScheduling.scheduleDeferredCallback;
 export const cancelDeferredCallback =
   ReactNativeFrameScheduling.cancelDeferredCallback;
+export const shouldYield = ReactNativeFrameScheduling.shouldYield;
 
 export const scheduleTimeout = setTimeout;
 export const cancelTimeout = clearTimeout;

packages/react-noop-renderer/src/createReactNoop.js

@@ -319,7 +319,7 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
           scheduledCallbackTimeout === -1 ||
           scheduledCallbackTimeout > newTimeout
         ) {
-          scheduledCallbackTimeout = newTimeout;
+          scheduledCallbackTimeout = elapsedTimeInMs + newTimeout;
         }
       }
       return 0;
@@ -333,6 +333,8 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
       scheduledCallbackTimeout = -1;
     },
 
+    shouldYield,
+
     scheduleTimeout: setTimeout,
     cancelTimeout: clearTimeout,
     noTimeout: -1,
@@ -512,35 +514,44 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
 
   let yieldedValues = null;
 
+  let didYield;
   let unitsRemaining;
 
-  function* flushUnitsOfWork(n: number): Generator<Array<mixed>, void, void> {
-    let didStop = false;
-    while (!didStop && scheduledCallback !== null) {
-      let cb = scheduledCallback;
-      scheduledCallback = null;
-      unitsRemaining = n;
-      cb({
-        timeRemaining() {
-          if (yieldedValues !== null) {
-            return 0;
-          }
-          if (unitsRemaining-- > 0) {
-            return 999;
-          }
-          didStop = true;
-          return 0;
-        },
-        didTimeout:
-          scheduledCallbackTimeout !== -1 &&
-          elapsedTimeInMs > scheduledCallbackTimeout,
-      });
+  function shouldYield() {
+    if (
+      scheduledCallbackTimeout === -1 ||
+      elapsedTimeInMs > scheduledCallbackTimeout
+    ) {
+      return false;
+    } else {
+      if (didYield || yieldedValues !== null) {
+        return true;
+      }
+      if (unitsRemaining-- > 0) {
+        return false;
+      }
+      didYield = true;
+      return true;
+    }
+  }
 
-      if (yieldedValues !== null) {
-        const values = yieldedValues;
-        yieldedValues = null;
-        yield values;
+  function* flushUnitsOfWork(n: number): Generator<Array<mixed>, void, void> {
+    unitsRemaining = n + 1;
+    didYield = false;
+    try {
+      while (!didYield && scheduledCallback !== null) {
+        let cb = scheduledCallback;
+        scheduledCallback = null;
+        cb();
+        if (yieldedValues !== null) {
+          const values = yieldedValues;
+          yieldedValues = null;
+          yield values;
+        }
       }
+    } finally {
+      unitsRemaining = -1;
+      didYield = false;
     }
   }