[Work-in-progress] Assign expiration times to updates

An expiration time represents a time in the future by which an update
should flush. The priority of the update is related to the difference
between the current clock time and the expiration time. This has the
effect of increasing the priority of updates as time progresses, to
prevent starvation.

This lays the initial groundwork for expiration times without changing
any behavior. Future commits will replace work priority with
expiration times.

src/renderers/art/ReactARTFiberEntry.js

@@ -534,6 +534,11 @@ const ARTRenderer = ReactFiberReconciler({
     );
   },
 
+  now(): number {
+    // TODO: Enable expiration by implementing this method.
+    return 0;
+  },
+
   useSyncScheduling: true,
 });
 

src/renderers/dom/fiber/ReactDOMFiberEntry.js

@@ -163,6 +163,22 @@ function shouldAutoFocusHostComponent(type: string, props: Props): boolean {
   return false;
 }
 
+// TODO: Better polyfill
+let now;
+if (
+  typeof window !== 'undefined' &&
+  window.performance &&
+  typeof window.performance.now === 'function'
+) {
+  now = function() {
+    return performance.now();
+  };
+} else {
+  now = function() {
+    return Date.now();
+  };
+}
+
 var DOMRenderer = ReactFiberReconciler({
   getRootHostContext(rootContainerInstance: Container): HostContext {
     let type;
@@ -431,6 +447,8 @@ var DOMRenderer = ReactFiberReconciler({
     }
   },
 
+  now: now,
+
   canHydrateInstance(
     instance: Instance | TextInstance,
     type: string,

src/renderers/native/ReactNativeFiberRenderer.js

@@ -376,6 +376,11 @@ const NativeRenderer = ReactFiberReconciler({
   },
 
   useSyncScheduling: true,
+
+  now(): number {
+    // TODO: Enable expiration by implementing this method.
+    return 0;
+  },
 });
 
 module.exports = NativeRenderer;

src/renderers/noop/ReactNoopEntry.js

@@ -204,6 +204,11 @@ var NoopRenderer = ReactFiberReconciler({
   prepareForCommit(): void {},
 
   resetAfterCommit(): void {},
+
+  now(): number {
+    // TODO: Add an API to advance time.
+    return 0;
+  },
 });
 
 var rootContainers = new Map();

src/renderers/shared/fiber/ReactFiberBeginWork.js

@@ -19,6 +19,7 @@ import type {HydrationContext} from 'ReactFiberHydrationContext';
 import type {FiberRoot} from 'ReactFiberRoot';
 import type {HostConfig} from 'ReactFiberReconciler';
 import type {PriorityLevel} from 'ReactPriorityLevel';
+import type {ExpirationTime} from 'ReactFiberExpirationTime';
 
 var {
   mountChildFibersInPlace,
@@ -75,6 +76,7 @@ module.exports = function<T, P, I, TI, PI, C, CX, PL>(
   hydrationContext: HydrationContext<C>,
   scheduleUpdate: (fiber: Fiber, priorityLevel: PriorityLevel) => void,
   getPriorityContext: (fiber: Fiber, forceAsync: boolean) => PriorityLevel,
+  recalculateCurrentTime: () => ExpirationTime,
 ) {
   const {
     shouldSetTextContent,
@@ -101,6 +103,7 @@ module.exports = function<T, P, I, TI, PI, C, CX, PL>(
     getPriorityContext,
     memoizeProps,
     memoizeState,
+    recalculateCurrentTime,
   );
 
   function reconcileChildren(current, workInProgress, nextChildren) {

src/renderers/shared/fiber/ReactFiberClassComponent.js

@@ -14,6 +14,7 @@
 
 import type {Fiber} from 'ReactFiber';
 import type {PriorityLevel} from 'ReactPriorityLevel';
+import type {ExpirationTime} from 'ReactFiberExpirationTime';
 
 var {Update} = require('ReactTypeOfSideEffect');
 
@@ -61,38 +62,42 @@ module.exports = function(
   getPriorityContext: (fiber: Fiber, forceAsync: boolean) => PriorityLevel,
   memoizeProps: (workInProgress: Fiber, props: any) => void,
   memoizeState: (workInProgress: Fiber, state: any) => void,
+  recalculateCurrentTime: () => ExpirationTime,
 ) {
   // Class component state updater
   const updater = {
     isMounted,
     enqueueSetState(instance, partialState, callback) {
       const fiber = ReactInstanceMap.get(instance);
       const priorityLevel = getPriorityContext(fiber, false);
+      const currentTime = recalculateCurrentTime();
       callback = callback === undefined ? null : callback;
       if (__DEV__) {
         warnOnInvalidCallback(callback, 'setState');
       }
-      addUpdate(fiber, partialState, callback, priorityLevel);
+      addUpdate(fiber, partialState, callback, priorityLevel, currentTime);
       scheduleUpdate(fiber, priorityLevel);
     },
     enqueueReplaceState(instance, state, callback) {
       const fiber = ReactInstanceMap.get(instance);
       const priorityLevel = getPriorityContext(fiber, false);
+      const currentTime = recalculateCurrentTime();
       callback = callback === undefined ? null : callback;
       if (__DEV__) {
         warnOnInvalidCallback(callback, 'replaceState');
       }
-      addReplaceUpdate(fiber, state, callback, priorityLevel);
+      addReplaceUpdate(fiber, state, callback, priorityLevel, currentTime);
       scheduleUpdate(fiber, priorityLevel);
     },
     enqueueForceUpdate(instance, callback) {
       const fiber = ReactInstanceMap.get(instance);
       const priorityLevel = getPriorityContext(fiber, false);
+      const currentTime = recalculateCurrentTime();
       callback = callback === undefined ? null : callback;
       if (__DEV__) {
         warnOnInvalidCallback(callback, 'forceUpdate');
       }
-      addForceUpdate(fiber, callback, priorityLevel);
+      addForceUpdate(fiber, callback, priorityLevel, currentTime);
       scheduleUpdate(fiber, priorityLevel);
     },
   };

src/renderers/shared/fiber/ReactFiberExpirationTime.js

@@ -0,0 +1,114 @@
+/**
+ * Copyright 2013-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @providesModule ReactFiberExpirationTime
+ * @flow
+ */
+
+'use strict';
+
+import type {PriorityLevel} from 'ReactPriorityLevel';
+const {
+  NoWork,
+  SynchronousPriority,
+  TaskPriority,
+  HighPriority,
+  LowPriority,
+  OffscreenPriority,
+} = require('ReactPriorityLevel');
+
+const invariant = require('fbjs/lib/invariant');
+
+// TODO: Use an opaque type once ESLint et al support the syntax
+export type ExpirationTime = number;
+
+const Done = 0;
+exports.Done = Done;
+
+const Never = Infinity;
+exports.Never = Infinity;
+
+// 1 unit of expiration time represents 10ms.
+function msToExpirationTime(ms: number): ExpirationTime {
+  // Always add 1 so that we don't clash with the magic number for Done.
+  return Math.round(ms / 10) + 1;
+}
+exports.msToExpirationTime = msToExpirationTime;
+
+function expirationTimeToMs(expirationTime: ExpirationTime): number {
+  return (expirationTime - 1) * 10;
+}
+
+function ceiling(time: ExpirationTime, precision: number): ExpirationTime {
+  return Math.ceil(Math.ceil(time * precision) / precision);
+}
+
+// Given the current clock time and a priority level, returns an expiration time
+// that represents a point in the future by which some work should complete.
+// The lower the priority, the further out the expiration time. We use rounding
+// to batch like updates together. The further out the expiration time, the
+// more we want to batch, so we use a larger precision when rounding.
+function priorityToExpirationTime(
+  currentTime: ExpirationTime,
+  priorityLevel: PriorityLevel,
+): ExpirationTime {
+  switch (priorityLevel) {
+    case NoWork:
+      return Done;
+    case SynchronousPriority:
+      // Return a number lower than the current time, but higher than Done.
+      return 1;
+    case TaskPriority:
+      // Return the current time, so that this work completes in this batch.
+      return currentTime;
+    case HighPriority:
+      // Should complete within ~100ms. 120ms max.
+      return msToExpirationTime(ceiling(100, 20));
+    case LowPriority:
+      // Should complete within ~1000ms. 1200ms max.
+      return msToExpirationTime(ceiling(1000, 200));
+    case OffscreenPriority:
+      return Never;
+    default:
+      invariant(
+        false,
+        'Switch statement should be exhuastive. ' +
+          'This error is likely caused by a bug in React. Please file an issue.',
+      );
+  }
+}
+exports.priorityToExpirationTime = priorityToExpirationTime;
+
+// Given the current clock time and an expiration time, returns the
+// corresponding priority level. The more time has advanced, the higher the
+// priority level.
+function expirationTimeToPriorityLevel(
+  currentTime: ExpirationTime,
+  expirationTime: ExpirationTime,
+): PriorityLevel {
+  // First check for magic values
+  if (expirationTime === Done) {
+    return NoWork;
+  }
+  if (expirationTime === Never) {
+    return OffscreenPriority;
+  }
+  const ms = expirationTimeToMs(expirationTime);
+  if (ms < 0) {
+    return SynchronousPriority;
+  }
+  if (ms === 0) {
+    return TaskPriority;
+  }
+  // Keep this value in sync with priorityToExpirationTime.
+  if (ms < 120) {
+    return HighPriority;
+  }
+  return LowPriority;
+}
+exports.expirationTimeToPriorityLevel = expirationTimeToPriorityLevel;

src/renderers/shared/fiber/ReactFiberReconciler.js

@@ -124,6 +124,8 @@ export type HostConfig<T, P, I, TI, PI, C, CX, PL> = {
   prepareForCommit(): void,
   resetAfterCommit(): void,
 
+  now(): number,
+
   // Optional hydration
   canHydrateInstance?: (instance: I | TI, type: T, props: P) => boolean,
   canHydrateTextInstance?: (instance: I | TI, text: string) => boolean,
@@ -196,6 +198,7 @@ module.exports = function<T, P, I, TI, PI, C, CX, PL>(
   var {
     scheduleUpdate,
     getPriorityContext,
+    recalculateCurrentTime,
     performWithPriority,
     batchedUpdates,
     unbatchedUpdates,
@@ -234,6 +237,7 @@ module.exports = function<T, P, I, TI, PI, C, CX, PL>(
       element.type.prototype != null &&
       (element.type.prototype: any).unstable_isAsyncReactComponent === true;
     const priorityLevel = getPriorityContext(current, forceAsync);
+    const currentTime = recalculateCurrentTime();
     const nextState = {element};
     callback = callback === undefined ? null : callback;
     if (__DEV__) {
@@ -244,7 +248,7 @@ module.exports = function<T, P, I, TI, PI, C, CX, PL>(
         callback,
       );
     }
-    addTopLevelUpdate(current, nextState, callback, priorityLevel);
+    addTopLevelUpdate(current, nextState, callback, priorityLevel, currentTime);
     scheduleUpdate(current, priorityLevel);
   }
 

src/renderers/shared/fiber/ReactFiberScheduler.js

@@ -17,6 +17,7 @@ import type {FiberRoot} from 'ReactFiberRoot';
 import type {HostConfig, Deadline} from 'ReactFiberReconciler';
 import type {PriorityLevel} from 'ReactPriorityLevel';
 import type {HydrationContext} from 'ReactFiberHydrationContext';
+import type {ExpirationTime} from 'ReactFiberExpirationTime';
 
 export type CapturedError = {
   componentName: ?string,
@@ -64,6 +65,8 @@ var {
   OffscreenPriority,
 } = require('ReactPriorityLevel');
 
+var {msToExpirationTime} = require('ReactFiberExpirationTime');
+
 var {AsyncUpdates} = require('ReactTypeOfInternalContext');
 
 var {
@@ -160,6 +163,7 @@ module.exports = function<T, P, I, TI, PI, C, CX, PL>(
     hydrationContext,
     scheduleUpdate,
     getPriorityContext,
+    recalculateCurrentTime,
   );
   const {completeWork} = ReactFiberCompleteWork(
     config,
@@ -175,12 +179,16 @@ module.exports = function<T, P, I, TI, PI, C, CX, PL>(
     commitDetachRef,
   } = ReactFiberCommitWork(config, captureError);
   const {
+    now,
     scheduleDeferredCallback,
     useSyncScheduling,
     prepareForCommit,
     resetAfterCommit,
   } = config;
 
+  // Represents the current time in ms.
+  let currentTime: ExpirationTime = msToExpirationTime(now());
+
   // The priority level to use when scheduling an update. We use NoWork to
   // represent the default priority.
   // TODO: Should we change this to an array instead of using the call stack?
@@ -1491,6 +1499,11 @@ module.exports = function<T, P, I, TI, PI, C, CX, PL>(
     scheduleUpdateImpl(fiber, TaskPriority, true);
   }
 
+  function recalculateCurrentTime(): ExpirationTime {
+    currentTime = msToExpirationTime(now());
+    return currentTime;
+  }
+
   function performWithPriority(priorityLevel: PriorityLevel, fn: Function) {
     const previousPriorityContext = priorityContext;
     priorityContext = priorityLevel;
@@ -1563,6 +1576,7 @@ module.exports = function<T, P, I, TI, PI, C, CX, PL>(
   return {
     scheduleUpdate: scheduleUpdate,
     getPriorityContext: getPriorityContext,
+    recalculateCurrentTime: recalculateCurrentTime,
     performWithPriority: performWithPriority,
     batchedUpdates: batchedUpdates,
     unbatchedUpdates: unbatchedUpdates,