[Draft][Transition Tracing] More Accurate End Time

packages/react-art/src/ReactARTHostConfig.js

@@ -451,3 +451,7 @@ export function preparePortalMount(portalInstance: any): void {
 export function detachDeletedInstance(node: Instance): void {
   // noop
 }
+
+export function requestPostPaintCallback(callback: (time: number) => void) {
+  // noop
+}

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

@@ -377,7 +377,10 @@ export const cancelTimeout: any =
   typeof clearTimeout === 'function' ? clearTimeout : (undefined: any);
 export const noTimeout = -1;
 const localPromise = typeof Promise === 'function' ? Promise : undefined;
-
+const localRequestAnimationFrame =
+  typeof requestAnimationFrame === 'function'
+    ? requestAnimationFrame
+    : scheduleTimeout;
 // -------------------
 //     Microtasks
 // -------------------
@@ -1379,3 +1382,9 @@ export function setupIntersectionObserver(
     },
   };
 }
+
+export function requestPostPaintCallback(callback: (time: number) => void) {
+  localRequestAnimationFrame(() => {
+    localRequestAnimationFrame(time => callback(time));
+  });
+}

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

@@ -609,3 +609,7 @@ export function preparePortalMount(portalInstance: Instance): void {
 export function detachDeletedInstance(node: Instance): void {
   // noop
 }
+
+export function requestPostPaintCallback(callback: (time: number) => void) {
+  // noop
+}

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

@@ -510,3 +510,7 @@ export function preparePortalMount(portalInstance: Instance): void {
 export function detachDeletedInstance(node: Instance): void {
   // noop
 }
+
+export function requestPostPaintCallback(callback: (time: number) => void) {
+  // noop
+}

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

@@ -473,6 +473,11 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
     logRecoverableError() {
       // no-op
     },
+
+    requestPostPaintCallback(callback) {
+      const endTime = Scheduler.unstable_now();
+      callback(endTime);
+    },
   };
 
   const hostConfig = useMutation

packages/react-reconciler/src/ReactFiberWorkLoop.new.js

@@ -260,6 +260,7 @@ import {
   suspendedThenableDidResolve,
   isTrackingSuspendedThenable,
 } from './ReactFiberWakeable.new';
+import {schedulePostPaintCallback} from './ReactPostPaintCallback';
 
 const ceil = Math.ceil;
 
@@ -360,6 +361,7 @@ export function getWorkInProgressTransitions() {
 }
 
 let currentPendingTransitionCallbacks: PendingTransitionCallbacks | null = null;
+let currentEndTime: number | null = null;
 
 export function addTransitionStartCallbackToPendingTransition(
   transition: Transition,
@@ -2639,6 +2641,36 @@ function commitRootImpl(
     markCommitStopped();
   }
 
+  if (enableTransitionTracing) {
+    // We process transitions during passive effects. However, passive effects can be
+    // processed synchronously during the commit phase as well as asynchronously after
+    // paint. At the end of the commit phase, we schedule a callback that will be called
+    // after the next paint. If the transitions have already been processed (passive
+    // effect phase happened synchronously), we will schedule a callback to process
+    // the transitions. However, if we don't have any pending transition callbacks, this
+    // means that the transitions have yet to be processed (passive effects processed after paint)
+    // so we will store the end time of paint so that we can process the transitions
+    // and then call the callback via the correct end time.
+    const prevRootTransitionCallbacks = root.transitionCallbacks;
+    if (prevRootTransitionCallbacks !== null) {
+      schedulePostPaintCallback(endTime => {
+        const prevPendingTransitionCallbacks = currentPendingTransitionCallbacks;
+        if (prevPendingTransitionCallbacks !== null) {
+          currentPendingTransitionCallbacks = null;
+          scheduleCallback(IdleSchedulerPriority, () => {
+            processTransitionCallbacks(
+              prevPendingTransitionCallbacks,
+              endTime,
+              prevRootTransitionCallbacks,
+            );
+          });
+        } else {
+          currentEndTime = endTime;
+        }
+      });
+    }
+  }
+
   return null;
 }
 
@@ -2780,28 +2812,21 @@ function flushPassiveEffectsImpl() {
   if (enableTransitionTracing) {
     const prevPendingTransitionCallbacks = currentPendingTransitionCallbacks;
     const prevRootTransitionCallbacks = root.transitionCallbacks;
+    const prevEndTime = currentEndTime;
     if (
       prevPendingTransitionCallbacks !== null &&
-      prevRootTransitionCallbacks !== null
+      prevRootTransitionCallbacks !== null &&
+      prevEndTime !== null
     ) {
-      // TODO(luna) Refactor this code into the Host Config
-      // TODO(luna) The end time here is not necessarily accurate
-      // because passive effects could be called before paint
-      // (synchronously) or after paint (normally). We need
-      // to come up with a way to get the correct end time for both cases.
-      // One solution is in the host config, if the passive effects
-      // have not yet been run, make a call to flush the passive effects
-      // right after paint.
-      const endTime = now();
       currentPendingTransitionCallbacks = null;
-
-      scheduleCallback(IdleSchedulerPriority, () =>
+      currentEndTime = null;
+      scheduleCallback(IdleSchedulerPriority, () => {
         processTransitionCallbacks(
           prevPendingTransitionCallbacks,
-          endTime,
+          prevEndTime,
           prevRootTransitionCallbacks,
-        ),
-      );
+        );
+      });
     }
   }
 

packages/react-reconciler/src/ReactFiberWorkLoop.old.js

@@ -260,6 +260,7 @@ import {
   suspendedThenableDidResolve,
   isTrackingSuspendedThenable,
 } from './ReactFiberWakeable.old';
+import {schedulePostPaintCallback} from './ReactPostPaintCallback';
 
 const ceil = Math.ceil;
 
@@ -360,6 +361,7 @@ export function getWorkInProgressTransitions() {
 }
 
 let currentPendingTransitionCallbacks: PendingTransitionCallbacks | null = null;
+let currentEndTime: number | null = null;
 
 export function addTransitionStartCallbackToPendingTransition(
   transition: Transition,
@@ -2639,6 +2641,36 @@ function commitRootImpl(
     markCommitStopped();
   }
 
+  if (enableTransitionTracing) {
+    // We process transitions during passive effects. However, passive effects can be
+    // processed synchronously during the commit phase as well as asynchronously after
+    // paint. At the end of the commit phase, we schedule a callback that will be called
+    // after the next paint. If the transitions have already been processed (passive
+    // effect phase happened synchronously), we will schedule a callback to process
+    // the transitions. However, if we don't have any pending transition callbacks, this
+    // means that the transitions have yet to be processed (passive effects processed after paint)
+    // so we will store the end time of paint so that we can process the transitions
+    // and then call the callback via the correct end time.
+    const prevRootTransitionCallbacks = root.transitionCallbacks;
+    if (prevRootTransitionCallbacks !== null) {
+      schedulePostPaintCallback(endTime => {
+        const prevPendingTransitionCallbacks = currentPendingTransitionCallbacks;
+        if (prevPendingTransitionCallbacks !== null) {
+          currentPendingTransitionCallbacks = null;
+          scheduleCallback(IdleSchedulerPriority, () => {
+            processTransitionCallbacks(
+              prevPendingTransitionCallbacks,
+              endTime,
+              prevRootTransitionCallbacks,
+            );
+          });
+        } else {
+          currentEndTime = endTime;
+        }
+      });
+    }
+  }
+
   return null;
 }
 
@@ -2780,28 +2812,21 @@ function flushPassiveEffectsImpl() {
   if (enableTransitionTracing) {
     const prevPendingTransitionCallbacks = currentPendingTransitionCallbacks;
     const prevRootTransitionCallbacks = root.transitionCallbacks;
+    const prevEndTime = currentEndTime;
     if (
       prevPendingTransitionCallbacks !== null &&
-      prevRootTransitionCallbacks !== null
+      prevRootTransitionCallbacks !== null &&
+      prevEndTime !== null
     ) {
-      // TODO(luna) Refactor this code into the Host Config
-      // TODO(luna) The end time here is not necessarily accurate
-      // because passive effects could be called before paint
-      // (synchronously) or after paint (normally). We need
-      // to come up with a way to get the correct end time for both cases.
-      // One solution is in the host config, if the passive effects
-      // have not yet been run, make a call to flush the passive effects
-      // right after paint.
-      const endTime = now();
       currentPendingTransitionCallbacks = null;
-
-      scheduleCallback(IdleSchedulerPriority, () =>
+      currentEndTime = null;
+      scheduleCallback(IdleSchedulerPriority, () => {
         processTransitionCallbacks(
           prevPendingTransitionCallbacks,
-          endTime,
+          prevEndTime,
           prevRootTransitionCallbacks,
-        ),
-      );
+        );
+      });
     }
   }
 

packages/react-reconciler/src/ReactPostPaintCallback.js

@@ -0,0 +1,26 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+import {requestPostPaintCallback} from './ReactFiberHostConfig';
+
+let postPaintCallbackScheduled = false;
+let callbacks = [];
+
+export function schedulePostPaintCallback(callback: (endTime: number) => void) {
+  callbacks.push(callback);
+  if (!postPaintCallbackScheduled) {
+    postPaintCallbackScheduled = true;
+    requestPostPaintCallback(endTime => {
+      for (let i = 0; i < callbacks.length; i++) {
+        callbacks[i](endTime);
+      }
+      postPaintCallbackScheduled = false;
+      callbacks = [];
+    });
+  }
+}

packages/react-reconciler/src/__tests__/ReactFiberHostContext-test.internal.js

@@ -67,6 +67,7 @@ describe('ReactFiberHostContext', () => {
         return DefaultEventPriority;
       },
       supportsMutation: true,
+      requestPostPaintCallback: function() {},
     });
 
     const container = Renderer.createContainer(
@@ -129,6 +130,7 @@ describe('ReactFiberHostContext', () => {
       getCurrentEventPriority: function() {
         return DefaultEventPriority;
       },
+      requestPostPaintCallback: function() {},
       supportsMutation: true,
     });